Optimization of a Direct-Injected 2-Stroke Cycle Snowmobile 2003-32-0074

A student design team at Colorado State University (CSU) has developed an innovative snowmobile to compete in the Clean Snowmobile Challenge 2003 competition. This engine concept was originally developed for the CSC 2002 competition and demonstrated the lowest emissions of any engine that competed that year. The team utilized a 3-cylinder, 594cc, loop-scavenged, two-stroke cycle engine (Arctic Cat ZRT600) and then modified the engine to operate with direct in-cylinder fuel injection using the Orbital OCP air-assisted fuel injection system. This conversion required that the team design and cast new heads for the engine. The direct-injection approach reduced carbon monoxide (CO) emissions by 70% and total hydrocarbon (THC) emissions by 90% from a representative stock snowmobile. An oxidation catalyst was then used to oxidize the remaining CO and THC. This combination of direct fuel injection and oxidation catalysts reduced CO by over 97% and THC by over 99% when compared to the 2002 SAE CSC control sled. The design discussed in this paper builds on the core technology developed in 2002 to improve performance and reduce noise.

The direct injected engine and supporting hardware were transferred to a lightweight 2002 Arctic Cat ZL600 chassis. The modern suspension and the reduced weight of the chassis resulted in improved handling, increased acceleration and improved fuel economy.

The 2002 entry exceeded the competition noise limit by one dBA. A comprehensive effort was undertaken to redesign the exhaust system to reduce noise, improve power, and to more effectively accommodate the oxidation catalyst. Analytical and experimental techniques were used to redesign the exhaust system which demonstrated a 20% improvement in peak power and mid-range torque over the 2002 entry. Improved materials are utilized to withstand the high temperatures produced by the oxidation catalyst. The new exhaust silencer design combines a diffusive silencer, a side resonator, and an absorptive silencer. Intake noise is attenuated with a combined diffusive silencer and side resonator silencer. The exhaust and intake silencers were effective in reducing the engine's firing frequency and the first four harmonics.

A cost analysis has shown that this complete design approach would add $473 to the production cost of manufacturing the snowmobile. The majority of this cost is incurred by the direct fuel injection system and the modifications to the exhaust system.