Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-04-29
2001-12-11
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...
C060S299000, C060S301000
Reexamination Certificate
active
06327851
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of elimination of nitrogen oxides discharged at the exhaust of internal-combustion engines, notably those running on lean mixture.
BACKGROUND OF THE INVENTION
There are various well-known catalytic formulations allowing to convert nitrogen oxides in the exhaust line before the exhaust gases are discharged to the atmosphere.
The most commonly used formulations are Platinum/Alumina, which are especially active at low temperatures (of the order of 200° C.) and the copper/zeolite formulations, which are active at higher temperatures (of the order of 350° C.).
However, the efficiency of nitrogen oxides reduction in an oxidizing medium depends on the running conditions of the engine and notably on the temperature and the flow of the exhaust gases.
The ratio of the reducers contained in the exhaust gases to the nitrogen oxides (NO
x
) is also very important, as explained hereafter.
The reducers involved in the catalytic reduction of nitrogen oxides in an oxidizing medium are mainly hydrocarbons (HC).
A problem arises when these reducers are not in sufficient quantities to ensure proper conversion of the nitrogen oxides. Diesel engines for example present this type of drawback. The HC/NO
x
ratios are then far less than one, whereas the activity of the catalysts is really significant only with HC/NO
x
ratios greater than one.
There are various known means allowing to increase the hydrocarbon content of exhaust gases.
It is well-known to inject hydrocarbons directly into the exhaust line, upstream from the catalytic conversion. A specific system, independent of the engine, is then used.
Engines equipped with a high-pressure fuel injection system referred to as <<common rail>> allow controlled hydrocarbon injections in the engine itself. Pilot injections of fuel before or after the main injection allow to change the composition of the gases at the exhaust and notably the reactivity to the catalyst.
The hydrocarbons can thus be significantly increased at the exhaust and a sufficient concentration can be obtained to reduce the nitrogen oxides on the catalyst.
It is well-known that the catalytic formulations used for nitrogen oxides reduction in an oxidizing medium are characterized by a relatively narrow temperature range, so that the major part of the operating process does not get a satisfactory conversion.
Known injections of additional fuel at the exhaust are furthermore performed continuously, which implies a certain <<additional consumption>>.
In order to remedy these drawbacks and to improve the activity of a deNO
x
catalyst, it is possible, according to the invention, to adopt a particular hydrocarbon injection strategy.
SUMMARY OF THE INVENTION
The object of the present invention thus is a process for controlled injection of hydrocarbons into an exhaust line of an internal-combustion engine running on lean mixture, comprising catalytic elimination of nitrogen oxides.
According to the invention, the process consists in injecting a certain amount of hydrocarbons upstream from the catalytic elimination, periodically and for a short time interval, by means of pulsed hydrocarbon injections. More precisely, said conversion is carried out with a catalyst having a Platinum/Alumina type formulation.
According to the invention, the frequency and the amplitude of the hydrocarbon pulses are controlled according to the running conditions of the engine.
According to a particular feature of the invention, injections are controlled by a computer.
Furthermore, the temperature of the exhaust gases can be measured upstream from the catalytic elimination.
Injection thus is controlled according to the temperature of the exhaust gases.
The process according to the invention is preferably implemented for temperatures allowing oxidation of the hydrocarbons sent to the catalyst in pulses.
The hydrocarbons injected are preferably gas-oil type hydrocarbons.
The temperatures used are preferably higher than 200° C. and they more particularly range between 230° C. and 300° C.
Without departing from the scope of the invention, it is possible to combine pulsed hydrocarbon injections with a continuous hydrocarbon injection.
According to the invention, the time between the end of an injection and the start of the next injection ranges between 1 and 10 s.
More precisely, the injection time ranges between 1 and 10 s.
The amount of hydrocarbons injected is advantageously such that a gas whose composition has a HC/NO
x
ratio ranging between 1 and 30 is obtained upstream from the catalytic elimination.
According to a particular embodiment of the invention, the amount of hydrocarbons injected is such that a gas whose composition has some excess oxidizer is obtained upstream from the catalytic elimination.
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Bouchez Mathias
Bourges Patrick
Martin Brigitte
Antonelli Terry Stout & Kraus LLP
Denion Thomas
Institut Francais du Pe'trole
Tran Diem
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