In order to solve the problems associated with rapid combustion process under high engine speeds, benzyl azides were chosen as a fuel additive blended with diesel fuel. The physical and chemical properties of the fuel blends were analyzed. A single-cylinder engine was built and the in-cylinder working process was studied thoroughly for the new diesel-azides blends. Results show that, compared with pure diesel fuel, diesel-azides blends lead to higher heat release rate peak of premixed combustion, shorter combustion duration, and improved cycle efficiency. This indicates that diesel-azides blends have the potential for promoting rapid combustion. The current study provides a new way to improve the diesel combustion process and has laid a foundation for increasing engine power. (C) 2011 Elsevier Ltd. All rights reserved.