Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Patent
1995-12-04
1997-08-19
Koczo, Michael
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
123256, 123563, 123570, 552571, F02B 4702, F02B 4708
Patent
active
056576307
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a large supercharged diesel engine, such as a main engine of a ship, comprising a turbocharger having a turbine driven by exhaust gas and a compressor driven by the turbine and supplying charging air to the cylinders of the engine, and a recycling passage for returning part of the exhaust gas to the engine cylinders.
Japanese patent publication No. 53-5321, for example, describes gasoline engines, wherein the NO.sub.x content of the exhaust gas has been restricted by recycling part of the exhaust gas to the intake system of the engine so that the maximum combustion temperature of the engine becomes lower. The amount of NO.sub.x produced by the combustion depends on the maximum combustion temperature in that an increasing temperature leads to a sharp increase in the amount of NO.sub.x. Recycling of 5-20 percent of the exhaust gas may result in a reduction of up to 30percent of the amount of NO.sub.x in the exhaust gas, using prior art.
Naturally, it is desirable to restrict the engine emission of environmentally harmful compounds at source, but the known method for recycling exhaust gas is not without its problems. For example, the recycling tends to increase the amount of particles in the exhaust gas, which is visible as smoke. This is probably due to the fact that the oxygen content of the charging air drops with the increased degree of recycling.
DE-A 25 04 308 describes an engine wherein part of the exhaust gas is purified by bubbling through a water bath before the recycling to the intake side. It is stated that the purified gas contains steam which does not contribute to lowering the NO.sub.x content, but instead results in reduced fuel consumption.
DE-C 41 23 046 describes an engine which by use of a pump or compressor presses recycled exhaust gas through a material with fine pores so that the gas passes through a water bath as finely distributed bubles. The engine is not supercharged.
It is known from WO 88/01016 to purify the exhaust gas from a diesel engine in a water bath and then recycle part of the purified and humidified gas to the intake side of the engine. The humidification in the water bath results in a certain cooling of the exhaust gas and contributes to keeping down the maximum combustion temperature. As the steam has a large specific heat capacity, the effect of recycling exhaust gas is greater than in the above methods. The engine is not supercharged, and the water consumption is large, because all the exhaust gas is humidified.
Large diesel engines normally use heavy fuel oil as fuel, which results in large amounts of combustion products which are very aggressive to the engine components in contact with the exhaust gas. The heavily polluting exhaust gas cannot be sufficiently purified by bubbling through a water bath. It is known from DT-A-24 43 897 to pass exhaust gas to the intake side of a diesel engine in order to reduce the NO.sub.x formation during combustion. To avoid the impurities from the diesel engine's own exhaust gas, the exhaust gas from a gasoline engine is used instead as the recycling gas for the diesel engine. This solution renders the engine plant substantially more complicated and is also inapplicable in a ship where normally only a very limited amount of fuel in the form of gasoline is allowed.
SE-B 314 555 and U.S. Pat. No.4,440,116 describe turbo-charged engines wherein water is injected in the intake air upstream of the compressor to limit the temperature increase of the intake air during compression. In large high-powered diesel engines, such a water addition may result in disadvantageously rapid corrosion of the sensitive compressor, as even a very small amount of fine drops of water can erode the blades of the compressor wheel.
The object of the invention is to enable recycling of exhaust gas in a large supercharged diesel engine in such a manner that the engine maintains high efficiency and a long life for the engine components, particularly expensive components, such as turbochargers, and that the components of the recycling syste
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Patent Abstracts of Japan, Publication No. 60-14097(A), published Jan. 24, 1985 (JP-A-58-120471).
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Berg-Sonne Peter
Kjemtrup Niels
Koczo Michael
Man B&W Diesel A/S
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