The present invention provides a diesel engine and methods and apparatus for premixing diesel fuel and oxidant for combustion. The methods and apparatus may include a two stage vortex, each stage accommodating different flow rate ranges. The vortex pulverizes diesel fuel and optimally mixes the diesel fuel with an oxidant prior to introduction into a combustion chamber. The premixing results in more complete combustion and, consequently, fuel efficiency is increased and pollution is decreased.