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Title:
IMPROVED EFFICIENCY IN COMBUSTION ENGINES
Document Type and Number:
WIPO Patent Application WO/2019/145724
Kind Code:
A1
Abstract:
A method of operating a combustion engine comprises: supplying a primary fuel to a combustion chamber from engine start-up according to the control of a primary fuel controller; and supplying a secondary fuel to the combustion chamber from engine start-up. The method may further comprise calibrating the primary fuel controller utilising feedback provided by a sensor during a calibration period following engine start-up, The sensor may for example be a torque sensor on the propeller shaft and/or a rotational speed sensor on the propeller shaft. A combustion engine, a kit of parts and a secondary fuel controller are also disclosed.

Inventors:
MCMAHON, Gary (12 Waters Way, Worsley, Salford Greater Manchester M28 2AH, M28 2AH, GB)
AYLES, Michael (c/o Red Kite Law LLPSt David's House, 48 Free Street, Brecon Powys LD3 7BN, LD3 7BN, GB)
Application Number:
GB2019/050206
Publication Date:
August 01, 2019
Filing Date:
January 24, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
EHT P AND L LIMITED (Langtons Chartered Accountants, The Plaza 100 Old Hall Street, Liverpool Merseyside L3 9QJ, L3 9QJ, GB)
International Classes:
F02D41/06; F02D19/06; F02D19/08; F02D41/00; F02D41/30
Domestic Patent References:
WO2013061094A12013-05-02
WO2015074143A12015-05-28
Foreign References:
US20100147262A12010-06-17
GB2458500A2009-09-23
GB2539906A2017-01-04
US20140209066A12014-07-31
US20120210988A12012-08-23
Attorney, Agent or Firm:
LEES, Gregory (Dehns, St. Bride's House10 Salisbury Square, London EC4Y 8JD, EC4Y 8JD, GB)
Download PDF:
Claims:
CLAIMS

1. A method of operating a combustion engine, comprising:

supplying a primary fuel to a combustion chamber of the combustion engine from engine start-up according to the control of a primary fuel controller; and

supplying a secondary fuel to the combustion chamber from engine start-up, wherein the quantity of the secondary fuel supplied is less than fifteen percent by volume of the primary fuel. 2. A method as claimed in claim 1 , further comprising calibrating the primary fuel controller utilising feedback provided by a sensor during a calibration period following engine start-up.

3. A method as claimed in claim 2, wherein the sensor comprises;

a torque sensor on the propeller shaft; and/or

a rotational speed sensor on the propeller shaft.

4. A method as claimed in claim 1 ,2, or 3, further comprising measuring the quantity of the primary fuel supplied to the combustion chamber according to the control of the primary fuel controller; and

determining a quantity of the secondary fuel to be supplied to the

combustion chamber;

wherein the quantity of the secondary fuel to be supplied to the combustion chamber is a calculated percentage of the measured quantity of the primary fuel, the percentage being based on a fuel mapping profile.

5. A method as claimed in claim 4, wherein the quantity of the secondary fuel supplied is less than ten percent by volume of the measured quantity of the primary fuel, preferably less than than five percent, further preferably less than four percent.

6. A method as claimed in claim 4, wherein the quantity of the secondary fuel supplied is between three and six percent by volume of the measured quantity of primary fuel. 7. A method as claimed in any preceding claims, further comprising; measuring an ambient pressure and/or temperature of the engine; and adjusting the quantity of the secondary fuel to be supplied based on a mapping profile for the ambient pressure and/or temperature.

8. A method as claimed in any preceding claim, wherein the primary fuel has a larger molecular structure than the secondary fuel;

preferably wherein the primary fuel is diesel and the secondary fuel is a gas, the gas preferably being at least one of liquefied petroleum gas (LPG), compressed natural gas (CNG), liquid natural gas (LNG), methane or hydrogen (Browns gas).

9. A method as claimed in any preceding claim, further comprising:

increasing the percentage of secondary fuel to be supplied as the quantity of the primary fuel being supplied increases below a threshold quantity of primary fuel; and

decreasing the percentage of secondary fuel to be supplied as the quantity of the primary fuel being supplied increases above the threshold quantity of primary fuel.

10. A method as claimed in any preceding claim, further comprising controlling the supply of the secondary fuel using a secondary fuel controller.

11. A combustion engine comprising:

a primary fuel controller for controlling a supply of a primary fuel to a combustion chamber of the combustion engine from engine start-up;

and

a supply mechanism for supplying a secondary fuel to the combustion chamber from engine start-up,

wherein the supply mechanism is configured to supply a quantity of the secondary fuel that is less than fifteen percent by volume of the quantity of the primary fuel.

12. A combustion engine as claimed in claim 11 , further comprising a sensor for providing feedback to the primary fuel controller for calibrating the primary fuel controller during a calibration period following engine start-up; preferab!y wherein the sensor comprises a torque sensor on the propeller shaft and/or a rotational speed sensor on the propeller shaft.

13. A combustion engine as claimed in claim 11 or 12, further comprising:

a means for determining from the primary fuel controller a measurement of the quantity of the primary fuel supplied to the combustion chamber; and

a secondary fuel controller configured to control the supply of secondary fuel, wherein the secondary fuel controller is configured to determine a quantity of the secondary fuel to be supplied to the combustion chamber, wherein the quantity of the secondary fuel supplied to the combustion chamber is a calculated percentage of the measured quantity of the primary fuel, the percentage being based on a fuel mapping profile.

14. A combustion engine as claimed in claim 13, wherein the quantity of the secondary fuel configured to be supplied is less than ten percent by volume of the measured quantity of the primary fuel, preferably less than five percent, further preferably less than four percent.

15. A combustion engine as claimed in claim 13, wherein the quantity of the secondary fuel configured to be supplied is between four and six percent by volume of the measured quantity of primary fuel.

16. A combustion engine as claimed in any of claims 13, 14 or 15, wherein the secondary fuel controller is configured to:

measure an ambient pressure and/or temperature of the engine; and adjust the quantity of the secondary fuel to be supplied based on a mapping profile for the ambient pressure and/or temperature.

17. A combustion engine as claimed in any of claims 11 to 16 wherein the primary fuel has a larger molecular structure than the secondary fuel;

preferably wherein the primary fuel is diesel and the secondary fuel is a gas, the gas preferably being at least one of liquefied petroleum gas (LPG), compressed natural gas (CNG), liquid natural gas (LNG), methane or hydrogen (Browns gas).

18. The combustion engine of any of claims 11 to 17, wherein the combustion engine is an internal combustion engine

19. A kit for retrofitting a combustion engine designed to combust a primary fuel supplied to a combustion chamber of the combustion engine from engine start-up, the kit comprising:

a tank for holding a secondary fuel; and

a supply mechanism for supplying the secondary fuel into the combustion chamber from engine start-up,

wherein the supply mechanism is configured to supply a quantity of the secondary fuel that is less than fifteen percent by volume of the quantity of the primary fuel.

20. A kit as claimed in claim 19, further comprising:

a secondary fuel controller for determining a quantity of the secondary fuel to be supplied to the combustion chamber as a calculated percentage of a measured quantity of the primary fuel supplied according to the control of a primary fuel controller of the combustion engine,

wherein the secondary fuel controller is configured to:

receive a first input indicating a measured quantity of the primary fuel being supplied to the combustion chamber according to the control of the primary fuel controller;

determine from a fuel mapping profile a quantity of the secondary fuel to be supplied to the combustion chamber by the supply mechanism, wherein the quantity of the secondary fuel is a calculated percentage of the measured quantity of the primary fuel supplied to the combustion chamber according to the control of the primary fuel controller; and

supply the quantity of the secondary fuel to the combustion chamber from engine start-up.

21. A secondary fuel controller for controlling a supply of a secondary fuel into a combustion chamber of a combustion engine, the secondary fuel controller comprising:

a first input for receiving an indication of a measured quantity of a primary fuel being supplied to the combustion chamber; and

a processor for determining a quantity of the secondary fuel to be supplied to the combustion chamber, the quantity of the secondary fuel being less than fifteen percent by volume of the quantity of the primary fuel;

wherein the secondary fuel controller is configured to cause a supply mechanism to supply the quantity of the secondary fuel to the combustion chamber from engine start-up.

22. A secondary fuel controller as claimed in claim 21 , further comprising a memory for storing a fuel mapping profile; wherein the processor is configured determine from the fuel mapping profile the quantity of the secondary fuel to be supplied to the combustion chamber as a calculated percentage of the measured quantity of the primary fuel.

Description:
IMPROVED EFFICIENCY IN COMBUSTION ENGINES

The present invention relates to improving efficiency in combustion engines, in particular vehicular combustion engines, in particular combustion engines utilising two different fuels. It relates to a method of operating a combustion engine, a combustion engine, a kit for retrofitting a combustion engine and a secondary fuel controller. A fuel system is described, in particular an additional fuel system which works with but does not directly alter a current fuel system for a combustion engine.

The automotive market is vast and comprises a range of vehicle sizes, including light and heavy goods vehicles. For transport of goods, the cost of fuel and impact on the environment is significant and it is desirable to reduce both of these by more efficiently and completely utilising any fuel required.

Combustion engines provide energy to systems by combusting hydrocarbon fuels in the presence of oxygen. The most efficient fuel combustion occurs, particularly in the context of diesel engines, when there is a homogeneous air/fuel mix which produces carbon dioxide (C0 2 ) and water (H 2 0) as the only waste products. If there is not enough oxygen, the subsequent incomplete combustion wiil lead to exhaust gases containing unburnt fuels, as well as harmful other waste products, such as carbon monoxide (CO) and nitrogen oxides (NO*). Thus to enable the most efficient use of fuel, air-fuel ratios which enable total homogenous combustion are the most desirable.

The primary liquid fuels used in most combustion engines are expensive, long-chain hydrocarbons. Due to the length of the hydrocarbons, complete combustion often does not take place and so the fuel is wasted.

