FR2960261A1 - Internal combustion engine e.g. diesel engine, combustion controlling method for motor vehicle, involves injecting fuel in homogeneous fuel-air mixture with mass ratio between two fuels during phase of compression of engine - Google Patents

Abstract

The method involves carrying homogeneous fuel-air mixture with recirculated exhaust gas, air and fuel i.e. petrol, in a combustion chamber (12) of an internal combustion engine during an intake phase of the engine. Another fuel i.e. diesel, is injected in the homogeneous fuel-air mixture with a mass ratio between the former fuel and the latter fuel during a phase of compression of the engine to carry out stratified partial fuel-air mixture so as to obtain combustion of the fuel-air mixture in three successive steps with diffusion flame of the stratified partial fuel-air mixture.

Description

The present invention relates to a method for controlling the combustion of an internal combustion engine, in particular for a motor vehicle. It relates more particularly to such an engine operating in bi-fueling.

As is widely known, the bi-fuel operation of such an engine is derived from two major families of internal combustion engines.

One of these families is the spark ignition engine that runs on fuel that produces a stoichiometric homogeneous fuel mixture, such as gasoline, natural gas or ethanol. This type of fuel generally has a high octane number, which is not conducive to auto-ignition. This therefore allows combustion of the mixture by flame propagation. However, this type of combustion has the advantage of minimizing the discharge of pollutant emissions, such as nitrogen oxides (NOx), through the action of exhaust gas pollution control means, such as a three-way catalyst.

The other of these families concerns the engine that operates with a combustion of the mixture with diffusion flame using a fuel type diesel or biodiesel. This fuel has a high cetane number which is favorable for autoignition.

This type of engine has the advantage of limiting fuel consumption, but its operation with a lean fuel mixture prevents post-treatment of NOx by the three-way catalyst.

An engine operating in bi-fueling has the major disadvantage of not being able to precisely control the unfolding of the combustion. This leads to disparities in energy releases that can cause damage to the engine after violent combustion and inconvenience to the comfort of driving, including combustion noise.

In addition, given the mixture of the two fuels, it can be difficult to maintain the operation of the engine with a rich stoichiometry. This disrupts the effectiveness of the three-way catalyst, which must operate at stoichiometry, thereby releasing untreated pollutants into the atmosphere.

The present invention proposes to overcome the above disadvantages by a simple combustion control method that uses conventional fuels.

For this purpose, the present invention relates to a method of controlling the combustion of an internal combustion engine operating in four-cycle bicarburation and comprising a combustion chamber in which the combustion of a fuel mixture is carried out, means for intake with at least one intake manifold associated with an intake valve, exhaust means with at least one manifold and an exhaust valve, means for injecting a first fuel and injection means a second fuel, characterized in that during the intake phase of the engine, it consists in producing a homogeneous fuel mixture with recirculated exhaust gases, air and a first fuel in the combustion chamber of the engine, the rate of recirculated exhaust gas being between 15 to 50%, - to inject, during the compression phase of this engine, a second fuel in the homogeneous fuel mixture with a booster. rt in mass between the first and the second fuel between 50 and 95% to achieve a stratified partial carburized mixture, so as to obtain the combustion of the fuel mixture in three successive stages with diffusion flame of the partial stratified mixture and the combustion by flame propagation followed by self-ignition combustion of the homogeneous fuel mixture.

The method may consist in producing the homogeneous fuel mixture in the intake manifold before it enters the combustion chamber.

The method may include injecting the second fuel at a crank angle between 30 and 40 ° before the end of the engine compression phase.

The method may involve using an engine with a volumetric ratio of between 12 and 15.

The method may involve using gasoline as the first fuel.

The process may involve using diesel as the second fuel.

