FR3064685A1 - METHOD FOR STABILIZING A CONTROLLED DEGRADATION OF A COMBUSTION OF A THERMAL ENGINE - Google Patents

Abstract

The invention relates to a method for stabilizing a degraded combustion of a heat engine controlled to increase calories emitted by the heat engine, the heat engine comprising at least one cylinder with a piston moving back and forth in its interior and a time advance of an ignition point of a mixture of air and a main amount (INJP) of fuel injected into said at least one cylinder with respect to a passage of the piston through a combustion upper dead point ( PMHcomb) being decreased during the degraded combustion. On the main amount (INJP) of injected fuel with a decreased time advance, an auxiliary amount (INJaux) injected after the Combustion Top Dead Point (PMHcomb) is taken, this auxiliary amount (INJaux) of fuel being less than 20% the main amount (INJP) of injected fuel.

Description

Holder (s): PEUGEOT CITROEN AUTOMOBILES SA Société anonyme.

Extension request (s)

Agent (s): PEUGEOT CITROEN AUTOMOBILES SA Public limited company.

FR 3 064 685 - A1

(54) METHOD FOR STABILIZING A CONTROLLED DEGRADATION OF A COMBUSTION OF A HEAT ENGINE.

The invention relates to a method for stabilizing a degraded combustion of a heat engine controlled to increase the calories emitted by the heat engine, the heat engine comprising at least one cylinder with a piston moving back and forth in its interior and a time advance of an ignition point of an air mixture and of a main quantity (INJP) of fuel injected into said at least one cylinder with respect to a passage of the piston through a Top Dead Center of combustion (PMHcomb) being reduced during degraded combustion. From the main quantity (INJP) of fuel injected with a reduced time advance, an auxiliary quantity (INJaux) injected after the Top Neutral combustion point (PMHcomb) is taken, this auxiliary quantity (INJaux) of fuel being less than 20% the main quantity (INJP) of fuel injected.

The invention relates to a process for stabilization of controlled degradation of the combustion of a heat engine. The present invention applies to any heat engine not necessarily fitted to a motor vehicle, although this mode of application is preferred. This engine is preferably a petrol fuel engine.

In what follows, it will be taken as controlled degradation of the combustion of a heat engine degradation for the purpose of heating a pollution control element present in an exhaust line of the heat engine of a motor vehicle . This is not, however, limiting for the present invention.

To initiate a pollution control element, that is to say to make it reach its minimum operating temperature, this pollution control element being for example a three-way catalyst, it is necessary to bring calories into the associated exhaust line to the engine. For this, the combustion must be degraded. This temperature can be 400 ° C.

The ignition advance is then sub-stalled, in other words delayed, in order to load the exhaust line with calories. This has the consequence of reducing the combustion stability, felt by the driver due to an instability of the engine speed then occurring. This instability limits the potential for degradation and therefore the calories that can be brought to the exhaust line.

[0005] Thus, delaying the ignition advance generates combustion instabilities in the engine. For reasons of approval, the ignition advance is bounded lower by a minimum advance to ensure a certain level of stability. The ability to supply calories to the exhaust line is therefore limited by the combustion stability of the engine which must be kept.

When priming a pollution control element, the engine control imposes an operating mode degrading combustion to heat the exhaust line. The latter will play on the combustion settings to bring maximum calories to the pollution control element, for example an increase in the idle speed, a modification of the injection settings, including the duration or the injection pressure, and an application of torque reserves for degrading combustion, a torque reserve being engine torque not intended for propulsion of the vehicle equipped with the engine. The calorie recovery potential is however limited by the instability of combustion.

The document FR-A-2 828 describes an injection of a main quantity of fuel in the vicinity of a top dead center and of an additional quantity of fuel, called post-injection, injected after the main quantity when the temperature of the oxidation catalyst or of the catalytic phase integrated into the particulate filter is less than a determined threshold, this threshold depending on the initiation temperature of the oxidation catalyst.

This document relates to a diesel engine. It is, in fact, known for such an engine to carry out post injections. This is not the case for heat engines running on other fuels such as petrol, ethanol or gas. Such post-injections in addition to the main quantity injected increase fuel consumption and do not solve the problem of instabilities occurring during a controlled degradation of combustion, a problem which this document does not even address. In addition, such post-injections can be dangerous for the element or the pollution control elements found in the exhaust line, in particular for petrol fueled engines.