Various dual-fuel systems are known, which provide two fuels to an engine. The main, primary fuel tends to be a more expensive long chain hydrocarbon, while the secondary fuel tends to be a cheaper short chain hydrocarbon. These systems may be part of an engine or vehicle, or retrofitted to an engine or vehicle.

In some systems, the quantity of primary fuel introduced into the engine is unchanged and secondary fuel is introduced in addition. This is known as an 'addition' system. The principle involved is that the introduction of the secondary fuel increases the power/torque of the engine and that an adaptation made either by the original engine control system or by the operator results in a net fuel cost saving. Some systems of this type also employ some crude forms of control in an attempt to reduce the primary fuelling, typically by changing the inputs from sensors or modifying torque or speed control inputs.

There are several limitations of such addition systems. The amount of secondary fuel that can be introduced is limited by the ability of the engine to combust the secondary fuel, primarily due to a lack of oxygen, commonly known as "oxygen depletion" and the secondary fuel "quenching" the combustion of the primary fuel. Operation in this mode leads to poor fuel consumption and high emissions due lu incomplete combustion and the pass through of un-bumt fuel products that exit the exhaust. The fuel saving generated is not guaranteed and can be negative as well as positive. Deliberate over powering of an engine will cause it to operate outside of its normal operational conditions. This will have negative implications in terms of manufacturer's warranty, insurance approvals, safety certification and potential engine life.

The second type of system works by introducing a secondary fuel in addition to a reduced quantity of the primary fuel. These are commonly known as

'substitution' systems. The principle involved is that both primary and secondary fuels are directly controlled and that both fuels when combusted simultaneously generate approximately the same power/torque as the original engine when operating only on the primary fuel.

The percentage of the two fuels employed gives rise to a further distinction between systems of this substitution-type. Systems which use a higher proportion of secondary fuel to primary fuel where the primary fuel is diesel and the secondary fuel is gaseous are known as diesel ignition gas engines. Systems which use a lower proportion of secondary fuel to primary fuel where the primary fuel is diesel and the secondary fuel is gaseous retain their classification as diesel engines.

WO 2013061094 A1 teaches a method in which, by using fuel mapping profiles, a secondary fuel can be injected into an engine alongside a primary fuel in proportions to optimise fuel efficiency. The fuel mapping profiles set out, for each operating state of the engine, an optimum quantity of secondary fuel to be injected into the engine as a percentage of the quantity of primary fuel which is being injected into the engine. The secondary fuel comprises a shorter chain

hydrocarbon in the form of a gaseous fuel. This fuel is injected with air into the engine, and the application describes that this secondary fuel cracks under pressure to form free radicals. The application describes that when the secondary and primary fuel are mixed, the free radicals act to crack the longer-chain hydrocarbon of the primary fuel into shorter chains, thereby allowing more efficient and complete fuel combustion. In other words, for a given amount of primary fuel, a greater energy output is achieved. Since an engine’s ECU (Engine Control Unit) is configured to adjust primary fuel to provide the desired energy output, in this case, the engine’s ECU will automatically adjust to provide less primary fuel to achieve the same energy output, thereby providing greatly improved efficiency.

According to a first aspect of the invention there is provided a method of operating a combustion engine comprising supplying a primary fuel to a combustion chamber of the combustion engine from engine start-up according to the control of a primary fuel controller; and supplying a secondary fuel to the combustion chamber from engine start-up, wherein the quantity of the secondary fuel supplied is preferably less than fifteen percent by volume of the primary fuel.

Thus, the quantity of secondary fuel supplied to the combustion chamber is preferably maintained below fifteen percent by volume of the primary fuel supplied to the combustion chamber at engine start-up and during on-going operation of the combustion engine. For example, the quantity of secondary fuel supplied to the combustion chamber may be maintained below fifteen percent by volume of the primary fuel supplied to the combustion chamber from engine start-up and until operation of the combustion engine stops.

In conventional dual-fuel engines, only primary fuel is supplied at engine start-up, secondary fuel is then added later. The secondary fuel is conventionally stored in liquid feed tanks at temperatures well below 0°C, for example at temperatures around -45°C. When the secondary fuel exits the liquid feed tank, it passes the engine regulator and, as the liquid secondary fuel absorbs the latent heat of vaporisation from its surroundings as it changes to a gaseous form, could lead to freezing of the regulator. Thus it is conventional wisdom to provide an engine temperature sensor for sensing a temperature of the regulator, to ensure that the regulator has reached an operating temperature above a predetermined threshold first before supplying the very cold secondary fuel. In this manner, freezing of the regulator is prevented and secondary fuel is supplied after a delay after start-up of the engine. Therefore, secondary fuel is always supplied after a warming-up period after engine start-up. However, as discussed further below, the inventor has found that supplying secondary fuel from engine start-up actually provides important advantages. Also, by supplying the secondary fuel in a quantity less than fifteen percent by volume of the primary fuel, a relatively small quantity of the secondary fuel can be used to optimise efficiency and reduce unnecessary and excessive fuel consumption. The addition of the secondary fuel in a quantity less than fifteen percent by volume of the primary fuel may take advantage of an effect whereby the presence of a relatively small quantity of the secondary fuel improves combustion of the primary fuel. That is to say, the secondary fuel is not providing significant additional fuel content, but rather is improving the extraction of energy from the primary fuel.

The method may further comprise calibrating the primary fuel controller.

The method may comprise calibrating the primary fuel controller utilising feedback provided by a sensor during a calibration period following engine start-up. The calibration may include adjusting a primary fuel mapping profile. The sensor may be a sensor that provides data indicative of the power output of the engine. For example, the sensor may be a torque sensor on the propeller shaft and/or a rotational speed sensor on the propeller shaft. More than one sensor may be provided. Such sensors are typically built into modern engines. The present inventor has recognised that such conventional engines perform an initial fuel calibration of the primary fuel during a calibration period following engine start-up (e.g. a 15-30 second calibration), to calibrate the quantity of primary fuel based on its quality. This involves adjusting (i.e. calibrating) the short-term and long-term fuel trims based on feedback from the sensors. The short-term fuel trim directly adjusts the fuel supplied at that point in time. The long-term fuel trim adjusts a primary fuel mapping profile for injecting the primary fuel into the engine based on sensor data, for example based on readings of torque and/or rotational speed measured from torque and/or rotational speed sensors fitted to the propeller shaft of the engine.

This primary fuel profile will be used over the course of the engine’s operation.

Thus preferably, in an embodiment, the calibration of the primary fuel controller includes adjusting the short-term and/or long-term fuel trims. The method preferably comprises adjusting the long-term and/or short-term fuel trims based on feedback provided by the sensor. The method may further comprise the long-term fuel trim modifying the primary fuel profile. These calibration/adjustment steps are carried out at (i.e. by) the primary fuel controller. The calibration of the primary fuel controller may be a self-calibration. The engine ECU provides fuel control so can be considered as, or to comprise, the primary fuel controller.

As mentioned above, the calibration period may be a 15-30 second calibration following engine start-up. The skilled person will be well familiar with such a calibration period.

The fuel trims also provide a safety feature, to prevent damage to the propeller shaft during low loading situations. The torque and rotational speed sensors measure the amount of torque and the rotational speed of the propeller shaft and the fuel trims take into account the state of loading of the vehicle when determining the quantities of the fuels to supply in order to avoid damage to the engine. This is necessary as the variable loads on a Heavy Goods Vehicle (HGV) would otherwise mean that full torque through an unloaded truck would twist or shatter the propeller shaft.

The inventor has discovered that in fact, by going against conventional wisdom and supplying the secondary fuel along with the primary fuel from engine start-up, substantial increases in efficiency can be obtained. Without wishing to be bound by theory, it is presently understood that if secondary fuel is supplied from engine start-up, unlike in conventional engines, the calibration of the primary fuel controller, e.g. the adjustment of the fuel trims, takes the effect of the secondary fuel (e.g. the effect on power output as measured by the sensor) into account.

Therefore, the adjustment of the short-term fuel trim is based on the presence of both fuels, and the adjustment of the long-term fuel trim (which in turn calibrates the primary fuel profile of the primary fuel controller) is also based on the presence of both fuels. In other words, the initial calibration of the primary fuel controller from engine start-up is based on both the primary and secondary fuel present from engine start-up.

The primary fuel profile enables the ECU to control the primary fuel injectors to inject the correct quantity of primary fuel into the engine during operation. The primary fuel profile may be termed a mapping profile. Preferably a single mapping profile is provided which maps a desired power output to the quantity of primary fuel to be supplied to achieve this output.

When the engine trims take into account the effect of the secondary fuel based on feedback by the sensor, the long-term fuel trim adjusts the mapping profile for supply ratio of air to primary fuel to maximise the efficiency of the engine by reducing the quantities of primary fuel required to be injected. The benefits of this adjusted profile, which achieves more optimised fuel efficiency, occurs over the course of the time that the engine is in operation, since the engine operation relies on the adjusted primary fuel profile adjusted, i.e. calibrated, during the calibration period following start-up of the engine.

The long-term engine fuel trim adjusts the primary fuel profile based on readings taken by the sensor. The sensor is for measuring an output of the engine in the form of torque or rotational speed of the propeller shaft, to determine the efficiency of combustion in terms of the amount of power output of the engine. The readings from the sensor are used to calibrate the primary fuel controller, for example they can be used by the long-term engine fuel trim to adjust the primary fuel profile to achieve a more efficient overall combustion and use of primary fuel.

