The present invention relates to the processing of fuels and recirculated exhaust gas for use in engines such as internal combustion engines and gas turbines.

Particularly, but not exclusively, the invention is concerned with engines that utilise recirculated exhaust gases to control the conditions for combustion in the engine cylinders, those which cool the recirculated exhaust gas, and those which use the recirculated exhaust gas to process fuels, by way of reforming or partial oxidation.

It is known to redirect a portion of the exhaust gas expelled from an engine following combustion for mixing with charge air to reduce the specific heat capacity of the cylinder contents and thereby lower the flame speed to lower the rate at which heat is released during combustion. Advantageously, this can suppress the formation of NOx (nitric oxide and/or nitrogen dioxide) and improve fuel economy (of particular importance at part load) and can also extend the "knock limit" (of

particular importance at high/full load) .

Conventionally, at full load some form of cooling is applied to the recirculated exhaust gases, which may be expelled from the engine at temperatures as high as 1000°C.

According to a first aspect of the invention, there is

provided an engine defined by claim 1.

According to a second aspect of the invention, there is provided an engine defined by claim 23. According to a third aspect of the invention, there is

provided a method of operating an engine according to claim 28.

According to a fourth aspect of the invention, there is provided a method of operating an engine according to claim 29.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an internal combustion engine having a known exhaust gas recirculation system in a first arrangement;

Figure 2 shows an internal combustion engine having a known exhaust gas recirculation system in a second arrangement;

Figure 3 shows an internal combustion engine having a known exhaust gas recirculation system in a third arrangement;

Figure 4 shows first, second and third embodiments of an internal combustion engine according to the present invention; Figure 5 shows a fourth embodiment of an internal combustion engine according to the present invention;

Figure 6 shows a fifth embodiment of an internal combustion engine according to the present invention; and

Figure 7 shows a sixth embodiment of an internal combustion engine according to the present invention;

Figure 8 shows a seventh embodiment of an internal combustion engine according to the present invention;

Figure 9 shows an eighth embodiment of an internal combustion engine according to the present invention,-

Figures 10a and 10b show a ninth embodiment of an internal combustion engine according to the present invention;

Figure 11 shows a tenth embodiment of an internal combustion engine according to the present invention; and Figure 12 shows an eleventh embodiment of an internal combustion engine according to the present invention.

Exhaust gas recirculation is applicable to both naturally aspirated engines and pressure charged engines . In both cases, the recirculated exhaust gas can be taken from various stages of the exhaust path and introduced into the air inlet path at various stages .

For example, in a turbocharged engine the exhaust gas can be extracted from the exhaust path 1015 upstream of the turbine 1040, and introduced into the air inlet path 1020 downstream of the compressor 1045 (see Fig. 1) or upstream of the

compressor 1045 (see Fig. 2) .

Alternatively, the exhaust gas can be extracted from the exhaust path 1015 downstream of the turbine, and introduced into the air inlet path 1020 upstream of the compressor 1045 (see Fig. 3) .

In the engines shown in Figures 1 to 3 , between being

extracted from the exhaust path 1015 and being delivered into the air inlet path 1020 the recirculated exhaust gas passes through an exhaust gas cooler 1030. Typically, this will be formed as a heat exchanger.

The engines shown in Figures 1 to 3 also comprise: an air filter 1100 for filtering air in the inlet path 1020; an intercooler 1110, for cooling air compressed by the compressor 1045; and a wastegate 1120, for providing a bypass path for exhaust gases from the engine to escape to atmosphere without passing through the turbine 1040. Any combination of these components may be optionally included in the engines of the following embodiments.

A first embodiment of an internal combustion engine according to the invention is shown schematically in Figure 4. The engine comprises a combustion chamber 110; an air induction system 120 for delivering air to the combustion chamber 110; an exhaust system 115 for relaying combusted gases from the combustion chamber to the atmosphere; and an exhaust gas recirculation system 125, 130, 135 to direct at least a portion of the combusted gases from the exhaust system 115 to be mixed with the air delivered by the air induction system.

The mixed air and recirculated exhaust gas are delivered to the combustion chamber 110 for combustion with a fuel delivered in any conventional way (for example, by injection into the mixed air and recirculated exhaust gas delivered to the combustion chamber) .

