1991-02-01

Air-Forced Fuel Injection System for 2-Stroke D.I. Gasoline Engine 910664

Late fuel injection directly into the cylinder of a 2-stroke engine is desirable to prevent escape of some fuel into exhaust system during cylinder scavenging. This leaves little time for fuel evaporation and mixture preparation and puts a premium on the degree of fuel atomization needed during the injection process. Although a respectable degree of atomization can be attained in fuel systems with high pressure, liquid-only injection, further improvements can be made when compressed air is used to assist atomization.
A novel air-forced (AFI) fuel injection system for in-cylinder injection in a 2-stroke engine is described. The system employs compressed air to force a metered quantity of fuel from the fuel injector internal cavity past a spring loaded poppet valve. A fog-like cloud containing a rich mixture of fuel and air is injected into the cylinder. As a result, an exceptionally fine atomization is achieved. At the same time, the shape of the air-fuel mixture spray can be varied as may be required by engine operating conditions.
The basic concept and operating principles of 2 generations of AFI systems are reviewed together with advantages and shortcomings of both systems. The injector flow test results, injection stability and fuel atomization are discussed. Use of the Coanda effect to create various spray shapes is demonstrated.

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