Over the last few years there has been an increased pressure from the government on auto manufacturers to reduce the emissions from internal combustion engines. However, this increased emission is associated with operating the vehicle at part-load. In the meantime, depleting reserves of fossil fuels and the increasing environmental pollution caused by burning of fossil fuels, have paved the way for fuel diversification. Cleaner and renewable fuel is being introduced worldwide. The use of ethanol as an alternative transportation fuel shows promise for several reasons. While ethanol can be produced from several types of biomass, it offers properties such as high octane number, higher oxygen content and high heat of evaporation, which make it a most attractive alternative fuel, in particular for the direct injection gasoline engine. In this research, a single cylinder camless engine equipped with an electro-hydraulic valve train system has been used to study and compare different engine operation modes in the SI and CAI combustion using gasoline and its ethanol blends. This book will be useful to those involved in combustion engine research and development.