In-cylinder measurement of mixture maldistribution in a L-head engine

The distribution of fuel-air mixtures in many L-head engines is not homogeneous. If the local mixture is too rich or too lean, then incomplete combustion occurs. This can play a major role in unburned hydrocarbon and carbon monoxide 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 components. Consequently, a more complete combustion process may result, and emissions reduced. An optical fiber bundle was used to measure the emissions of CH and C2 radicals in this research to map the mixture uniformity in the combustion chamber. The experimental results showed that there exists a relationship between the intensity ratio (IC2/ICH) and the fuel equivalence ratio. The local fuel equivalence ratios can be obtained after the relationship between the light intensity ratio and fuel equivalence ratio is established. In addition, fuel-rich combustion zones were identified in the vicinity of spark plug and valves. Two fuels, propane (C3H8) and Indolene (CH1.86)7, were used for investigating the effects of different types of fuel on the intensity ratio. A L-head spark-ignition engine was selected for this study since this type of engine uses a conventional carburetor in which the fuel-air mixture is relatively nonhomogeneous which produces high hydrocarbon emissions. Furthermore, the flat cylinder head supplies sufficient space for the installation of the optical fiber bundles.