Achieving Consistent Maximum Brake Torque with Varied Injection Timing in a DI Diesel Engine

Abstract

The brake torque of a direct-injection diesel engine is known to plateau over a range of injection timings. Injection timing affects the engine’s ignition delay and the fractions of fuel which burn in premixed and diffusion modes. Therefore, the characteristics of combustion for swept injection timings along the maximum brake torque plateau are determined. The research is conducted by varying injection timing at constant engine speed and load while measuring engine emissions and in-cylinder pressure, revealing the premixed and diffusion burn fractions as well as important engine and exhaust design criteria such as maximum in-cylinder pressure and exhaust composition. These results are significant in diesel engine design because cheaper, lighter engines may be built if desired maximum brake torque may be produced with lower peak in-cylinder pressures. More critically, different emissions composition profiles exist for the desired maximum brake torque, which will allow designers to choose injection calibrations which favor some emissions over others. In fact, both favorable emissions and in-cylinder pressure criteria can be achieved by implementing more retarded timings along the brake torque plateau without losses in efficiency or power output.