Performance of Biodiesel Blends of Different FAME Distributions in HCCI Combustion

As the world market develops for biodiesel fuels, it is likely that a wider variety of biodiesels will become available, both locally and globally, and require engines to operate on a wider variety of fuels than experienced today. At the same time, tighter emissions regulations and a drive for improved fuel economy have focused interest on advanced combustion modes such as HCCI or PCCI, which are known to be more sensitive to fuel properties. This research covers two series of biodiesel fuels. In the first, B20 blends of natural methyl esters derived from palm, coconut, rape, soy, and mustard were evaluated at light load in an HCCI research engine to determine combustion and performance characteristics. These fuels showed performance differences between the biodiesels and the base #2 ULSD fuel, but did not allow separation of chemical effects due to the small number of fuels and correlation of various properties. In a second engine study, narrower cuts of various biodiesels were used to blend fourteen fuels of different composition. These diesel fuel blends varied in biodiesel content from B5 to B30 and the neat ester cuts covered a carbon number range of C6:0 to C22:6, resulting in a wide variation of oxygen content, iodine number, and boiling point distribution. Results show how fuel properties vary with ester chemistry and biodiesel content and how these properties affect engine performance and control requirements. The experimental results are also analyzed statistically to develop predictive models for biodiesel effects.