The other features and advantages of the invention will become apparent on reading the description which follows, given by way of illustration only and without limitation, and to which are appended: FIG. 1 which shows an internal combustion engine with bi-fueling using the method according to the invention and - Figure 2 which is a graph with the energy release curve according to the crank angle obtained with the method according to the invention. In FIG. 1, the internal combustion engine illustrated is an internal combustion engine operating with two fuels of different type (or bi-fueling) and in a four-stroke (or four-phase) mode with a phase of admission, compression , relaxation and escape. For ease of description, the first fuel is gasoline (RON type 95) to obtain a homogeneous fuel mixture close to stoichiometry while the second fuel is diesel with a cetane number compatible with a fuel. self-ignition to obtain a combustion with flame of premix and diffusion. The combination of these two fuels thus makes it possible to obtain a global fuel mixture which is stoichiometric.

Of course any other combination of two fuels can be considered, such as natural gas with diesel as an example.

This engine comprises at least one cylinder 10 having a combustion chamber 12 in which the combustion of a fuel mixture occurs. This combustion chamber is delimited by the peripheral wall 14 of the cylinder, the upper face 16 of the piston 18 sliding in this cylinder and the portion 20 of a cylinder head 22 facing the piston.

This cylinder head also carries an intake means 24 which comprises at least one intake manifold 26 controlled by a closure means, such as an intake valve 28. The cylinder head also carries a gas exhaust means 30 burners comprising at least one exhaust pipe 32 associated with a closure means 20, such as an exhaust valve 34. These exhaust means 30 are connected to an exhaust line (not shown) which comprises means for depollution of the exhaust gas (not shown), as a three-way catalyst, for the treatment including NOx. Injection means 36 of the first fuel of the gasoline type, in the form of a single or multi-port injector, are placed on the intake manifold so as to inject the fuel into this manifold in order to produce a fuel mixture therein. Injection means 38 of the second diesel type fuel, here also in the form of a single or multi-port injector, are located on the cylinder head 22 for injecting this fuel directly into the combustion chamber 12.

Of course, this engine also comprises a calculation unit (not shown), said engine-calculator, which contains maps or data tables making it possible to control the various parameters related to the operation of the engine, such as fuel injection parameters. , during the operation of this engine, a fuel-based homogeneous fuel mixture is conventionally admitted into the combustion chamber 12 during its intake phase during which the piston moves. between his top dead center and his bottom dead center. For this, the injector of the first fuel 36 is operational by introducing fuel into the intake manifold 26. This fuel mixes with the fluid present in the tubing to achieve a fuel mixture slightly lower than the richness 1.

Fluid means external air (at ambient or supercharged pressure) or a mixture of air (or supercharged air) and recirculated exhaust gas (abbreviated to EGR for Exhaust Gas Recirculation). By way of example, these recirculated exhaust gases can come from an EGR circuit (not shown) which starts with exhaust means 30 to reach the intake means 24 and more particularly on the intake manifold 26, as illustrated by the dotted EGR line 40.

This mixture is then introduced into the combustion chamber, during the opening of the intake valve 28, during the entire intake phase by occupying the entire volume of the combustion chamber in the form of a homogeneous fuel mixture air, fuel and EGR.

In the known configuration where the recirculated exhaust gases are residual burnt gases of the combustion chamber, said internal EGR, the EGR circuit with its pipe 40 is non-existent. By this, the fuel mixture produced in the intake manifold is a mixture of air and fuel gasoline. This mixture is then admitted into the combustion chamber inside which it mixes with the residual flue gases so as to obtain at the end of the intake phase a mixture of air (or supercharged air), fuel gasoline and EGR.

At the end of this intake phase, the fuel injector 36 is stopped and the intake valve 28 is controlled in the closed position.

In both cases of fuel mixture mentioned above, the recirculated gas content is between 15 to 50% of the total mass of air contained in the combustion chamber. Following this intake phase, the engine follows a compression phase with a displacement of the piston 18 from its bottom dead center to its top dead center.

During this movement, the previously defined gasoline fuel mixture is compressed. In this case, the engine used is an engine with a volumetric ratio between 12 and 15.

