EP2171259A2

EP2171259A2 - Combustion engine and method of controlling a combustion engine

Info

Publication number: EP2171259A2
Application number: EP08826725A
Authority: EP
Inventors: Maxime Makarov; André AGNERAY; Marc Bellenoue; Julien Sotton; Sergueï LABUDA
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2007-07-25
Filing date: 2008-07-21
Publication date: 2010-04-07
Also published as: BRPI0814068A2; FR2919343B1; JP2010534294A; US20100212631A1; KR20100057621A; FR2919343A1; WO2009016310A2; WO2009016310A3; CN101796293A; RU2010106652A

Abstract

Internal combustion engine comprising: a pulse current generator (6); at least one electrode (5) provided with at least one tip; a means (7) for controlling the electrical supply to said electrode (5) by said generator (6); and a combustion chamber (1) in which the tip of said electrode (5) is positioned, this tip being separated from the inner wall of the chamber (1) by a minimum separation distance (D). The current generator (6) and the electrode (5) are designed such that the power density (R) generated while said electrode (5) is being supplied is less than 105 watts per cubic centimetre, this power density (R) being equal to the electrical supply power (Pmax) of said electrode (5) divided by the minimum separation distance (D) cubed.

Description

COMBUSTION ENGINE AND METHOD OF CONTROLLING A MOTOR

COMBUSTION

The present invention generally relates to the field of ignition of fuel / oxidant mixture in a combustion chamber of an internal combustion engine.

More particularly, the invention relates to an internal combustion engine comprising: - a pulse current generator; at least one electrode having at least one tip;

a means for controlling the power supply of said electrode by said generator; and a combustion chamber in which is positioned the tip of said electrode, this point being remote from the inner wall of the chamber by a minimum distance (D) away.

The invention also relates to a method of controlling an internal combustion engine comprising:

a pulsed current generator; at least one electrode having at least one tip;

a means for controlling the power supply of said electrode by said generator; and a combustion chamber in which is positioned the tip of said electrode, said tip being remote from the inner wall of the chamber by a minimum distance (D); a piston slidably mounted in the chamber between a top dead center position and a bottom dead center position. Combustions inside a combustion chamber are often not phased at the most opportune moments to optimize the operation of an engine. A dispersion of the ignition timing from one cycle to another or from one engine speed to another can adversely affect engine performance and can promote the generation of pollutants or unburnt materials.

In this context, the present invention aims to provide an engine and a method for better control of the moment of ignition of the combustion / fuel mixture in the combustion chamber.

To this end, the engine of the invention, which is also in accordance with the generic definition given in the preamble defined above, is essentially characterized in that the current generator and the electrode are adapted so that the power density (R ) generated during the supply of said electrode is less than 10 power 5 watts per cubic centimeter, this power density (R) being equal to the power supply power (Pmax) of said electrode divided by the minimum distance (D) of high distance to the cube.

For the same purpose, the control method of the invention, which is moreover in conformity with the generic definition given in the preamble defined above, is essentially characterized by admitting a mixture of oxidant and fuel in the chamber of combustion and during the passage of the piston from its bottom dead position to its top dead position, prior to the arrival of the piston at the top dead center, generates a pulsed supply current of said electrode such that the power density generated when powering said electrode is less than 10 power 5 watts per cubic centimeter, this power density being calculated by dividing the power supply power of said electrode by the minimum distance of high distance cube.

For the understanding of the invention it should be noted that the "minimum distance of distance D" is the smallest distance measurable in a straight line between the tip of the electrode of the candle and the wall of the chamber and without intersection with an element of this candle. This minimum distance is the shortest path between the tip of the spark plug electrode and the ground electrode formed by the chamber wall. If an electric discharge should occur between the tip of this electrode and the chamber wall, the minimum length of the electric arc formed by this discharge would be equal to this minimum distance D.

Thus the risk of occurrence of an electric discharge is determined by the minimum distance D and the power supply of the electrode or by the power density depending on the power supply and this minimum distance D.

In this regard see the detail view on the left of Figure 1 which shows an enlarged side view of the chamber and the candle shown in Figure 1. The minimum distance D above is visible on the enlarged coast view and on Figure 1. It should be noted that the spark plug has a single pointed electrode which is electrically insulated from the inner chamber wall. Preferably, this inner wall constitutes a ground electrode. For the understanding of the present invention, it should be noted that the power supply noted by the sequence Pmax is the average power, that is to say the average value of the electrical power delivered to the electrode over a period of time. uninterrupted supply of this electrode.