The problem underlying the present invention is to stabilize degraded combustion of a heat engine, in particular degraded combustion controlled for the purpose of heating an element present in the vehicle, for example one or more elements of depollution present in the exhaust line of the heat engine.

To achieve this objective, there is provided according to the invention a method for stabilizing a degraded combustion of a heat engine controlled to increase the calories emitted by the heat engine, the heat engine comprising at least one cylinder with a piston moving back and forth inside and a time advance of a point of ignition of a mixture of air and a main amount of fuel injected into said at least one cylinder with respect to a passage of the piston by a combustion top dead center being reduced during degraded combustion, characterized in that, from the main quantity of fuel injected with a reduced time advance, an auxiliary quantity injected is taken after the combustion top dead center, this quantity auxiliary fuel being less than 20% of the main quantity of fuel injected.

The technical effect is to obtain stabilization of the degraded combustion, which the prior art could not achieve. The potential for degraded combustion is limited by combustion stability. The ignition advance cannot be delayed beyond the minimum advance to avoid misfires. The injection of an auxiliary quantity of fuel after the ignition point stabilizes combustion by creating turbulence in the combustion chamber, as well as a locally strong richness close to the spark plug.

It could be that a fuel injection is done in several parts depending on the state of the art. It is for example known to carry out up to at least three injections. On the other hand, these injections, in particular the last of these injections, do not resemble the injection of an auxiliary quantity of fuel, since part of these known injections do not occur after Top Dead Center and are not intended to stabilize degraded combustion.

There may also be additional post injections of fuel, therefore not taken from a main amount of fuel, these post injections can happen after the passage of Top Dead Center of combustion. These post injections do not form with air a stoichiometric mixture burning in the cylinder but self-igniting in the exhaust line.

In the context of the invention, the air and fuel mixture coming from the auxiliary quantity of fuel is stoichiometric with a richness of 1, which is not the case for a post injection of the state of the technical. Finally and above all, according to the invention, the auxiliary quantity of fuel injected is not an additional quantity of fuel added but is taken from the main quantity of fuel to be injected. This can cause a delayed ignition of an air mixture with the auxiliary amount of fuel. The fuel expenditure is also lower.

Advantageously, the auxiliary amount of fuel is between 2 and 20% of the main amount of fuel injected.

Advantageously, the auxiliary quantity of fuel is injected around the top dead center of combustion, an injection of the auxiliary quantity of fuel occurring between 0 ° and 110 ° taking as reference a crankshaft angle connected to the piston of said au minus one cylinder, the 0 ° crankshaft angle being associated with the passage of the Top Dead Center for combustion.

The auxiliary quantity of fuel is therefore injected in the vicinity of the combustion top dead center in order to be ignited by a delayed ignition in the cylinder.

Advantageously, the auxiliary quantity of fuel varies according to an effective engine operating point, the auxiliary quantity being a function of the engine speed and the engine torque. The main quantity of fuel varies according to the engine speed and engine torque: as the auxiliary quantity is taken from this main quantity, the auxiliary quantity can increase according to an increase in the main quantity. In addition, certain engine operating points are prone to the appearance of instability. For these points, it is possible to increase the auxiliary quantity injected to create more turbulence and combat the instability of combustion. This can be done independently of the main amount of fuel, therefore without increasing this main amount of fuel. The opposite is also possible with a reduction in the auxiliary quantity injected without a reduction in the main quantity of fuel.

Advantageously, an injection instant of the auxiliary quantity of fuel is calibrated with respect to the last Top Dead Center and / or to the ignition point.

Advantageously, during the controlled degraded combustion, a modification is made to the combustion settings concerning the following parameters taken individually or in combination: a main quantity injected, an injection pressure, an injection duration and a reserve of torque corresponding to the creation of an additional torque by the heat engine not used for propulsion of a vehicle equipped with the heat engine.

The invention also relates to a method of heating an exhaust line of a heat engine of a motor vehicle, for which there is carried out a heating of the exhaust line by controlled degraded combustion of the heat engine for a heating duration ending as soon as a predetermined temperature in the exhaust line is reached, characterized in that it implements such a stabilization process, a gain in combustion stability thus obtained making it possible to increase degradation controlled combustion of the combustion engine and to reach the predetermined temperature in the exhaust line with a reduced heating time or to less degrade the combustion of the combustion engine while reaching the predetermined temperature in the exhaust line after a duration heating equivalent to that obtained during unstabilized degraded combustion and am improve the performance regarding engine stability.