The exhaust gas recirculation system comprises a first transfer duct 125 which receives hot exhaust gas from the exhaust system 115 and delivers the hot exhaust gas to a conventional exhaust gas cooler 130 in the form of a heat exchanger 130, and a second transfer duct 135 which receives cooled exhaust gas from the heat exchanger 130 and delivers the cooled exhaust gases to the air induction system 120.

The exhaust gas recirculation system further comprises a source of a fluid 150 which delivers fluid directly into the flow of recirculated exhaust gas.

The source of fluid is preferably a fluid injector 150 (for example, having the structure of a conventional fuel injector) , which may deliver coolant into the recirculated exhaust gas. In this embodiment the fluid injector 150 injects fluid directly into the transfer ducting 125, 135, which provides a closed path for the exhaust gases

recirculated from the exhaust system 115 to the air induction system.

The source of fluid 150 may be positioned either upstream or downstream of the exhaust gas cooler 130 or, alternatively, replace the cooler 130 (in which case only a single continuous transfer duct is required) .

In the embodiment depicted in Figure 4, the coolant is delivered directly into the second transfer duct 135

downstream of the heat exchanger 130.

Coolants with high latent heats can be particularly effective in cooling the exhaust gas.

A second embodiment of the invention provides an internal combustion engine having the same components as the first embodiment. In this embodiment, the coolant delivered by the injector 150 is a fuel. Possible fuels for use as coolants include alcohols, such as ethanol or methanol, and blends of alcohols .

As shown below, the amount of fuel required to cool the recirculated exhaust gas by a desired amount will be less than the amount required for the desired operation of the engine, e.g. the amount required for a stoichiometric air- fuel ratio. The rest of the fuel required for combustion will be delivered in the conventional way (for example, by direct fuel

injection) . This will be reduced so that the total quantity of fuel delivered for combustion is maintained at the desired level .

In various preferred embodiments the engine may run on a fuel formed as a blend of a plurality of components. In such embodiments it is possible for the blended fuel to be

delivered both by conventional means and via the recirculated exhaust gas .

Alternatively, it is possible in such cases for a first fuel component to be delivered via the recirculated exhaust gas, while a second component is delivered in the conventional way to the charge air (inlet air mixed with recirculated exhaust gas, which already includes the first component) .

For the simple case in which the same fuel is delivered in both the conventional way and also to the recirculated exhaust gas, the following table sets out examples of the proportion of each required to achieve a desired amount of cooling.

TABLE 1. Gasoline E85 Fuelling Methanol

Fuelling Fuelling

Charge mass 1 kg/s 1 kg/s 1 kg/s flow inc. EGR

% EGR (mass) 10% 25% 20%

EGR 100 degC 200 degC 500 degC temperature at

fuel

introduction

point

Desired EGR 30 degC 30 degC 30 degC delivery

temperature

Cp of EGR 1.03 kJ/kgK 1.03 kJ/kgK 1.03 kj/kgK

Thermal energy 7.2 kJ 43.8 kJ 96.8 kj to be removed

Latent heat of 280 kJ/kg 838 kJ/kg 1170 kJ/kg fuel

Fuel flow rate 0.026 kg/s 0.052 kg/s 0.083 kg/s

Stoichiometric 14.5 :1 9.74 :1 6.4 : 1

AFR

Lambda 1 1 1

Air mass flow 0.9 kg/s 0.75 kg/s 0.8 kg/s

Total fuel for 0.062 kg/s 0.077 kg/s 0.125 kg/s AFR

Proportion of 41.5% 67.8% 66.2% total fuel

used for EGR

cooling

A third embodiment of the invention provides an internal combustion engine having the same components as the first embodiment. In this embodiment, the coolant delivered by the injector 150 is not a fuel. For example, the coolant may be water.

Preferably, water will be delivered directly into the flow of recirculated exhaust gas and remain in the flow to be mixed 2011/001473

- 8 - with intake air and delivered to the combustion chamber 110. The water may then be recaptured from the exhaust expelled from the engine. Alternatively, and less preferably, a coolant such as water can be recaptured following delivery into the flow of recirculated exhaust gas and prior to entry into the combustion chamber 110.