In other words, the generator and the spark plug are adapted so that the power density subsequently denoted R defined by R = Pmax / D ³ is such that R <10 ⁵ Watts / cm3.

Thanks to such a dimensioning of the generator and the electrode, it is certain that during the feeding of the electrode an ionization of the air surrounding the electrode is obtained without the temperature of this air exceeding a threshold of ignition of the oxidant / fuel mixture. This local ionization without ignition of the mixture is used to generate free radicals such as ozone and / or intermediate hydrocarbon species produced by ionization. This results in a stratification of the mixture contained in the chamber with zones more or less rich in ionizing air and in free radicals.

Thanks to this chemical stratification, it is found that the self-ignition moment of the mixture can be determined with greater precision, which makes it possible to avoid too much dispersion of the self-ignition moment.

It is found that the auto ignition of the oxidant / fuel mixture is triggered in a preferred manner at the location of the stratum containing the free radicals and / or the hydrocarbon species produced by the ionization when the pressure and temperature conditions in the room are expected.

Preferably, the invention is applied to engines of the HCCI type, that is to say engines whose combustion is not initiated by a spark plug but whose combustion is self initiated when the only pressure conditions , temperature and mixing composition in the chamber are combined. On this type of self-igniting motor, the ionization of the mixture by supplying the electrode, makes it possible to prepare the auto-inflammation by creating preferred areas of self-ignition, without it being the power supply of the electrode that triggers this inflammation. Indeed, on this type of engine, the auto-ignition can take place while the electrode is no longer powered.

The creation of such preferred zones / strata of self-ignition by local modification of the chemical properties of the mixture makes it possible to avoid the danger of a sudden burning mass in the combustion chamber.

The power supply of the electrode with a low level of electrical power is also energy efficient compared to a power supply with a high electrical power.

For example, the power density generated during the supply of said electrode may be less than 10 watts per cubic centimeter. This embodiment makes it possible to define a volume power range for which it is certain that no self-ignition can be triggered by the ionization, at the moment of this ionization, the self-ignition occurring only later, once the pressure in the chamber has increased due to the rise of the piston towards the top dead center of the engine. Thus the self-ignition is not initiated by the electrode but is initiated by the conditions of pressure and temperature which improves the quality of combustion.

For example, the power density R generated during the supply of said electrode may be between 10 power and 10 power 4 watts per cubic centimeter.

This embodiment makes it possible to define a range for which it is certain that no autoignition can be triggered by the ionization alone, and for which it is certain that the level of ionization is sufficient to reduce the autoignition dispersions. in a significative way.

For example, it is possible for the pulse current generator to be adapted to generate a single-pulse current.

This embodiment facilitates the development of the motor power supply because only the transmitted power and the discharge rate are to be defined.

For example, it is possible for the pulse current generator to be adapted to generate an alternating current.

This alternative embodiment of the above allows an ionization of the mixture over a longer period than in the single pulse embodiment, which favors the creation of ionized strata of greater volume.

In this embodiment the pulse current generator is preferably adapted to generate an alternating current of frequency between 1 and 10 Megahertz and preferably between 1 and 5 Megahertz. This choice of frequency appears desirable to improve the quantity of radical species produced. With reference to the process of the invention mentioned above, it is possible to create the self-ignition conditions of the oxidant and fuel mixture by increasing the pressure in said combustion chamber by moving the piston towards its neutral position. high and prior to the self-ignition of said mixture is made to interrupt the supply of said pulse current electrode.

This embodiment makes it possible to prevent the ignition being initiated by the electrode, this ignition being triggered on its own as soon as the pressure and temperature conditions in the chamber are reached.

According to a preferred embodiment of the method of the invention, it is ensured that the pulsed current supply duration of the electrode is between 1 and 20 milliseconds. This time corresponds to the time necessary to generate sufficient free radicals and allow self-ignition repeatable over time. Still according to the method of the invention, it is possible to make sure that the pulsed supply current of the electrode is a single pulse current or is a radio frequency current of frequency between 1 and 5 Megahertz.

