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Gasoline Direct Injection engines can have significantly higher particulate mass (PM) and particulate number (PN) emissions relative to equivalent displacement Port Fuel Injected engines. Both the EPA and California Air Resources Board have adopted new stringent standards to be phased in over the next 10 years. The California regulations continue to tighten to a 1 mg/mi PM limit that is phased-in beginning with model year 2025 with full compliance by model year 2028. This study examines the different fuel injection system technology improvements that will be used to attain the standards to as well as their relative costs, market penetration potential, emission reduction and fuel economy impacts. The identification of alternative approaches and the analysis of their impacts was performed in two tasks. The first task was a comprehensive literature review and the findings of the review are presented.

The overall objectives of this study are to establish the relationship between a spark ignition, or Otto cycle, engine energy efficiency and the octane number (and potentially, the composition) of the fuel through a comprehensive review of recently published literature. The efficiency of the ideal Otto cycle is a function of the compression ratio (CR), but increasing compression ratio is limited by the onset of knock, which can be prevented by increasing fuel octane number. Hence, in an ideal case, there is a direct connection between engine efficiency and fuel octane number. In the real world, other factors also contribute to the relationship and spark timing is the primary control variable that affects both knock and efficiency. The literature review found that the relationship between octane number and efficiency was influenced by a number of intermediate variables covering engine type, operating condition, and fuel formulation.