In-cylinder Air Injection for Diesel Combustion Improvement

For further improvement of diesel combustion performance, in-cylinder air injection was applied to enhancing air entrainment in an attempt to shorten the combustion duration. A modified commercially available gasoline injector was used for air injection. The original six-hole nozzle was removed, and a three-hole nozzle (ϕ0.43 mm × 1 hole, ϕ0.5 mm × 2 holes) was used. The air injector was installed near the fuel injection nozzle on a single-cylinder diesel engine, and a performance test was conducted to investigate the effects of the air injection duration, timing, and pressure under the operating conditions of an engine speed of 1200 rpm, fuel injection pressure of 120 MPa, natural aspiration, and without exhaust gas recirculation. In addition, the effects of supplying different gases were considered. Compared with conventional diesel combustion, both air injection and nitrogen injection resulted in a higher peak of the heat release rate, improvement in the indicated work, and decrease in smoke emissions. The results suggest that air injection near the fuel injection nozzle can improve the combustion performance by increasing the turbulence energy of the ambient air and promoting air entrainment into the diesel spray flame.