Effect of Using Biodiesel (B-20) and Combustion Phasing on Combustion and Emissions in a HSDI Diesel Engine

The use of biodiesel and its blends with ultra low sulfur diesel (ULSD) is gaining significant importance due to its ability to burn in conventional diesel engines with minor modifications. However the chemical and physical properties of biodiesel are different compared to the conventional ULSD. These differences directly impact the injection, spray formation, auto ignition and combustion processes which in turn affect the engine-out emissions. To understand the effect of fueling with B-20, tests were conducted on a single cylinder 0.42L direct injection research diesel engine. The engine is equipped with a common rail injection system, variable EGR and swirl control systems and was operated at a constant engine speed of 1500 rpm and 3 bar IMEP to simulated turbocharged conditions. Injection timing and duration were adjusted with B-20 at different locations of peak premixed combustions (LPPC) and two different swirl ratios to achieve 3 bar IMEP. ULSD was then injected using the same injection strategy as developed for B-20. A comparison is made between the engine operations with ULSD after it has been optimized to run on B-20. The results indicate that the auto ignition reactions in B-20 are more prominent as compared to ULSD which requires more retarded injection timing with B-20. Also the premixed combustion fraction with B-20 is lower which leads to a lower peak of premixed combustion and subsequent lower mass average cylinder temperatures and NOx emissions.