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Power Split Hybrids are unique when compared to conventional powertrains from the perspective that the engine speed is directly controlled by the motor/generator at all times. Therefore, traditional methods of detecting variations in fuel volatility do not apply for Power Split Hybrid based configurations. In their place, the Ratio-metric Fuel Compensation (RFC) method has been developed for Power Split Hybrid generator configurations to detect and compensate for engine hesitations within milliseconds of the first injection event. Furthermore, test results have shown that in the presence of low volatility fuel, RFC provides robust starts at the ideal lean air fuel ratio required for PZEV emissions compliance.

A program to explore the effects of natural and additive-derived cetane on various aspects of diesel performance and combustion has been carried out. Procedures have been developed to measure diesel engine fuel consumption and power to a high degree of precision. These methods have been used to measure fuel consumption and power in three heavy-duty direct-injection diesel engines. The fuel matrix consisted of three commercial fuels of cetane number (CN) of 40-42, the same fuels raised to CN 48-50 with a cetane improver additive, and three commercial fuels of base CN 47-50. The engines came from three different U.S. manufacturers and were of three different model years and emissions configurations. Both fuel economy and power were found to be significantly higher for the cetane-improved fuels than for the naturally high cetane fuels. These performance advantages derive mainly from the higher volumetric heat content inherent to the cetane-improved fuels.

The homogeneous charge, compression-ignition (HCCI) combustion process has the potential to significantly reduce NOx and particulate emissions, while achieving high thermal efficiency and the capability of operating with a wide variety of fuels. This makes the HCCI engine an attractive technology that can ostensibly provide diesel-like fuel efficiency and very low emissions, which may allow emissions compliance to occur without relying on lean aftertreatment systems.