Influences of the end of injection and ambient temperature on biodiesel combustion

Influence of the injection pressure and ambient temperature at the end of injection of biodiesel spray has been studied using Rapid Compression Machine (RCM). The experiments were conducted on a RCM for the premixed combustion with a single injection at 21% intake oxygen concentration. RCM is designed to simulate combustion phenomenon that observes the ignition, combustion process, and combustion characteristics under high injection pressure and variant ambient temperatures. Two types of biodiesel blend namely, B5 and B10 were tested in the RCM at the injection pressures of 80 MPa and 90 MPa. The ambient temperature of RCM was varied at 700 K to 1100 K. The result showed that higher ambient temperature produced shorter ignition. The initial combustion rate became low and the combustion duration became longer. Too short ignition delay resulted in decreased premixed combustion, which cannot provide enough time for air-fuel premixing. Under low ambient temperature, longer long ignition delay influenced the ignition that occurred late in the expansion stroke that caused incomplete combustion process, reduced power output, and poor fuel conversion efficiency. The emission showed that under the condition of higher ambient temperature, the product of CO, O2, and HC became lower but resulted in the increase of NOx level. Increased blends of biodiesel ratio were found to enhance the combustion process, resulted in decreased HC emissions. The improvement of combustion process is expected to be strongly influenced by oxygenated fuel in B10 biodiesel content.