Internal-combustion engines – Charge forming device – Auxiliary air or gas used to inject fuel
Patent
1987-03-11
1988-07-26
Tapolcai, William E.
Internal-combustion engines
Charge forming device
Auxiliary air or gas used to inject fuel
239 5, F02M 2300
Patent
active
047593350
DESCRIPTION:
BRIEF SUMMARY
This invention is directed to fuel injection systems for internal combustion engines and in particular injection of fuel directly into the combustion chamber. The invention has particular applicability to spark ignited two stroke and four stroke cycle engines.
Considerable effort has been expended in developing direct (in-cylinder) injection systems for internal combustion engines. Most of the work has been for diesel injectors but recently spark ignited engines have received more detailed attention.
In U.S. patent application Ser. No. 740067 and corresponding Australian Patent Application No. 32132/84 there is described a direct injection system particularly suited for use on spark ignited engines. A metered amount of fuel is delivered into a holding chamber, and a valve is opened to allow compressed air to propel the fuel through the valve into a combustion chamber of the engine. The metered amount of fuel is varied in accordance with the engine load. The injector nozzle incorporates the above mentioned valve, so the valve performs the function of timing the fuel delivery and effecting atomisation of the fuel.
The characteristics of the spray of the fuel droplets issuing from the nozzle into a combustion chamber have major effects on the efficiency of the burning of the fuel, which in turn affects the stability of the operation of the engine, the fuel efficiency, and the exhaust emissions. To optimise these effects, in a spart ignited engine, the desirable characteristics of the spray pattern of the fuel issuing from the nozzle include small fuel droplet size, controlled penetration of the fuel spray into the combustion chamber, and at least at low engine loads a relatively contained evenly distributed cloud of fuel droplets.
In the control of the harmful components of the engine exhaust, it is desirable to control the placement of the fuel within the gas charge in the combustion chamber to meet a number of different parameters. Ideally the fuel should be distributed in the gas charge so that the resultant fuel-air mixture is readily ignitable at the spark plug, all the fuel has access to sufficient air to burn completely, and the flame maintains a sufficient temperature to extend to all the fuel before being extinguished. There are other factors that must also be considered, such as charge temperature that may promote detonation, or the formation of undesirable contaminants in the exhaust gas.
It has been found from our experiments on direct fuel injection of two stroke engines that, under light enging loads, the most favourable combustion characteristics are achieved when the fuel is introduced to the combustion chamber in as fine a droplet size as possible, and in a diffused cloud but relatively confined in the area of the spark plug.
In addition it has been found that for high engine loads, the most favourable combustion characteristics are achieved when the fuel is again introduced in as fine a droplet size as possible but with a much more extensive spacial distribution of the fuel cloud deeper into the combustion chamber than for the fuel cloud under light load conditions.
Although the pneumatic injection systems described in the above patent applications provide the desirable fine atomisation of fuel droplets, and an injection period sufficiently short to be used in modern two stroke engines, it has also been found up until this time that an injection valve which provided the correct fuel spray distribution for low engine loads gave a less acceptable distribution for high engine loads. Similarly, an injection valve which provided the required distribution for high engine loads did not perform as well at low loads. Thus in practice it was found necessary to use an injection valve which compromised performance at both extremes of operational load range in order to achieve the best overall performance from the engine.
One technique which has been partly successful in overcoming this problem has been to vary the pressure of the propellant air, but this can produce both insufficient atomization of the
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Brooks Roy S.
McKay Michael L.
Ragg Peter W.
Orbital Engine Company Proprietary Limited
Tapolcai William E.
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