1997-02-24

Design of a Fuel Efficient Uniflow Two Stroke Semi-Direct Injection Engine 970367

A highly efficient two stroke engine was designed for a small vehicle to race in a fuel economy competition.The engine must power a lightweight prototype vehicle with a total mass of 80 kg on a closed circuit. This paper describes the approach taken to the design of this engine.An uniflow two stroke engine assisted by crankcase supercharging was chosen to provide the best trapping efficiency and reduce fresh mixture short circuiting. This design allows an increased transfer port area and improved swirl control inside the cylinder. The engine has two exhaust valves at the head, various cylinder transfer ports and a crankcase reed valve.To further reduce brake specific fuel consumption a fully digital electronic fuel injection system and two spark plug ignition are used. The injection is a semi-direct system, spraying the fuel into the cylinder at approximately two thirds of its height. The first prototype uses no air assistance for the injection.Special attention was taken on detail design in order to reduce mass and friction to best overall efficiency.

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