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The results of an experimental study of the low speed and low load operation of an optical research engine are presented for spark-ignition (SI) and spark-assisted, controlled auto-ignition (SA-CAI). A direct injection gasoline engine was modified for optical access into the combustion chamber. At 1000 rpm and 3 bar NIMEP, stable SA-CAI combustion was achieved with predicted EGR rates in excess of 45%. The coefficient of variation (CoV) in NIMEP was 4.8% compared to 6.5% recorded in the SI case, with no EGR. Particle image velocimetry measurements of the airflow showed lower mean and turbulent velocities in the SA-CAI case at the end of the compression stroke. Planar Laser Induced Fluorescence (PLIF) measurements of the fuel vapour signal in the air-fuel-residual distribution were significantly lower than in the SI case. Indicating analysis showed that the main combustion burn duration was considerably greater in the SA-CAI case.

Two experimental techniques, Particle Image Velocimetry (PIV) using a water-analogy Dynamic Flow Visualisation Rig (DFVR) and Laser Doppler Anemometry (LDA) in a motored research engine, were used to investigate the flow pattern generated within the combustion chamber of a gasoline direct injection (G-DI) engine. The in-cylinder flow was also modelled for the two cases using the Computational Fluid Dynamics (CFD) code VECTIS; that is, models were created using first water and then air as the working fluid. The experimental and computational results were converted into the same format and hence compared qualitatively and quantitatively. All results showed good agreement and were used to validate the different techniques. The correlation between the CFD air simulation results and the LDA results demonstrates that the CFD code can be used to predict reliably the air motion created in the combustion chamber of a G-DI engine.