As previously mentioned, the injection of an auxiliary quantity of fuel taken from the main quantity stabilizes the combustion by creating turbulence in the combustion chamber. The instability of combustion is then reduced.

Two options are then offered. The first option is a possibility of increasing the controlled degradation of combustion. In fact, the gain in stability makes it possible to degrade combustion more and therefore to rise faster in temperature in the exhaust line. The eventual priming of one or more pollution control elements present in the line will be faster.

The second option is to take advantage of this gain in stability by maintaining the same level of degradation of combustion. In fact, the gain in stability makes it possible to degrade combustion less to remain at iso heating performance of the exhaust line and of a possible priming of an element or elements of pollution control. In this case, the comfort directly felt by the driver will therefore be better.

Advantageously, the heating is carried out for at least one pollution control element present in the exhaust line, said at least one pollution control element requiring obtaining a minimum temperature to ensure its operation, the heating process being effective as long as the minimum temperature of said at least one pollution control element is not reached.

This is one of the main objectives of the invention, given that a pollution control element only works effectively once a minimum temperature has been reached. Instead of possibly carrying out additional fuel post-injections, the present invention provides for a different distribution of the fuel injections ensuring adequate heating of the depollution element.

The invention relates to a powertrain comprising a heat engine, an engine control unit in charge of combustion in the heat engine and an exhaust line for the evacuation of combustion gases from the heat engine, characterized in that the engine control unit presents the means for implementing such a stabilization process or such a heating process.

Advantageously, when the exhaust line comprises at least one pollution control element requiring obtaining a minimum temperature to ensure its operation, at least one temperature sensor or a model is associated with said at least one pollution control element, the engine control unit comprising means for receiving the temperatures recorded by the temperature sensor or estimated by the model, means for comparing the temperatures recorded with a minimum operating temperature of said at least one pollution control element stored in the unit engine control by memory means and thermal engine control means for implementing stabilized degraded combustion as long as the minimum operating temperature is not reached.

This allows optimal control of the heating of the element or pollution control elements by degradation of the engine combustion, this degraded combustion being controlled by the engine control unit to start when the minimum temperature is not reached. and finally as soon as this minimum temperature is reached, the combustion in the heat engine returning to its optimal operation according to the parameters stored in the engine control unit.

The priming of the element or pollution control elements is done at lower cost. Indeed, the solution proposed by the present invention is purely software, requiring only a modification of the fuel injection and requiring no addition of heating equipment.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with regard to the attached drawing given by way of non-limiting example and in which:

- Figure 1 is a schematic representation of part of a combustion cycle in a cylinder of a motor vehicle, a main fuel injection and an auxiliary injection being carried out as part of the stabilization process of degraded combustion of the engine thermal according to the present invention.

It should be borne in mind that the figure is given by way of example and is not limitative of the invention. It constitutes a schematic representation of principle intended to facilitate the understanding of the invention and is not necessarily on the scale of practical applications.

Referring to Figure 1, the present invention relates to a method for stabilizing a degraded combustion of a heat engine controlled to increase the calories emitted by the heat engine. This degraded combustion is therefore desired and implemented by an engine control unit of the heat engine.

The heat engine comprises at least one cylinder with a piston moving back and forth inside. It is known that a time advance of an ignition point of an air mixture and of a main quantity INJP of fuel injected into said at least one cylinder with respect to a passage of the piston through a Top Dead Center PMHcomb combustion is generally implemented on most internal combustion engines when they are adjusted.

An INJP main quantity of fuel injected with a reduced time advance is taken from an INJaux auxiliary quantity injected after the Top dead center of combustion PMHcomb, this INJaux auxiliary quantity of fuel being less than 20% of the main INJP quantity. fuel injected. There is therefore no increase in the quantity of fuel injected, only a redistribution of the total quantity injected which remains the same as that previously calculated by the engine control unit but which is distributed differently by being split in at least two quantities, a main INJP quantity injected before passing the Top Dead Center for combustion PMHcomb and an auxiliary INJaux quantity injected after passing the Top Dead Center for combustion PMHcomb.

It may be that the main quantity INJP or the auxiliary quantity INJaux of fuel are injected in several injections. This also applies especially for the main quantity INJP of fuel but this does not change the relationships between the total main quantity INJP and the total auxiliary quantity INJaux in the context of the present invention.

