Hydrocarbon emission sequence related to cylinder mal-distribution in a L-head engine.

Abstract

The distribution of fuel-air mixtures in many L-head engines is not homogeneous. If local mixture is too rich or lean, incomplete combustion occurs. Such incomplete combustion plays a major role in unburned hydrocarbon emissions. Fuel-air mixture distribution depends on in-cylinder swirl and turbulence and is directly related to intake manifold configuration, fuel delivery system design and combustion chamber shape. Understanding the spatial mixture distribution may help improve the design of these aforementioned elements. Consequently, a more complete combustion process may result, and emissions reduced. A method that measures the light emission of CH and C$\sb2$ radicals using an optical fiber bundle has been developed in this research to map the mixture uniformity in the combustion chamber. The intensity ratio (I$\sb{\rm C2}$/I$\sb{\rm CH}$) was use to indicate the local fuel-air equivalence ratio. The mixture mal-distribution was then correlated with the hydrocarbon emission sequence. The exhaust gas was sampled by a port mounted sampling valve and analyzed by a FID. Two fuels, propane and Indolene, were used with a Tecumseh horizontal shaft L-head engine. Two levels of mixture mal-distribution were investigated for each fuel. For both fuels, high hydrocarbon emissions early in the exhaust process were identified as resulting from a locally overrich mixture in the valve region of the chamber. For propane, the hydrocarbon content of the gases leaving the cylinder last was independent of mixture distribution and was likely due to wall quenching. On the other hand, for Indolene, mixture mal-distribution was found to contribute to the hydrocarbon emission late in the exhaust process.