Internal-combustion engines – Precombustion and main combustion chambers in series – Chamber temperature control means
Patent
1994-07-20
1997-03-18
Dolinar, Andrew M.
Internal-combustion engines
Precombustion and main combustion chambers in series
Chamber temperature control means
123259, F02B 1918
Patent
active
056113072
DESCRIPTION:
BRIEF SUMMARY
REFERENCE TO CO-PENDING APPLICATION
This is a continuation-in-part Application of International PCT/AU92/00552, filed 14 Oct. 1992, for INTERNAL COMBUSTION ENGINE IGNITION DEVICE, which Application designated the United States, and is now abandoned.
FIELD OF THE INVENTION
This invention relates to ignition devices for internal combustion engines, and more particularly hydrogen assisted jet ignition (HAJI) devices for improving combustion efficiency. In the present specification, the term "hydrogen" is intended to include hydrogen and other fast-burning fuels.
BACKGROUND OF THE INVENTION
Simultaneous control of exhaust emissions and thermal efficiency is an established goal in engine design. Optimization of engine design is limited by Cycle by Cycle Variability (CBCV), especially for spark ignition engines. CBCV is observed as either variations in the pressure diagram or as variations in flame propagation between consecutive engine cycles. In the vehicle the consequent unsteadiness in delivered engine power results in uneven vehicle progress which has been termed surge. Combustion variations require compromises in engine design, the setting of mixture composition and spark timing. This reduces engine power and efficiency at full load in order to meet roughness, noise, and octane requirements and at part load and idle reduces fuel economy and increases exhaust emissions in order to control surge.
If CBCV could be eliminated, the engine would run at its best economy settings and still produce a smooth and steady output. In addition, the fuel octane requirements could be reduced, or the compression ratio raised, with a consequent improvement in efficiency. Further, the lean limit of engine operation could be extended, resulting in a reduction in exhaust emissions and an improvement in thermal efficiency. It has been shown that the reduction of CBCV in lean-burn engines, together with control of ignition timing, can reduce NOx emissions and at the same time improve engine thermal efficiency. Another important benefit arising from control of cycle variations is the reduction in engine surge and improved vehicle driveability while cruising.
Much research has been conducted on lean-burn engines with the intention of improving efficiency and reducing emissions. The benefits from the lean combustion approach can be theoretically explained as follows. The excess air improves the engine's thermal efficiency by increasing the overall specific heats+ ratio, by decreasing the energy losses from dissociation of the combustion products, and by reducing the thermal losses to the engine cooling system. In addition, as the flame temperature drops with decreasing fuel air ratio, the NOx production is exponentialy reduced and the excess air may promote a more complete reaction of CO and hydrogen fuel emission from crevices and quench layers.
It is concluded that at the present state of development, U.S. emission standards present a considerable challenge to the realization of the fuel economy advantages theoretically inherent in lean burn engines. On the other hand, even though the incentives for lean burn application to automotive engines are valid and have good theoretical foundation, its implementation is a complex problem that requires several conflicting requirements to be satisfied simultaneously. Lean burn operation increases the CBCV and deteriorates vehicle driveability. CBCV increases with increasing air-fuel ratio.
Many attempts have been made to improve combustion efficiency. Such attempts include fuel stratification with a rich mixture in the spark plug region, divided or pre-chamber engines alone or in combination with stratification, and hydrogen enrichment of the whole fuel charge. None of these attempts have been entirely successful and the problems referred to above remain in evidence.
In the case of non-fuelled divided chamber engines, including the Bosch spark plug patented around 1978, the size (volume, connecting passage length and aperture) of the pre-chamber can only improve combustion at a partic
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Dolinar Andrew M.
The University of Melbourne
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