The fuel can be gasoline, a mixture of gasoline with ethanol or pure ethanol, gas but also a diesel fuel, although the latter is not preferred. In the case of petrol, ethanol or a similar product or a mixture of two fuels, a stoichiometric ratio adapted to the type of fuel used is taken into account.

Advantageously, the auxiliary quantity INJaux of fuel can be between 2 and 20% of the main quantity INJP of fuel injected. This auxiliary quantity INJ of fuel is of reduced proportion compared to the main quantity INJP of fuel while being sufficient to create turbulence and stabilize the degraded combustion.

The auxiliary quantity INJaux of fuel can be injected around the Top dead center of combustion PMHcomb, an injection of the auxiliary quantity INJaux of fuel occurring between 0 ° and 110 ° taking as reference a crankshaft angle connected to the piston of said at least one cylinder, the 0 ° crankshaft angle being associated with the passage of the Top dead center of combustion PMHcomb.

Figure 1 shows a top dead center of admission PMHadm, this top dead center having been a top dead center of combustion for the previous combustion cycle, and a top dead center of combustion PMHcomb with a bottom dead center PMB interposed between the two High Dead Points.

The TDC Top Dead Center is the moment when the piston is at the highest point of its stroke in a cylinder, that is to say when the volume of the chamber formed in the cylinder between the piston and the wall internal of the cylinder is the weakest which corresponds to the moment of the maximum pressure before the combustion of the air and fuel mixture begins. The PMB Low Dead Center is the moment when the piston is at the lowest point of its stroke in a cylinder with the largest volume of the chamber, which corresponds to the end of the admission.

The main injection of the main fuel quantity INJP occurs between the top dead center intake PMHadm and the bottom dead center PMB. The injection of the main injection INJP can be started at 180 ° from the crankshaft angle, which is not limiting.

The auxiliary injection of the auxiliary quantity INJaux of fuel occurs in the vicinity of the top dead center of combustion PMHcomb, either before or after exceeding this point PMHcomb. The auxiliary injection INJaux can be done between 60 ° and -110 ° of crankshaft angle, the Top dead center of combustion PMHcomb being at 0 ° of crankshaft angle.

It is however preferable that all the injection of the auxiliary quantity INJaux is done after passing from the Top dead center of combustion PMHcomb, for example between 0 ° to -110 ° of crankshaft angle. It may however be possible that the start of the injection of the auxiliary quantity INJaux takes place before the Top dead center of combustion PMHcomb but ends after the Top dead center of combustion PMHcomb.

The Ign reference indicates the delayed ignition point. The duration of the INJaux auxiliary injection is less than the duration of the INJP main injection given the less amount of fuel to be injected.

The main injection INJP and the auxiliary injection INJaux can be done in predetermined ranges respectively Pla P and Pla aux. In FIG. 1, these areas Pla P and Pla aux are included between the respective horizontal lines having an arrow at each of their ends. The auxiliary injection INJaux of the auxiliary quantity INJaux of fuel can, for example, start before the Top dead center of combustion PMHcomb and finish after the Top dead center of combustion PMHcomb, preferably after passing this point PMHcomb. However, it is preferable that all the injection of the auxiliary quantity INJaux is injected after the Top Dead Center for combustion PMHcomb.

The percentage of the fuel mass of the main injection INJP can be equal to the total mass of fuel injected that decreases the fuel mass of the auxiliary injection INJaux.

The auxiliary quantity INJaux of fuel can vary according to an effective engine operating point, the auxiliary quantity INJaux being a function of the engine speed and the engine torque. Indeed, the main quantity INJP of fuel is a function of the engine speed and of the engine torque and therefore the same can be true for the auxiliary quantity INJaux of fuel. On the other hand, by experience, it can be noted that at equivalent engine speed and engine torque, the auxiliary quantity INJaux can be advantageously increased since it allows better stabilization of degraded combustion. A reduction in the auxiliary quantity INJaux as a function of the main quantity INJP can also be implemented when the instabilities of degraded combustion decrease.

It is possible to calibrate an injection instant of the auxiliary quantity INJ of fuel with respect to the last Top Dead Center PMHcomb and / or to the ignition point. The durations of the main INJP and auxiliary INJaux injections can therefore change and the respective ranges Pla P and Pla aux can also be offset from a previous range.

