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Computational Fluid Dynamics (CFD) simulation has been used to investigate the fuel air mixing regimes of an open chamber gasoline direct injection (GDI) engine. Acceptable homogeneous stoichiometric charge operation was predicted by the CFD simulation and confirmed by data from engine experiments with early injection timing. The simulation also predicted that late injection timing would be inoperable with the open chamber geometry employed. This was confirmed by injection timing experiments on the test engine. Subsequent initial engine development using a different engine geometry with top-entry inlet ports and a piston containing a spherical bowl has demonstrated very stable combustion with an unthrottled late injection strategy. The use of recycled exhaust gas (EGR) is demonstrated to produce better emissions and fuel consumption than purely lean operation. The effect of throttling is found to provide emissions improvements at the expense of fuel economy.