WO2021214511A1

WO2021214511A1 - Ignition system

Info

Publication number: WO2021214511A1
Application number: PCT/IB2020/053709
Authority: WO
Inventors: Diego CACCIATORE; Fabio MINARELLI; Luca Rizzi; Giuseppe FORMISANO
Original assignee: Automobili Lamborghini S.P.A.
Priority date: 2020-04-20
Filing date: 2020-04-20
Publication date: 2021-10-28

Abstract

An ignition system for an internal combustion engine comprises a first housing (2) that defines a main combustion chamber and a second housing (3) that defines a pre combustion chamber. The system also comprises a sparking device (4) facing the pre chamber and a supply device (5) configured to feed a predetermined quantity of air (A) to the pre chamber.

Description

IGNITION SYSTEM

Technical field

This invention addresses the automotive sector.

More specifically, this invention relates to an ignition system which can advantageously be installed in an internal combustion engine. Background art

Prior art internal combustion engines normally include, amongst the other basic components, an engine block with one or more cylinders associated with the engine block and reciprocating pistons that move inside the cylinders. Generally speaking, fuel combustion occurs inside the cylinders to start the movement of the pistons and the pistons in turn set a crankshaft in rotation inside the engine block.

It is therefore evident that the overall efficiency of the engine is directly connected with the quality of the combustion process. In this sector, therefore, great importance is placed on possible solutions aimed at optimizing fuel ignition and the propagation of the flame front inside the main combustion chamber defined by the single cylinders.

In this context, the prior art teaches the implementation of an auxiliary combustion chamber or pre combustion chamber, which is disposed in fluid communication with the main chamber and the inside of which is made to face a sparking device, such as a spark plug, for example.

During normal operation of the engine, the fuel is fed into the main chamber and from there propagates into the pre chamber.

At this point, the sparking device ignites the fuel present in the pre chamber, generating a flame front which reaches the main chamber and ignites the part of the fuel inside the main chamber, thereby setting the piston in motion. The presence of the pre chamber allows increasing the turbulence in the combustion chamber, thus significantly increasing the speed, and hence the efficiency, of the combustion process, especially when the engine is running at low rpm.

Although it allows improving the general efficiency of the engine, however, this solution is not free of disadvantages which, as a whole, make it difficult to implement.

In particular, the presence of the pre chamber makes it more difficult to evacuate combustion exhaust gases, which remain at least partly trapped inside it and make it harder and less efficient to ignite the fuel in the subsequent engine cycles.

In pre chambers of this kind, called “passive, the exhaust gases can only partly be removed because the removal is effected solely by the flow of fuel from the main chamber.

These devices therefore require complex and onerous studies of the geometry of the pre chambers in order to maximize this effect.

Generally speaking, it may be observed that the design requirements of a passive pre chamber to evacuate exhaust gases at low rpm/loads contrast with the design requirements for high rpm/loads.

Pre chambers known as “active” pre chambers are also known. These comprise an injector configured to inject a predetermined quantity of fuel directly into the pre chamber.

Injection helps promote evacuation of the exhaust gases but only in a partial and poorly controllable manner. In this case, too, therefore, the advantages offered by the presence of the pre chamber are substantially nullified by the greater difficulty of igniting the fuel in the pre chamber.

Direct injection of the liquid fuel into the pre chamber also makes it much more complex to create a homogeneous mixture that is optimal for ignition and, what is more, leads to problems of fuel droplets settling on the walls of the pre chambers, resulting in particulate emissions.

In this context, the technical purpose which forms the basis of the present invention is to propose an ignition system which overcomes at least some of the above mentioned disadvantages of the prior art. Aim of the invention

More specifically, this invention has for an aim to provide an ignition system capable of optimizing the combustion efficiency of the fuel without suffering from the disadvantages due to the build-up of exhaust gases. The technical purpose indicated and the aims specified are substantially achieved by an ignition system comprising the technical features described in one or more of the appended claims.

According to this invention, an ignition system for an internal combustion engine comprises a first housing that defines a main combustion chamber and a second housing that defines a pre combustion chamber.

The system also comprises a sparking device facing the pre chamber and a supply device configured to feed a predetermined quantity of air to the pre chamber.

Advantageously, the system described herein allows promoting in a simple and efficient manner the removal of residual exhaust gases from the pre combustion chamber, thereby ensuring the highest possible engine efficiency at every engine cycle.

