Four techniques were investigated for the characterization and quantification of fuel films in the intake port in a small four-stroke, air-cooled utility engine modified to use a fuel injector mounted in the place of the carburetor float bowl: step-fueling with constant air flow, step-throttle with constant fuel flow, skip-injection, and stop-injection tests. In the first two tests the exhaust air-fuel (A/F) ratio was measured with a fast-response universal exhaust gas oxygen (UEGO) sensor, while a fast flame ionization detector (FFID) was used in the latter two test methods. The engine was fueled with indolene, iso-octane, and propane to investigate and separate combustion and oil absorption / desorption from fuel film effects. The results indicate that the air flow through the intake port had the largest impact on the fuel film dynamics. Step-fueling tests showed only a short (less than 5 engine cycles) period during which the inducted A/F differed from the delivered A/F, whereas step-throttle tests showed a more pronounced A/F excursion that persisted for close to 20 engine cycles. The skip- and stop-injection tests indicated that vaporization from the fuel film contributed approximately 30% of the fuel inducted per cycle, regardless of load or the liquid fuel type. The overall film mass was found to be directly proportional to engine load (throttle position).
Investigation of Intake Port Fuel Films in a Small Utility Air-Cooled Engine
Sae Technical Papers
Small Engine Technology Conference & Exposition ; 2001
01.12.2001
Aufsatz (Konferenz)
Englisch
Liquid-cooled V-twin small utility engine with electronic fuel injection system
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