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Field of the invention

The present invention relates to the f ield o f Otto cycle engines with fuels alternative to hydrocarbons and in particular to the field of engines fuelled by liquids with a high latent evaporation heat , such as alcohols or LPG .

State of the art

Spark ignition engines are generally equipped with a fuel inj ection system, which can be direct or indirect . This system takes care of dosing the liquid fuel in the correct proportions with the supply air . One of the characteristics of liquid fuels , in particular of the so-called " fuels" , i . e . fuels capable of forming explosive mixtures in the vapor phase , is that they absorb a lot of heat during evaporation . The phenomenon is linked to the latent heat of evaporation, a value which changes from substance to substance . Alcohols have a latent heat of evaporation more than double than gasolines . In addition, they have a lower calori fic content . The high latent heat and the low calori fic value mean that it is necessary to dose approximately double compared to gasolines with great cooling of the charge . The difficulty of evaporating liquid fuels hinders the correct formation of the mixture and, above all with a cold engine, the correct combustion. Corrective measures to the problem are known, ranging from choking of the supply air or increasing the metering, to create excess fuel, to heating the supply air by means of heat exchange with the exhaust manifolds or suitable electric heaters, generally arranged around the fuel duct that supplies the injectors. Generally, this duct is called "rail" according to the automotive lexicon.

The rail generally comprises a main duct, longitudinal in shape, to which so-called "branches" are connected which connect the rail to the injectors.

The branches can have variable length. According to some known solutions, the branches consist of hydraulic fittings for interconnecting the injectors to the rail, so that the branches have a minimum length.

Excess fuel injection is only effective with gasolines. In fact, these are made up of thousands of different hydrocarbon fractions, some of which evaporate at very low temperatures. Excess fuel therefore leads to an increase in these fractions with an improvement in combustion but with the simultaneous impinging of the walls of the admission ducts. This solution does not fit with alcohols because they, like LEG, are compounds containing one or at most two fractions, which are difficult to evaporate.

It is clear that in the context of this description, LPG is considered as a liquid fuel, which is injected in liquid form. Therefore, no LPG regasification procedure is envisaged.

Heating the air is useful for cold starting for all fuels, but it is very energy expensive and in any case suffers from a certain heat exchange latency between fuel droplets and combustion air. It is also difficult to adjust due to thermal inertia and therefore can only be used at cold start .

It should be considered here that the correct evaporation of the fuel also serves to reduce the particulate matter, hereinafter referred to as PM, emitted by the engine. Wherever there is a drop that has not completely evaporated during combustion, it burns on the surface, charring the heart of the drop itself, which forms PM as a Diesel cycle engine. Therefore, it is important to have a system with low energy consumption and rapid response that can guarantee the correct evaporation of the usable fuel throughout the engine's operating range.

In the context of diesel engines, fuel heating systems in the filter are known to obviate the risk of freezing in extremely cold climates.

Unless specifically excluded in the detailed description that follows , what is described in thi s chapter is to be considered as an integral part of the detailed description .

Summary of the invention

The obj ect of the present invention is to present a liquid fuel conditioning system that is at least alternative to known systems .

The basic idea o f the present invention is to arrange two fuel heating devices , in succession along the fuel path, wherein the first is arranged to be fed by the engine cooling liquid and the second device comprises at least an electrical res istance .

In other words , the first device comprises a heat exchanger between the engine cooling liquid and the fuel . While the second device, more expensive from an energy point of view, is of the electric type .

In terms of method, the fuel , while reaching the inj ectors , is first heated by the first device and subsequently heated by the second heating device .

The temporal success ion "before" and " after" as well as the concept of succession is linked to the arrangement of the two devices along the fuel path . The fuel first encounters the first device and then the second heating device .

Both the first device and the second heating device can be adj usted and deactivated according to the operating conditions of the engine and in particular, at least according to the temperature of the engine coolant .

Advantageously, the heating using the engine coolant is much more ef ficient from an energy point of view, but since it cannot be used at cold start , it is combined with the second electric heating device .

In other words , the present solution is optimal from an energy point of view in all thermal operating fields of the engine .

According to a preferred variant of the invention, the first device and the second device are arranged immediately upstream of the rail .

