Emission characteristics of premixed lean diesel combustion with extremely early staged fuel injection

Abstract

There is a gradient of fuel concentration in the spray of conventional direct-injection diesel engines. Therefore, a region of stoichiometric mixture ratio exists in the injected spray and a high concentration of NOx is produced. In this study, fuel injection timing was widely advanced to promote the mixing of fuel and air. Using this injection method, the engine could be driven with premixed lean diesel combustion (PREDIC), and NOx emissions were greatly reduced. To avoid the fuel spray contacting the cylinder liner, the fuel was injected by two side injectors simultaneously. The two sprays from the side injectors collided with each other and remained in the center region of the cylinder. Thus mixing of fuel and air was promoted by a long ignition delay period. In the case of conventional injection methods, NOx could not be reduced to under 400 ppm (λ=2.7). In contrast, in the case of PREDIC, NOx emissions were reduced to as low as 20 ppm(λ=2.7).