In Figure 1, the auxiliary injection INJaux is shown spaced from the last Top Dead Center which is the Top Dead Center of combustion PMHcomb but this is not limiting, the injection can start a little before the Top Dead Center of PMHcomb combustion or just after the change from the Top dead center of combustion PMHcomb, the auxiliary injection INJaux advantageously ending after the change from the Top dead center of combustion PMHcomb. It is however preferred that the auxiliary injection INJaux starts after the passage of the Top dead center of combustion PMHcomb.

During the controlled degraded combustion, a modification of the combustion settings can be carried out concerning the following parameters taken individually or in combination: an INJP main injection quantity, an injection pressure, an injection duration and a phasing and a torque reserve corresponding to the creation of an additional torque by the heat engine not used for the propulsion of a vehicle equipped with the heat engine.

In fact, the main quantity INJP of fuel injected will necessarily decrease compared to a main quantity INJP of fuel injected under the same running conditions of the vehicle, following the withdrawal of an auxiliary quantity INJaux of fuel injected with delay. The injection parameters of this main INJP quantity must be readjusted accordingly.

Such a method of stabilizing a combustion degradation of a heat engine can also be implemented for an undesired degradation of the combustion, that is to say not controlled by an engine control unit. In the context of the present invention, the stabilization process is however implemented for degradation of combustion controlled by the engine control unit.

The present invention avoids the use of a heating system of the exhaust line to raise its temperature faster. This would otherwise require the addition of additional equipment, for example a heating system with electrical resistances. This would also generate an additional cost on the exhaust line which the present invention makes it possible to avoid.

One of the main objectives of the present invention is to heat at least one pollution control element present in the exhaust line. This is not, however, the only objective of the present invention and the present invention can be applied to the stabilization of any degraded combustion, for example a degraded combustion for heating the passenger compartment or one of the elements present in a powertrain, such as the engine itself or a gearbox or clutch.

The invention also relates to a method of heating an exhaust line of a thermal engine of a motor vehicle, for which there is performed a heating of the exhaust line by controlled degraded combustion of the thermal engine for a heating time ending as soon as a predetermined temperature in the exhaust line is reached. Reaching this temperature is necessary to place, for example, at least one pollution control element under optimal operating temperature conditions and in particular of priming the pollution control element.

For such an increase in temperature in the exhaust line, it is known to implement degraded combustion of the heat engine, but this degraded combustion causes instabilities. The invention implements a stabilization process as previously described with the achievement of a gain in stability of degraded combustion.

Such gain in stability offers two possibilities. The first is that it is possible to increase a controlled degradation of the combustion of the heat engine and to reach the predetermined temperature in the exhaust line with a reduced heating time or to less degrade the combustion of the heat engine while reaching the predetermined temperature in the exhaust line. Such an increase in controlled degradation was not possible according to the prior art with degraded combustion not stabilized because further increasing the instabilities. According to the invention, the instabilities can increase during the increase in the degradation ordered but have been or will be attenuated by the implementation of the method.

The second possibility offered by the implementation of the method according to the present invention is to less degrade the combustion of the heat engine while reaching the predetermined temperature in the exhaust line after a heating time equivalent to that obtained during '' Unstabilized degraded combustion. The disadvantages of degradation of combustion, namely instabilities, are then reduced, or even avoided.

Without the implementation of the invention which is a purely software solution and therefore less expensive, it would be necessary to provide for the use of new equipment such as an exhaust line heating system which would make it possible to make increase the temperature of the pollution control system faster, which would increase the cost of heating.

The present invention, in its preferred application, allows the element or the pollution control elements to be started more quickly without adding elements to the exhaust line by improving combustion stability. This improvement in stability is advantageous in itself even when the benefits gained from heating the exhaust line are not considered.

In the case where the heating is carried out for one or more pollution control elements present in the exhaust line, the pollution control element or elements requiring obtaining a minimum temperature to ensure its operation, the heating process can be effective as long as the minimum temperature of the element or elements of pollution control is not reached.

The invention relates to a powertrain comprising a heat engine, an engine control unit in charge of combustion in the heat engine and an exhaust line for the discharge of combustion gases from the heat engine. It is the engine control unit that is in charge of combustion degradation when sensors inform it, for example, that the temperature is too low. This engine control unit presents the means for implementing a stabilization process or a heating process as previously described.