Another object of this invention is an internal combustion engine which advantageously comprises an ignition system according to this invention. The engine also comprises the supply sources necessary for its operation. More specifically, the engine comprises a main fuel supply line connected to the main chamber of the ignition system.

The engine also comprises a pneumatic pressure source, connected to a supply source, preferably configured to operate at a pressure between 3 bar and 15 bar.

The engine also comprises a fuel supply line, connected to an injector, preferably configured to operate at a pressure between 3.55 bar and 25 bar. Further, the supply device is configured to selectively inject the predetermined quantity of air or a mixture of air and fuel into the pre chamber.

The dependent claims, which are incorporated herein by reference, correspond to different embodiments of the invention.

Brief description of the drawings

Further features and advantages of this invention are more apparent in the following non-limiting description of a preferred but non-exclusive embodiment of an ignition system, as illustrated in the accompanying drawings, in which:

Figures 1A and 1 B show possible different operating configurations of a preferred embodiment of the system according to this invention. Detailed description of preferred embodiments of the invention The reference numeral 1 in the accompanying drawings generically denotes an ignition system for an internal combustion engine which, hereinafter in this description, is referred to simply as system 1 .

More specifically, the system 1 of this invention is particularly suitable for installation in an internal combustion petrol engine.

Structurally, the system 1 comprises a first housing 2, a second housing 3, a sparking device 4 and a supply device 5.

The first housing 2 defines a main combustion chamber which is connectable to the main fuel supply line 9 for the engine.

More specifically, the first housing 2 may be made in the form of a cylinder in which a piston is slidably inserted and with which it combines to define the main combustion chamber.

The cylinder may also have a fuel intake channel and a fuel exhaust channel for evacuating the exhaust gases at the end of each engine cycle.

The second housing 3, on the other hand, defines a pre combustion chamber, hereinafter in this description also denoted by the reference numeral 3, which is placed in direct fluid communication with the main combustion chamber.

More specifically, the second housing 3 shares with the first housing 2 a wall 3a that is provided with a plurality of holes which not only allow the fuel to be taken into the pre chamber but also allow the flame front to pass from the pre chamber to the main chamber. The sparking device 4 may, for example, be a plug capable of producing a spark that starts combustion of the fuel inside the pre chamber 3, thus creating a flame front which propagates into the main chamber and ignites the main quantity of fuel inside it.

The presence of the pre chamber allows maximizing the turbulence in the flame front, enhancing the efficiency of the combustion process and thereby improving engine performance.

The supply device 5, on the other hand, is configured to feed at least one predetermined quantity of air A into the pre chamber.

Injecting an air flow A into the pre chamber allows completely removing any residual exhaust gas that may still be present in the pre chamber following the fuel combustion process.

That way, the system 1 is guaranteed to operate under optimum conditions at all times, in particular in the absence of residues from preceding cycles which could negatively affect the correct functioning of the sparking device 4 or worsen the overall performance of the engine.

Injecting air A may serve to remove the exhaust gases completely or to keep them under a predetermined critical so that they do not negatively affect the correct operation of the system 1 .

For this purpose, the system 1 may comprise or be connected to a control unit configured to activate the supply device 5 to deliver the predetermined quantity of air A to the pre chamber at the end of each engine cycle or after a preset number of engine cycles suitably selected to ensure optimum engine operation.

Structurally, the supply device 5 comprises a supply source 6, alternatively identifiable as air supply source 6, which is connectable to a pneumatic pressure source and which is configured to feed the predetermined quantity of air A into the pre chamber.

The pneumatic pressure source thus generates a flow of air A which is fed into the pre chamber through the supply source 6. The supply source 6 may thus comprise an open nozzle, facing the pre chamber to deliver the predetermined quantity of air A into the pre chamber. In other words, the nozzle places the pre chamber in fluid communication with the supply source 6.

In this case, the pre chamber is configured as a passive pre chamber in that the fuel needed for its operation is fed into it solely from the main chamber through the wall 3a.

The supply device 5 may comprise an injector 7, alternatively identifiable as fuel injector 7, which is connectable to a supply line of fuel C and which is configured to inject a predetermined quantity of fuel C into the pre chamber. The supply line of fuel C thus generates a flow of fuel C which is fed into the pre chamber through the injector 7.

The injector 7 may in turn comprise a nozzle which is selectively operable, for example through the above mentioned control unit, to deliver the predetermined quantity of fuel C into the pre chamber.

