Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1998-10-19
2001-03-06
Chapman, Jeanette (Department: 3711)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S285000, C060S307000, C123SDIG001
Reexamination Certificate
active
06195985
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for reducing the pollutant emission of an internal combustion engine according to the introductory part of claim
1
.
Various devices and methods for exhaust purification are already known.
EP-B-0 561 311 for example relates to an exhaust purification device comprising a zeolite-based adsorber for the short-time intermediate storage of pollutants, and a catalytic converter disposed downstream thereof for the conversion of the pollutant. In the exhaust tube section lying therebetween there opens a tube which is sufficiently distanced from the adsorber and which comes from a burner with its own fuel and air supply. By way of this arrangement it is made possible that on the one hand the gases produced by the burner heat the catalytic converter and bring it quickly to its operating temperature without compromising the zeolite adsorber, and that on the other hand thermic secondary reactions of exhaust components are achieved in the mentioned exhaust tube section, i.e. still before the entry into the converter.
According to DE-OS 41 41 946 it is suggested in a similar context to blow secondary air into the exhaust stream between the internal combustion engine and the catalytic converter. To this effect however an air pump is provided whose starting up is effected in a directed manner only for so long until the operating temperature of the catalytic converter is reached.
In addition with DE-OS 37 23 703 air is mixed in with the exhaust stream before entry into the catalytic converter. In contrast to the two above-mentioned solutions a separate gas or air delivery means is done away with in that the internal combustion engine itself forms the delivery means. To this effect it is provided for some of the cylinders not to be fired but to be applied as air pumps.
DE-PS 40 29 672 suggests the improvement of cutting off individual cylinders only for a short time, i.e. to let a short interruption follow several working strokes so that the temperature of the cylinders remains maintained. Generally it is also advantageous to cut off the ignition according to the interruption of the supply of the mixture.
The documents cited hereinabove relate to improvements in the starting procedure of an internal combustion engine, i.e. in particular of an Otto engine of a road vehicle. Indeed the pollutant emission during the starting of a vehicle is increasingly important, since on the one hand exhaust regulations are becoming more restrictive and on the other hand the pollutant emission during the normal operation is reduced thanks to more effective catalytic converters.
BRIEF SUMMARY OF THE INVENTION
Although a pollutant reduction on starting an internal combustion engine may well be achieved with these suggestions, it is the object of the present invention to provide a further improvement with respect to this.
The method according to the invention is based on the unexpected discovery that with respect to pollutant emissions in the first operating minutes of an internal combustion engine, in particular of an Otto motor, not only the starting procedure is of a significance but also the preceding switching off procedure.
For the purpose of as small a pollutant formation as possible, on starting up an internal combustion engine the method according to the invention not only provides for optimal conditions during the starting up procedure but also on switching off the internal combustion engine.
In contrast to an essentially uncontrolled manner of switching off an internal combustion engine with conventional road vehicles, it is suggested according to the present invention to subject the internal combustion engine and the catalytic converter to a cleaning or scavenging phase before the standstill of the motor. With this cleaning or scavenging phase as illustrated in flow chart of FIG.
6
.
the movement of the internal combustion engine is still maintained for a certain time before standstill of the motor either by letting it run out, by sparking or by an external drive step (S
1
in FIG.
6
), and
at least temporally in at least individual cylinders of the internal combustion engine the supply of fuel is interrupted and exclusively air is delivered (step S
2
in FIG.
6
).
By way of this it is achieved that the remaining pollutants accumulated in the internal combustion engine are supplied to the catalytic converter which is still at the operating temperature and that the catalytic converter is enriched with oxygen.
In other words with the method according to the invention the “old waste” from the preceding operation may be reduced for the subsequent warm or cold start.
During a usual, randomly effected switching off procedure of an internal combustion engine a substantial quantity of pollutants does not necessarily arise, but the pollutants accumulated from the last operation remain in the internal combustion engine, i.e. in the cavities of the internal combustion engine concerned, such as for example the intake duct, combustion duct, exit duct and/or the crankcase. With a subsequent cold start these pollutants pass the exhaust purification device which is not at operating temperature and thus is not capable of functioning well. This is also substantially the case when means for the accelerated starting up of the exhaust purification device are present, i.e. for example with additional, externally heatable catalytic converters, a prior-arranged burner, etc.
This disadvantage is alleviated by the solution according to the invention since a certain switching off procedure is provided with which the pollutants accumulated in the internal combustion engine are scavenged out and get into the exhaust purification device which is located at its operating temperature and is fully functioning.
Basically with an Otto motor three pollutant components are to be named: carbon monoxide, unburned hydrocarbons as well as nitrogen oxide, hereinafter also indicated as CO, HC and NO
x
respectively.
The carbon monoxide formation is first of all to be attributed to air or oxygen deficiency and thus may be influenced via the air-fuel ratio. Carbon monoxide may also arise with an excess of oxygen on account of local mixture inhomogeneities as well as the freezing of reactions in the wall vicinity.
Furthermore with large heat dissipations in the wall vicinity, a cooling arise so that the flame extinguishes (quench-effect), and in regions in which the flame may not get into, i.e. in the various gaps of the combustion space (piston rings, cylinder head gasket, piston ignition web, etc.) there arise unburned hydrocarbons such as aromatic compounds, olefins and paraffins. Since a cooling off in the wall vicinity leads to a HC formation, the percentage HC content of the exhaust is dependent on the surface area/volume ratio of the combustion space, which means that the HC formation with motors of a lower piston-swept volume per cylinder is more significant. A further source for unburned hydrocarbons in the exhaust is formed by the releasing of the lubricating film and the subsequent transport into the exhaust duct, where only a part-oxidation takes place. Generally the HC emission may be effectively reduced with a lambda-control.
Nitrogen oxides in the combustion space arise particularly at high temperatures and with a slight excess of air. With extreme rich or thin mixtures on the other hand the temperatures for splitting up N
2
and O
2
are hardly reached. Amongst other things the NO
x
production may also be contained by way of a lambda-control.
Since the method according to the invention provides for the addition of a phase before switching off the internal combustion engine, with which on average more oxygen is added than with a stoichiometric operation, in particular the hydrocarbons and carbon monoxide accumulated in the internal combustion engine may be led to the catalytic converter which is still at its operating temperature and is operational. Furthermore in this manner, as mentioned, the oxygen reserve of the catalytic converter may be replenished so that with
Apter Robert
del Re Luigi
Handschin Daniel
Chapman Jeanette
Griffin & Szipl, P.C.
The Swatch Group Management Services AG
Varma Sneh
LandOfFree
Method for reducing the pollutant emission of an internal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for reducing the pollutant emission of an internal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for reducing the pollutant emission of an internal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2487092