Investigations on a Homogenous Charge Compression Ignition Engine Operated with Biodiesel and its Emulsions with Water

The carbon-neutral biodiesel is a promising renewable substitute for fossil diesel that renders the traditional oxides of nitrogen-particulate matter (NO_x-PM) trade-off into a unidirectional NO_x control problem. Low-temperature combustion (LTC) modes such as homogenous charge compression ignition (HCCI) are attractive for obtaining ultra-low NO_x and PM emissions. Studies on utilizing biodiesel fuel for HCCI combustion mode are sparsely available. Moreover, biodiesel emulsions in the HCCI combustion mode have not been attempted so far. Based on this premise, the present work explored the potential to utilize biodiesel and its emulsions having 20% and 25% water by volume under HCCI operating conditions. Biodiesel was prepared from a non-edible Karanja oil. The biodiesel emulsions were prepared using a heated magnetic stirrer apparatus with 3% by volume of the raw Karanja oil as a surfactant. A production light-duty diesel engine is modified to run in external mixture preparation based HCCI mode. An air-preheater and a fuel vaporizer aid in vaporizing the low volatile biodiesel injected into the inner surface of the vaporizer at 300 bar pressure using a common rail direct injection (CRDI) system. The engine compression ratio was fixed at 15, the maximum operable value with biodiesel. The results show that the engine could be operated only up to 20% of the rated load with biodiesel. With biodiesel-water emulsion, 30% of the rated load could be achieved. The maximum cylinder pressure was higher, and the heat release rate was advanced with emulsions compared to neat biodiesel. The brake specific fuel consumption was reduced by 35%, and the brake thermal efficiency increased by 2.4%, along with ultra-low NO_x and smoke emissions with emulsions. The present study shows the potential to utilize biodiesel-water emulsions in HCCI mode with reduced exhaust emissions. Suitable charge dilution methods must be adopted to extend the HCCI operating load range with emulsions.