When the exhaust line comprises at least one pollution control element requiring obtaining a minimum temperature to ensure its operation, at least one temperature sensor or a model can be associated with said at least one pollution control element.

The engine control unit then comprises means for receiving the temperatures recorded by the temperature sensor or estimated by the model, means for comparing the temperatures recorded with a minimum operating temperature of said at least one stored depollution element. in the engine control unit by storage means and engine control means for implementing stabilized degraded combustion as long as the minimum operating temperature is not reached.

The invention is in no way limited to the embodiments described and illustrated which have been given only by way of examples.

Claims (10)

Claims: 1. Method for stabilizing a degraded combustion of a heat engine controlled to increase the calories emitted by the heat engine, the heat engine comprising at least one cylinder with a piston in reciprocating movement inside and a time advance of an ignition point of an air mixture and of a main quantity (INJP) of fuel injected into said at least one cylinder with respect to a passage of the piston through a Top Dead Center of combustion (PMHcomb) being reduced during degraded combustion, characterized in that, from the main quantity (INJP) of fuel injected with a reduced time advance, an auxiliary quantity (INJaux) injected after the Top Dead Center for combustion (PMHcomb) is taken, this auxiliary quantity (INJaux) of fuel being less than 20% of the main quantity (INJP) of fuel injected. 2. Method according to claim 1, in which the auxiliary quantity (INJaux) of fuel is between 2 and 20% of the main quantity (INJP) of injected fuel. 3. Method according to claim 1 or 2, wherein the auxiliary quantity (INJaux) of fuel is injected around the Top Dead Center of combustion (PMHcomb), an injection of the auxiliary quantity (INJaux) of fuel occurring between 0 ° and 110 ° by taking as reference a crankshaft angle connected to the piston of said at least one cylinder, the 0 ° crankshaft angle being associated with the passage of the Top Dead Center for combustion (PMHcomb). 4. Method according to any one of the preceding claims, in which the auxiliary quantity (INJaux) of fuel varies according to an effective engine operating point, the auxiliary quantity (INJaux) being a function of the engine speed and the engine torque. 5. Method according to any one of the preceding claims, in which a calibration is carried out of an instant of injection of the auxiliary quantity (INJaux) of fuel with respect to the last Top Dead Center (PMHcomb) and / or to the point ignition. 6. Method according to any one of the preceding claims, in which, during the controlled degraded combustion, a modification is made to the combustion settings concerning the following parameters taken individually or in combination: a main quantity (INJP) injected, a injection pressure, an injection duration and a torque reserve corresponding to the creation of an additional torque by the heat engine not used for propulsion of a vehicle equipped with the heat engine. 7. A method of heating an exhaust line of a thermal engine of a motor vehicle, for which heating of the exhaust line is carried out by controlled degraded combustion of the thermal engine for a heating period ending as soon as '' a predetermined temperature in the exhaust line is reached, characterized in that it implements a stabilization process according to any one of the preceding claims, a gain in combustion stability thus obtained making it possible to increase degradation controlled combustion of the combustion engine and to reach the predetermined temperature in the exhaust line with a reduced heating time or to less degrade the combustion of the combustion engine while reaching the predetermined temperature in the exhaust line after a duration heating equivalent to that obtained during non-sta degraded combustion stabilized. 8. Heating method according to the preceding claim, wherein the heating is carried out for at least one element of pollution control present in the exhaust line, said at least one element of pollution control requiring obtaining a minimum temperature to ensure its operation, the heating process being effective as long as the minimum temperature of said at least one pollution control element is not reached. 9. Powertrain comprising a heat engine, an engine control unit responsible for combustion in the heat engine and an exhaust line for the evacuation of combustion gases from the heat engine, characterized in that the unit engine control presents the means for implementing the stabilization method according to any one of claims 1 to 6 or the heating method according to claim 7 or 8. 10. Powertrain according to the preceding claim, wherein, when the exhaust line comprises at least one pollution control element requiring obtaining a minimum temperature to ensure its operation, at least one temperature sensor or a model is associated with said at least one pollution control element, the engine control unit comprising means for receiving the temperatures recorded by the temperature sensor or estimated by the model, means for comparing the temperatures recorded with a minimum temperature 5 for operating said at least one pollution control element stored in the engine control unit by storage means and control means of the heat engine for implementing stabilized degraded combustion as long as the minimum operating temperature is not reached. 1/1 Ign ^- ^