In various embodiments, the coolant may comprise both fuel and non-fuel coolants.

A fourth embodiment of an internal combustion engine according to the invention is shown schematically in Figure 5. The engine comprises a combustion chamber 210; an air induction system 220 for delivering air to the combustion chamber 210; an exhaust system 215 for relaying combusted gases from the combustion chamber to the atmosphere; and an exhaust gas recirculation system 225, 230, 235 to direct at least a portion of the combusted gases from the exhaust system 215 to be mixed with the air delivered by the air induction system.

An internal combustion engine of the fourth embodiment further comprises a plurality of coolant sources 250a, 250b, 250c.

The recirculated exhaust gas passes through one or more transfer ducts 225, 235 in order to flow from the exhaust path 215 to the air inlet path 220.

In addition to the cooling effect of any heat exchangers provided, the temperature of the exhaust gas will decrease, as it passes through the transfer ducting 225, 235, from a maximum temperature as it is directed from the main flow of exhaust gas exiting the combustion chamber 210. There is therefore a temperature gradient along the transfer ducting 225, 235.

Furthermore, the further upstream a coolant is delivered to the transfer ducting 225, 235 the longer the coolant will be present in the recirculated exhaust gas and thus the greater the cooling effect.

By altering the location along the transfer ducting 225, 235 at which coolant is delivered, it is possible to manipulate the amount of cooling of the recirculated exhaust gas.

As shown in Figure 5, a rail 260 is provided having a

plurality of coolant sources 250a, 250b, 250c (in this case fluid injectors) to allow coolant to be delivered at different locations along the rail 260.

In this embodiment an individual fluid injector can be chosen to deliver the coolant at a particular location along the transfer ducting 225, 235 in order to obtain a desired amount of cooling.

A further advantageous effect of embodiments of the invention is that when fuel is delivered to the recirculated exhaust gas at high enough temperatures, in addition to cooling of the recirculated exhaust gas, reforming of the fuel can occur.

In an internal combustion engine that runs on a blended fuel, the rail would deliver the components of the fuel separately; the rail would have a passage for each component.

Alternatively, a rail could be provided for each component. The rail(s) would be arranged to hold fuel injectors at 2011/001473

- 10 - different locations that each deliver a component of the blended fuel into the transfer ducting.

While alcohol-based fuels reform at temperatures as low as 250°C, paraffinic fuels, such as the major components of gasoline, require temperatures as high as 600°. Heat

exchangers are unable to provide sufficient heat to achieve reformation of these fuels. Conventionally, additional energy sources are required, for example plasma-based energy input.

However, exhaust gases can exit the engine with temperatures of 900°C to 1000°C and therefore can be used to reform fuels that reform at these temperatures .

There is a temperature gradient along the transfer ducting from temperatures as high as 1000°C at the upstream point to lower temperatures downstream. As a result, there are regions of the transfer ducting 225, 235 at which the temperature is sufficient for different fuels to be reformed.

In this embodiment, the fuel components that reform at higher temperatures can be introduced into the recirculated exhaust gas further upstream than the fuel components that reform at lower temperatures. For example, paraffinic components or gasoline itself can be introduced upstream of alcohol

components .

In some embodiments, a heat exchanger can be included in the transfer ducting to lower the temperature of the recirculated exhaust gas. In these embodiments, each fuel component can be introduced upstream and/or downstream of the heat exchanger. In order to aid and control reforming of the fuels, one or more reforming catalysts may be introduced along the path of the recirculated exhaust gas. For example, for a hydrocarbon fuel a reforming catalyst may be used so that acetylene and ethane are produced. Such products can aid combustion in the combustion chamber under various loading conditions.

In any of the embodiments set out above, the recirculation of exhaust gas and the delivery of fluid into recirculated exhaust gas may be optional depending on the mode of operation of the engine. For instance, the engine may work without recirculation in low temperature conditions, e.g. following starting of the engine and be activated only when the engine is operating in a normal temperature range.

