Development of an Externally-Scavenged Direct-Injected Two-Stroke Cycle Engine

Two-stroke cycle engines used for modern snowmobiles produce high-levels of carbon monoxide and unburned hydrocarbons. In order to address the emissions and noise issues resulting from the use of snowmobiles, the Clean Snowmobile Challenge 2000 was held under the auspices of the Society of Automotive Engineers. The CSC 2000 competition was intended to facilitate the development of high-risk concepts to address the negative impact of snowmobiles. Hydrocarbon emissions from two-stroke cycle snowmobile engines are primarily due to short-circuiting of the air/fuel mixture during the scavenging process. Carbon monoxide emissions are due to rich combustion mixtures and poor combustion produced by inefficient scavenging. A student research team at Colorado State University undertook an ambitious engine development project for the competition. An externally-scavenged, direct-injected engine was designed to reduce emissions, improve fuel economy, maintain or improve power, and reduce exhaust noise. A twin-screw compressor was used to provide external scavenging for the engine. The Ficht™ impact-type fuel injection system was used to provide direct in-cylinder fuel injection. A high efficiency multistage reaction/absorption silencer was designed which also houses an oxidation catalyst. The engine was developed to the point that it is operational, although it was not used in the CSC 2000 competition. This paper describes the design concept for CSU's new snowmobile engine.