Emission Characteristics of Premixed Lean Diesel Combustion with Extremely Early Staged Fuel Injection

There is a gradient of fuel concentration in the conventional direct injection diesel engine fuel spray. Therefore, a region of stoichiometric mixture ratio exists in the spray and this results in production of large amounts of NOx. In this study, the fuel injection timing was advanced greatly to promote fuel and air mixing. Using this injection method, the engine could be operated with PREmixed lean DIesel Combustion (PREDIC), and NOx emissions were reduced greatly.

To avoid collision of the fuel spray with the cylinder liner. the fuel was injected simultaneously with two side injectors. The two side injector sprays collided with each other and remained in the center region of the cylinder. Thus, mixing of the fuel and air was promoted by a long ignition delay period. Using conventional injection methods, NOx could not be reduced below 400ppm at an excess air ratio of 2.7. On the contrary. in the case of PREDIC, NOx emissions could be reduced to 20ppm at the same excess air ratio.