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Recent advances in natural gas (NG) recovery technologies and availability have sparked a renewed interest in using NG as a fuel for commercial vehicles. NG can potentially provide both reduced operating cost and reductions in CO2 emissions. Commercial NG vehicles, depending on application and region, have different performance and fuel consumption targets and are subject to various emissions regulations. Therefore, different applications may require different combustion strategies to achieve specific targets and regulations. This paper summarizes an evaluation of combustion strategies and parameters available to meet these requirements while using NG in a spark ignited engine. A single-cylinder research engine using a modified diesel cylinder head was employed for this study. Both stoichiometric combustion with cooled exhaust gas recirculation (EGR) and lean-burn were evaluated.

Engine downsizing and downspeeding using GTDI technology improves fuel economy while maintaining vehicle performance. The downsizing potential of an engine application is limited by engine knock at low engine speeds as well as turbocharger inlet and catalyst temperatures at high speeds, requiring high spark retard and fuel enrichment, respectively. Both spark retard and fuel enrichment reduce the overall real world fuel economy benefit. Cooled exhaust gas recirculation (EGR) has been investigated as a way of reducing knock and lowering exhaust gas temperatures. This paper discusses the use of low-pressure route cooled EGR for knock mitigation at low engine speeds in order to improve full load performance and fuel consumption and increase the potential for engine downsizing.