The sensor data is representative of the output of the engine (e.g.

torque/rotational speed, dependent on the sensor in question. The use of the secondary fuel in combination with the primary fuel will produce a higher power and torque output. However, the primary fuel controller is unaware that secondary fuel is being utilised in combination with the primary fuel. Therefore, the primary fuel controller simply determines from the sensor data that for a certain known quantity of primary fuel input, the engine is producing more than the expected power output. As a result, the engine trims are adjusted so that less primary fuel is used, e.g. the long-term fuel trim adjusts (calibrates) the primary fuel profile so that less primary fuel is injected to reach the same power output. In this manner, a more efficient primary fuel profile is set up during the calibration period following engine start-up, and so a more efficient combustion which uses less primary fuel can be achieved.

Significant fuel savings are achieved by using secondary fuel on start-up. Experimental data illustrating this is described later in this specification. In addition to improvements in fuel savings, it has been found that C0 2 , NOx and particulate matter (PM) emissions are also reduced. Indeed, it has been seen that the characteristic "belch” of black smoke typically seen from a diesel engine when it starts up has disappeared by use of the invention.

The sensor may comprise a torque or rotational speed sensor on the propeller shaft. In this arrangement, the sensor measures the power output of the engine.

The engine may further comprise at least one sensor in the exhaust (such as a lambda sensor), for monitoring the products of the exhaust in order to control the quantity of primary fuel to be injected into the combustion chamber of the engine, as is known in the art. By measuring the combustion products in the exhaust, the engine fuel trims can be adjusted to provide optimised quantities of primary fuel being injected into the combustion chamber. Such control and any possible calibration of the fuel trims may take place only after the calibration period following engine start-up described above.

The skilled person will appreciate that the adjusted primary fuel mapping profile is different to the fuel mapping profile that maps the quantity of primary fuel to secondary fuel as in embodiments described below.

By engine start-up, the skilled person would readily appreciate that this means the point when the engine is initially started up into a state of operation from a state of non-operation. Engine start-up may therefore be considered as the commencement of the combustion cycle. Following this, the engine enters a calibration period to calibrate the engine to optimum efficiency based upon readings from sensors, such as torque sensors and/or rotational speed sensors, which enable determination of the quality of the fuel being used, as discussed above.

The secondary fuel may be a gaseous fuel and may be stored in a secondary fuel tank in the form of a liquid. For example, the secondary fuel may be Liquid Petroleum Gas (LPG). The secondary fuel tank may be a liquid feed tank, meaning that the secondary fuel is drawn in liquid form from the bottom of the tank.

More preferably however, the secondary fuel tank is a vapour feed tank, meaning that the secondary fuel is drawn in gaseous form from the top of the tank. The benefits of this arrangement compared to a liquid feed tank are that the secondary fuel will not need to change state from a liquid to a gas. During such a state change, secondary fuel would absorb thermal energy from its surroundings, due to the latent heat of vaporisation. Since in the invention the secondary fuel is supplied to the combustion chamber of the combustion engine from start-up, and initially after start-up the engine has not yet warmed up significantly, various components of the system may freeze during the state change as the thermal energy is removed if a liquid feed tank were used. For example, as the secondary fuel evaporates, the water within the regulator may freeze. Effects such as this can therefore be prevented by using a vapour feed tank. Therefore, in an embodiment, the method comprises supplying the secondary fuel from a vapour feed tank to the combustion chamber.

Such vapour feed tanks are not conventionally known to be used in vehicles to which the invention may typically be applied, e.g. diesel engine vehicles, such as dual-fuel diesel trucks, vans, lorries, and other larger and smaller freight hauling or cargo carrying vehicles.

The benefits of the invention, i.e. supplying secondary fuel from engine start- up, are relevant to vehicles of all sizes, and particularly advantageous for HGVs and similar sized engines.

The method may further comprise measuring a quantity of the primary fuel supplied to the combustion chamber according to the control of the primary fuel controller; and determining a quantity of the secondary fuel to be supplied to the combustion chamber, wherein the quantity of the secondary fuel to be supplied to the combustion chamber is a calculated percentage of the measured quantity of the primary fuel, the percentage being based on a fuel mapping profile. A secondary fuel controller may determine the quantity of secondary fuel to be supplied. The secondary fuel controller may be separate to the primary fuel controller.

By selectively supplying a quantity of the secondary fuel which is a percentage of the quantity of primary fuel being supplied into the combustion chamber of the combustion engine, according to a fuel mapping profile, a desired ratio of the two fuels can be obtained so as to achieve optimised fuel efficiency and enhanced combustion.

The quantity of primary fuel supplied according to the control of the primary fuel controller may be measured by reading data from the primary fuel controller. Using this method, no extra sensors are required to measure any data relating to the quantity of fuel being supplied. Instead, this same data can be retrieved and read from the primary fuel controller where it is already being sensed and used.

This method therefore reduces complexity in and cost of the system.

The quantity of the secondary fuel supplied may be less than ten percent by volume of the measured quantity of the primary fuel, preferably less than five percent and even further preferably less than four percent. In one embodiment, the quantity of the secondary fuel supplied may be between three and six percent by volume of the measured quantity of the primary fuel.

The method may comprise: measuring an ambient pressure and/or temperature of the engine; and adjusting the quantity of the secondary fuel to be supplied based on a mapping profile for the ambient pressure and/or temperature. The mapping profile for the ambient pressure and/or temperature may be termed an ambient conditions mapping profile. Since the density and viscosity of the secondary fuel may be affected by ambient conditions, by adjusting the proportion of secondary fuel to be supplied additionally as a function of ambient conditions (as well as based on the quantity of primary fuel), a desired quantity of secondary fuel to be supplied to the combustion chamber of the combustion engine can be controlled to optimise efficiency. The adjustment can be done using the ambient conditions mapping profile, which provides an indication of the correct duty cycle for an injector to be able to supply the appropriate quantity of the secondary fuel, based on measured temperature, pressure and/or other conditions. The appropriate quantity of the secondary fuel may be a volumetric quantity.

The primary fuel may have a larger molecular structure than the secondary fuel. Preferably, the primary fuel is diesel and the secondary fuel is gas. The gas may be at least one of liquefied petroleum gas (LPG), compressed natural gas (CNG), liquid natural gas (LNG), methane or hydrogen (Browns gas).

The step of supplying the secondary fuel may comprise injecting the air with secondary fuel during a compression stage of the engine operation for splitting the secondary fuel into radicals, which are for splitting the primary fuel into smaller molecules during a combustion stage of the engine operation.

The injected secondary fuel may cause the splitting of the primary fuel into smaller molecules.

It is presently believed that the secondary fuel which is supplied to the engine provides a chemical effect. Upon supply of the secondary fuel, the secondary fuel undergoes chemical cracking to form free radicals. These free radicals react with the primary fuel with which they are mixed under pressure, so that the long chain hydrocarbons of the primary fuel are cracked into shorter chain hydrocarbons. Since shorter chain hydrocarbons can achieve a more complete combustion, then this dual cracking effect releases more energy and thus a greater torque is output. This torque is registered by torque sensors, and the engine fuel trims respond to this accordingly by reducing the amount of primary fuel required to be supplied to the combustion chamber so that the engine stays within its pre-set performance profiles, i.e. operates at the conditions required by the engine ECU.

The splitting of the primary fuel into smaller molecules may occur substantially simultaneously with the combustion of the smaller molecules.

In this way, no extra time or apparatus is required to provide the cracking steps and thus enhanced combustion resulting in increased efficiency can take place using pre-existing apparatus. In this way, the present invention provides a very simple arrangement without the need for complex modifications of the pre- existing engine.

The method may comprise: increasing the percentage of secondary fuel to be supplied as the quantity of the primary fuel being supplied increases below a threshold quantity of primary fuel; and decreasing the percentage of secondary fuel to be supplied as the quantity of the primary fuel being supplied increases above the threshold quantity of primary fuel. In other words, once the quantity of the primary fuel exceeds a threshold quantity, the percentage of secondary fuel to be supplied decreases as the quantity of primary fuel being supplied increases.

Below a threshold quantity of primary fuel, as the quantity of primary fuel increases, the percentage of secondary fuel to be supplied should be increased in order to achieve optimised combustion and therefore improved combustion efficiency. Above the threshold quantity of primary fuel, as the quantity of primary fuel increases, the percentage of secondary fuel to be supplied should be decreased in order to achieve optimised combustion.

Since, in this method, the quantity of the secondary fuel to be supplied is not increased indefinitely, this provides a safety measure. In particular, if the secondary fuel is a gaseous fuel, then the possibility of accidents, for example in the event of system failure, is reduced by the presence of less gaseous (secondary) fuel, as can the extent of damage caused by such an accident. Since the quantity of the secondary fuel supplied to the combustion chamber as a percentage of the quantity of primary fuel is decreased above the threshold quantity of primary fuel, the quantity of the secondary fuel can never get to dangerous levels that could cause damage through overheating.

As mentioned above, the method may comprise controlling the supply of the secondary fuel using a secondary fuel controller.

With this method, no significant alterations need to be made to the primary fuel controller in order for the secondary fuel to be supplied in accordance with the invention. In this way, the system can be used in conjunction with many

conventional engines by retrofitting a secondary fuel system having its own controller.

According to a second aspect of the invention, there is provided a combustion engine comprising: a primary fuel controller for controlling a supply of a primary fuel to a combustion chamber of the combustion engine from engine start- up; and a supply mechanism for supplying a secondary fuel to the combustion chamber from engine start-up. wherein the supply mechanism is preferably configured to supply a quantity of the secondary fuel that is less than fifteen percent by volume of the quantity of the primary fuel.

Thus, the supply mechanism is preferably configured to supply a quantity of secondary fuel to the combustion chamber that is maintained below fifteen percent by volume of the quantity of primary fuel supplied to the combustion chamber at engine start-up and dunng on-going operation of the engine. For example, supply mechanism may be configured to supply a quantity of secondary fuel to the combustion chamber that is maintained below fifteen percent by volume of the primary fuel supplied to the combustion chamber from engine start-up and until operation of the combustion engine stops.

With this arrangement, a relatively small quantity of the secondary fuel can be used to optimise efficiency and reduce unnecessary and excessive fuel consumption.

