Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-09-25
2003-11-11
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S297000, C060S303000, C123S299000, C123S399000, C123S676000
Reexamination Certificate
active
06644020
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates to a method for regenerating an exhaust gas aftertreatment device in the exhaust system of an internal combustion engine, and more particularly to a particulate filter in the exhaust system of a diesel engine. According to-the method the temperature of the exhaust gases, the hydrocarbon concentration of the exhaust gases, or both are increased by post injection of fuel into the engine. In addition, the invention relates to an internal combustion engine, in particular a diesel engine, designed to carry out the aforesaid method.
2. Background of the Invention
To reduce the harmful emissions from internal combustion engines, exhaust gas aftertreatment devices are placed in the exhaust gas path to process legislated exhaust gas constituents. One such device is a particulate filter which removes unburned particulates of soot from the exhaust gas. Particulate filters are regenerated periodically by burning the accumulated filter residues. The carbon contained in the filter residues ignite only at relatively high temperatures of approximately 550° C., if there is no catalytic support. Such temperatures are only reached under conditions with at high engine speeds and torques. To ensure the operation of the particulate filter, measures are taken to increase exhaust gas temperature sufficiently during a regeneration under all operating conditions of the engine.
Various procedures have been proposed for increasing exhaust gas temperature. For example, by switching on electrical loads, it is possible to increase the engine loading. Additional fuel can be injected into the combustion space or into the exhaust gas ducts. As a result, unburned hydrocarbons are fed to a catalytic converter arranged upstream of the particulate filter. These hydrocarbons are oxidized, thereby creating an exotherm in the catalytic converter and raising the exhaust temperature.
Post injection of fuel has proven particularly effective in raising exhaust temperature. Post injection is injection of an additional quantity of fuel into one or all cylinders after the main injection, i.e., during the expansion stroke. Depending on the quantity and the start of the post injection event, a portion of the injected fuel burns in the cylinder and contributes both to engine torque and to an increase in the exhaust gas temperature at the outlet of the engine. The remaining part of the fuel vaporizes and leaves the engine in the form of unburned hydrocarbons. If an oxidation catalytic converter is arranged upstream of the particulate filter and if said oxidation catalyst converter has a sufficiently high temperature, the unburned hydrocarbons oxidize in an exothermic reaction cause a temperature increase in the exhaust gases. However, if the temperature of the oxidation catalytic converter is too low, the hydrocarbons do not oxidize and, thus, leave the exhaust gas system unburned.
While post injection is being carried out, the injected quantity of fuel, and in particular the time of the injection, are to be matched very precisely in to ensure that:
the maximum temperature limits of the turbine and of the exhaust system are not exceeded;
the enthalpy release rate in the catalytic converter does not exceed acceptable limits;
emission of unburned hydrocarbons does not exceed acceptable limits;
additional torque generated by the post injection does not cause the total generated torque to exceed desired torque.
While compliance with all these conditions is already demanding under normal conditions, an aggravating factor is that, in practice, ambient conditions vary considerably. These affect the conditions (temperature, pressure) which prevail in the cylinder at the time of post injection and have a decisive influence on the proportion of post-injected fuel which is burned. An excessively high proportion of unburned hydrocarbons can lead to cooling of the oxidation catalytic converter to below the threshold temperature for oxidation. This leads to an additional drop in the exhaust gas temperature so that the desired regeneration of the particulate filter does not occur. In addition, an excessively high concentration of hydrocarbons downstream of the catalytic converter leads to an unpleasant unacceptable smell. The torque may also be less in such a situation than is expected on the basis of the position of the accelerator pedal.
SUMMARY OF INVENTION
Against this background, the present invention provides a method for regenerating an exhaust gas aftertreatment device which enables the effects of a post injection to be stabilized. In particular, the present invention is a method for regenerating an exhaust gas aftertreatment device disposed in the exhaust system of an internal combustion engine, the engine having a throttle valve disposed in the engine intake and a fuel injector disposed in a combustion cylinder of the engine capable of multiple injections during a combustion cycle. Fuel is injected into the combustion cylinder at least twice in a single engine cycle, including a main injection followed by a post injection. The throttle valve is regulated to provide a desired value of an exhaust gas parameter.
In one embodiment, the exhaust gas parameter is exhaust gas temperature. Alternatively, the exhaust gas parameter is exhaust gas hydrocarbon concentration.
The proposed method for regenerating an exhaust gas aftertreatment device in the exhaust system of an internal combustion engine may be used in particular for regenerating a particulate filter in the exhaust system of a diesel engine. In the method, the temperature of the exhaust gases and/or the concentration of the unburned hydrocarbons in the exhaust gas are increased by a post injection of fuel in the working cycle of the internal combustion engine. The method is defined by virtue of the fact that the values predetermined by the engine controller for the intake pressure (MAP) and/or for the air mass flow rate (MAF) are changed as a function of a variable whose value is correlated with the ambient temperature of the engine or of the internal combustion engine, in such a way that stable values of the exhaust gas temperature and/or of the concentration of hydrocarbons in the exhaust gas are achieved by the post injection.
The method according to the invention thus achieves stable effects of the post injection with respect to the exhaust gas temperature and the concentrations of hydrocarbons by virtue of the fact that the ambient temperature of the engine or of the motor vehicle is taken into account in the setting of the intake pressure and/or of the air mass flow rate. They are taken into account here in the form of a correction of the values predetermined by the engine controller on the basis of other, conventional criteria. It has become apparent that such a measure can enable a reliable regeneration of the exhaust gas aftertreatment device, for example of the particulate filter in the exhaust gas system of a diesel engine, to take place even under greatly varying ambient conditions. Here, the strategies used for the stabilization are relatively simple, i.e., regulating the intake pressure or air mass flow rate. An advantage of the present method is that complex measures, for example preheating of the supplied air mass flows to ensure uniform temperature in the combustion space is not necessary.
The predetermined values for the intake pressure and/or the air mass flow rate can be changed in such a way that at the time of the post injection, the temperature in the combustion space of the internal combustion engine does not drop below a predetermined threshold. It has become apparent that the temperature in the combustion space at the time of the post injection has a decisive influence on how complete combustion of the post-injected quantity proceed or whether fuel leaves the engine without being burned. By regulating the throttle valve, temperature in the combustion chamber is regulated in such a way that it does not drop below a specific threshold so that the desired exhaust gas temperature and/or t
Christen Urs
Kuenstler Johannes
Moraal Paul Eduard
Yacoub Yasser M.
Brehob Diana D.
Denion Thomas
Ford Global Technologies LLC
Nguyen Tu M.
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