A Study of the Potential of Propane Fuel to Reduce Utility Engine Exhaust Emissions 921696
The small engine industry is currently faced with the challenge of meeting the pending 1994 and 1999 California emissions requirements. Possible alternatives include engine design modifications, more sophisticated carburetion, fuel injection, catalysts, and alternative fuels including propane. The object of this study was to quantify the emissions improvements that can be obtained by using propane instead of gasoline and to compare that to the California requirements. A secondary goal was to develop a carburetor that would minimize emissions from a propane-fuelled engine. Current applications of propane-fuelled small engines include forklifts, generators and power floor buffers. Typically, these are indoor applications that use propane because it is considered a clean burning fuel.
The test engine in this study is a single cylinder, 400cc, overhead-valve, air-cooled, four stroke utility engine. Other than the fuel system, no engine changes were made to accommodate the fuel being tested. A propane carburetor has been developed that provides vastly improved emissions output as compared to the current production propane carburetor. The results show that, compared to gasoline, propane provides a one-third reduction in emissions and 14% better fuel economy. The engine produced 6% less power with propane. It is apparent that neither fuel system, as currently produced, has an optimum emissions calibration. With improved calibration, both fuel systems should allow the test engine to meet the 1994 standards. While propane can provide substantially better emissions than gasoline, it appears that neither fuel system will allow the test engine to meet the 1999 standards, without the addition of some form of exhaust aftertreatment.