A fifth embodiment of an internal combustion engine according to the invention is shown schematically in Figure 6. The engine comprises a combustion chamber (not shown) ; an air induction system 320 for delivering air to the combustion chamber 310; an exhaust system 315 for relaying combusted gases from the combustion chamber to the atmosphere; and an exhaust gas recirculation system 330, 350, 375, 380, 385, 390 to direct at least a portion of the combusted gases from the exhaust system 315 to be mixed with the air delivered by the air induction system.

The exhaust gas recirculation system comprises an air inlet 390, through which air can be introduced into the flow of recirculated exhaust gas prior to its entry into the air induction system 320. Preferably, a pump (not shown) is provided to force pressurised air through the air inlet 390. By delivering fuel and air into the hot flow of recirculated exhaust gas, it is possible to enable partial oxidation of the fuel within the hot flow. This embodiment is particularly advantageous if hydrocarbon fuel or fuel with a large

proportion of hydrocarbon is used, since hydrocarbons require the presence of oxygen and high temperatures to reform. This contrasts with alcohols and alcohol-based fuels, since the molecules of alcohols contain oxygen and therefore are less reliant upon the source of air at the air intake. For gasoline reforming an excess of air is needed in part load conditions of the engine to allow for gasoline reforming. The reforming reaction requires heat. This heat is supplied solely by the recirculated exhaust gas. No extra provision of heating (e.g. electrical) is needed.

Although partial oxidation of the fuel reduces the amount of energy released by the fuel during combustion, by partially oxidising a small amount of fuel, preferably about 6%, a significant amount of hydrogen can be added to the charge for combustion. The presence of the hydrogen molecules during combustion can improve flame speed, offsetting the retarding effect of the recirculated exhaust gas molecules. The reformed gases also assist in dethrottling the engine to improve part- load fuel consumption.

In preferable embodiments, a partial oxidation catalyst 380 for enhancing the partial oxidation of fuel may be included in the exhaust gas recirculation system prior to the supply of recirculated exhaust gas to the air induction system 320.

The partial oxidation catalyst 380 receives recirculated exhaust gas from the air inlet 390 and source of fuel 350. The heat of the exhaust gas can improve the effectiveness of the partial oxidation catalyst 380.

A valve A is provided to control the flow of exhaust gas from the partial oxidation catalyst 380 into the air induction system 320.

The engine includes a recirculated exhaust gas catalyst 375, which receives recirculated exhaust gas from the exhaust system 315. The catalyst can reduce the amount of NOx and promote oxidation of hydrocarbons and thereby extend the

"knock limit" .

The recirculated exhaust gas catalyst 375 supplies

recirculated exhaust gas to a recirculated exhaust gas cooler 330 (which could be a conventional heat exchanger and/or a fluid injector) . A valve B is provided to control flow of recirculated exhaust gas through the recirculated exhaust gas catalyst 375 and the recirculated exhaust gas cooler 330.

The recirculated exhaust gas cooler 330 supplies recirculated exhaust gas to the partial oxidation catalyst 380.

A bypass passage 385 may be provided to allow recirculated exhaust gas to be supplied to the partial oxidation catalyst 380 without passing through the recirculated exhaust gas catalyst 375 or the recirculated exhaust gas cooler 330. The flow of recirculated exhaust gas through bypass passage 385 is controlled by a valve C.

Each of valves A, B, and C may be either binary valves

(switching valves, which are either open or closed) , or more preferably metering valves (which allow the rate of flow to be controlled) .

The engine can further comprise a main exhaust catalyst 370 through which exhaust gas passes before being released into the atmosphere .

Such an engine may be used in the following modes of

operation.

In a cold start mode, valves A and B are closed and valve C is open. In this mode of operation, the air introduced into the exhaust gas recirculation system through the air inlet 390 can flow into the exhaust system 315. Advantageously, such a flow of air can aid the light-off of the main exhaust catalyst 370.

In a part- load mode, valve B is closed and valves A and C are open. The bypass passage 385 allows hot recirculated exhaust gas to enter the exhaust gas recirculation system without passing through the recirculated exhaust gas catalyst 375 or the recirculated exhaust gas cooler 330. Fuel introduced into the hot recirculated exhaust gas can be partially oxidised. This can improve combustion and increase tolerance to the presence of recirculated exhaust gas in the combustion

chambe .

