Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-04-28
2002-08-06
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S278000, C060S280000, C060S292000, C060S605200, C060S602000, C123S572000
Reexamination Certificate
active
06427436
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns improvements in emissions control. More especially, the invention concerns improvements in the control of NOx from diesel engines.
The use of emission control catalysts for engine exhaust clean-up is well established. Diesel engines have different characteristics from gasoline-fuelled engines, with a different mix of pollutants caused by the different fuels, the different combustion characteristics in each engine and the lower temperatures met with in exhausts from diesel engines. Additionally diesel engines emit more noticeable particulates, especially under heavy load and upon start-up, than gasoline engines. In general, it can be said that diesel engines emit less NOx than a gasoline engine under most conditions, but because diesel engines mostly or exclusively operate on a high air to fuel ratio, that is are “lean”-bum engines, the chemistry of the exhaust gas does not favour NOx reduction, because of the excess of oxidising species.
To meet the various emission regulations already or about to enter force, it has become necessary to treat diesel exhausts in various ways. Oxidation catalysts, which catalyse the oxidation of unburnt hydrocarbons (“HCs”) and carbon monoxide (“CO”) are now regularly fitted to light duty diesels, and particulate traps of various types are becoming commonplace on heavy duty diesels as used in trucks, buses and some stationary engines. A technique for improving exhaust gas emissions, especially NOx emissions from diesel engines is exhaust gas recirculation (“EGR”), which takes a proportion of the exhaust gas and recirculates it into the engine cylinders. Generally, about 30 to 60 vol % of the exhaust gases are recirculated, depending upon the characteristics of the particular engine and the emission limits which must be met. Although EGR has been used with gasoline engines for about ten years, it has only been more recently fitted to diesel engines; we believe that most vehicles currently fitted with EGR are passenger car light duty diesel engines. In the case of engines fitted with a catalyst, the exhaust gas is always taken from upstream of the catalyst. It is generally expected that EGR would have a significant effect on emissions from heavy duty diesel engines, that is those fitted to heavy trucks and buses. Because of the engineering problems caused by the very different exhaust characteristics compared to light duty diesel engines, however, this has proved difficult to achieve. In particular, there is no commercial source of an EGR valve of suitable size and materials to be fitted to a heavy duty diesel engine.
We refer also to a device marketed as the “CRT” by Johnson Matthey PLC. This device is described in U.S. Pat. No. 4,902,487 and is a continuously regenerative particulate trap. Unlike the vast majority of particulate traps, however, this device regenerates in situ without the need for periodic replacement or electrical heating to ignite the soot. Such device relies upon a catalyst system which generates NO
2
which we found is effective to cause low temperature combustion of trapped soot particles.
The principle of the CRT has been adopted by Hino in their published Japanese patent applications JP 8338320 and JP 9088727, in combination with EGR. However, such systems as described are not believed to be capable of use in true heavy duty diesel applications.
BRIEF SUMMARY OF THE INVENTION
We have surprisingly found that a novel diesel engine system can offer very low levels of NOx. The present invention provides a diesel engine system comprising a diesel engine and an exhaust system therefor, the exhaust system incorporating a catalyst effective to convert NO to NO
2
under normal operating conditions, a trap for particulates mounted downstream of the catalyst and an exhaust gas recirculation valve with cooling means to cool the portion of exhaust gas which is recirculated, characterised in that the cooling means is mounted upstream of the exhaust gas recirculation valve.
The invention also provides a process for the reduction of NOx in diesel engine exhaust gases, comprising, in order, converting at least a portion of the NO in the gases to NO
2
by passing the gases over a catalyst, trapping at least the majority of carbonaceous particles in the gases on a trap and continuously oxidising said particles and cooling and recirculating at least a portion of the cleaned gases leaving the trap, to the engine cylinders, characterised in that the gases are cooled before passing over an exhaust gas recirculation valve.
BRIEF OF THE DESCRIPTION DRAWING
FIG. 1
shows a diesel engine incorporating an exhaust system of the present invention;
FIG. 2
shows NOx reduction in the system of the present invention.
REFERENCES:
patent: 4231338 (1980-11-01), Sugasawa et al.
patent: 4406126 (1983-09-01), Yokokura et al.
patent: 4534173 (1985-08-01), Tsukamoto
patent: 4902487 (1990-02-01), Cooper et al.
patent: 5050376 (1991-09-01), Stiglic et al.
patent: 5440880 (1995-08-01), Ceynow et al.
patent: 5564283 (1996-10-01), Yano et al.
patent: 5785030 (1998-07-01), Paas
patent: 5806308 (1998-09-01), Khair et al.
patent: 6062026 (2000-05-01), Woollenweber et al.
patent: 6240721 (2001-06-01), Ito et al.
patent: 6301888 (2001-10-01), Gray, Jr.
patent: 6338245 (2002-01-01), Shimoda et al.
patent: 8338320 (1996-12-01), None
patent: 9088727 (1997-03-01), None
UK Search Report, dated Nov. 5, 1997, for corresponding GB application.
International Search Report, dated Nov. 26, 1998; for corresponding EPO application.
Allansson Ronny
Andreasson Klas Anders
Myers Nils
Uusimaki Ari
Warren James Patrick
Denion Thomas
Johnson Matthey Public Limited Company
Ratner & Prestia
Tran Binh
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