A fuel emulsion for powering a diesel engine contains water, a fuel, and an emulsifier package which contains a quaternary ammonium surfactant. A method for powering a diesel engine with the fuel emulsion involves preparing the fuel emulsion by emulsifying a fuel and water in the presence of the emulsifier package. An emulsifier package for emulsifying a fuel and water contains a quaternary ammonium surfactant and at least one nonionic surfactant, which is an alkoxylate. The quaternary ammonium surfactant is obtainable by reacting a quaternizable nitrogen compound containing at least one quaternizable, especially tertiary, amino group with a quaternizing agent; which converts the at least one quaternizable, especially tertiary, amino group to a quaternary ammonium group, where the quaternizing agent is a hydrocarbyl epoxide in combination with a free hydrocarbyl-substituted polycarboxylic acid.