Preferably, the engine further comprises a sensor for providing feedback to the primary fuel controller for calibrating the primary fuel controller during a calibration period following engine start-up. The sensor may comprise a torque sensor on the propeller shaft and/or a rotational speed sensor on the propeller shaft. The supply mechanism may typically comprise intake valves, or gas injection solenoids.

The secondary fuel may be supplied from a vapour feed tank. The engine may therefore further comprise a vapour feed tank configured to provide secondary fuel to the supply mechanism.

By supplying the secondary fuel along with the primary fuel from engine start-up. unlike in conventional engines, the fuel trims take the secondary fuel into account and provide a more efficient adjustment of the primary fuel mapping profile, which achieves more optimised fuel efficiency over the course of the engine use, since the engine use relies on the adjusted fuel mapping profile adjusted, i.e.

calibrated, during the calibration period following start-up of the engine.

The combustion engine may comprise a means for determining from the primary fuel controller a measurement of the quantity of the primary fuel supplied to the combustion chamber it may further comprise a secondary fuel controlier for controlling the supply of secondary fuel. The secondary fuel controller may be configured to determine a quantity of the secondary fuel to be supplied to the combustion chamber, wherein the quantity of the secondary fuel supplied to the combustion chamber is a calculated percentage of the measured quantity of the primary fuel. The percentage may be based on a fuel mapping profile. Such a fuel mapping profile may be called a“primary to secondary fuel mapping profile” or “primary to secondary fuel map” since it maps the quantity of primary fuel to the amount of secondary fuel that should be supplied.

The measured quantity of the primary fuel supplied to the combustion chamber is a measurement of the quantity of the primary fuel supplied to the combustion chamber. By selectively supplying a quantity of the secondary fuel which is a percentage of the injected primary fuel into the engine, according to a fuel mapping profile, a desired ratio of the two fuels can be obtained so as to achieve optimised fuel efficiency and enhanced combustion.

The quantity of the secondary fuel configured to be supplied may be less than ten percent by volume of the measured quantity of the primary fuel, preferably less than five percent, and even further preferably less than four percent. In one embodiment, the quantity of secondary fuel to be supplied may be between three and six percent by volume of the measured quantity of primary fuel.

The secondary fuel controller may be configured to: measure an ambient pressure and/or temperature of the engine; and adjust the quantity of the secondary fuel to be supplied based on a mapping profile for the ambient pressure and/or temperature. The mapping profile for the ambient pressure and/or temperature may be termed an ambient conditions mapping profile.

With this arrangement, since the density and viscosity of the secondary fuel may be affected by ambient conditions, by adjusting the proportion of secondary fuel to be supplied additionally as a function of ambient conditions, a desired quantity of fuel to be supplied into the engine can be controlled to optimise efficiency. The adjustment can be done using the ambient conditions mapping profile, which provides an indication of the correct duty cycle for an injector to be able to inject the appropriate quantity of the secondary fuel, based on measured temperature, pressure and/or other conditions. The appropriate quantity of the secondary fuel may be a volumetric quantity.

The primary fuel may have a larger molecular structure than the secondary fuel; preferably wherein the primary fuel is diesel and the secondary fuel is a gas, the gas preferably being at least one of liquefied petroleum gas (LPG), compressed natural gas (CNG), liquid natural gas (LNG), methane or hydrogen (Browns gas). It is presently understood that the secondary fuel which is supplied to the combustion chamber of the combustion engine provides a chemical effect. Upon supply of the secondary fuel, which may be injected with air during a compression stage of the engine operation, the secondary fuel undergoes chemical cracking to form free radicals. It is believed that these free radicals react with the primary fuel with which they are mixed under pressure during a combustion stage of the engine operation, so that the long chain hydrocarbons of the primary fuel are cracked into shorter chain hydrocarbons. Since shorter chain hydrocarbons can achieve a more complete combustion, then this dual cracking effect releases more energy and thus a greater torque is output. This torque is registered by the torque sensors, and the fuel trims respond to this accordingly by reducing the amount of primary fuel so that the engine stays within its pre-set performance profiles, i.e. operates at the conditions required by the engine ECU.

The splitting of the primary fuel into smaller molecules may occur substantially simultaneously with the combustion of the smaller molecules. In this way, no extra time or apparatus is required to provide the cracking steps and thus enhanced combustion resulting in increased efficiency can take place using pre- existing apparatus. In this way, the present invention provides a very simple arrangement without the need for complex modifications of the pre-existing engine.

The combustion engine may be an internal combustion engine.

According to a third aspect of the invention, there is provided a kit for retrofitting a combustion engine designed to combust a primary fuel supplied to a combustion chamber of the combustion engine from engine start-up, the kit comprising: a tank for holding a secondary fuel; and a supply mechanism for supplying the secondary fuel into the combustion chamber from engine start-up, wherein the supply mechanism is preferably configured to supply a quantity of the secondary fuel that is less than fifteen percent by volume of the quantity of the primary fuel.

Thus, the supply mechanism is preferably configured to maintain the quantity of the secondary fuel supplied to the combustion chamber below fifteen percent by volume of the quantity of the primary fuel supplied to the combustion chamber at engine start-up and during on-going operation of the engine. For example, the supply mechanism may be configured to maintain the quantity of secondary fuel supplied to the combustion chamber below fifteen percent by volume of the primary fuel supplied to the combustion chamber from engine start-up and until operation of the combustion engine stops.

The supply mechanism may typically be an injector, or may typically comprise intake valves, or gas injection solenoids.

By supplying the secondary fuel along with the primary fuel from engine start-up, unlike in conventional engines, the fuel trims take the secondary fuel into account and provide a more efficient adjustment of the primary fuel mapping profile, which achieves more optimised fuel efficiency over the course of the engine use, since the engine use relies on the adjusted fuel mapping profile adjusted, i.e.

calibrated, during the calibration period following start-up of the engine.

The kit may comprise a secondary fuel controller for determining a quantity of the secondary fuel to be supplied to the combustion chamber as a calculated percentage of a measured quantity of the primary fuel supplied according to the control of a primary fuel controller of the combustion engine. The secondary fuel controller may be configured to: receive a first input indicating a measured quantity of the primary fuel being supplied to the combustion chamber according to the control of the primary fuel controller; determine from a fuel mapping profile a quantity of the secondary fuel to be supplied to the combustion chamber by the supply mechanism, wherein the quantity of the secondary fuel is a calculated percentage of the measured quantity of the primary fuel supplied to the combustion chamber according to the control of the primary fuel controller; and supply the quantity of the secondary fuel to the combustion chamber from engine start-up.

By selectively supplying a quantity of the secondary fuel which is a percentage of the supplied primary fuel into the engine, according to a fuel mapping profile (e.g. a primary to secondary fuel map), a desired ratio of the two fuels can be obtained so as to achieve optimised fuel efficiency and enhanced combustion.

Since the kit comprises its own tank, injector and controller, no significant alterations need to be made to the primary fuel controller or primary fuel system of the combustion engine in order for the secondary fuel to be supplied. In this way, the system can be used in conjunction with many conventional engines by retrofitting a secondary fuel system having its own controller.

According to a fourth aspect of the invention, there is provided a secondary fuel controller for controlling a supply of a secondary fuel into a combustion chamber of a combustion engine, the secondary fuel controller comprising: a first input for receiving an indication of a measured quantity of a primary fuel being supplied to the combustion chamber; and a processor for determining a quantity of the secondary fuel to be supplied to the combustion chamber, the quantity of the secondary fuel preferably being less than fifteen percent by volume of the quantity of the primary fuel; wherein the secondary fuel controller is configured to cause a supply mechanism to supply the quantity of the secondary fuel to the combustion chamber from engine start-up.

Thus, the secondary fuel controller is preferably configured to supply a quantity of the secondary fuel to the combustion chamber that is less than fifteen percent by volume of the quantity of the primary fuel supplied to the combustion chamber at engine start-up and during on-going operation of the engine. For example, the secondary fuel controller may be configured to supply a quantity of secondary fuel to the combustion chamber that is maintained below fifteen percent by volume of the primary fuel supplied to the combustion chamber from engine start-up and until operation of the combustion engine stops.

By supplying the secondary fuel along with the primary fuel from engine start-up, unlike in conventional engines, the fuel trims take the secondary fuel into account and provide a more efficient adjustment of a primary fuel mapping profile during a calibration period following engine start-up, which achieves more optimised fuel efficiency over the course of the engine use, since the engine use relies on the adjusted fuel mapping profile adjusted at start-up of the engine.

Since there is a secondary fuel controller to control the flow of secondary fuel, no significant alterations need to be made to the primary fuel controller in order for the secondary fuel to be supplied. In this way, the system can be used in conjunction with many conventional engines by retrofitting a secondary fuel system having its own controller.

By selectively supplying a quantity of the secondary fuel which is a percentage of the supplied primary fuel into the engine, according to a fuel mapping profile (e.g. a primary to secondary fuel map), a desired ratio of the two fuels can be obtained so as to achieve optimised fuel efficiency and enhanced combustion.

The secondary fuel controller may further comprise a memory for storing a fuel mapping profile. The processor may be configured to determine from the fuel mapping profile the quantity of the secondary fuel to be supplied to the combustion chamber as a calculated percentage of the measured quantity of the primary fuel. It will be appreciated that the various preferred and optional features described in relation to particular aspects set out above are equally applicable to the other aspects of the invention, and vice versa.

