The Effects of Multirow Nozzles on Diesel Combustion

Abstract

In a diesel engine, the combustion and emissions formation are governed by the spray formation and mixing processes. To meet the stringent emission legislations of the future, which will demand substantial reductions of NO x and particulate emissions from diesel engines, the spray and mixing processes play a major roll. Different fuel injection systems and injection strategies have been developed to achieve better performance and lower emissions from the diesel engine almost without investigating the influence of the injector nozzle orifices. A reduction in the nozzle orifice diameter is important for an increased mixing rate and formation of smaller droplets which is beneficial from emissions and fuel consumption point of view, as long as the local air-to-fuel ratio (AFR) is kept at a sufficiently lean level. A drawback with decreased orifice diameter is a shorter liquid fuel spray penetration length, which can lead to a worse air utilization and increased emissions, but this negative effect can be reduced by the use of a more compact piston bowl. In this study, the effects of reduced orifice diameters, arranged in both single and multi rows, were investigated using two different piston bowl designs at constant compression ratio. The injection rate was also varied by using two different injection pressures. The experiments were performed on a single cylinder, heavy duty, direct injection engine. The results show that a multirow nozzle with optimized umbrella angle and smaller piston bowl diameter can, at constant fuel consumption, obtain lower levels of NO x and soot than the reference engine configuration.