In this case, the pre chamber 3 is configured as an active pre chamber in that the fuel needed for its operation may be injected directly into it through the injector 7 without having to receive it from the main chamber.

More specifically, the injector 7 may have a nozzle and operating conditions such as to allow the fuel C delivered to the pre chamber to be nebulized and mixed with the air A already inside the pre chamber to produce a mixture M that is ready to be ignited.

In this context, the fuel C may be injected just after air A has been injected so as to ensure that there are no residual exhaust gases inside the pre chamber 3 and that the fuel C is mixed correctly only with air A. Alternatively, the supply device 5 may inject both air A and fuel C into the pre chamber simultaneously.

This feature allows producing inside the pre chamber a mixture M having a mix ratio that is precise and accurate in that it is guaranteed to contain only air A and fuel C because any other substance foreign to it is suitably removed by the injection process itself. That way it is also possible, for example, to inject into the pre chamber 3 a mixture M which has a low mix ratio and which is thus more easily ignitable (but provides lower thermal efficiency), while the main chamber is filled with a mixture M (fuel) which has a higher ratio, providing higher thermal efficiency, but whose lower ignitability is not significant because the sparking device 4 acts on the mixture M that is present inside the pre chamber.

More specifically, the predetermined quantity of fuel C fed to the pre chamber 3 in one engine cycle is sufficient to produce, with the air A present therein, a quantity of mixture M between 2% and 5% of the fuel requirement of the engine cycle, while the remaining fuel portion needed for the correct functioning of the engine is supplied directly to the main chamber through the main fuel supply line 9.

According to an aspect of this invention, the supply source 6 and the injector 7 may directly face the pre chamber 3 to inject into the pre chamber the predetermined quantity of air A and fuel C, respectively.

Alternatively, in accordance with a preferred embodiment, shown schematically in Figures 1A-1 B, the supply device 5 comprises a third housing 8 which defines a pre mixing chamber.

More specifically, the third housing 8 is interposed between the pre chamber and both the supply source 6 and the injector 7.

In other words, the third housing 8 is interposed between the pre chamber and the supply source 6 and also between the pre chamber and the injector 7.

For convenience, the pre mixing chamber is also denoted by the reference numeral 8 of the housing that defines it.

In other words, the third housing 8 is disposed along the feed path from the pneumatic pressure source and the supply line of the fuel C to the pre chamber.

The third housing 8 is in communication with the pneumatic pressure source, with the supply line of the fuel C and with the pre chamber 3. Thus, the pre mixing chamber 8 is configured to receive both the predetermined quantity of air A and the predetermined quantity of fuel C prior to their injection into the pre chamber.

The presence of the pre mixing chamber 8 allows mixing the fuel C with the air A in such a way as to prepare the fuel for its use in the pre chamber.

For this purpose, the pre mixing chamber has an optimized volume of between 1 cm³ and 4 cm³.

The size of the pre mixing chamber is particularly important because it directly affects the behaviour of the system in use.

In effect, reduced volumes speed up the dynamics of the system because injection of the fuel C into the pre mixing chamber and of the mixture M into the pre chamber can take place in the same engine cycle, allowing it to adapt rapidly to the operating conditions of the engine.

Excessively reduced volumes, however, may impair the efficiency of the mixing process because of the greater negative influence of spray and evaporation of the fuel C.

On the contrary, a larger volume causes slower dynamics in which the pre mixing chamber fulfils the function of reserve of the mixture M produced inside it, thus reducing the negative impact of the effects of spray and evaporation of the fuel C.

In this case, furthermore, the step of injecting the fuel C and the step of injecting the mixture M can be kept distinct from each other.

Excessively large volumes, however, may lead to excessive slowing of the system’s capacity to adapt to the operating conditions of the engine and to greater difficulty of transferring the mixture M into the pre chamber.

More specifically, the pre mixing chamber 8 is configured to receive a predetermined quantity of air A and a predetermined quantity of fuel C such as to produce a mixture M having a mix ratio between 0.7 and 1 .5.

Further, the predetermined quantity of air A and the predetermined quantity of fuel C may be varied in such a way as to modify the mix ratio of the mixture M that is produced inside the pre mixing chamber. It is thus possible to guarantee with even greater accuracy the precision of the mix ratio of the mixture M that is injected into the pre chamber, modulating it according to the specific operating needs of the engine.