Preferred embodiments of the invention will now be described by way of example only, and with reference to the following drawings in which:

Figure 1 is a block diagram showing components of a combustion engine;

Figure 2 shows schematically an exemplary primary to secondary fuel mapping profile;

Figure 3 shows an exemplary fuel flow mapping profile;

Figure 4 shows schematically a hardware arrangement for a gas controller;

Figure 5 shows schematically a kit that can be retrofitted to an existing engine;

Figure 6a shows a side view of a vehicle before a retrofit of the gas controller system;

Figure 6b shows a side view of a vehicle after a retrofit of the gas controller system;

Figure 6c shows an opposite side view to Figure 6b of a vehicle after a retrofit of the gas controller system;

Figure 7 shows a method of operating a combustion engine comprising a primary fuel controller and a sensor for providing feedback to the primary fuel controller;

Figures 8 shows a screenshot from an experimental trial, showing the flow rate of primary (liquid) fuel when the engine was started up without secondary (gaseous) fuel;

Figures 9 shows a screenshot from an experimental trial, showing the flow rate of primary (liquid) fuel when the engine was started up with secondary (gaseous) fuel; and

Figures 10a and 10b show an enlarged portion of Figures 8 and 9 respectively, showing the primary fuel flow rates.

As is well known, a conventional internal combustion engine such as combustion engine 100 represented in Figure 1 , comprises a piston that reciprocates within a cylinder and a crank mechanism for converting the reciprocating movement of the piston into a rotational output. The operation and efficiency of an internal combustion engine depends on a great number of factors, including the type and mixture of fuel used, the compression ratio, the dimensions of the piston / cylinder, the valve timing, the ignition timing, the temperature and distribution of temperature within the combustion chamber.

One of the main factors however, that determines the overall efficiency of the engine is the manner in which the fuel is burned, which is typified by the speed and completeness and/or homogeneity of the air-fuel mixture of the combustion process.

Relatively complex hydrocarbon fuels such as diesel have a molecular structure which is long and relatively slow to combust which prevents some of the hydrocarbons from fully burning. Moreover, these long-chain hydrocarbons have a tendency to coalesce, preventing efficient mixing with air or oxygen during the combustion process.

Also, diesel burnt in an enclosed chamber that is externally cooled will tend to ignite first in the centre of the chamber and the ignition will then spread outwards towards the edges of the chamber. If the spread of this flame front is incomplete or inefficient then smoke and particulate matter will result which will be emitted during the exhaust phase of the engine.

A conventional 4-stroke diesel engine has the following stages:

1. an intake stroke, in which air is drawn in;

2. a compression stroke, in which the air is compressed and primary fuel is injected;

3. a combustion stroke, in which the primary fuel combusts due to the heat generated during compression and the piston is displaced; and

4. an exhaust stroke, in which the un-com busted particulate is driven out the exhaust.

In a conventional 4 stroke engine, combustion (burning of the fuel) occurs during the "combustion" or "power" stroke of the piston and in most engines the geometry of the engine fixes the displacement and acceleration of the piston during the power stroke.

To maximise the efficiency of an engine it is important to burn as much of the primary fuel as possible during the power stroke. However, the chemistry and thermodynamics of combustion place practical limits on the maximum percentage of the fuel that can actually be combusted during the power stroke which generally leads to amount of un-combusted fuel remaining in the cylinder after the power stroke. Typically, a conventional heavy duty diesel engine combusts only up to 80% of the fuel present in the cylinder during the power stroke. Embodiments of the invention aim to increase this percentage figure, for example closer to 100%, by enhancing the combustion process.

The main factors that affect the proportion of the available fuel that can be burnt include:

a) The nature of the fuel itself. The combustion characteristics including the cetane number and octane rating.

b) The dimension of the cylinder. The larger the cylinder volume the longer it will take for the "flame front" to reach the boundaries of the cylinder, which for large dimensions or slow flame fronts at high engine speeds may never occur.

c) The timing of the engine. The valve timing and the timing of the initiation of combustion will affect the proportion of fuel burnt.

In embodiments, the engine efficiency is improved by controlling the homogeneity or uniformity of the combustion process. If the combustion process can be spread evenly and equally by ensuring the greatest uniformity of the air/fuel mix throughout the combustion chamber, then the combustion process will be less compromised by flame front effects, or temperature variations in the combustion cylinder.

These factors are equally applicable to rotary or turbine engines.

Figure 1 is a block diagram showing components of an exemplary embodiment of a combustion engine 100, having a combustion chamber 112. The combustion engine 100 has a supply of primary fuel in the form of diesel, stored in a primary fuel tank 110, and a supply of secondary fuel in the form of a gaseous fuel, stored in a secondary fuel tank 118. As is known in the art, gaseous hydrocarbon fuels may be short-chain hydrocarbons, while primary fuels, such as diesel for example, may be long-chained hydrocarbons.

The secondary fuel tank 118 may be a liquid feed tank, or alternatively, may be a vapour feed tank. Additionally, it may be capable of both liquid and vapour feeds. Preferably, it is a vapour feed tank.

A turbocharger 106 is located upstream of the combustion chamber 112.

The turbocharger has a rotating turbine (not shown) that sucks air in, via air-intake 102, to aid in the combustion process. The air from the air intake 102 passes through an air filter 105 designed to block entry of contaminants. Some of this filtered air is then redirected via a take-off to the engine compressor 103. A gas controller 116 (i.e. a secondary fuel controller) is provided for controlling the quantities of secondary fuel injected into the remaining filtered air by an (or multiple) injector(s) 128. The injector 128 is provided on a gas supply line 124 which extends between the secondary fuel tank 118 and the section containing the remaining filtered air which has not been taken off to the compressor 103. A pressure regulator (reducer) 119 is located between the gas tank 118 and injector 128. By controlling the injector 128, the gas controller 116 can control the amount of secondary fuel that is injected into the filtered air prior to the turbocharger 106.

When the secondary fuel is injected into the filtered air, the fuel and air mix together, and pass to the turbocharger 106, where further mixing occurs, creating an even distribution of the air and secondary fuel in a mixture. The mixture may be passed through an intercooler 108, located between the turbocharger 106 and the combustion chamber 112.

The mixture is then passed, for example via intake valves or gas injection solenoids, to the combustion chamber 112, where it undergoes compression. The compression of the air and secondary fuel mixture splits the short-chained gaseous secondary fuel into even shorter-chained molecules (or even atoms), known as radicals or free radicals.

As an alternative, the secondary fuel may not be injected into the filtered air before the turbocharger unit 106. Instead, in one embodiment there is a post-turbo injection unit (not shown). In another embodiment, the secondary fuel is directly injected into the combustion chamber 112. In either case, air is incorporated with the secondary fuel and forms a mixture before and/or within the combustion chamber 112 and the above-described radicals produced by compressing the mixture are formed.

Primary fuel from the primary fuel tank 110 is injected into the combustion chamber in quantities determined by an Engine Control Unit (ECU) 104, which controls the primary fuel supply and related apparatus only and not the secondary fuel supply or its related apparatus, which is instead controlled by the gas controller 116 as described above. The ECU may therefore be considered as (or comprising) a primary fuel controller. The ECU 104 transmits instructions by any form of communication such as wired or wireless, for example, to primary fuel injectors 127, which regulate the flow of primary fuel released into the combustion chamber. The flow can be adjusted, i.e. regulated, by the ECU, by adjusting the duty cycle of the primary fuel injectors 127 in the combustion chamber 112. A sensor 126 may be provided to sense the pressure and/or flow rate of the primary fuel as it leaves the primary fuel tank 110 to be injected into the combustion chamber 112. This pressure and/or flow rate data is transmitted along data transmission line 130 to the ECU 104, which can calculate from the pressure data and/or read from the flow rate data the flow rate of the primary fuel. The data transmission line may be any form of transmission, including wire, optical fibre or other physical connections, but may also be wireless such as radio transmission for example.

In response to the received data from the sensor 126, the ECU 104 transmits control instructions along data transmission line 125 to the primary fuel injectors 127 to adjust the flow accordingly, for example in the manner described above. The data transmission line may be any form of transmission, including wire, optical fibre or other physical connections, but may also be wireless such as radio transmission for example.

Once the primary fuel has been injected into the combustion chamber 112, the radicals produced from the secondary fuel, which are present in the combustion chamber 112, can bind with the longer-chained primary fuel (diesel) hydrocarbons, causing the primary fuel long chain hydrocarbons to split into shorter molecules that are more easily combusted. The combustion products leave the combustion chamber 112 via the exhaust 114.

The exhaust 114 may contain at least one sensor 115, connected to the ECU 104 for monitoring the products of the exhaust 114 in order to control the quantity of primary fuel to be injected into the combustion chamber 112, as is known in the art. Data measured by this sensor may be transmitted via

transmission line 132 to the ECU 104. As described above, the transmission line 132 may be tangible, e.g. a wire, or intangible, e.g. wireless. Alternatively or additionally, torque and/or rotational speed sensors 120 on the propeller shaft can be used to monitor the output power of the engine, in order to control the quantity of primary fuel to be injected into the combustion chamber 112. Data measured by these sensors may be transmitted via a transmission line 121 to the ECU 104. The transmission line may be tangible, e.g. a wire, or intangible, e.g. wireless. This data is used by the ECU to adjust the short- and long-term fuel trims of the engine 100 which are stored in the ECU. The short- and long-term fuel trims provide the mapping for how the duty cycle of the primary fuel injectors 127 needs to be regulated to adjust the flow of primary fuel to the combustion chamber 112 at any particular time. By measuring the combustion products in the exhaust, the engine fuel trims can be adjusted to provide optimised quantities of primary fuel being injected into the combustion chamber 112. Such control and any possible calibration of the fuel trim may take place only after a calibration period following engine start-up.

The engine ECU conventionally performs an initial fuel calibration of the primary fuel during a calibration period following engine start-up (e.g. a 15-30 second calibration), to calibrate the performance profile of the primary fuel based on its quality, i.e. calibration procedures of the long-term fuel trim and the short-term fuel trim. This may be considered as calibration of the primary fuel controller. This may comprise utilising one or more of a torque sensor 120 and a rotational speed sensor 120 on the propeller shaft of the engine, to provide feedback 121 concerning the power output of the engine, which enables the quality of the fuel to be assessed. The better the fuel quality, the more torque and Brake Horse Power (BHP) is generated. The BHP is a measure of power at the crankshaft. This in turn alters the rotational speed of the propeller shaft rotation.