For the implementation of the motor and the method of the invention, the power density R generated by the generator around the electrode is such that the temperature around the electrode at the time of ionization is less than 800 ° Kelvin and preferably less than 500 ° Kelvin. This feature prevents the power supply of the electrode from being the cause of the inflammation.

Other features and advantages of the invention will emerge clearly from the description which is given below, for information only and in no way limitative, with reference to the accompanying drawings, in which: FIG. 1 represents a sectional view of a combustion chamber of an engine according to the invention; FIG. 2 represents three types of electrodes that may be suitable for the implementation of the invention; Figure 3 shows two types of power supply currents that may be suitable for supplying the electrode of an engine of the invention; FIG. 4 shows pressure evolution curves in a combustion chamber of a motor of the prior art, each curve of this figure corresponds to a clean engine cycle, the superposition of these curves on the same graph highlights the dispersion over time of the autoignition moments between the different motor cycles; FIG. 5 represents a graph similar to that of FIG. 4 but whose measurements of evolution of pressure are performed on an engine according to the invention, this graph highlighting the reduction of the autoignition dispersion.

As previously announced, the invention relates to an internal combustion engine such as that shown in Figure 1. This engine comprises a combustion chamber 1 in which slides a piston movable between a top dead center in which the volume of the chamber is minimum and a bottom dead point in which the volume of the chamber is maximum. This motor comprises a single pointed electrode whose tip is disposed inside the chamber at a distance D from the inner wall of the chamber. This distance D is the minimum distance

(measured in straight line and without obstacle) existing between the tip of the electrode and the wall, this distance is a determining factor of the maximum electrical power admissible by the electrode without this electric energy being discharged on the wall of the bedroom . The electrode 5 is selectively powered by a pulse current generator 6 as a function of a command generated by a control means 7.

The metal electrode 5 is pointed and is electrically insulated by a ceramic body of the wall of the combustion chamber 1 also called cylinder head. When supplied by the current generator with a voltage of 20 to 30 kV, the electrode causes the formation of a corona discharge also known by the term "corona" discharge associated or not with a homogeneous discharge known under the term of glow 8 discharge for incandescent discharge. This type of discharge occurs when the volumetric power supply electrical power is less than 10 power 5 watts per cubic centimeter. It should be noted that this power density R is equal to the average power supply power Pmax of said electrode 5 divided by the minimum distance D of high distance to the cube. This discharge modifies the chemical composition of the gas by partially cracking the gas in a zone limited to a few millimeters, or even 1 or 2 centimeters around the tip of the electrode. Preferably, both for the motor and for the method of the invention, it is ensured that the feeding of the electrode allowing this partial cracking takes place after the valves 3 and 4 of the engine are closed and shortly before the start of operation. compression or during this compression.

It is arranged that the energy or power supply of the electrode is chosen by the control means 7 which is a calculator, this power being variable as a function of the engine speed. Preferably, the duration of the power supply is chosen to be between 1 and 20 milliseconds. The partial cracking thus produces product of free radicals and / or intermediate hydrocarbon species initially at the zone 8 near the tip of the electrode 5. During compression, the turbulences which are preferably of spiral type (also known under the English term "swirl") widen the stratification zone 9 which contains the products of partial cracking. During the passage of the piston from its bottom dead point to its top dead center and subsequent to the power supply of the electrode which allowed the cracking, the pressure in the chamber increases to trigger auto ignition of the air / fuel mixture. This triggering is done in particular in the zones containing free radicals and / or intermediate hydrocarbon species.

FIGS. 2a, 2b and 2c show three types of electrodes respectively having one, two or four points, each of these electrodes being adapted to form the electrode of the motor according to the invention and to implement the method of the invention . It has been found that it is preferable for an electrode to have no more than four points in order to promote the quality of the discharge.

Preferably, the tip (s) of each electrode is (are) provided with a peak radius of curvature of between 10 and 100 μm.

Each of these electrodes can be fed in a single pulse manner with an electric current of the type of that of FIG. 3a or with a multi-pulse current with an alternating electric current of frequency 1 and 5 Megahertz. In each case, it is ensured that the power supply is limited, below a level which could generate premature ignition and above a level allowing partial cracking.

For this, the power supply power of said electrode must be between 10 power 2 and 10 power 4 watts per cubic centimeter and the duration of this power between 1 and 20 ms. FIGS. 4 and 5 each show examples of pressure changes in combustion chambers of engine for portions of motor cycles or auto-inflammations occur.