According to another preferred variant of the invention, the first heating device is arranged immediately upstream of the rail or integrated in the rail , while the second heating device is integrated in at least one interconnection branch of the fuel inj ector to the rail or is integrated directly into the inj ector . According to a preferred aspect of the present invention, the fuel is heated only when necessary and, as far as possible , with thermal energy recovered from the engine cooling circuit . An example of a method for controlling the final temperature of the charge entering the cylinder is also presented, in order to maximi ze the ef ficiency of the present invention and reduce the impact o f energy absorption which penali zes fuel consumption . The dependent claims describe preferred variants of the invention, forming an integral part of the present description .

Brief description of the figures

Further objects and advantages of the present invention will become clear from the detailed description that follows of an embodiment of the same (and of its variants) and from the annexed drawings given for purely explanatory and non-limiting purposes, in which:

Fig. 1 shows a first diagram, seen in section, of a liquid fuel conditioning system according to a first preferred variant of the invention;

Fig. 2 shows a detail of figure 1 in a front view which allows you to see the complete layout.

Fig. 3 shows a further detail of fig.l and in particular the internal part of the electric heating element.

Fig. 4 shows a further preferred variant of the invention.

Fig. 5 shows an exemplary flow diagram of the methods of controlling the temperature of the fuel and the charge drawn by the engine .

The same reference numbers and letters in the figures identify the same elements or components or functions.

It should also be noted that the terms "first", "second", "third", "superior", "inferior" and the like may be used herein to distinguish various items. These terms do not imply a spatial , sequential , or hierarchical order for the modi fied items unless specifically indicated or inferred from the text .

The elements and characteristics illustrated in the various preferred embodiments , including the drawings , can be combined with each other without however departing from the scope of protection of the present application as described below .

Detailed description

Figs . 1 - 4 show a fuel supply system for a spark-ignition combustion engine according to preferred variants of the present invention . Fig . l shows a longitudinal section of a preferred variant of a cylinder of an Otto cycle engine according to the present invention, in which a portion of a combustion chamber CCHM is connected to a fresh air intake duct IM through an inlet valve V . Fig . 2 shows a plan view of a portion o f the engine of figure 1 .

Figure 1 shows an intake duct IM into which a fuel inj ector I J faces . The transversal section of the rail RI can be seen, which feeds the inj ector through a branch SEH . Two galleries are identi fied in rail RI , a f irst gallery FG for the circulation of the fuel and the second gallery CG for the circulation of the coolant of the same engine .

The first and second galleries are arranged in such a way that the same rail acts as a liquid/ liquid heat exchanger . Preferably, the rail is made o f an extruded metal material , preferably aluminium .

According to the same variant , the second heating device is integrated in the branch SEH .

In particular , the branch may comprise an electrical resistor wound on the branch SEH or it may compri se a so- called " glow plug" which may be a glow plug similar to the preheating plug of Diesel engines . In other words , the second device can comprise a glow plug, which screws into a suitable threaded hole made in the branch SEH so that the active part of the glow plug, under operating conditions , is submerged in the fuel flowing towards the inj ector .

Figure 2 shows a set of inj ectors for as many cyl inders of the Otto cycle engine , fed by rail RI . It can be seen that the flow of coolant circulating in the second gallery CG is counter-current with respect to the flow of fuel circulating in the first gallery EG .

The first gallery comprises an inlet port Fl operatively connected with a high pressure fuel pump HPP . In the opposite position to the inlet opening FI , a pressure sensor RPS is preferably arranged which acts as a stopper for the f irst gallery .

The second gal lery, intended for the circulation of the coolant compri ses an inlet opening Cl and an outlet opening CO arranged so as to provide counter-current circulation of the coolant with respect to the circulation of the fuel .

Figure 3 shows an example of branch SHE , which interconnects the first gallery EG o f the rail with an inj ector I J through the respective branch SEH . In addition to the channel FC in which the fuel passes , it includes a heating element HE . In particular, the heating element is represented as a res istance wound around the channel FC . At least one of the branches comprises a fuel temperature sensor FTS , useful for control ling the f inal temperature of the fuel itself in closed loop control . The temperature sensor is pre ferably arranged downstream of the heating element considering the direction of circulation of the fuel .

