Comparison of Single and Multiple Injection Strategies in a Butanol Diesel Dual Fuel Engine

A turbocharged three cylinder automotive common rail diesel engine was modified to operate in the n-butanol diesel dual fuel mode. The quantity of butanol injected by the port fuel injectors and the rail pressure, injection timing, and number of injection pulses of diesel were varied using open engine controllers. Experiments were performed in the dual fuel mode at a constant speed of 1800 rpm at varying brake mean effective pressure (BMEPs). Butanol to diesel energy share was varied, and the injection timing of diesel was always set for highest brake thermal efficiency (BTE). Single pulse injection (SPI) and two pulse injection (TPI) of diesel were evaluated. In SPI, with increase in the butanol to diesel energy share, the BTE remained unchanged. At high loads and high amounts of butanol, the heat release rate (HRR) variation indicated that butanol auto ignited before diesel with both SPI and TPI of diesel. NO emission always decreased because of reduced temperatures due to evaporation of butanol. Butanol also reduced the smoke levels except at high loads. HC levels were always higher. With optimized injection parameters, TPI of diesel resulted in lower NO, similar smoke, and BTE with lesser rate of pressure rise as compared to SPI of diesel in the dual fuel mode at high loads. On the whole, the SPI mode is suitable for low to medium outputs and the TPI mode is suitable for high outputs.