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Nowadays, investigating underhood airflow by using numerical simulation is a standard task in the development process of passenger cars and commercial vehicles. Numerous publications exist which deal with simulating the airflow through the engine compartment of road vehicles. However, hardly anything can be found which deals with off-road vehicles and nothing exists which focuses on snowmobiles. In the presented paper the airflow and the thermal conditions inside the engine compartment of a snowmobile are investigated by the usage of computational fluid dynamics (CFD) as well as experimental methods. Field tests at arctic conditions have been conducted on a serial snowmobile to measure temperatures inside the compartment and to gain realistic boundary conditions for the numerical simulation. Thermocouples (type K) were attached under the hood to measure exhaust, air, coolant and surface temperatures of several components at previously defined load cases.

Customers are demanding propulsion systems giving as much as possible riding pleasure while still considering strict environmental regulations. BRP-Powertrain developed an engine for their snowmobile brand Ski-Doo fulfilling both needs. The Inline two cylinder four stroke engine using a multi port fuel injection system significantly contributes to an impressive and up to now second-to-none cruising range of 29 miles per gallon. With 42 kW at 7250 1/min the performance target was achieved. Excellent combustion stability allows Lambda values of 1.1 and higher in part load. This also contributes to the good fuel efficiency. The geometrical layout of the engine was driven by vehicle boundaries. All the power pack components had to be installed using a minimum of space. A low center of gravity was an absolute need for stable riding properties of the snowmobile. Therefore the crankshaft was put as low as possible which left no room for an oil pan underneath the engine.