FR2849103A1 - Determining mass of soot burned off during exhaust filter regeneration, comprises measuring exhaust gas flowrate and oxygen concentration before and after filter - Google Patents

Abstract

The oxygen content is determined in a gas, upstream (O2e) and downstream (O2s) of a filter (26). The exhaust gas flowrate (Qv) is determined. From these results, the mass of soot burned off (mcons) in the filter is determined. Differences in oxygen concentration are integrated over time, and converted in terms of the molar weight of carbon, the molar volume of gas and the exhaust volumetric flowrate at corresponding temperatures, to yield the mass of carbon burned off. Instantaneous values of oxygen concentration are used similarly, to determine the instantaneous rate of regeneration. Oxygen concentrations are deduced from lambda sensors (40, 42) in the exhaust gas tract. Regeneration is activated. An Independent claim is included for the corresponding equipment.

Description

Method and system for determining soot mass

in a particle filter.

  The invention relates to a method and a system for determining the mass of soot in a particulate filter which may comprise a catalytic phase.

  The heterogeneity of the combustion processes in lean-mixture engines, in particular in diesel engines, has the effect of generating carbon particles, which cannot be burnt efficiently in the engine. This is reflected for example by the appearance , at the outlet of the exhaust line 10, black smoke This phenomenon is a source of pollution which we seek to reduce.

  The presence of a particulate filter in the engine exhaust line makes it possible to considerably reduce the quantity of particles, dust and other soot, emitted into the atmosphere, and to comply with antipollution standards.

  Regeneration devices controlled by a computer make it possible to periodically burn the particles trapped in the filter and to avoid clogging of the latter. The soot particles are essentially carbon elements, and their combustion consumes oxygen to form gas. carbonic. This is done by raising the temperature within the particulate filter to a temperature of the order of 550 to 600 OC, the temperature above which the carbon particles retained in the filter ignite spontaneously.

  Numerous techniques have been developed in this direction. They can be based on modifications of the parameters of the operation of the engine such as the exhaust gas recirculation rate, the supercharging, the delay in injection, the valve winnowing. exhaust, winnowing on intake They can also be linked to the use of an oxidation catalyst placed upstream of the filter element coupled to a post-injection They can also involve an external energy supply in the exhaust gas or at the level of the filter by means of an electrical resistance, a burner, a microwave, a plasma, etc. It is then necessary to control these various devices by an external control supported by the computer.

  The combustion of these particles causes an energy release. This energy can be evacuated by the flow of exhaust gases from the engine, transmitted to the soot bed with which the filter is charged or be transmitted to the various elements forming part of the constitution. the particulate filter, or, in general, the pollution control system.

  However, under certain conditions, the combustion of the particles can become very rapid while the evacuation of the combustion energy is no longer sufficient. This results in a rise in temperature, in particular of the filter, to a level which causes deterioration of the filter, such as cracking of the filter.

  The Applicant has already proposed a method for controlling the regeneration of the filter based on the determination of a parameter representative of the operating conditions of the filter, in particular during the regeneration phases. This parameter is for example a ratio between the gas flow rate exhaust and the soot burning speed. In a first situation, in the case where the parameter is less than a first threshold, it is considered that the regeneration is proceeding normally.

  In a second situation where the parameter is between the first threshold and a second upper threshold, it is considered that the regeneration 15 involves a risk of runaway Finally, in a third situation, if the parameter is above the second threshold, regeneration is considered to have run out and the filter has been damaged.

  To avoid arriving in the third situation, a backup control procedure is triggered when the second situation is detected. This backup procedure corresponds for example to the stopping of the means which made it possible to route regeneration and which have been presented previously.

  The process which has just been described requires evaluating the mass of soot consumed over a period of time, or the rate of combustion of the soot. The rate of combustion of the soot is evaluated for example by an estimate of the internal temperature of the filter. , which is a weighted average of the temperatures upstream and downstream of the filter The temperature of the filter is converted into combustion speed using a map stored in memory. Document FR 2 805 174 discloses a method for controlling a regeneration system of a particulate filter, in which it is determined from when regeneration is initiated and no longer needs to be initiated. by means of ignition In fact, the ignition means consume 10 energy, and it is advantageous to stop energy consumption as soon as possible.

  For this, the method evaluates the oxygen content upstream and downstream of the filter, and compares these contents.

  As soon as the difference in oxygen contents reaches a predetermined threshold, the regeneration is considered to have started. The oxygen contents are measured by oxygen probes placed in the flow of the exhaust gases. This process does not provide any evaluation of the speed. combustion of the 20 soot or of the mass of soot consumed.

  The object of the present invention is to propose another method for determining the rate of combustion and the mass of soot consumed during regeneration in a particulate filter.

