Colorado State University Clean Snowmobile Challenge 2002 2002-01-2758
A student design team at Colorado State University (CSU) has developed an innovative snowmobile to compete in the Clean Snowmobile Challenge 2002 competition. The team selected a 600cc two-stroke cycle engine (Arctic Cat ZRT600) due to its favorable power/weight ratio. In order to reduce emissions, the team adapted the engine to operate with direct in-cylinder fuel injection, using the Orbital Combustion Process (OCP) air-assisted fuel injection system. This conversion required that the team design and cast new heads for the engine. The direct-injection system reduced carbon monoxide (CO) emissions by 70% and total hydrocarbon (THC) emissions by 90%. An oxidation catalyst was placed in the engine's silencer to oxidize the remaining CO and hydrocarbons. The combination of direct injection and oxidation catalyst reduced both CO and THC by over 99%. In order to reduce noise, the team switched from the use of three expansion chambers (i.e. “triple pipes”) on the stock ZRT600 to a single expansion chamber. An exhaust silencer was then fitted to reduce exhaust noise, and a new intake airbox was designed to reduce intake noise. A layer of acoustic foam was applied to the interior of the engine compartment to reduce radiated engine noise. An acoustic analysis of the engine shows that the noise level of the snowmobile is dominated by noise at the engine's firing frequency and at twice the firing frequency. Quarter-wave reaction tubes were fitted to the intake and exhaust to reduce noise. The steps taken reduced the noise from the unmodified level of 83 dBA to 75 dBA, which did not meet the competition requirements of 74 dBA. Direct injection has improved the fuel efficiency from 13 miles per gallon (MPG) with the unmodified engine to approximately 20 MPG. The performance of the engine has been improved. The peak horsepower has been reduced by approximately 4 horsepower due to the switch from triple-pipes to a single pipe exhaust. However, the engine torque in the mid-range has been increased, and the throttle response is improved across the entire range. These factors combine to give the direct-injected snowmobile the same elapsed times in a 500-foot acceleration test as the unmodified snowmobile. In summary, the CSU snowmobile has reduced emissions by 99%, reduced fuel consumption by 35%, reduced noise by 8 dBA, and improved overall performance and ridability. A cost analysis has shown that the team's technical approach would add approximately $497 to the cost of manufacturing a snowmobile.