This feedback is used to calibrate the air/fuel map of, or air to primary fuel ratios to be used by, the engine, i.e. calibration of the long-term and short-term fuel trims, during a calibration period following engine start-up. As described above, the long-term fuel trim is adjusted based on readings of torque and/or rotational speed measured by the torgue and/or rotational speed sensors fitted to the propeller shaft of the engine. The long-term fuel trim adjusts the primary fuel profile for injecting the primary fuel into the engine, resulting in reduced quantities of primary fuel being used and therefore greater efficiency, and also reduced emissions. .

The fuel trims also provide a safety feature, to prevent damage to the propeller shaft during low loading situations. As described above, the torque and/or rotational speed sensors 120 measure the amount of torque and/or the rotational speed of the propeller shaft and the fuel trims take into account the state of loading of the vehicle when determining the quantities of the fuels to supply in order to avoid damage to the engine. This is necessary as the variable loads on a Heavy Goods Vehicle (HGC) would otherwise mean that full torque through an unloaded truck would twist or shatter the propeller shaft.

If the ECU (e.g. the primary fuel controller) reduces the output of the engine, e.g. by reducing the primary fuel supplied, it will likely reduce the amount of air going in by reducing the throttle opening position along with the primary fuel to maintain the air fuel ratio (AFR) required for the desired emissions/output target. Otherwise, if just the primary fuel is required, then this could put the engine into a lean state which could lead to higher exhaust gas temperature, engine damage and higher emissions.

By supplying the secondary fuel along with the primary fuel from engine start-up, unlike in conventional engines where the secondary fuel is not supplied until after a warm-up period of the engine, the long-term fuel trim takes the secondary fuel into account in adjusting a primary fuel profile in the primary fuel controller (i.e. the engine ECU) during the calibration period following engine start- up. The primary fuel profile enables the ECU to control the primary fuel injectors to inject the correct quantity of primary fuel into the engine during operation. When the engine trims take into account the secondary fuel because the secondary fuel is present during the calibration period following engine start-up, it is presently understood that the long-term engine trim adjusts the primary fuel profile by reducing the quantities of primary fuel required to be injected. The benefits of this adjusted (i.e. calibrated) profile, which achieves more optimised fuel efficiency, occurs over the course of the time that the engine is in operation, since the engine operation relies on the adjusted primary fuel profile adjusted, i.e. calibrated, during the calibration period following start-up of the engine.

Figures 8, 9, 10a and 10b are screenshots of experimental data illustrating the improved efficiency provided when the secondary fuel is provided from engine start-up, as an example of the invention. As seen in Figure 8, and in more detail in Figure 10a, during experimental trials on an engine, when the engine was started up without the secondary gaseous fuel, i.e. in the manner of conventional dual-fuel systems where the gaseous fuel is not introduced until after a warm-up period of the engine following engine start-up, an average fuel flow rate for the primary fuel was found to be 2.55 litres/hour.

As seen in Figure 9, and in more detail in Figure 10b, during experimental trials on an engine, when the engine was started up with the secondary gaseous fuel, i.e. in accordance with the invention, an average fuel flow rate for the primary fuel was found to be 1.58 litres/hour in order to achieve the same engine power output. In other words, less primary fuel was required to provide the same power output.

It can therefore be seen that the present invention provides substantial benefits over prior art systems, since by introducing the small percentage of gaseous fuel from engine start-up, without waiting for the engine warm-up period to elapse, significant fuel savings were achieved. The savings are quantified as 0.97 litres/hour (i.e. 2.55 minus 1.58 l/h), or equivalently, more than 38% reduction in usage of primary fuel. The present invention has thus been shown to provide significant fuel savings by introducing secondary fuel from engine start-up as opposed to after the engine warm-up following start-up of the engine has elapsed as conventionally done.

The combustion chamber 112 may comprise a variety of different configurations. For example in a six-cylinder vehicle, the combustion chamber 112 may comprise six corresponding manifold branches feeding into six corresponding pistons (not shown). The operation of the whole primary fuel side of system is controlled by the ECU 104, which monitors and activates the various components of the internal combustion system as is required. Most of the links from the ECU to the various engine components are not shown. Some of these links between the ECU 104 and the components are optional depending on the vehicle configuration.

The gas controller 116 can read data which has been provided to the ECU by the various engine components, as indicated by communication line 134. The communication line 134 may be tangible, e.g. wired, or intangible, e.g. wireless.

The gas controller 116 can obtain data including the primary fuel flow rate data which has been supplied to the ECU 104. Using this data, the gas controller 116 can determine how much secondary fuel should be supplied to the combustion chamber using the method of a mapping profile described below. In one

embodiment, the gas controller 116 is implemented using a microprocessor for executing a computer program or algorithm stored in memory of the controller.

The algorithms which control the operation of the system, for example stored in the memory of the gas controller 116 in Figure 1 , can be implemented in software (SW), firmware (FW) or a combination of both.

The gas controller 116 determines the quantity of the secondary fuel which is to be input into the combustion chamber 112 as a fraction, or percentage, of the quantity of primary fuel flowing into the combustion chamber using a fuel mapping profile. An exemplary fuel mapping profile 200 is shown in Figure 2. This may be considered as a primary to secondary fuel mapping profile, which the skilled man would readily appreciate is different to the primary fuel mapping profile adjusted during the calibration period of the engine (which only relates to the primary fuel quantities). The x-axis in Figure 2 indicates the absolute percentage of primary fuel flow rate, he. the flow as a percentage of the maximum possible fuel flow rate of the primary fuel. The y-axis in Figure 2 indicates the quantity of the secondary fuel which needs to be injected as a relative percentage of the quantity of primary fuel to be injected. For example, if the primary fuel flow rate had a maximum flow rate of 100 litres per hour, then if the primary fuel flow rate was at 50 litres per hour, which is 50% of the total flow rate, then the corresponding quantity of secondary fuel, value 202, can be read from the fuel mapping profile as 3.8%. 3.8% of 50 litres per hour is 1.9 litres per hour, and so this is the correct quantity of the secondary fuel that should be injected. Thus, the quantity of the secondary fuel to be injected is a calculated percentage of the measured quantity of primary fuel supplied by the primary fuel controller (i.e. ECU 104 and primary fuel injectors 127), the percentage being based on a fuel mapping profile such as that shown in Figure 2.

As can be seen from Figure 2, the exemplary fuel mapping profile 200 has two distinct portions 204 and 206. In portion 204, as the quantity of primary fuel being injected increases, the relative percentage of secondary fuel which should be injected with the primary fuel to achieve optimum efficiency increases. The increase of the secondary fuel relative percentage is steep at first and then increases gradually towards a 4% relative percentage of secondary fuel, up until a threshold 208 of primary fuel flow. Above this threshold, in portion 206 of the fuel mapping profile, optimum efficiency of the engine can be achieved by the relative percentage of the amount of secondary fuel to be injected decreasing as the absolute quantity of primary fuel to be injected increases.

It is presently understand that there may be multiple reasons for the existence of the threshold. As the quantity of the primary fuel required increases, the quantity of air required to match the fuel, in order to retain the required ratio of fuel to air must necessarily increase. At low quantities of injected secondary fuel, there is sufficient air to obtain complete or near complete combustion, i.e. optimised combustion. However, as the required quantity of secondary fuel increases and the quantity of primary fuel increases, the injected secondary fuel may begin to displace some of the required air, thus starving the engine of the requisite quantity of oxygen for optimised combustion. As a result, a threshold is reached, above which, in order to achieve optimised combustion, the quantity of secondary fuel to be injected should decrease. Further, at higher engine speeds, the cracking effect may be diminished, as there is insufficient time for the cracking chain effect to fully take place with all of the fuel within the combustion chamber. As a result the percentage of secondary fuel required (as a fraction of the quantity of primary fuel) decreases, as there is an upper limit in how much primary fuel can be cracked which reduces with increasing engine speed.

Further, it has been found that the cracking process creates a self- sustaining chemical chain reaction within the combustion chamber which frees up additional free radicals, thus sustaining the cracking effect. As a result, once sufficient quantities of secondary fuel have been introduced into the combustion chamber, a threshold is achieved after which lower quantities of the secondary fuel are required to maintain the cracking effect as a result of the chain reaction freeing up further radicals.

Figure 3 shows an exemplary fuel flow mapping profile 300, similar to that shown in Figure 2. Fuel mapping profile 300 has a threshold primary fuel flow rate 308, above which the proportion of secondary fuel to be injected to achieve optimum efficiency decreases as the fuel flow rate of the primary fuel increases.

This threshold 308, above which the amount of secondary fuel cannot be increased, provides an advantage that the amount of gaseous fuel is limited to a maximum fuel flow rate. Since gaseous fuel is volatile and easily combusted, allowing too much gaseous fuel to flow can be a safety hazard, especially if large quantities of gas escape the fuel flow system. Thus limiting the secondary fuel flow rate in this manner provides a balance between fuel efficiency (where the engine is more efficient than conventional engines but possibly less efficient than it might otherwise be) and engine safety.

Thus, as described above, the fuel mapping profile allows the gas controller 116 to determine the fraction or relative percentage of the secondary fuel to be injected as a function of the quantity of the primary fuel being injected. The fuel mapping profile is based on maintaining the engine in an enhanced combustion mode of operation across the range of an engine's operation. In other words, just the right amount of secondary fuel (gas) is injected to maintain the vehicle in this enhanced combustion mode across its range of operation. By optimising the burn (or combustion process), it is possible to use less of the diesel or primary fuel, which results in greater fuel efficiency. it is presently understood that the enhanced combustion mode of embodiments of the invention is achieved by a chemical "cracking" process, which fundamentally alters the burn at a chemical level. Specifically, it is believed that the secondary fuel is used to crack the primary fuel such that the primary fuel is split into smaller molecules that are easier and more completely combusted. This means that less primary fuel is needed to achieve the same engine power and torque output, resulting in improved efficiency of an internal combustion engine.

