EP1171696B1 - Combustion control by particle filter regeneration - Google Patents

Description

The present invention relates to a method and a device for Regeneration control of a carbon element collection system such as a particulate filter implanted on a gas flow system, for example that of an internal combustion engine, by means of a Differential measurement of the richness of the gases at the terminals of the element filter.

State of the art

The filtration means make it possible to collect the particles exhausted from an internal combustion engine with significant filtration efficiencies, of the order of 80%. As an illustration, can be cited the ceramic monolith made from cordierite marketed by the company Corning or the ceramic monolith in silicon carbide marketed by Ibiden or the wound ceramic cartridge.

The technical difficulty encountered for the development and the implementation of particle filters is that they must be periodically regenerated by burning soot deposition to avoid a clogging of the filter element which will penalize the performance of the engine and will jeopardize its proper functioning. This combustion is sometimes occurs naturally when the temperature of the gases that through the filter reaches a level sufficient to initiate the oxidation of particles. However, the temperature levels encountered at the exhaust of diesel engines for example remain, on a very large operating range, far too low, to allow the initiation of soot combustion. It is then necessary to actions to trigger the regeneration of the filter.

Many techniques have been developed in this direction. They may be based on changes in the parameters of the engine operation such as EGR, over-charging, delay in the injection, the escape valve, the winnowing admission, they may be linked to the use of a catalytic converter of oxidation placed upstream of the filter element coupled to a post injection, or they may involve an external supply of energy in the exhaust or at the level of the filter through electrical resistance, burner, microwave, plasma etc. It is then necessary to control these different devices by a command external supported by the calculator.

The criterion for triggering the regeneration of the element Filtering can be the variation of the backpressure or pressure loss measured at the terminals of the filter element that can be correlated to its state fouling by soot, as described for example in the patent FR 2 755 623 from the applicant. This detection method is very suitable in steady state. The measurement of the back pressure also allows detect the combustion of soot accumulated in the filter element, because, in steady state, it drops with the combustion of the carbonaceous deposit. However, the exhaust backpressure is subject to large fluctuations when the engine conditions are not stabilized (temperature, air flow, etc.) This is the case for a motor of vehicle which, under normal traffic conditions, operates very often under transient conditions (acceleration, deceleration). The mastery of clogging of a filter element using this type of measurement is difficult in practice.

Triggering the regeneration action of the filter element can also be controlled through a measure of the variation of the electrical resistance measured between spaced points along the filter element, variation that is directly related to its state fouling, as described for example in FR 2,760,531 the applicant.

The regeneration of the filter can be facilitated by the use additives in the fuel based on, for example, organometallic elements or rare earths, which ends up in the soot deposit and catalyzes the oxidation of soot which results in a lowering of the initiation temperature of the combustion of the carbonaceous deposit. From most commonly used products are cerium, strontium, iron, etc. The use of these elements makes it possible to obtain regenerations at temperatures between 200 ° C and 450 ° C according to the nature of the soot deposit. However, the temperatures encountered by example to the exhaust of supercharged diesel engines, can remain, for certain types of use such as urban journeys, insufficient triggering the combustion of soot. The implementation of specific strategies making use of the different elements already mentioned becomes indispensable for the proper functioning of the system. Different examples of using these different techniques are described by example in the following patents: EP 913.559, JP 10141113, GB 2 261 613, EP 488 386 or DE 35 38 109.

Whatever the means used to trigger the regeneration of the filter element, it is a source of energy consumption. A good System management goes through the control of the regeneration phase. More precisely, the detection of the beginning of regeneration of the filter makes it possible define the moment when the means implemented to increase the gas temperature can be stopped. Soot combustion can then self-sustaining because of the strong exothermicity of the reaction oxidation of soot. This is reflected in particular by a limitation of overconsumption of the motor linked to the implementation of the strategies of regeneration of the filter element.

The method and the device according to the invention

The present invention makes it possible to carry out a very effective control of the regeneration phase of filter elements and operations necessary for their cleaning

The method according to the invention makes it possible to control the regeneration periodical of a filter element particles carried by a stream gaseous, by combustion thereof. It is characterized in that involves detecting the change in the oxygen concentration of the gas flow between at least a first point upstream of the element filter receiving the flow, relative to the direction of flow and at least one second point downstream of the first, resulting from a triggered reaction combustion of particles accumulated in the filter element, to accurately adjust the duration of the warm-up necessary to trigger combustion and thus to limit better the energy required.

According to one embodiment, the method makes it possible example control the periodic regeneration of a filter element such exhaust, designed to retain particles or soot transported by a gas stream escaping from an engine, by combustion of these particles. It is characterized in that it comprises the detection of the variation of the richness of the exhaust gases between least a first point upstream of the filter element relative to the flow direction, and at least one second point downstream of the first, resulting of a combustion reaction of particles accumulated in the element filter, triggered by a management body sensitive to the variation of detected wealth, in order to precisely adjust the duration of the temperature necessary to trigger combustion.

