This study deals with the development of controlled-ignition technology for high performance compression ignition alcohol engines. The objective of this study is to make clear the main factors that govern auto-ignition phenomenon of an alcohol spray. Spray mixture formation and auto-ignition phenomena of ethanol-diethyl ether blended fuels were visualized by shadowgraph method and images were recorded with high-speed camera (8213 fps). Effects of surrounding gas conditions such as oxygen concentration on spray mixture formation up to auto-ignition were experimentally investigated by the use of a large constant volume electrical heating chamber. Result showed that the controlled ignition was possible by the control of surrounding gas oxygen concentration for spray of ethanol and diethyl ether blended fuels.