Only a relatively small amount of gas or secondary fuel is needed to improve the combustion of the diesel or primary fuel. Initially, the gas is split into smaller components in the form of radicals or free radicals before and/or in the turbocharger 106 when mixed with air and compressed. These radicals then crack the diesel into smaller components in the combustion chamber 112 when they are compressed together during the combustion stage.

It is believed that the splitting and cracking process encourages a chemical chain reaction to take place throughout the combustion chamber 112 which results in a more homogeneous fuel/air mix. In a spark ignition engine for example, the gas mixes easily with the air and pervades the interior of the engine's combustion chamber. Moreover the gas burns easily so that it is entirely combusted and in doing so ensures that ail the fuel ignites also. A greater majority of the primary fuel is combusted in both engine types (spark ignition and compression ignition).

Accordingly, the efficiency of the engine is enhanced.

The term "cracking" is broadly understood as a chemical process for the splitting of molecules. In the sense of fuels, different fuels have different molecular structures; some have more complex molecular structures or longer-chained hydrocarbons as compared to others. Different fuels may contain different lengths of hydrocarbon chains or complexity of molecular structure. According to one embodiment the internal combustion engine is designed for use with a primary fuel, such as diesel. Diesel is constituted by relatively long-chained hydrocarbon molecules. Cracking enables these long-chained hydrocarbon molecules to be split into shorter-chained hydrocarbon molecules that are more efficiently combusted.

Thus, according to an embodiment the fuel is cracked to improve the efficiency of an internal combustion engine. In one embodiment, this is achieved by ionisation of the gas by mixing it with air and compressing it to produce radicals, which in turn crack the longer diesel hydrocarbon-chains. The principle of cracking, as is presently believed to occur, is specifically applied in the present invention by injecting a small amount of a secondary fuel constituted from relatively shorter-chained hydrocarbons, which results in increased efficiency of an internal combustion engine, for example improved fuel efficiency, less emissions, etc.

The amount of gas injected is carefully controlled based on the measured quantity of the diesel being used by the engine. More particularly, the exact amount of gas is based on a determined fuel mapping profile (envelope), described above, which according to various embodiments also takes into account other variables such as the state of the engine and/or the particulate emissions in the exhaust.

According to an embodiment, cracking enables the secondary fuel to act as both an accelerant and a reagent (or reactant). Specifically, a reagent brings about a chemical reaction and/or is consumed in the course of the chemical reaction. The radicals, produced by the cracking, induce a chemical reaction by attaching to, and breaking up, the primary fuel into shorter-chained hydrocarbons. Moreover, the resulting shorter chained hydrocarbons are more easily and more quickly combusted.

According to an embodiment and present understanding, cracking in the sense of splitting molecules is carried out twice. First, the gas is cracked and second, the diesel is cracked. More specifically, the gas is cracked during a compression phase of the engine cycle, which puts the gas into the physical condition necessary to crack the diesel by producing radicals. That is, the produced radicals are then present within the air mass during the ignition and combustion phase, splitting up the diesel molecules into smaller molecules that are more easily combusted. In this embodiment, the diesel cracking and

ignition/combustion occur simultaneously, but the gas cracking precedes it.

Although enhancement may occur with a quantity of secondary fuel of up to 25% by volume of the measured quantity of primary fuel, according to a preferred embodiment maximum enhancement occurs with a quantity of secondary fuel in the range from about 1% up to 15% by volume, further preferably between 3% and 6% by volume and even more preferably less than 4% by volume of the measured quantity of primary fuel.

In one embodiment, the quantity of the secondary fuel injected may be between four and six percent by volume of the measured quantity of the primary fuel. The functionality of the gas controller 116 will now be described. Figure 4 shows an exemplary arrangement 400 for the gas controller 116 according to one embodiment. The microcontroller includes a microcontroller 402, an analogue input protection 404, a UART (Universal Asynchronous Receiver / Transmitter) 406, a voltage regulator 408, an isolation switch 410, an injector driver 412 and an isolation solenoid driver 414.

The microcontroller 402 reads data from the CAN bus (Controller Area Network bus) of the ECU 104, as indicated by the arrows 452, 454. This can include data relating to fuel flow rate of the primary fuel, for example.

More particularly, the microcontroller may listen to the CAN bus for the SAE J 939 Parameter Group Name 65266 (0x0FEF2) - Liquid Fuel Economy (LFE). Bytes 0-1 of this data detail the primary fuel consumption, i.e. the primary fuel flow rate, and can be calculated to 0.125 litres per hour resolution. The microcontroller can then use a fuel mapping profile, which may be in the form of a lookup table or other format, to pulse injectors (described below) with varying duty cycles to adjust the amount of secondary fuel in order to maintain the target relative percentage of secondary fuel compared to the flow rate of primary fuel.

The microcontroller 402 sends information via the UART 406, which provides asynchronous serial communication in which the data format and transmission speeds are configurable. The UART enables communication with a Configuration PC 474 which holds profiling and configuration software.

Communication between the microcontroller 402 and the Configuration PC 474 via the UART may be bidirectional, i.e. data may be sent from the microcontroller 402 to the Configuration PC 474 and may be received by the microcontroller 402 from the Configuration PC, e.g. system data at the Configuration PC 474 may be read and monitored by the microcontroller 402.

The microcontroller 402 also receives data relating to the secondary fuel pressure from the analogue input 404a, which in turn receives pressure data measured by a rail pressure sensor 472 at the fuel injectors, in accordance with UN ECE R67 regulations for liquid petroleum gas injection. The analogue input 404a provides the means to monitor the pressure to enable a safety cut-off, should the pressure of the secondary fuel exceed an upper threshold pressure or drop below a lower threshold pressure, in which case the secondary fuel supply is cut off. A pressure which is too high may indicate a blockage and a pressure which is too low may indicate a leak, for example. The analogue input 404a is protected by input protection 404b, which provides electrical protection for the input to ensure the sensitive analogue inputs are protected and will remain functional.

A further cut-off safety measure is provided by a CAN bus data timeout (not shown), i.e. when no data is received from the CAN bus for a time longer than a predetermined time, the secondary fuel supply is cut off. This CAN bus data timeout is designed to be in accordance with UN ECE R67 regulation.

Further safety cut-off measures are not shown but are envisaged. For example, there may be a tilt sensor, for example in bus or coach applications, which instructs cut-off when the bus or coach tilts beyond a certain angle. Such extreme tilting may indicate an accident, at which time gas supply may be dangerous. Thus the gas supply may then be cut off on the basis of this data.

The microcontroller 402 instructs the injector drivers 412 to open and close injectors 464, 466 (corresponding to injector 128 of Figure 1 ) to open and close for the required duty cycle determined by the fuel mapping profile. Although two injectors 464, 466 are shown, it is also envisioned that there may be one injector, or more than two injectors, such as three, four, five or six injectors for example. There may be further injectors as well.

As a safety measure, in order for the secondary fuel to be supplied from the tank 118, the microcontroller 402 communicates with isolation solenoid drivers 414, which in turn communicate with a tank solenoid 468 and a reducer solenoid 470. If power is lost to the microcontroller, the tank solenoid 468 and reducer solenoid 470 will lose power and be biased closed, thereby cutting off the gas supply from the tank 118 as a physical safety means. Removal of power from any one of the tank solenoid and the reducer solenoid will cause the gas supply to be isolated from the engine. Removal of power from all of the injectors will also cause the gas supply to be isolated from the engine.

Power is provided to the gas controller 116 by means of a battery 458 and the vehicle ignition 460. The power is directed through an isolation switch 410, which is capable of shutting down the gas controller 116 in the event of electrical loss of power as a safety device. The isolation switch 410 may divert some of the power via a 24V-12V voltage step-down transformer in order to power the injector drivers 412. This enables use of relatively common 12 volt LPG (liquid petroleum gas) equipment. Alternatively, the isolation switch may send the power at 24V directly to the injector drivers 412 if LPG components which are suitable for use with 24 volts are used. The system also supports 12V in, 12V out configurations, e.g. for 12V automotive systems. In other words, where the power directed through the isolation switch 410 is 12V, the isolation switch may send this 12V power to the injector drivers.

The isolation switch 410 also diverts some of its received power to a voltage regulator 408, which sends this regulated power on to the microcontroller 402, for powering the microcontroller 402.

A further safety device may be provided by an emergency stop button or kill switch (not shown) on the vehicle, connected to the power system.

The gas controller 116 is grounded to the chassis at connection 456. Other ground connections are envisaged but are not shown, neither are the sensor power supplies shown. The ECU has a voltage supply output intended to power the sensors. The sensor may have a sensitive input voltage requirement (e.g. 5V) which is not commonly available on an HGV. This function could be built into the gas controller 116 to reduce the requirement for an additional voltage converter to power the sensor from the vehicles own power.

It is also envisaged that there may be a real time clock (RTC) for giving a date stamp for data logging, and an external memory for data logging.

The system may have the potential to tie in with the vehicle telematics system. This could be done via the CAN bus connection 452, 454, or via the UART connection 474.

Figure 5 shows a kit 500 that can be retrofitted to an existing engine according to an embodiment of the present invention.

The kit comprises a gas controller 116 that controls the injectors 128 (via a control line 538) for supplying a quantity of gas from the gas tank 118 to the existing internal combustion supply line 124 (see Figure 1 ). Thus, this kit is intended to be bolted onto an existing internal combustion engine. The kit can be retrofitted to a conventional internal combustion engine with no modifications to the ECU, the combustion chamber or control of the connections supplying it.

