Internal-combustion engines – Charge forming device – Auxiliary air or gas used to inject fuel
Patent
1985-04-02
1987-09-15
Wolfe, Jr., Willis R.
Internal-combustion engines
Charge forming device
Auxiliary air or gas used to inject fuel
123457, 123458, F02M 6702
Patent
active
046932240
DESCRIPTION:
BRIEF SUMMARY
This invention is directed to the injection of fuel into the combustion chamber of an internal combustion engine and is particularly applicable to engines which operate at a high cycling rate.
For convenience of explanation within this specification, the invention is particularly described in relation to spark ignition 2-stroke cycle reciprocating engines. However, the invention is also applicable to compression ignition engines and to four stroke cycle engines, rotary engines and engines with circular oscillating pistons, e.g. that described in U.S. Pat. No. 4,037,997.
There is an increasing requirement for less expensive and more efficient fuel injection systems for internal combustion engines. In-cylinder injection has distinct and well-known advantages in comparison with manifold injection and throttle-body injection carburettors. However with existing apparatus there are large cost penalties relating to the high degree of precision engineering required in the manufacture of hardware for in-cylinder injection systems.
A further disadvantage arising in in-cylinder fuel injection is the constraint on the timing and duration of the injection of fuel into the working chamber. This is aggravated by the increasingly high speeds of revolution of modern engines. The use of modern materials and construction techniques has made 6,000 rpm not uncommon for mass produced engines. At this speed, in a four-stroke cycle engine, the time interval for injection of fuel to the working chamber is of the order of 6 to 9 ms.
Despite their many advantages, 2-stroke cycle engines are today restricted from many applications for two major reasons, excessive hydrocarbon emissions and excessive fuel consumption. Both problems arise primarily from the scavenging process for the working chamber in these engines which allows part of the incoming fuel air charge to escape directly through the exhaust system prior to combustion, and also allows excessive dilution of the incoming charge under throttled conditions, thereby inducing misfiring. It is known that such problems can be greatly reduced by the use of in-cylinder fuel injection of such an engine, and this is discussed in the introductory passages to U.S. Pat. No. 3,888,214. In-cylinder fuel injection also offers greater opportunity to achieve a stratified charge in the working chamber which can give improved combustion effects.
However, the efficient performance of such an engine is to a large degree dictated by the performance of its fuel injection system. In comparison with the requirements regarding the short time interval available for injection discussed above for 4-stroke cycle engines, an in-cylinder fuel injection system for a 2-stroke cycle engine requires an even better performance. In a piston ported, crankcase scavenged, reciprocating 2-stroke cycle engine running at only 6,000 rpm a desired time interval for injection is a mere 2-3 ms. If any fuel is injected outside this time interval the engine's efficiency suffers considerably. If injection commences too early there can be considerable loss of unburnt fuel through the still open exhaust port and, if continued too late, the fuel can be injected into already burning mixture with undesirable combustion consequences.
Conventional in-cylinder fuel injection systems have previously required a high pressure fuel pump and high differential pressure metering apparatus. Also the efficiency of in-cylinder fuel injection is dependent on fine atomization of the fuel at the point of delivery. Both these requirements result in a high cost in componentry due to the high standards of engineering required in production due to the close tolerances on manufacturing dimensions.
The use of pneumatic fuel metering is described in SAE Technical Paper 820351 by McKay, and although the method described therein achieves exceptionally fine fuel atomization on delivery, and is eminently suited to multi-point injection to the inlet manifold of internal combustion engines, some difficulty can be encountered in applying the system directly to i
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Orbital Engine Company Proprietary Limited
Wolfe, Jr. Willis R.
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