A Comparative Study of Different Methods of Using Animal Fat as a Fuel in a Compression Ignition Engine

This work explores a comparative study of different methods of using animal fat as a fuel in a compression ignition engine. A single-cylinder air-cooled, direct-injection diesel engine is used to test the fuels at 100% and 60% of the maximum engine power output conditions. Initially, animal fat is tested as fuel at normal temperature. Then, it is preheated to $70°C$ and used as fuel. Finally, animal fat is converted into methanol and ethanol emulsions using water and tested as fuel. A drop in cylinder peak pressure, longer ignition delay, and a lower premixed combustion rate are observed with neat animal fat as compared to neat diesel. With fat preheating and emulsions, there is an improvement in cylinder peak pressure and maximum rate of pressure rise. Ignition delay becomes longer with both the emulsions as compared to neat fats. However, preheating shows shorter ignition delay. Improvement in heat release rates is achieved with all the methods as compared to neat fats. At normal temperature, neat animal fat results in higher specific energy consumption and exhaust gas temperature as compared to neat diesel at both power outputs. Preheating and emulsions of animal fat show improvement in performance as compared to neat fat. Smoke is lower with neat fat as compared to neat diesel. It reduces further with all the methods. At peak power output, the smoke level is found as $0.89m−1$ with methanol, $0.28m−1$ with ethanol emulsions, and $1.7m−1$ with fat preheating, whereas it is $3.7m−1$ with neat fat and $6.3m−1$ with neat diesel. Methanol and ethanol emulsions significantly reduce NO emissions due to the vaporization of water and alcohols. However, NO increases with fat preheating due to high in-cylinder temperature. Higher unburned hydrocarbon and carbon monoxide emissions are found with neat fat as compared to neat diesel at both power outputs. However, these emissions are considerably reduced with all the methods. It is finally concluded that adopting emulsification with the animal fat can lead to a reduction in emissions and an improvement in combustion characteristics of a diesel engine.