Before the piston reaches its top dead center position (TDC of FIG. 2) and at a crankshaft angle of between 30 ° and 40 ° before this TDC, the second diesel fuel injector 38 is actuated. This second fuel is introduced into the compressed homogeneous fuel mixture contained in the combustion chamber so as to produce a partial stratified mixture which is located around this injector. This fuel is admitted into the chamber with a quantity such that the ratio between the quantity of gasoline and the amount of diesel (by mass) is between 50 and 95%.

Once the second diesel fuel is injected, the carburetted mixture (with two fuels) present in the combustion chamber has an overall richness of 1 to 10. The combined effect of the heat released by the compressed carburetted mixture and the radicals of the In the diesel engine, the stratified fuel mixture self-ignites after the TDC during a portion of the engine expansion phase with a release of energy, as illustrated by the curve portion Cd of Figure 2. The EGR rate associated with engine compression controls the triggering of this auto-ignition. Following this combustion with a pre-mix and diffusion flame, the release of heat makes it possible to start the combustion of the fuel mixture via a propagation flame with a release of energy as illustrated by the curve portion Ce of FIG. 2. By this, the gasoline fuel mixture is ignited at several points of the combustion chamber and several flames propagate simultaneously in this chamber. Following this combustion at several points, the increase in temperature and pressure in the combustion chamber will trigger a self-ignition with a high energy release (curve CAI of Figure 2) of the fuel mixture which n ' has not yet burned and is essentially located near the cylinder wall.

This allows for a three-stage combustion process that provides a motor with a high efficiency that works stoichiometry thus promoting the post-treatment of NOx by the three-way catalyst.

Moreover, this process makes it possible to have very good results in terms of fuel consumption, reduction of combustion noise as well as reduction of the risk of occurrence of knocking.

Thanks to the invention, the emission of soot can be limited by the use of a small amount of the second diesel fuel in favor of large quantities of first gasoline fuel.

An increase in the rate of combustion is also obtained thanks to the multiple combustion points of the homogeneous fuel mixture.

It is also possible to maintain a flame spread in the gasoline fuel mixture despite the presence of a high level of EGR.

The present invention is not limited to the example described but encompasses all variants and all equivalents.

Claims (6)

1. A method for controlling the combustion of an internal combustion engine operating in four-cycle bicarburation and comprising a combustion chamber (12) in which the combustion of a fuel mixture is carried out, means of admission ( 24) with at least one intake manifold (26) associated with an intake valve (28), exhaust means (30) with at least one manifold (32) and an exhaust valve (34), means for injecting a first fuel (36) and means for injecting a second fuel (38), characterized in that it consists - during the intake phase of the engine, to produce a fuel mixture homogeneous with recirculated exhaust gas, air and a first fuel in the combustion chamber of the engine, the recirculated exhaust gas content being between 15 to 50%, to be injected, during the compression phase of this engine, a second fuel in the homogeneous fuel mixture with a mass ratio between the first and second fuel of between 50 and 95% to produce a stratified partial carburized mixture, so as to obtain the combustion of the fuel mixture in three successive stages with a diffusion flame of the partial stratified mixture and then combustion by flame propagation followed by combustion by self-ignition of the homogeneous fuel mixture. 2) Control method according to claim 1, characterized in that it consists in producing the homogeneous fuel mixture in the intake manifold (26) before admission into the combustion chamber. 3) Control method according to claim 1 or 2, characterized in that it consists in injecting the second fuel at a crank angle between 30 and 40 ° before the end of the compression phase of the engine. 4) Control method according to one of the preceding claims, characterized in that it consists in using a motor with a volumetric ratio of between 12 and 15. 5) Control method according to one of the preceding claims, characterized in that it consists in using gasoline as the first fuel. 6) Control method according to one of the preceding claims, characterized in that it consists of using diesel as a second fuel.