It is possible to identi fy, from the entropy and/or enthalpy diagram of the fuel itsel f , the boiling temperature as a function of the pressure . Thus , according to a preferred aspect of the invention, the fuel temperature is regulated as a function of the pressure present in the rail and measured continuously by the pressure sensor RPS shown in figure 2 . In particular, the fuel temperature is controlled so as to always slightly below the boiling temperature of the fuel . In thi s way, it is possible to avoid the formation of vapour bubbles which would distort the inj ected quantities , with the detriment of combustion, and would quickly destroy the inj ector due to cavitation phenomena . The fuel pump HPP and inj ectors I J are operational ly controlled by the engine control processing unit ECU . Preferably, the same ECU is conf igured to control the power supply of the second heating device .

Preferably, the second gallery CG, or any point of the refrigeration circuit, which feeds the second gallery, is equipped with a thermostatic valve TV or one that can be controlled electrically by the processing unit ECU . The valve is arranged to open when the engine coolant temperature exceeds a predetermined temperature di f ference between the coolant and the fuel .

The second heating device can be activated independently of the operating conditions of the thermal engine , however, the possibility of deactivating the first device by means of the valve TV is very advantageous , as this allows to avoid any heat dissipation in the engine cooling circuit .

In the case of a thermostatic valve , this temperature threshold is fixed . On the other hand, when the valve is controllable , the proces sing unit ECU is configured to control the opening of the valve so as to ensure an advantageous heat exchange .

For example , the ECU can vary the opening threshold of the valve TV according to the ambient temperature .

According to a preferred aspect of the invention, the ECU is configured to close the valve TV so as to prevent the fuel from boiling.

According to a further preferred aspect of the invention, the ECU is configured to close the valve TV when the engine exceeds a predetermined throttle point. In other words, when the engine works at high load, i.e. at high rpm and high torque, it is advantageous to interrupt the heating of the fuel in order to avoid, maximizing the heat absorbed by evaporation from the supply air, the detonation of the engine and at the same time virtually increasing the volumetric filling coefficient, which allows to increase the power.

Fig. 4 shows another preferred variant of the invention in which, as with the previous variant, the first heating device is integrated into the rail.

The rail, in this case, is U-shaped, with two rectilinear portions approximately parallel to each other.

The first portion is connected to the injectors by the branches SEH as previously shown.

The second portion, it alone, defines a liquid/liquid heat exchanger as described above.

Thus, of the first gallery EG a first portion FG1 is identified, thermally coupled with the second gallery CG to define a liquid/liquid heat exchanger, while a second portion FG2 of the first gallery EG is thermally separated from the second gallery. Preferably, the first and second portions of the first gallery FG are thermally disconnected, by means of a thermal break interconnection element RTC, for example made of plastic material , or by thinning the wall of the rail . This variant turns out to be an improvement over the previous one , since the heat exchange with the coolant liquid is carried out integrally upstream of the interconnection branches with the inj ectors . This fact is advantageous because it guarantees an identical fuel temperature for all the inj ectors of the battery .

Instead, according to the variant of figure 2 , the heat exchange could disadvantage some inj ectors compared to others .

Preferably, also in this case , the circulation o f the coolant liquid and of the fuel are mutually countercurrent . Also in thi s case there is an inlet opening Cl and an outlet opening CO o f the liquid of the second gal lery arranged so as to carry out the aforementioned countercurrent circulation . Advantageously, the fuel i s heated uni formly and at a constant temperature , it enters the second portion o f the first gallery FG2 where it meets one or more electric heaters EH which in this case can be of the wound type as shown in Figure 3 or can preferably be of the glow plug type GP, designed to heat the fuel uniformly before it reaches the temperature sensor FTS . According to the variant of figure 4 , it can also be stated that the first heating device is arranged upstream of the rail or is integrated in the rail depending or not on whether the first portion of the U is one with the second portion of the U .

Preferably, the second portion of the U can be suitably insulated so as not to lose heat towards the outside as well as presenting, i f necessary, the thermal cut RTC between the first FG1 and the second FG2 portion of the U rail .

The present variant can be combined with the previous one , providing that the branches are also equipped with electric heaters EH .

In this case , it can be stated that the second heating device is partially integrated in the rail and partially integrated in the interconnection branches SEH of the rail to the inj ectors . A first electric heating stage is therefore defined upstream of the second portion FG2 of the rail and a second electric heating stage on each branch SEH .

According to thi s preferred variant of the invention, the inj ector furthest away from the first electric heating stage is equipped with a further temperature sensor, so that the operation o f the first and second electric heating stages can be better coordinated with each other . According to a preferred aspect of the invention, the hardware of figures 1 to 4 is controlled by a method exempli fied by the flow chart of figure 5.

