Potential to reduce the diesel engine emissions of Diesel-Ethanol-Biodiesel blends of high ethanol fraction (DEB blends) has been investigated. Experiments were performed for three DEB blends with oxygen contents of 7.78%, 12.21%, and 14.53% by weight (ethanol content 20%, 30% and 40% by volume) on diesel engines with significantly different engine configurations. The results showed that the HC emissions mainly depend on in cylinder temperatures, and significantly increased for DEB blends at low loads in case of low in cylinder temperature engine. CO emissions are governed by the combination of excess air and in cylinder temperature and oxygen in fuel helped to reduce it when the engine works with richer mixtures. NO emissions are predominantly dependent on excess air compared to the in cylinder temperature and oxygen in fuel has minor effect on it. The effect of oxygen in fuel on smoke reduction is more significant if the engines are working with rich mixtures. However, peak smoke during free acceleration mainly depends on fuel combustion quality, excess air and air fuel mixing ability of the engine rather than the oxygen in fuels and in cylinder temperature.