Depending on the case, the method may include a process control spontaneous regeneration of the filter element or the triggering an action on the engine's operating parameters for to obtain a substantial rise in the temperature of the gases exhaust or the triggering of heating means associated with the filter element.

The device according to the invention makes it possible to control the regeneration periodical of a filter element retaining particles transported by a gas flow by combustion thereof. It is characterized in that comprises means for detecting the variation of the oxygen content of the gas flow between at least a first point upstream of the element filter receiving the flow, relative to the direction of flow and at least one second point downstream of the first (downstream of the filter element of preference), heating means for raising the temperature of the filter element sufficiently to burn the particles, and means connected to the detection means to adjust the duration of the heating required to trigger combustion, by action on the heating means.

In an application to the control of periodic regeneration a filter element retaining oxidizable particles or soot transported by a gas stream escaping from a heat engine, by combustion of these particles, the device comprises a first probe of wealth disposed at a first point upstream of the element filtering relative to the direction of flow and a second wealth probe disposed at a second point downstream from the first (preferably downstream of the filter element), relative to the direction of the gas flow, means of heating to raise the temperature of the filter element enough to burn the particles, and a calculator connected to the detection means to adjust the duration the duration of the setting temperature required to trigger combustion, by action heating means, depending on the variation in exhaust gas between the first and the second probe.

The heating means may for example be constituted by the engine, the computer being programmed to modify parameters of operation to increase the temperature of gases exhaust, or be associated with the filter element.

Presentation of figures

• la Fig.1 montre schématiquement un dispositif de contrôle appliqué à la surveillance de l'encrassement d'un élément filtrant à la sortie d'un moteur ;
• la Fig.2 montre un exemple de variation au cours du temps de l'écart de richesse ΔR entre l'amont et l'aval de l'élément filtrant avec une montée progressive de l'écart jusqu'à un seuil S fixé au-delà duquel la combustion des suies s' amorce ; et
• la Fig.3 montre les variations comparées, en fonction du temps, de la richesse R_A, en amont de l'élément filtrant, de la richesse R_B en aval et de la contre-pression CP à l'échappement.

Other characteristics and advantages of the method and of the device according to the invention will become apparent on reading the following description of a nonlimiting embodiment, in a particular application where the gas flow comes from a heat engine and with reference to the accompanying drawings in which:

• Fig.1 schematically shows a control device applied to the monitoring of the fouling of a filter element at the output of an engine;
• FIG. 2 shows an example of variation over time of the difference in richness Δ R between the upstream and the downstream of the filter element with a gradual rise in the difference up to a threshold S fixed at beyond which the combustion of soot begins; and
• FIG. 3 shows the variations, as a function of time, of the richness R _A , upstream of the filtering element, the richness R _B downstream and the backpressure CP at the exhaust.

detailed description

The device is adapted, in the described application, to control the periodic regeneration of a filter element 1 interposed on a circuit 2 of a combustion engine 3, by combustion of particles carbonaceous pollutants (soot) accumulated therein, by means of a detection of wealth variations between the upstream and the downstream of the element consecutive filtering of this combustion.

The term wealth is here taken in its particular meaning used by motorists and defined by the following relation: Wealth = (m_carb / m_air) / (m_carb / m_air) stoech, or
m_carb is the mass of fuel injected into the engine (kg / h),
m_air, the mass of air sucked by the motor (kg / h), and
(m_carb / m_air) stoech is the ratio between the fuel flow and the air flow at the stoichiometry of the combustion reaction. This ratio depends on the nature of the fuel and is close to 1 / 14.5.

To measure this variation of richness, the device comprises a first wealth probe 4 of a known type, as found currently in the engine exhaust systems, which is disposed here upstream of the filter element 1 relative to the direction of the exhaust gas flow, for example. It also includes minus a second wealth probe 5 of the same type arranged downstream of the first probe 4, towards the outlet of the filter element 1 for example. The two wealth probes 4, 5 are connected to an element computer 6, such as a programmed processor adapted to monitor the evolution of the wealth gap between their respective measures.

The soot accumulating in the filter element 1 consists mainly of carbon elements that react with oxygen to form with it essentially CO ₂ and CO. Part of the oxygen entering the filter element is therefore consumed by the carbon present in the deposit. The combustion of soot in the filter element is therefore reflected downstream by a deficit of oxygen relative to the upstream measured richness relative to the flow direction of the filter element and this from the first moments of the combustion of soot.

There are certain engine operating conditions (typically when it runs at high load) that allow to achieve, without any modification of the engine parameters, levels sufficient temperature to trigger the regeneration of the filter. The calculator is therefore able in this case to detect the processes of spontaneous regeneration of the filter element.

