Oxygen-enriched combustion of diesel engine can reduce smoke emission and improve thermal efficiency, but also lead to the increase of NO emission. In this research, experiments were conducted on a turbo-charged direct injection diesel engine under the two conditions of 2000 rpm and 180 Nm equivalent power (57% of the original max load at 2000 rpm) as well as 100% load of this speed. The combination of intake oxygen enrichment and water emulsified diesel was used to improve the NO-smoke emissions without serious penalty in brake specific fuel consumption (BSFC). The results showed that when engine load was 180 Nm with the conditions of 0%-20% water emulsion ratio and 21% -21.5% intake oxygen concentration, as well as under the condition of 100% load with 10%-15% water emulsion ratio and 21%-22% intake oxygen concentration, the NO-Smoke emissions were lower than that of original engine and BSFC was not exceeding 5% of the original engine by optimized combination of water emulsion ratio and oxygen concentration. (C) 2013 Elsevier Ltd. All rights reserved.