Application of Exhaust Pipe Restriction Technique to a Small Two-Stroke Engine 2007-32-0032
A simple method to reduce HC emissions caused by fuel short-circuiting in a two-stroke engine is to apply a certain restriction to the exhaust gas flow in the exhaust pipe. This technique, developed for motorcycles, vehicles and outboards, has been applied to a small off-road two-stroke engine with a constant speed operating condition. In order to assess the feasibility and effectiveness of this technique for the reduction of HC and CO emissions in such an engine, a butterfly valve was installed in the exhaust pipe next to the exhaust port. Based on test results using the butterfly valve, a cylindrical restrictor was developed to generate various restrictions to the gas flow in the exhaust pipe and consequently reduce the fuel short-circuiting. The effectiveness of the restrictor on emission reduction was further improved by leaner air/fuel mixture. The experimental results showed improved engine performance including the best 24% reduction of total weighted HC and 25% reduction of total weighted CO when the exhaust pipe restriction was 50%. Additionally, Mota, a two-stroke engine simulation program, was used to simulate the engine performance with reduced diameter of the exhaust pipe. The outcomes of this simulation support and explain the experimental results.
Finlay Llewyn Watson, Guang Hong
Small Engine Technology Conference & Exposition