For each given pressure curve, the pressure in the chamber 1 is recorded as a function of time, this chamber containing a propane / air mixture of richness 0.5. The first rise in pressure is due to compression, that is to say the displacement of the piston from its bottom dead center to its top dead center.

The second pressure rise offset in time with respect to the first corresponds to the self-ignition of the mixture.

In FIG. 4, which shows the operation of a motor of the prior art, it can be seen that the delay between the beginning of the first rise in pressure (around 100 milliseconds) and the beginning of the second rise in pressure is variable as a function of cycles and a disparity of almost 100 ms can be observed between an early self-ignition cycle and a late self-ignition cycle. On the other hand, in FIG. 5, which represents the operation of an engine according to the invention and operating according to the method of the invention, it can be seen that the distortion of the ignition delay between different cycles is practically nil. It is thus easier to anticipate the moment of self-ignition from one motor cycle to another by performing partial cracking by supplying the electrode with reduced power prior to self-ignition.

Claims

claims

1) Internal combustion engine comprising:

- a pulse current generator (6); - a candle with a single electrode (5) having at least one tip; control means (7) for powering said electrode (5) with said generator (6); and a combustion chamber (1) in which the tip of said electrode (5) is positioned, this point being remote from the inner wall of the chamber

(1) with a minimum distance (D) and the electrode being electrically insulated from the inner wall, characterized in that the current generator (6) and the electrode (5) are adapted so that the power density (R) generated during the supply of said electrode (5) is between 10 power 2 watts per cubic centimeter and 10 power 5 watts per cubic centimeter, this power density (R) being equal to the average power of power supply (Pmax) of said electrode (5) divided by the minimum distance (D) of high distance to the cube.

2) Internal combustion engine according to claim 1, characterized in that the current generator (6) and the electrode (5) are adapted so that the power density (R) generated during the supply of said electrode is lower than at 10 power 4 watts per cubic centimeter. 3) Internal combustion engine according to claim 2, characterized in that the current generator (6) and the electrode (5) are adapted so that the power density (R) generated during the supply of said electrode is between 10 power 2 and 10 power 4 watts per cubic centimeter, the generator having a maximum power limit that can be generated defined so as to said power density is always lower at 10 power 4 watts per cubic centimeter.

4) Internal combustion engine according to any one of the preceding claims, characterized in that the pulse current generator (6) is adapted to generate a single-pulse current.

5) Internal combustion engine according to any one of claims 1 to 3, characterized in that the pulse current generator (6) is adapted to generate an alternating current.

6) Internal combustion engine according to the preceding claim, characterized in that said pulse current generator (6) is adapted to generate an alternating current of frequency between 1 and 10 Megahertz and preferably between 1 and 5 Megahertz.

A method of controlling an internal combustion engine comprising:

a pulsed current generator; - a candle with a single electrode having at least one tip;

a means for controlling the power supply of said electrode by said generator; and a combustion chamber in which is positioned the tip of said electrode, said tip being remote from the inner wall of the chamber of a minimum distance away (D) and the electrode being electrically isolated from the inner wall;

- a piston (2) slidably mounted in the chamber

(1) between a top dead center position and a bottom dead center position, characterized by admitting a mixture of oxidant and fuel in the combustion chamber (1) and during the passage of the piston from its position of bottom dead center towards its top dead center position, prior to the arrival of the piston (2) at the top dead center, a pulse current of supply of said electrode (5) is generated such that the power density (R) generated during the supply of said electrode (5) is between 10 power 2 watts per cubic centimeter and 10 power 5 watts per cubic centimeter, this power density (R) being calculated by dividing the average power supply power (Pmax) of said electrode (5) by the minimum distance (D) of high distance to the cube.

8) Process according to claim 7, characterized in that creates the conditions of self ignition of the mixture of oxidizer and fuel by increasing the pressure in said combustion chamber (1) by the movement of the piston to its stitch position high dead and prior to the self-ignition of said mixture is interrupted the supply of said electrode (5) pulsed current.

9) Method according to at least one of claims 7 and 8, characterized in that ensures that the pulse current supply duration of the electrode (5) is between 1 and 20 milliseconds. 10) Method according to at least one of the claims

7 to 9, characterized in that the supply pulse current of the electrode is either a monopulse current or a radio frequency current of frequency between 1 and 5 Megahertz.