Application of Computational Fluid Dynamics to the Study of Conditions Relevant to Autoignition Damage in Engines 961963

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.
In this paper Computational Fluid Dynamics (CFD) has been used to study conditions of severe autoignition in a spark ignition engine, particularly in regions where piston to cylinder or cylinder head clearances are small. It is shown that very high pressures are generated in regions of small clearance as supersonic pressure waves are decelerated as they enter these spaces.


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