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The process of autoignition in an internal combustion engine cylinder produces large amplitude high frequency gas pressure waves accompanied by significant increases in gas temperature and velocity, and as a consequence large convective heat fluxes to piston and cylinder surfaces. Extended exposure of these surfaces to autoignition, results in their damage through thermal fatigue, particularly in regions where small clearances between the piston and cylinder or cylinder head, lie in the path of the oscillatory gas pressure waves. The ability to predict spatial and temporal' variations in cylinder gas pressure, temperature and velocity during autoignition and hence obtain reasonable estimates of surface heat flux, makes it possible to assess levels of surface fatigue at critical zones of the piston and cylinder head, and hence improve their tolerance to autoignition.

The Computational Fluid Dynamics (CFD) Code KIVA II has been applied to model combustion pressure oscillations in the Indirect Injection Diesel Engine. These oscillations are attenuated and transmitted by the engine structure to the surroundings as noise. The computational model was used to evaluate changes in design and operating characteristics of an engine, and the effect of these on the intensity of gas pressure oscillation. The results in general corroborate the trends of published experimental measurements of combustion noise. A 40% increase in grid resolution showed minor changes in the magnitude of cylinder pressure oscillation and approximately 0.5ø crank angle phase advance in the oscillation cycle compared with the grid used for the results presented here.

Combustion noise produced by the direct injection Diesel engine is a consequence of the dynamic equilibration of the high local pressures created in the combustion space following autoignition that stimulates the resonance modes, over a range of frequencies, of the gas contents of the engine cylinder. In this paper Computational Fluid Dynamics has been used to study the effects of changes in engine design and operating parameters that, from empirical experience, are known to influence the noise output of an engine, and explanations confirmed or given for well-established behaviour.

The Computational Fluid Dynamics (CFD) code KIVA has been modified to include a combustion model and the Shell autoignition mechanism, and has been applied to a disk-chambered homogeneous charge spark ignition engine. The effects of ignition timing, turbulent kinetic energy and EGR were investigated for offset ignition. The effects of swirl and central ignition were separately investigated. For the central ignition case the influence of asymmetry of piston and cylinder head surface temperatures was also considered. The results of the computational study are in general agreement with experimentally observed trends regarding heat release rate and phasing and their influence on cylinder pressure development, autoignition and knock. With the CFD code it was possible to observe, following autoignition, large amplitude pressure waves and acoustic resonant modes in the combustion chamber, which are generally in agreement with the published literature.

Application of the engine CFD code KIVA II with the inclusion of the SHELL model for autoignition chemistry, and the discrete transfer radiation heat transfer model, has enabled the technically important problem of non luminous radiation from the major emitting species CO2 and H2O in the combustion products within the cylinder of a spark ignition engine to be considered as a combustion diagnostic aid, and also as a method of controlling individual cylinder Air/Fuel ratio. Results from a parametric study using CFD have been found to corroborate the experimental findings of other workers over a range of operating conditions including knock.