The method comprises a first step of acquisition of

- a temperature value of the air entering the engine using an ATS temperature sensor shown in figure 1 , an engine coolant temperature value , by means of a temperature sensor not shown and preferably associated with a point of the refrigeration circuit located at the outlet of the heat engine ,

- a fuel pressure value , preferably measured us ing the RSP sensor described above, e

- an air pressure value entering the engine, preferably measured using a pressure sensor APS or estimated using a model .

Knowing the law o f temperature variation due to the compression of the stoichiometric mixture inside the cylinder and knowing the minimum temperature that guarantees ef ficient evaporation of the inj ected fuel , it is possible to know the average temperature that the charge , i . e . the air- fuel mixture , must have which enters the cylinder at each filling cycle .

Then, once the temperature and pressure of the air and the temperature and pressure of the fuel are known, it is possible to calculate the amount of heat to be suppl ied to the fuel and/or to the air.

However, not all of the heat can be supplied to the fuel. It may in fact happen that this would reach the boiling point .

Thus, according to the present invention, a limited amount of heat is transferred to the fuel such as to avoid, once the fuel pressure is known, its boiling and the remaining heat is transferred to the air entering the engine, by means of a grid heater GH arranged on the air inlet manifold and shown in figure 1.

In other words, the heat is primarily transferred to the fuel, but when it is not possible to ensure adequate heating of the charge by heating the fuel alone, then the air entering the cylinder is also heated.

With reference to Figure 5, the method comprises the following steps in cyclical succession:

- Step 1: acquisition of

. a temperature value of the air entering the engine,

. an engine coolant temperature value,

. a fuel pressure value,

. an air pressure value entering the engine;

- Step 2: calculation of a heat Q_CH to be transferred to the charge so that there is complete evaporation of the fuel at the end of the compression of the charge inside the cylinder of the heat engine and calculation of a temperature value T_F of the fuel after having acquired the heat calculated Q_CH before the respective engine cylinder inj ection;

- Step 3 : check if the temperature T_F of the fuel exceeds a boiling temperature T_boil o f the same fuel as a function of the pressure value of the fuel , i f said temperature T_F is lower than the boiling temperature then

Step 4 : fuel heating by trans ferring to it said calculated heat Q_CH, otherwise ,

- Step 5 : calculation of the limit heat Q_CH_L, which can be trans ferred to the fuel and

- Step 6 : heating of the fuel by trans ferring said limit heat Q_CH_L and heating of the air entering the engine by trans ferring to it a residual heat equal to Q_CH - Q_CH_L . This solution is optimal , since the heat exchange efficiency with the fuel is much better than the heat exchange with the engine inlet air .

When the coolant is suf ficiently hot , the heat to be supplied to the charge through the first heating device may be such as to allow the second heating device to be deactivated .

A first cold phase is therefore identified in extremely rigid conditions , in which the heating of the fuel is achieved only through the second heating device, subsequently, the first heating device operates in tandem with the second heating device , subsequently, as the of the coolant temperature , the second heating device is gradually deactivated .

In parallel , the possibi lity of deactivating the grid heater is being considered .

Preferably, the grid heater can be deactivated early enough i f a deactivatable gas/gas heat exchanger is arranged between the exhaust line of the heat engine and the intake line of the heat engine itsel f .

When the walls of the engine are hot enough to al low total deactivation first of the air heating and then al so of the fuel heating, the various devices are deactivated .

A deactivation sequence for the devices described above is proposed below : to . grid heater , b . second heating device , c . gas/gas heat exchanger if present , d . first heating device .

The present invention can advantageously be implemented and/or controlled via a program for suitable computational means such as ECUs , which compri ses coding means for implementing one or more steps of the method, when this program is executed on a suitable computational means . Therefore, it is understood that the scope of protection extends to said program and al so to computer-readable means comprising a recorded message , said computer-readable means comprising program coding means for carrying out one or more steps of the method, when said program is executed on a computational medium.

Variants of the non-limiting example described are possible , without however departing from the scope of protection of the present invention, including all equivalent embodiments for a person skilled in the art , to the contents o f the claims .

From the description given above , the person skilled in the art is capable of reali zing the obj ect of the invention without introducing further constructive details .