Bio-diesel effects on combustion processes in an HSDI diesel engine using advanced injection strategies

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the combustion process using different fuels including European low sulfur diesel and bio-diesel fuels with advanced multiple injection strategies. Influences of injection timings and fuel types on combustion characteristics and emissions were studied under similar loads. In-cylinder pressure was measured and used for heat release analysis. High-speed combustion videos were captured for all the studied cases using the same frame rate. NO_x emissions were measured in the exhaust pipe. Different combustion modes including conventional diesel combustion and low-temperature combustion were observed and confirmed from the heat release rates and the combustion images. Natural luminosity was found consistently lower for bio-diesel than the European low sulfur diesel fuel for all the cases. However, for NO_x emissions, under conventional combustion cases such as cases 2 and 3, it was found that bio-diesel leads to increased NO_x emissions. Under a certain injection strategy with retarded main injections like case 4 and 5, it is possible to have up to 34% lower NO_x emissions for B100 than B0 for case 4 with low-temperature combustion mode. Simultaneous reduction of NO_x and natural luminosity was achieved for advanced low-temperature combustion mode. It is hypothesized based on the results that the lower soot generation for bio-diesel fuel is believed due to a lower soot formation rate and a higher soot oxidation rate. The NO_x increase problem for bio-diesel fuel can be amended by employing advanced injection strategies with low-temperature combustion modes.