In particular, the quantity of mixture M that can be produced inside the pre chamber is between 2% and 5% of the fuel requirement of one engine cycle, while the remaining fuel needed for the correct functioning of the engine is supplied directly to the main chamber through the main fuel supply line 9. The system 1 may also comprise a heating device operating on the pre mixing chamber to modify the temperature of the mixture M that is produced inside it.

This feature allows improving the evaporation of the liquid fuel, especially in cold starts.

Operatively, the system thus provides a multifunctional pre chamber with different possible operating states which are selectively operable as a function of the specific operating needs of the engine.

In particular, as shown in Figure 1A, the supply device 5 may feed only air A to the pre chamber so as to completely scavenge it of all residual exhaust gases.

As shown in Figure 1B, on the other hand, the supply device 5 may also feed directly to the pre chamber a mixture M specifically balanced to optimize engine performance and ready to be ignited.

Advantageously, this invention overcomes the abovementioned disadvantages of the prior art and achieves the preset aims by providing the user with an ignition system 1 that guarantees high performance at all times thanks to a pre chamber from which all residual exhaust gases from preceding engine cycles can be efficiently evacuated.

Another object of this invention is an internal combustion engine which comprises an ignition system 1 having one or more of the features described above. The engine also comprises a main fuel supply line 9 connected to the main chamber to feed it with a main flow of fuel, preferably in a quantity between 95% and 98% of the fuel requirement of one engine cycle.

The engine also comprises a pneumatic pressure source, connected to the supply source 6, preferably configured to operate at a pressure between 3 bar and 15 bar.

The engine also comprises a fuel supply line, connected to the injector 7, configured to operate at a pressure preferably between 3.5 bar and 25 bar and, still more preferably, equal to 7 bar. These values allow ensuring the correct supply of air A and fuel C through the supply device 5 during normal operation of the engine.

More specifically, the above mentioned values are particularly optimized for operating the engine when the fuel C used is, or comprises, petrol.

More specifically, the supply device 5 is configured to selectively feed the predetermined quantity of air A or a mixture of air A and fuel C into the pre chamber.

Claims

1 . An ignition system for an internal combustion engine, comprising:

- a first housing (2), defining a main combustion chamber which is connectable to a main fuel supply line;

- a second housing (3), defining a pre combustion chamber, the pre combustion chamber being in direct fluid communication with the main combustion chamber;

- a sparking device (4), facing the pre chamber;

- a supply device (5) configured to feed a predetermined quantity of air (A) to the pre chamber.

2. The system according to claim 1 , wherein the supply device (5) comprises a supply source (6), connectable to a pneumatic pressure source and configured to feed the predetermined quantity of air (A) into the pre chamber.

3. The system according to claim 2, wherein the supply device (5) comprises an injector (7), connectable to a supply line of fuel (C) and configured to inject a predetermined quantity of fuel (C) into the pre chamber.

4. The system according to claim 3, wherein the supply source (6) and the injector (7) directly face the pre chamber.

5. The system according to claim 3, wherein the supply device (5) comprises a third housing (8), defining pre mixing chamber, interposed between the pre chamber and the injector (7) and in fluid communication with the supply source, the pre mixing chamber being configured to receive the predetermined quantity of air (A) and/or the predetermined quantity of fuel (C) prior to their being injected into the pre chamber.

6. The system according to claim 5, wherein the pre mixing chamber is configured to receive a predetermined quantity of air (A) and the predetermined quantity of fuel (C) such as to produce a mixture (M) having a mix ratio between 0.7 and 1 .5.

7. The system according to claim 6, wherein the supply device (5) is configured to feed to the pre chamber in each engine cycle a quantity of mixture (M) between 2% and 5% of the fuel requirement of the engine cycle.

8. The system according to any one of claims 5 to 7, wherein the pre mixing chamber has a volume of between 1 cm³ and 4 cm³.

9. The system according to any one of claims 5 to 8, comprising a heating device operating on the pre mixing chamber.

10. An internal combustion engine, comprising: a system according to any of the claims from 5 to 9;

- a main fuel supply line, connected to the main chamber; - a pneumatic pressure source, connected to the supply source (6) and preferably configured to operate at a pressure between 3 bar and 15 bar;

- a supply line of fuel (C), connected to the injector (7) and preferably configured to operate at a pressure between 3.5 bar and 25 bar; wherein the supply device (5) is configured to selectively feed the predetermined quantity of air (A) or a mixture (M) of air (A) and fuel (C) into the pre chamber.