In a mid- load mode, valve A is open and valves B and C can modulate the flow of recirculated exhaust gas through the recirculated exhaust gas catalyst 375 and the recirculated exhaust gas cooler 330 and through the bypass passage 385. To use this mode, valves B and C must be metering valves, but valve A could be a binary valve. Accordingly, the temperature of flow through the partial oxidation catalyst 380 can be controlled. As with the part-load mode, this can improve combustion and increase tolerance to the presence of

recirculated exhaust gas in the combustion chamber.

At high load, valve A is open, valves C is closed and valve B can be used to modulate the flow of recirculated exhaust gas.

In each of the above modes, the flow of air into the air inlet 390 can be modulated or prevented by the use of the pump (not shown) and/or suitable valving.

A sixth embodiment is shown in Figure 7. This is a variant of the Figure 6 embodiment, modified by the addition of a second bypass passage 395 to allow recirculated exhaust gas to bypass the partial oxidation catalyst 380. Flow through bypass passage 395 can be modulated by use of valve X.

Valves A and X could be binary valves to determine whether the recirculated exhaust gas passes through the partial oxidation catalyst 380, or metering valves to determine the proportion of the exhaust gas that passes through the partial oxidation catalyst 380.

In the embodiments of Figures 6 and 7 partial oxidation of fuel is carried out in the presence of recirculated exhaust gas. In these embodiments, the heat of the recirculated exhaust gas aids the action of the partial oxidation catalyst 380. However, it is not necessary to use recirculated exhaust gas to provide heat to the catalyst, and any hot gases can be used.

Figure 8 shows a seventh embodiment of a system for use in engines for reforming of fuels (for example, by partial oxidation) , comprising a supply conduit 400, a reforming catalyst 480, a delivery conduit 410, a conventional fuel supply means 420 (for example, a fuel injector) , a first fluid injector 450a, and a second fluid injector 450b.

In use, hot gas flows along the supply conduit 400 and

entrains fuel introduced by the fuel supply means 420. The flow of hot gas entraining the fuel passes over the reforming catalyst 480. The delivery conduit 410 carries the reformed fuel to be delivered to the combustion chamber of an engine.

The temperature of the reforming catalyst 480 can be closely controlled despite fluctuations in the temperature of the supplied hot gas by injection of a coolant, to directly contact the hot gas, using the first fluid injector 450a to introduce coolant at appropriate times. The first fluid injector 450a is arranged to introduce coolant into the supply conduit 400.

The temperature of the reformate exiting the reforming

catalyst 480 may be undesirably high. This can be reduced using the second fluid injector 450b to introduce coolant at appropriate times. The second fluid injector 450b is arranged to introduce coolant into the supply conduit 410.

Coolants for use in such an embodiment may be fuels, such as alcohols or paraffinic fuels or non- fuels, such as water. If water is used, then a dedicated water tank can be provided to store the water. Either the tank can be refilled, or the water can be recaptured before or after combustion, and

recirculated . Figure 9 shows an eighth embodiment of a system for use in engines for reforming of fuels (for example, by partial oxidation), comprising a supply conduit 500, a reforming catalyst 580, a delivery conduit 510, an air introduction means 520 (preferably, a pump) , a first fuel injector 550a, and a second fuel injector 550b. The supply conduit 500 and the delivery conduit 510 carry recirculated exhaust gases from the exhaust path of an engine to the air intake of the engine.

The first fuel injector 550a is shown to be located downstream of the catalyst 580. However, the first fuel injector 550a may be located so as to deliver fuel directly onto the

catalyst 580.

The second fuel injector 550b is located upstream of the catalyst 580.

At times of low engine load, it is desirable to reform the fuel. In this case, fuel is introduced into the recirculated exhaust gas by the first fuel injector 550a, so that a mixture of the fuel, recirculated exhaust gas and air from the air introduction means 520 passes over the catalyst 580, thereby promoting reforming of the fuel.

