PURPOSE: To increase an output, to reduce fuel consumption, and to enable reduction of production of CO, HC, and NOx, by a method wherein, in an electronic fuel injection system diesel engine, fuel and air fed in a combustion chamber are independently ionized.

CONSTITUTION: An electrode 5 is located between an intake manifold 9 and a cylinder block 8, and a negative high voltage is applied on air. By posittive corona discharge, nitrogen and oxygen in air are electrified in a minus manner, combination of nitrogen is difficult to make, and combination of oxygen is apt to make. A fuel hose 7 of an insulating material is attached in a position in the vicinity of an injector 6, and a positive high voltage pulse is applied on fuel by means of an ionizing device 4 for an electric conductor attached in a manner to be firmly adhered around the fuel hose 7. By negative corona discharge, fuel is electrified in a plus manner, and combination of the fuel with oxygen ion is facilitated. Further, a high voltage generating device for ionization use only employing an ignition coil 3, capable of separately generating a positive and a negative high voltage pulse, is used.