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Novel Combustion technologies and strategies show high potential in reducing the fuel consumption of gasoline spark ignition (SI) engines. In this paper, a comparison between various gasoline combustion concepts at two representative engine operating points is shown. Advantages of the combustion concepts are analyzed using thermodynamic split of losses method. In this paper, a tool for thermodynamic assessment (Split of Losses) of conventional and new operating strategies of SI engine and its derivatives is used. Technologies, like variable valve actuation and/or gasoline direct injection, allow new strategies to run the SI engine unthrottled with early inlet valve closing (SI-VVA) combined with high EGR, charge stratification (SI-STRAT) and controlled auto ignition (CAI), also known as gasoline homogeneous charge compression ignition (HCCI). These diverse combustion concepts show thermodynamic gains that stem from several, often different sources.

The controlled auto-ignition1 (CAI) improves dramatically the efficiency of a gasoline engine and brings it in close competition to the diesel engine without penalties in emissions. With CAI run in part-load, the gasoline engine reaches a standard driving cycle advantage of 12% in fuel economy compared to current commercial engines operating solely in homogeneous gasoline direct injection (GDI) with a stoichiometric charge. CAI is run lean in fuel and thus limited in load similar to the second generation spray guided stratified GDI strategy that promises at least the same fuel efficiency but is plagued with high NOx emissions requiring complex after-treatment systems. Although CAI produces negligible NOx, and a simple three-way catalyst suffices, it depends strongly on judiciously operating the engine within the dynamic operating cycle. Direct injection, valve actuation flexibility and advanced controls based on combustion state sensing are indispensable for this.

Novel combustion technologies, which de-throttle the gasoline spark ignition (SI) engine, show high potential in reducing the fuel consumption. Technologies like variable valve actuation and/or gasoline direct injection, allow new strategies to run the SI engine unthrottled with early inlet valve closing (SI-VVA), charge stratification (SI-STRAT) and controlled auto ignition (CAI), also known as gasoline homogeneous charge compression ignition (HCCI). These diverse combustion concepts show thermodynamic gains that stem from several, often different, sources. A multitude of definitions of thermodynamic gas exchange potentials arise when looking at the various publications concerning de-throttled combustion concepts. This paper shows a summary and comparison of these definitions and points out which one can be applied in general to evaluate various combustion concepts under the same basis of evaluation.