At times of high engine load, it may be less desirable to achieve reforming of the fuel. In this case, fuel is

introduced into the recirculated exhaust gas by the second fuel injector 550b. A mixture of the fuel and recirculated exhaust gas will not pass over the catalyst 580 and therefore reforming of the fuel is either prevented or significantly reduced. Optionally, the introduction of air by the air introduction means 520 may be prevented in this case. Optionally, the temperature of the reforming catalyst 580, and the temperature of the reformate exiting the reforming

catalyst 580, can be finely controlled by additionally

including fluid injectors 450a and 450b as described above with respect to Figure 8.

Figures 10a and 10b show a ninth embodiment of a system for use in engines for reforming of fuels (for example, by partial oxidation), comprising a supply conduit 600, a reforming catalyst 680, a delivery conduit 610, an air introduction means 620 (preferably, a pump), and a fuel injector 650.

In this embodiment, a movable cover 670 is provided to move between a first position (see Figure 10a) in which the

catalyst 680 is exposed, and a second position (see Figure 10b) , in which the catalyst 680 is shielded.

Preferably, the fuel injector 650 is arranged to deliver fuel directly onto the catalyst 680 when the cover 670 is in the first position to thereby allow the catalyst 680 to enhance reforming of the fuel, and onto the cover 670 when the cover 670 is in the second position to thereby prevent the catalyst 680 from enhancing reforming of the fuel. Put another way, in the second position the cover 670 can shield the catalyst from the delivered fuel .

Alternatively, the fuel injector 650 can be arranged to deliver fuel upstream of the catalyst 680, and the cover 670 in the second position can prevent the mixture of fuel and recirculated exhaust gas from contacting the catalyst. Put another way, in the second position the cover 670 can shield the catalyst from the mixture of fuel and recirculated exhaust gas . In either case, the cover 670 can be used so that, at times of low engine load it is in the first position to allow the catalyst to promote reforming of the fuel in the recirculated exhaust gas. At times of high engine load the cover 670 is in the second position to prevent the catalyst from promoting reforming of the fuel in the recirculated exhaust gas.

Figure 11 shows a tenth embodiment of the invention, which provides a system for use in engines for reforming of fuels (for example, by partial oxidation) , the system comprising a supply conduit 700, a reforming catalyst 780, a delivery conduit 710, an air introduction means 720 (preferably, a pump), and a fuel injector 750.

Additionally, the system comprises a bypass valves 770a, 770b and a bypass conduit 775 to provide an alternative path for the mixture of fuel and recirculated exhaust gas to reach the engine's air intake.

The bypass valves can be used so that, at times of low engine load, valve 770b is open and valve 770a is closed to force all the fuel in the recirculated exhaust gas to pass over the catalyst 780 to promote reforming of the fuel. At times of high engine load valve 770b is closed and valve 770a is open to allow the fuel in the recirculated exhaust gas to flow along the bypass conduit 775 without passing over the catalyst 780, thereby preventing or substantially reducing reforming of the fuel .

Alternatively, and as shown in the eleventh embodiment of the invention depicted in Figure 12, a single valve 770c can be provided to control the flow path of the recirculated exhaust gas. This valve can switch the flow path between ducts 710 and 775 and/or control the proportion of total flow which passes through each duct 710 and 755.

Valves 770a, 770b, 770c may be binary or metering valves. In the latter case, the ratio of the volume flow rate of

recirculated exhaust gas over the catalyst 780 to the volume flow rate of recirculated exhaust gas along the bypass passage 775 can be controlled in dependence upon engine load.

For example, the ratio of the flow of the mixture of fuel and recirculated gas over the catalyst 780 to the flow of the mixture of fuel and recirculated exhaust gas along the bypass passage 775 may increase with increasing load on the engine.

The variation may occur only above a first threshold value of engine load, below which all of the fuel and recirculated exhaust gas is directed over the catalyst. Furthermore, the variation may occur only below a second threshold value of engine load, above which all of the fuel and recirculated exhaust gas is directed along the bypass passage 775.

Whilst the embodiments set out above are internal combustion engines, the principal of cooling the recirculated exhaust gas and processing the fuel are also applicable to other types of engine that can utilise recirculated exhaust gas, for example a gas turbine .