The effects of the combustion chamber geometry and a double-row nozzle on the diesel engine emissions

Abstract

This paper presents how injector nozzle distributions and the combustion chamber geometry affect the emission characteristics of diesel engines. The number of nozzle holes was increased from seven to 12 by a using double-row nozzle distribution to enhance the air–fuel mixing and the spatial distribution of the spray while avoiding spray overlap. The combustion chamber geometry was modified to have a wide shallow two-step bowl, which ensured adequate spray penetration with the double-row nozzle, to observe the influence of the spray–piston interaction on the combustion and emissions. Three hardware combinations (a seven-hole single-row nozzle with a conventional piston, a 12-hole double-row nozzle with a conventional piston, and a two-step piston) were tested in a single-cylinder direct-injection diesel engine under three boost and exhaust gas recirculation conditions. The injection timing was adjusted to result in a similar power by maintaining 50% of the total fuel mass fraction burned points for each hardware combination. For a conventional boost pressure (1.10 bar) and 30% exhaust gas recirculation, the 12-hole double-row nozzle with a conventional piston exhibited the best emission characteristics with a significant reduction in the particulate matter emissions. For a high boost pressure (1.30 bar) and 30% conventional exhaust gas recirculation, the nitrogen oxide emissions slightly increased and the particulate matter emissions decreased for the 12-hole double-row nozzle with a conventional piston compared with those for the seven-hole single-row nozzle. The two-step piston resulted in decreased particulate matter emissions but increased nitrogen oxide emissions under a high boost pressure. For 60% high exhaust gas recirculation, which is characterized by low-temperature combustion, the particulate matter emissions, the carbon monoxide emissions, and the total hydrocarbon emissions decreased simultaneously without an increase in the nitrogen oxide emissions using the 12-hole double-row nozzle with a two-step piston.