Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Patent
1995-06-06
1996-09-24
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
123570, 123571, F02M 2507
Patent
active
055580700
DESCRIPTION:
BRIEF SUMMARY
This invention relates to internal combustion engines operating on the two stroke cycle and to the management of the combustion process thereof to control the level of contaminants in the exhaust emissions.
It has in the past been recognised that two stroke cycle engines exhibit poor performance in the area of fuel consumption and also in the area of the level of harmful emissions in the engine exhaust. However, there are substantial benefits to be obtained by wider use of engines operating on the two stroke cycle. Firstly, because of their relatively simple construction, and secondly, because of their relatively small physical size and resultant high power to weight ratio. There has accordingly been considerable development in recent years directed to the control of the combustion process of two stroke cycle engines in a manner to reduce the level of emissions in the exhaust, and/or reduce the fuel consumption.
It has been recognised that the introduction of exhaust gas into the fuel/air mixture prior to the ignition thereof can contribute to a reduction in the production of NO.sub.x (oxides of nitrogen) during the combustion process, as the presence of exhaust gas in the fuel/air mixture reduces the resultant temperature and pressure in the engine cylinder resulting from the combustion, which is contrary to the high temperature and pressure conditions that promote the creation of NO.sub.x. This process of mixing exhaust gas with the fuel/air mixture is commonly referred to as exhaust gas recirculation (EGR) and is typically achieved by bleeding a controlled quantity of exhaust gas from the exhaust system into the air induction manifold of the engine.
Although this procedure has been used successfully in four stroke cycle engines, it is not as effective when applied to two stroke cycle engines, due principally to the low level of vacuum existing downstream from the conventional throttle in the air induction system. Hence, this would result in a low rate of intake of exhaust gas and in the case of a multi cylinder engine, a poor distribution of the exhaust gas in the induced air. Further, particularly in the case of a crankcase scaveneged engine, there is a significant time lag in the response by the engine to the introduction of the exhaust gas to the induction system due to the distance it is required to travel before entering the combustion chamber. Also, where exhaust gas is introduced into the inducion system of a crankcase scavenged two stroke cycle engine as the air capacity of the crankcase is greater than that of the cylinder, there is a further time lag in a change in rate of exhaust gas supply to the crankcase being seen in the engine cylinder. Also, the particulate materials normally present in exhaust gas can build up on mechanisms in the induction system of such two stroke cycle engines such as throttle valves and crankcase reed valves, and hence interfere in the effective operation thereof.
It has been previously proposed in publications such as International Patent Publication WO 79/00757 by J. P. Soubis and U.S. Pat. No. 3,581,719 by Gau to recycle exhaust gas into the combustion chamber for the purpose of returning thereto any unburnt fuel that may be in the exhaust gas. It has long been recognised that carburetted two stroke cycle engines exhibit the problem that part of the air and fuel charge that enters the combustion chamber passes out through the exhaust port prior to the commencement of combustion. The above referred to prior patents each are directed to overcoming this problem by re-directing the fuel rich portion of the exhaust gas back into the air intake or crankcase for recycling into the combustion chamber. As the recycled portion of the exhaust gas is primarily fuel and fresh air, it will not have a significant effect in the control of the generation of NO.sub.x, the problem the present invention is directed to overcoming.
It is proposed in U.S. Pat. No. 4,213,431 by Onishi to recycle exhaust gas into the air induction system of a two stroke cycle engine with the intent of c
REFERENCES:
patent: 3581719 (1971-06-01), Gau et al.
patent: 4213431 (1980-07-01), Onishi et al.
patent: 4318373 (1982-03-01), Soubis
patent: 4546751 (1985-10-01), Jarnuszkiewicz et al.
patent: 4682571 (1987-07-01), Kaufman et al.
patent: 5357919 (1994-10-01), Ma
patent: 5377650 (1995-01-01), Warner
patent: 5425346 (1995-06-01), Mavinahally
patent: 5443547 (1995-08-01), Morikawa
WO,A,79/00757 published Oct. 4, 1979.
Bell Gregory B.
Worth David R.
Orbital Engine Company (Australia) Pty. Limited
Wolfe Willis R.
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