Mixtures of gaseous and liquid fuels have the potential to induce flash boiling under in-cylinder conditions close to the top dead center, something that can be expected to be suitable for a premixed diesel combustion that demands a way to enhance lean mixture formation. The present study mixes ethane, which is a natural gas component, into diesel fuel as ethane has a high vapor pressure that facilitates flash boiling and as ethane has a low cetane number that prolongs the ignition delay. This paper investigates spray characteristics of a diesel fuel-Ethane mixture, and the engine performance and exhaust emissions are evaluated in a single cylinder engine. The test results show that the flash boiling enhances the lean mixture formation, and realizes combustion with low soot and low NOx without EGR (exhaust gas recirculation) while also improving thermal efficiency. An additional test was performed to identify the effects of the flash boiling and the ignition delay, and the results show that the long ignition delay plays the most important role in the thermal efficiency and emission changes and that the flash boiling facilitates the formation of leaner mixtures that lower the overall combustion rate and achieves very low NOx emissions.