Application of ethanol and biodiesel in diesel engine: A review

Depletion of fossil fuels like coal and petroleum products and harmful emissions emitted by burning of these energy sources are the main reasons that are forcing mankind to search alternative energy sources, which should be renewable and ecofriendly. Fuel additives are used to enhance the properties of fuel to improve combustion, performance and emission characteristics. Techniques such as co-combustion, fumigation, dual injection, blending, and emulsification are some of the promising methods to use two fuels in dual fuel mode of an engine. Ternary and quaternary blends are also reported as performance enhancers. Biofuels are already in use, which may solve the above problems to some extent; however, research and development are still going on to optimize the production and blending techniques of biofuels. In this regard, ethanol is a liquid phase fuel which is already in use for blending with gasoline in petrol engines. Ethanol may be derived from renewable energy sources such as natural fermentation of sugars. The present study carries out a critical review on the use of ethanol with diesel in diesel engines. Ethanol may be used in diesel engine through a number of pathways such as fumigation, co-combustion, dual injection, blending with diesel and emulsification with diesel. It has been concluded in many studies that the use of alcohol such as ethanol, improves performance and emission characteristics of diesel engine. Several studies have reported that the use of ethanol in diesel engine improves cylinder pressure and heat release rate, increases brake thermal efficiency, reduces brake-specific fuel consumption, decreases emissions of carbon monoxide, oxides of nitrogen, unburnt hydrocarbon, particulate matter, and opacity of smoke. Ethanol contains 34.8 wt.% of oxygen, which helps in combustion as well as lowers emissions of carbon monoxide, oxides of nitrogen, unburnt hydrocarbon, particulate matter, and opacity of smoke. However, some studies reported an increase in oxides of nitrogen emission due to high oxygen availability during combustion.