An Examination of the Effects of Charge Inhomogeneity on the Compression Ignition of Fuel-Air Mixtures

The paper examines the rapid compression process of methane-air mixtures while using a zero-dimensional simulation and a detailed chemical kinetic scheme involving 137 reaction steps for methane-air combustion with an account made for heat transfer. The results of this simulation are compared with the corresponding values obtained when using multi-dimensional CFD simulation of the temporal and spatial evolution of the physical properties inside the cylinder while using KIVA-3 code both for reactive and non-reactive “methane”-air mixtures. The reaction rate data used in the code were overall rates of varyingly fitted data based on results of the full detailed kinetic scheme under the same local conditions. The effects of the non-uniformity in the charge physical properties due to heat transfer and compression effects on the evolution of the chemical processes leading to autoignition are presented and discussed. It is shown that major errors may result from the inadequate modelling of the nonuniform properties of the reactive charge during compression. These have serious implications to the interpretation of autoignition and knock phenomena in engines as well as the derivation of chemical kinetic parameters of reactive systems when obtained from observations made in motoring engines or rapid compression ignition apparatus.