COMPRESSION WAVE INJECTION: A MIXTURE INJECTION METHOD FOR TWO-STROKE ENGINES BASED ON UNSTEADY GAS DYNAMICS

This paper describes the fundamental principles of operation of a mixture injection system now called the Compression Wave Injection system (CWI). The system has been initially designed for use in handheld lawn and garden equipment but is also appropriate for use in other two stroke applications. The designed engines must demonstrate greatly reduced emissions of unburned hydrocarbon to attain present and future emission regulations. Because of the constraints of the market for the handheld products, the system was designed for low-cost production and adaptation to existing products. It was also required, from cost and operation considerations, that the system is capable of operating with fuel metering based on a carburetor.

The CWI system described utilizes a compression wave derived from the combustion process of a two-stroke engine to inject a rich mixture into the cylinder of the engine. The hot gases from the combustion process are used to partially vaporize the fuel charge prior to entry into the cylinder. Reflected compression wave behavior is utilized to aid in the preparation of the fuel charge and deliver the charge to the cylinder after the initiation of the scavenging behavior. By utilizing the Compression Wave Injection method; low-cost, carbureted engines can be produced that operate with well-vaporized delayed fuel entry into the cylinder in a similar fashion to direct-injected engines. Such engines display 30 percent improvement in brake specific fuel consumption and 70-85 percent reduction in emission of unburned hydrocarbon.