  With this objective in view, the invention relates to a method for determining a variation in the mass of soot consumed during regeneration in a particulate filter intended to filter exhaust gases, an initial mass of soot being contained in the particulate filter, a process characterized in that an oxygen content of the exhaust gases is measured upstream and downstream of the filter, an exhaust gas flow is determined, and the flow is deduced and the difference in oxygen content between upstream and downstream a mass of soot 5 consumed in the filter or an instantaneous rate of combustion. The regeneration of the filter occurs by the combustion of the soot retained in the filter This combustion occurs by absorbing oxygen from the exhaust gases By measuring the difference in oxygen content, and by relating it to the gas flow, it is possible to quantify the instantaneous rate of combustion or, equivalently by numerical integration, the mass of soot consumed, which is the objective of the invention.

  Preferably, the mass of regenerated soot meons is determined by the formula: mcons (t) = Qv (t) 2 e (t) 02 s (t)} It in which: Me is the molar mass of carbon; Vmol is the molar volume of a perfect gas at 273 K; Qv is the volume flow rate of the exhaust gases, expressed at 273 K; 02 e is the oxygen content upstream of the filter; 02 S is the oxygen content downstream of the filter; TO is the start time of the regeneration.

  The soot is essentially composed of carbon, which reacts with oxygen in a ratio of one mole to one mole The oxygen deficit downstream reflects the amount of soot consumed The above formula is for example evaluated by numerical integration. Equivalently, the instantaneous rate of combustion vons is determined by the formula: vcons (t) = M Qv (t) l 02 e (t) 02 s (t) l Vmol According to a particular embodiment, the 10 contents oxygen are deduced from measurements of proportional richness probes placed in the exhaust gases. This type of probe is well known from the state of the art and is for example designated by the term UEGO probe. richness, it is easy to find information on oxygen content.

  In an application of the method according to the invention, the method acts on means of action to optimize the regeneration. More particularly, the method determines whether the regeneration involves a risk of runaway, as a function of the instantaneous combustion speed of the soot. and orders the means of action to eliminate the risk of runaway.

  A subject of the invention is also a system for determining a variation in mass of soot consumed during regeneration in a particulate filter intended to filter exhaust gases, an initial mass of soot being contained in the 30 particle filter, characterized in that the system comprises a probe for measuring the oxygen content upstream of the filter, a probe for measuring the oxygen content downstream from the filter, means for measuring a gas flow d exhaust, and a computer 5 to deduce from the flow and the difference in oxygen content between upstream and downstream a mass of soot consumed in the filter.

  The invention will be better understood and other features and advantages will appear on reading the description which follows, the description referring to the drawings annexed to FIG. 1, unique, schematically showing a pollution control system with filter particles.

  In FIG. 1, the engine, designated by the general reference 10, is a diesel type engine supercharged by a turbocharger.

  In the example shown, the engine 10 has four cylinders, such as 12, arranged in line. It is supplied with fresh air via an intake distributor 14, itself supplied by a supply line 16 provided an air filter (not shown) and equipped with a flow meter 18.

  Furthermore, the engine 10 is provided with an exhaust manifold 20, in communication with an exhaust line 22 provided with a particle filtration system, essentially consisting of an oxidation catalytic converter 24 and d '' a particulate filter 26.

  An exhaust gas recycling circuit 28, which is provided with a recycling valve 30, recovers part of the exhaust gases from the combustion and reinjects them into the intake distributor 14.

  The engine 10 is supplied with fuel via a supply circuit 32 For example, this supply circuit is a high pressure circuit with a common rail.

  Finally, a duly programmed computer, designated 10 by the general reference numeral 34, manages the operation of the engine 10, in particular the quantity of fuel injected or the instant of ignition of the engine, so as to deliver the torque requested by the driver. In particular, the computer 34 receives a measurement signal from the flow meter 18 equipping the intake pipe 16, and has the value of other engine operating variables, such as the engine operating speed, the temperature of the ambient air, that of the operating liquid, as is well known to those skilled in the art.

  It also receives an upstream richness signal Re from an upstream proportional probe 40 and a downstream richness signal 25 Rs from a downstream proportional probe 42, the probes being placed in the exhaust gas flow respectively upstream and downstream of the filter 26.

  The computer 34 incorporates all of the hardware and software means 30 for controlling the various operating parameters of the engine, such as the injection of fuel, the lifting of the intake and exhaust valves, the quantity of gas recycled, from 'a map 38 stored in memory in the computer 34.

  In particular, it monitors the value of the level of loading of the particulate filter, and, when this value exceeds a predetermined threshold value, it implements means of priming 10 of the filter. These priming means are constituted by means of conventional type, well known to those skilled in the art They will therefore not be described in detail below.

  It will be noted, however, that these means make it possible to create a particular gaseous environment in the particle filter, which is heated to a temperature of the order of 550 to 600 ° C., to provide the energy necessary for the spontaneous ignition of the particles. of carbon contained in the filter 26.

