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Design of experiments (DoE) has been used to optimise the accuracy of CFD predictions for diesel combustion and emissions simulations. Eight CFD simulation variables concerning grid geometry and simulation time step were used as the basis for a twenty-two point DoE analysis. The results showed that for practical CFD simulations the CFD predictions were heavily dependent on local grid distribution and the calculation timestep. From the DoE statistical models, two CFD setups were predicted to give optimal combustion and emissions results with CPU times of 11 and 44 hours, model (A) and model(B), respectively. These two CFD model setups were then used to assess the accuracy of CFD combustion and emissions predictions against a series of detailed measurements performed on a single cylinder engine fitted with a common rail fuel injection system.

A unique high swirl bomb (max. swirl rate of 22,000 rev/min.) has been constructed to simulate conditions in the small direct injection Diesel engine with direct and positive control of pressure, temperature and injection rate. The bomb is equipped with 3 alternative heads as follows: a) an anemometer head for pre injection velocity surveys b) an instrumented head for heat release tests c) a photography head. In mode b) the bomb operates with a high speed data acquisition system and in mode c) with a 8000 frame per second camera. An extensive series of heat release and photogr^hy tests has been performed and the paper summarises these results.