Apart from this case of spontaneous regeneration, when the element filter must be regenerated, calculator 6 can trigger combustion soot by ordering by any appropriate means an increase substantial temperature of the exhaust gas. It could be an action on the operating parameters of the engine itself or, depending on the case or application envisaged, an action on elements external to the engine itself (such as Heated). The device makes it possible to precisely define when the regeneration procedure can be stopped and thus limit the required energy consumption.

The device must be calibrated beforehand to determine the periodicity of soot combustion operations in the filter. The amount of soot that is deposited is either estimated for example on the basis particle emission maps of the engine either by use a filter fouling sensor of a known type.

The integration of wealth difference throughout the entire phase of soot combustion also helps to define the amount of soot accumulated in the filter element. This value can then be compared to the amount of soot that has burned on the filter and define if the regeneration of the filter was complete or partial.

In Fig.2, 3, we see the results of tests on a vehicle engine. The curves R _A and R _B represent the respective variations of the richness measured by the probes 4 and 5 placed upstream and downstream of the filter, while the curve CP represents the variation of the exhaust backpressure. The curves R _A and R _B follow an evolution parallel to the point S where the progressive oxidation of the accumulated soot, results in a widening gap between the richnesses. It should be noted that the maximum D of the CP backpressure before the fall occurs well after a significant difference between the two richness signals R _A and R _B does not appear.

An example of application of the method to the control of clogging of a filter element in the exhaust system of a heat engine. It is obvious, however, that the process can apply to the regeneration of a filter element accumulating particles carried in a gaseous flow containing some oxygen concentration, as long as these particles are combustible and modify the oxygen flux content. To detect the variation of this concentration, we use in this case probes measuring the oxygen concentration.

Claims (9)

1. Process for controlling the periodic regeneration of a filter element intended to retain particles carried by a gas flow, by combustion of these, characterised by the fact that it includes detection of the variation in the oxygen concentration of the gas flow between at least a first point towards the upstream zone of the filter element receiving the flow, relatively to the direction of the latter, and at least a second point downstream of the first, resulting from an initiated reaction of combustion of the particles accumulated in the filter element, so as to precisely adjust the period for which the temperature is maintained which is necessary to initiate combustion, and therefore best limit the energy required.
2. Process for controlling the periodic regeneration of a filter element (1) such as an exhaust silencer, intended to retain particles or soots carried by a gas flow leaving an engine (3), by combustion of these particles, characterised by the fact that it includes detection of the variation in richness of the exhaust gases between at least a first point towards the upstream zone of the filter element (1) relatively to the direction of the flow, and at least a second point downstream of the first, resulting from a reaction of combustion of the particles accumulated in the filter element, initiated by a management organ (6) sensitive to the detected variation in richness, so as to precisely adjust the period for which the temperature is maintained which is necessary to initiate combustion, and therefore best limit the energy required.
3. Process as described in claim 2, characterised by the fact that it includes detection of a spontaneous process of regeneration of the filter element.
4. Process as described in claim 2, characterised by the fact that it includes action on the operating parameters of the engine (3) to obtain a substantial rise in temperature of the exhaust gases.
5. Process as described in claim 2, characterised by the fact that it includes the use of heating means associated with the filter element to obtain controlled combustion of the particles.
6. Device for controlling the periodic regeneration of a filter element (1) retaining particles carried by a gas flow by combustion of these, characterised by the fact that it includes means (4, 5) for detection of the variation in the oxygen content of the gas flow between at least a first point towards the upstream zone of the filter element receiving the flow, relatively to the direction of this, and at least a second point towards the downstream zone of the filter element, heating means intended to raise the temperature of the filter element sufficiently to burn the particles, and management means (6) connected to the detection means (4, 5) to adjust the period for which the temperature is maintained which is necessary to initiate combustion, by action on the said heating means.
7. Device for controlling the periodic regeneration of a filter element (1) retaining oxidizable particles or soots carried by a gas flow leaving an engine (3), by combustion of these particles, characterised by the fact that it includes a first richness probe (4) arranged at a first point towards the upstream zone of the filter element (1) relatively to the direction of the flow and a second richness probe (5) arranged at a second point downstream of the first, relatively to the direction of the gas flow, heating means intended to raise the temperature of the filter element sufficiently to burn the particles, and a computer (6) connected to the detection means (4, 5) to adjust the period for which the temperature is maintained which is necessary to initiate combustion, by action on the said heating means depending on the variation in richness of the exhaust gases between the first and the second probe.
8. Device as described in claim 6 or 7, characterised by the fact that the heating means are formed by the engine (3), the computer (6) being programmed to modify operating parameters of the engine (3) in order to raise the temperature of the exhaust gases.
9. Device as described in claim 6 or 7, characterised by the fact that the heating means are associated with the filter element.

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