WO2007036351A1

WO2007036351A1 - Method for the operation of an internal combustion engine comprising a particulate filter

Info

Publication number: WO2007036351A1
Application number: PCT/EP2006/009357
Authority: WO
Inventors: Britta Sliwinski; Jürgen Schnitzler; Andreas Wiartalla
Original assignee: Fev Motorentechnik Gmbh
Priority date: 2005-09-29
Filing date: 2006-09-26
Publication date: 2007-04-05
Also published as: DE102005046830A1

Abstract

The invention relates to a method for operating an internal combustion engine comprising a particulate filter in which substantially graphitized soot particles produced during fuel combustion are collected for emission control. Soot particles that are not fully graphitized and have an ignition temperature ranging approximately from 300 to 550 °C are made to attach to the forming soot particle layer by adequately modifying control of the operation of the internal combustion engine, and burning of the soot particles is cyclically initiated to regenerate the particulate filter with the aid of an ignition process by increasing the temperature to the ignition temperature of the not fully graphitized soot particles.

Description

Method for operating an internal combustion engine with a particle filter

The invention relates to a method for operating an internal combustion engine with a particle filter.

In the operation of internal combustion engines in the form of diesel engines or gasoline engines with direct injection, the exhaust gas also contains particles substantially in the form of graphitized soot. It is known to filter out these particles essentially by means of a particle filter. Known diesel particulate filters reduce particulate emissions by up to 90%. However, since the load of particles in the filter is limited, they must be regenerated at certain intervals.

This regeneration can be carried out catalytically at relatively low temperature by addition of additives in the form of oxygen-releasing metal complexes (such as cerium / platinum or iron organyls), which, however, lead to ash formation in the filter. So that the ash residue does not adhere to the environment are discharged, the filter surface and thus the entire filter must be correspondingly large, in order to provide even with ash load still sufficient free filter surface available.

It is also known to thermally make the regeneration by the particles collected in the filter are oxidized at a temperature of about 600 ° C by the oxygen contained in the exhaust of the engine, for example, over a period of about 15 min at 650 ⁰ C. To a To ensure safe thermal regeneration under all driving conditions, this regeneration temperature on the filter throughout the operating range of the internal combustion engine must be able to be represented, except that there is a corresponding temperature load such as a turbocharger or an oxidation catalyst upstream of the particulate filter and an increase in fuel consumption.

The object of the invention is to provide a method for operating an internal combustion engine with a particle filter, which makes it possible to carry out without additives a regeneration of the particulate filter at a relatively low temperature.

This object is achieved according to the features of claim 1.

Accordingly, a method for operating an internal combustion engine with a particulate filter is provided, are collected in the fuel combustion resulting, substantially graphitized soot particles for exhaust gas purification, wherein the forming soot particle layer by corresponding change in the control of the operation of the internal combustion engine incompletely graphitized soot particles with an ignition temperature be deposited between 300 and 550 ^β C and for regenerating the particulate filter cyclically burning off the soot particles by ignition by means of temperature increase is initiated to ignition temperature of the incompletely graphitized soot particles.

Incomplete graphitized carbon black particles having an ignition temperature between about 300 and 55O ⁰ C have an amorphous structure and contain hydrogen atoms from the hydrocarbon chain of the fuel, that is reactive Components like H ₂ or HC-. They are generated by changing the operating state of the internal combustion engine by modifying the internal engine process control by adjusting engine parameters such as adjustment of the air path, such as adaptation of the airflow (such as the exhaust gas recirculation valve, the throttle valve, the turbine geometry of the engine Turbocharger) and / or injection timing and quantities (such as multiple injection, post-injection, injection into the exhaust) can be influenced, so that there is a corresponding, igniting at low temperature particle phase, which is caused by a correspondingly slowed or delayed in-engine combustion.