The kit 500 has further optional elements located between the gas tank 118 and the injectors 128. For example, a first pressure and temperature sensor 520, two electrical gas valves 524 and 530 able to perform as a solenoid or electrical shut-off, a vaporiser 526 capable of performing a gas regulation function and attached to a temperature sensor 528, a second pressure sensor 532 and a manual gas valve for providing a mechanical shut-off function. The gas tank may be equipped with a float 540. Electrical and mechanical valves may be installed for safety reasons to enable the gas supply to be shut off in the event of a fault mode or otherwise.

Figures 6a-6c show examples of a vehicle before and after a retrofitting operation according to an embodiment of the invention. More specifically, Figure 6a shows a side view of a vehicle before a retrofit of the gas controller system. In Figure 6a is shown a side view in which air tanks and a battery pack are fitted to a left hand side of the undercarriage of a truck. In Figure 6b, after the retrofit, the air tanks have been moved inside the chassis of the truck and have been replaced by a gas tank (i.e. secondary fuel supply). In Figure 6c, after the retrofit, and when viewed from the opposite side, the vehicle shows gas flowing from the gas tank through a gas solenoid (performing a similar function to the gas valves 524 and 530 in Figure 5) and a gas regulator (performing a similar function to the gas vaporiser 526 of Figure 5).

Figure 7 shows a method 700 of operating a combustion engine comprising a primary fuel controller (such as ECU 104) and a sensor for providing feedback to the primary fuel controller.

At step 710, the engine is started up. Step 712 depicts supplying primary fuel and secondary fuel to the combustion chamber of the engine from engine start up.

The method then splits into two branches which take place concurrently.

The method steps 702, 704, 706 and 708 shown in the left-hand branch of Figure 7 and described in more detail below may also be carried out at step 712 described above.

Referring now to the right-hand side of Figure 7, following engine start-up, i.e. once the combustion cycle has begun, the calibration period begins at step 714. Although the calibration period 714 is depicted as occurring after the primary and secondary fuels have been supplied to the combustion chamber at step 712, these two steps may start simultaneously.

During the calibration period, at step 706, data is received from one or more sensors, which may be torque and/or rotational sensor(s) 120 on the propeller shaft of the engine. The data received from the sensor(s) can be used at step 718 to calibrate the primary fuel controller, in the manner described above.

Steps 720 and 722 show that if the calibration period has not ended, the method keeps looping through steps 716 and 718, calibrating the primary fuel controller based on data from the sensors. The calibration period may be for example 15-30 seconds.

Once the calibration period ends, the system may perform a further constant calibration loop. At step 724, data may be received from one or more sensors, which may be torque and/or rotational sensor(s) 120 on the propeller shaft of the engine, or may be a combustion sensor, such as a lambda sensor, arranged in the exhaust of the engine to monitor the opacity of the exhaust from the engine.

At step 26, this received data is used to further calibrate the primary fuel controller, in the manner described above. The method carries on performing this loop while the engine continues to run.

Turning now to the left-hand branch of Figure 7, at step 702, the quantity of the primary fuel (e.g. diesel) supplied by the primary fuel controller is measured. This step may include reading the required data from the CAN bus 452, 454 of the ECU 104 as described above. The volume of the primary fuel supplied can also be determined by measuring the pressure in the primary fuel rail and the opening time of the injector used to introduce the primary fuel into the engine. This applies to both common rail injectors and unit injectors which are the most common primary fuel delivery systems in use on vehicular engines. Additionally the temperature of the primary fuel may be used in the volume calculation.

In an alternative embodiment the flow rate of the primary fuel is used in the determination of the instantaneous volume of the primary fuel used. This would be applicable to steady state engines, commonly found in plant or marine applications. In yet an alternative embodiment the pressure in the primary fuel rail could be determined directly from the RPM of the engine. In yet an alternative embodiment the opening time of the primary fuel injector could be determined using data obtained from a data bus connection such as, but not limited to, a CAN bus.

At step 704, the primary to secondary fuel mapping profile is used in conjunction with the measured primary fuel flow to determine a relative percentage of secondary fuel (e.g. gas) which is required to be input into the combustion chamber 112.

At step 706, the relative percentage is converted into a volume of secondary fuel required. The amount of secondary fuel required is translated into instructions for a supply mechanism, e.g. the required opening times for injectors (e.g. injectors 128 of Figure 1 ) which control the delivery of the secondary fuel, using a lookup table or similar. This is then used to instruct the injectors to open for the corresponding duty cycle to allow the correct volume of secondary fuel to enter the combustion chamber 112. The injectors can have different characteristics with respect to different fuel flow rates. They may also have different electrical or opening characteristics. The translation of the secondary fuel requirement into activation times for a plurality of injectors may take into account the characteristics of the secondary fuel injectors, in particular the minimum opening or operating time, below which the delivery of a minimum amount of the secondary fuel cannot be guaranteed.

The relationship between the individual injector opening times and the delivery of the secondary fuel can be determined experimentally by a calibration process. The results of this calibration procedure can then be stored in non-volatile memory in the system.

The injector opening times can be adjusted according to the pressure and temperature of the secondary fuel.

The injectors which control the delivery of the secondary fuel may then be driven with an electrical signal designed to open and close the injector with a minimum of latency and also to minimise the steady state electrical power dissipation in the injector. Typically this would be achieved using a peak and hold pulse width modulation technique.

At step 708, the method goes back in a loop to step 702. The method keeps repeating until the system is shut off.

In summary, a primary fuel consisting of relatively long chain hydrocarbon molecules is designed to be combusted in the cylinder of an internal combustion engine. A secondary fuel is introduced into the engine cylinder such that there is an improvement in the efficiency of the combustion process and hence the efficiency of the engine. It is believed that the secondary fuel is able to act as an accelerant, reagent, reactant or catalyst and which is able to co-combust. The simultaneous combustion of both primary and secondary fuels causes the engine to operate with greater efficiency than if the fuels had been combusted individually.

This enhanced combustion effect, or combustion improvement can, according to current understanding, be attributed to the addition of the secondary fuel causing more complete combustion of the primary fuel and also faster combustion of the primary fuel. This is characterised by greater engine efficiency and lower emission of particulates. Such effects are brought about in one embodiment, according to present belief, by splitting the long chain hydrocarbon molecules of the primary fuel into smaller chain hydrocarbon molecules (commonly known as cracking), ionisation of the fuel air mixture in the engine cylinder, increasing the speed and spread of the flame front when combustion occurs and more favourable distribution of the fuel air mixture in the engine cylinder.

A more complete combustion of the primary hydrocarbon fuel is encouraged by introducing a secondary fuel, or a plurality of fuels, to act both as an accelerant and a reagent to create a more homogenous or uniform combustion, resulting in Increased efficiency. Increasing the efficiency of an engine means that better fuel economy and/or greater power is available while at the same time improving the emissions standard of the engine by the introduction of a secondary fuel.

Embodiments of the present invention provide a convenient method of delivery and control of a secondary fuel so that both primary and secondary fuels may be combusted simultaneously. Embodiments of the present invention also provide a convenient method of delivery and control of a secondary fuel, where the secondary fuel is in the gaseous state when introduced into the engine.

Embodiments of the present invention provide a secondary fuel delivery and control system that can be easily retrofitted to existing engines to convert them from operating on a single fuel to a plurality of fuels without extensive modification to the engine or its control system.

Embodiments of the present invention provide a secondary fuel delivery and control system that can be incorporated by engine suppliers or vehicle

manufacturers to facilitate operation with a plurality of fuels without the necessity to re map or re-calibrate the original engine management system.

Thus, embodiments of the present invention provide improved efficiency of an internal combustion engine without controlling and/or modifying the ECU, the main combustion chamber or the primary fuel supply of the engine. Instead, the quantity of primary fuel (for example, diesel) being supplied is measured and a controller is able to determine from a pre-determined fuel mapping profile, the optimal fractional amount of secondary fuel (for example, gas) that is to be injected.

An embodiment of the invention controls only the supply of the secondary fuel, relying on the existing controller (ECU) to operate as it is designed to, i.e. to control the supply of the primary fuel (that the engine was designed for). The original ECU monitors and adjusts the primary fuel volume to compensate for how efficiently the fuel is combusted. By operating in co-combustion mode, i.e. where both primary and secondary fuels are injected in optimum proportions, in effect the same efficiency (or energy given off) can be achieved with less primary fuel, and the ECU will only notice that less primary fuel is required. There is no overt control of the primary fuelling of the engine and any adaptation to the operation of the engine is affected primarily by the improvement in combustion.

Whereas many conventional systems describe controlling the quantity of primary fuel, embodiments of the inventions are concerned with controlling the quantity of the secondary fuel based on a measured fractional quantity of the primary fuel. Thus, the system is able to react, rather than invasively control the behaviour of the engine. The ECU of the vehicle will act as per normal, except that the engine will just achieve a more efficient burn.

Notably, the secondary fuel is supplied from engine start-up and not after a period of delay, i.e. a warm-up period of the engine. Conventional engines perform an initial fuel calibration during a calibration period following engine start-up, to calibrate the performance profile of the fuel based on its quality, i.e. calibration procedures of the long-term fuel trim and the short-term fuel trim. The long-term fuel trim adjusts the fuel profile for injecting the primary fuel into the engine based on e.g. readings of torque and/or rotational speed indicative of the power output of the engine, the readings being measured from torque and/or rotational speed sensors 120 fitted to the propeller shaft of the engine. The fuel trims also provide a safety feature, to prevent damage to the propeller shaft during low loading situations. By supplying the secondary fuel along with the primary fuel from engine start-up, unlike in conventional engines, the fuel trims take the secondary fuel into account and provide a more efficient adjustment of the primary fuel mapping profile, which achieves more optimised fuel efficiency over the course of the engine use, since the engine use relies on the adjusted fuel mapping profile adjusted, i.e.

calibrated during a calibration period following start-up of the engine.