  As regards the determination of the loading level of the filter, this can be carried out by various means, for example by measuring the pressure difference prevailing upstream and downstream of the particulate filter, or by interpolation on the basis of engine particle emission maps.

  Furthermore, care should be taken to avoid regeneration being carried out under conditions such as to risk damaging the elements forming part of the treatment system for gaseous effluents. For this, the computer 34 calculates, at during engine operation, and in particular during regeneration, a parameter representative of the operating conditions of the regeneration means It controls said regeneration means, as a function of the value of parameter 5 thus calculated, so as to prevent the regeneration is not carried out in situations such that the energy released by the combustion of soot can no longer be evacuated, which would result in deterioration of the particulate filter.

  In the event that a risky situation is detected, the computer performs a backup procedure to limit or stop the regeneration.

  The backup procedure acts, for example, on the priming means by stopping them, or by making them operate so that they create conditions for slowing down or stopping regeneration.

  The above-mentioned parameter takes into account, for example, the mass of soot consumed over a given period, covered by the regeneration period, or the instantaneous speed of combustion, expressed in mass consumed per unit of time.

  According to the method of the invention, when a regeneration step is launched by the computer 34, an initial mass of soot m O is memorized. The 25 upstream Re and downstream Rs richness signals are measured, converted into an oxygen content value. 02 e and 02 s and stored as the current value.

  Then a loop is performed, in which the following steps are carried out: a) storing the current values of oxygen content and of remaining soot mass as previous values; b) measurement of the upstream Re and downstream Rs richness signals, and conversion into an upstream 02 e and downstream 02 s oxygen content value, and storage as a current value; c) evaluation of the mass of soot consumed from the previous instant tl to the current instant t by: mcons (t) = V, 1, Qv (t) l 02 e (t) 02 s (t)} td) calculation of the mass remaining in the filter at time t by: m (t) = m (tl) -mcons (t) e) calculation of the regeneration speed by: vcons (t) = Me Qv (t ) l 02 e (t) 02 s (t) l Vmol Thus, at any time during the regeneration phase, the combustion speed and the mass remaining in the filter are known.

  It has been assumed that the amount of soot generated by the engine during the regeneration phase is negligible. In fact, the duration of the regeneration is relatively short compared to the cycle time between each regeneration. In addition, the engine operates with little emission of particles during the regeneration phase, as a consequence of the objective of maintaining a high temperature of the exhaust gases arriving in the particulate filter However, it is perfectly possible to take into account the amount of soot generated during this phase, for example during step a), by adding the amount of soot generated to the remaining mass of soot.

  The invention is not limited to the embodiment which has just been described solely by way of example. It may in particular be implemented on an atmospheric diesel engine, or a lean mixture engine.

Claims (5)

  1 Method for determining a variation in mass of soot consumed during regeneration in a particulate filter (26) intended to filter exhaust gases, an initial mass of soot 5 being contained in the particulate filter ( 26), a method characterized in that an oxygen content of the exhaust gases is measured upstream (02 e) and downstream (02 s) of the filter (26), an exhaust gas flow rate is determined ( Qv), and from the flow and from the difference in oxygen content between upstream and downstream, a mass of consumed soot (mcons) in the filter (26) is deduced.   2 The method of claim 1, wherein the mass of regenerated soot mcons is determined by the formula: imcons (t) = VMI O Qv (t) l 02 e (t) 02 s (t)} Jt in which: Mc is the molar mass of carbon; Vmol is the molar volume of a perfect gas at 273 20 K; Qv is the volume flow rate of the exhaust gases, expressed at 273 K; 02 e is the oxygen content upstream of the filter; 02 S is the oxygen content downstream of the filter; TO is the start time of the regeneration.   3 The method of claim 1, wherein the instantaneous speed of regeneration vcons is determined by the formula: vcons (t) = M Qv (t) l 02 e (t) 02 s (t) l Vmol in which: Mc is the molar mass of carbon; Vmol is the molar volume of a perfect gas at 273 K; Qv is the volume flow rate of the exhaust gases, expressed at 273 K; 02 e is the oxygen content upstream of the filter; 02 S is the oxygen content downstream of the filter.   4 The method of claim 1, wherein the oxygen contents are deduced from 15 measurements of proportional richness probes (40, 42) placed in the exhaust gases.   Method according to claim 1, according to which it acts on means of action to optimize the regeneration.   6 System for determining a variation in mass of soot consumed during regeneration in a particulate filter (26) intended to filter exhaust gases, an initial mass of soot (m O) being contained in the filter with particles (26), characterized in that the system comprises a probe for measuring the oxygen content upstream (40) of the filter, a probe for measuring the oxygen content downstream (42) of the filter, means measuring a flow rate of exhaust gas (18), and a computer (34) for deducing from the flow rate and the difference in oxygen content between upstream and downstream a mass of soot consumed in the filter.