The operation of the internal combustion engine can accordingly take place in four phases, namely the normal operating phase with superstoichiometric combustion of the fuel in the internal combustion engine, followed by a subsequent short-term operating phase for generating the highly reactive particle phase, an operating phase with increased exhaust gas temperature and a burn-off phase with superstoichiometric combustion of the fuel in the internal combustion engine, which emits after burning in the first phase.

To form a highly reactive particle phase, it is expedient if the combustion is carried out with λ <1, while in the normally provided operating condition with λ> 1 only virtually completely graphitized soot is produced. The stoichiometric combustion with λ <1 is effected for example by changing the internal engine combustion process management. For ignition, a corresponding oxygen excess is to be provided either via the exhaust gas of the internal combustion engine or via a separate source, eg secondary air supply. Due to the incomplete graphitization, this particle phase supplies the energy for the burnup of the essentially graphitized soot particles accumulated in the particle filter. As a result, not only the temperature load is lowered, but also the fuel consumption for regeneration, which can be reduced to more than half compared to thermal regeneration, lowered and no additive needed. The engine operation of the internal combustion engine can be returned during the regeneration phase before the end of a complete regeneration in the normal operating condition with stoichiometric or stoichiometric combustion of the fuel, since the regeneration after ignition of the highly reactive particulate phase independently practically continues until the substantially complete emptying of the particulate filter. Usually, the regeneration operation for the particulate filter is in the range of a few seconds.

In accordance with sufficient oxygen content generally result in a jump from rich operation (stoichiometric combustion) to lean operation (superstoichiometric combustion) high local temperatures by igniting the highly reactive phase, which bring the surrounding, substantially graphitized soot particles to their ignition temperature and thus an effective burn of the Allow particles in the particle filter.

However, the highly reactive particle phase does not necessarily require substoichiometric combustion for its production, but can also be produced by delayed combustion by changing the injection times and quantities (for example via secondary injection or multiple injection), optionally in combination with substoichiometric combustion.

By adjusting the mass ratio of highly reactive particle phase to substantially graphitized carbon black in the particulate filter, which are expediently embedded in alternating layers, and by adjusting the individual layer thicknesses, the burning rate and the completeness of the burnup can be influenced. Both parameters are influenced by the frequency of introduction and the duration of the highly reactive particle phase. On the one hand, these parameters can be modeled and regulated in a motor control or, on the other hand, regulated via a suitable sensor technology, for example pressure or lambda sensors.

The preferred desired layer structure of the particles collected in the particle filter is produced by interval-like switching to substoichiometric and / or delayed combustion. - However, it can also be quasi-continuous be burned by, during or after each interval in which the highly reactive particle phase is generated, provided for a corresponding oxygen supply, which leads to the ignition of the highly reactive particle phase.

A control of the different operating intervals for constructing the layer structure depends in detail on the respective engine, the combustion process in normal operation and the respective operating phase of the associated vehicle. When driving, the respective strategy can be controlled via maps, suitable sensors and monitoring of the operating modes or simulation models or adapted to the respective operating mode in order to achieve the lowest possible emission of pollutants.

Although the formation of the reactive particle phase leads to increased fuel consumption, this is overcompensated by the very low fuel consumption during ignition and burning of the particles collected in the particulate filter, since not the entire exhaust gas must be heated to ignite, but the energy for burning in the essentially graphitized carbon black particles from the highly reactive particulate phase.

Optionally, a NOx adsorption catalyst may be downstream of the particulate filter, wherein the combustion of the particulate filter content via the oxygen supply is controlled so that both are not exposed to high temperatures, but safely regenerated. Other catalysts such as Oxi-KAT or 3-way catalysts can be combined with the particle filter according to the combustion method used in the internal combustion engine.

