The development of a fuel-air injection nozzle that injects a premixed fuel and air and then a quantity of clean air into the combustion chamber is described. The new injection nozzle provides better controllability of fuel-air mixing and fuel evaporation. Additionally, the clean air injection following the fuel-air mixture injection prevents stagnant fuel accumulations in the nozzle tip. Therefore, the fuel-air injection nozzle is of particular advantage for use with difficult fuels such as plant oils for long term operation.The fuel-air injection nozzle was tested in an engine running on sunflower oil giving significant reduction in carbon buildup. No engine modifications were necessary for the fuel-air injection nozzle installation.