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DISI engine emissions and fuel economy are strongly dependent upon fuel injection and spark timings, particularly when the engine is operating in stratified charge mode. Experimental studies of the effects of injection and spark timings and the interaction between these are described. The sensitivity of HC and NOx emissions to timings during stratified charge operation, the comparison of performance under stratified and homogeneous charge modes of operation and the rationale for mode switch point settings are investigated. The high sensitivity of emissions to injection and spark timing settings gives rise to potential robustness issues. These are described.