Fig. 1 shows two diagrams in which lambda or the temperature in the filter is plotted against time. As is apparent from the lambda time diagram of this embodiment, at regular intervals (briefly, for example in the range of a few seconds (eg between 1 to 10 s) compared to the intermediate normal operating intervals, the fat time t ₂ «lean time t,) of a normal operation with λ> 1 (= 1, 6) (lean mode) briefly switched to an operation with λ <1 (= 0.9) (rich operation). In rich operation, the temperature in the filter increased from below about 300 ^° C to slightly above 500 ⁰ C after the end of the interval and increased with appropriate oxygen supply after switching back from rich to lean operation, resulting in each case an effective and thus quasicontinuierlicher particle burn in the particle filter. In this way it can be achieved that the maximum particle loading of the particulate filter does not exceed an extremely low level.

FIG. 2 shows, by way of example, the dependence of the particle loading in the particle filter on a defined, constant loading time compared to the increase in the fat time with a constant lean time in the lean / rich cycle, using a diagram. From this it can be seen that with a higher proportion of reactive particle phase in the particle filter, the total particle mass in the particle filter decreases and thus an improvement of the burning behavior can be achieved.

If the temperature in the particulate filter is not increased during or after each rich operation, particulate loading will increase with each interval. Then the burning can be done at predetermined intervals. However, if a predetermined limit load is detected during such a time interval, the burnup may be initiated and the time interval shortened for this and / or the phases t _{2 of} the rich operation extended and / or by increasing the fuel injection amount during rich operation.

Since the highly reactive particle phase is only needed to ignite by their ignition, the substantially graphitized soot particles, this is sufficient for a relatively small amount of about 0.5 wt .-% highly reactive particle phase based on the total carbon black. However, an amount of about 1% by weight, in particular more than 2% by weight, of highly reactive particle phase based on the total carbon black is preferred.

Claims

claims

1. A method for operating an internal combustion engine with a particulate filter, are collected in the fuel combustion resulting, substantially graphitized soot particles for exhaust gas purification, wherein the forming soot particle layer by corresponding change in the control of the operation of the internal combustion engine incompletely graphitized soot particles with an ignition temperature between about 300 and 55O ⁰ C are deposited and to regenerate the particulate filter cyclically burning off the soot particles by ignition by means of temperature increase is initiated to ignition temperature of the incompletely graphitized soot particles.

2. The method according to claim 1, characterized in that an excess of oxygen for initiating the ignition is provided.

3. The method according to claim 2, characterized in that the oxygen excess is supplied to initiate the ignition by the exhaust gas of the internal combustion engine.

4. The method according to claim 2, characterized in that the oxygen excess for initiating the ignition is supplied by a separate source of oxygen.

5. The method according to any one of claims 1 to 4, characterized in that the incompletely graphitized soot particles are stored with an ignition temperature approximately between 300 and 550 "C in alternating layers in the substantially graphitized carbon black particles.

6. The method according to any one of claims 1 to 4, characterized in that alternately a layer of substantially graphitized soot particles and a layer of incompletely graphitized soot particles with an ignition temperature between about 300 and 550 ^° C are generated and then the ignition is initiated.

7. The method according to any one of claims 1 to 6, characterized in that the incompletely graphitized soot particles with an ignition temperature about between 300 and 550 ^° C by switching the operation of the internal combustion engine from a superstoichiometric combustion to a stoichiometric combustion.

8. The method according to any one of claims 1 to 7, characterized in that the incompletely graphitized soot particles are generated with an ignition temperature approximately between 300 and 550 "C by switching the operation of the internal combustion engine to a delayed combustion.

9. The method according to claim 7 or 8, characterized in that the incompletely graphitized soot particles with an ignition temperature approximately between 300 and 550 ⁰ C by intermittently made brief switching the operation of the internal combustion engine to the stoichiometric combustion in the range of a few seconds are generated.

10. The method according to any one of claims 1 to 9, characterized in that the incompletely graphitized soot particles with an ignition temperature of between about 300 and 550 ^° C in an amount of about 0.5 wt .-%, preferably about 1 wt .-% and in particular more than 2% by weight, based on the total carbon black quantity, can be produced.