The main purpose of the current research is to evaluate the effects of enhanced tumble flow on combustion and the emission characteristics in a spray-guided direct injection spark ignition engine fueled with n-butane, which is the main component of liquefied petroleum gas(LPG) in South Korea. In the engine test, the range of stable operation was slightly reduced with the application of the enhanced tumble flow, but the coefficient of variance of indicated mean effective pressure(IMEP) was lowered.
IMEP was increased because the enhanced tumble flow can promote the mixture formation process, so that the local rich mixture region will decrease and the combustion speed will become faster. The emission characteristics of nitrogen oxides(NOx) were higher while particulate matter was reduced with the enhanced tumble flow. As a representative result from the direct flame visualization test, both intensity and area of soot incandescence were reduced with the application of enhanced tumble flow, which explained the reduced particulate matter emission.