Analysis of particulate number emissions during dynamic load changes for port fuel injection on an optically accessible, turbocharged four-cylinder spark ignition engine

Abstract

For cost-sensitive markets, port fuel injection is still an important injection concept even though disadvantages compared to direct injection are well known. In the context of future emission legislations, it is necessary to further optimize port fuel injection engines with respect to particulate and gaseous emissions. When comparing direct injection and port fuel injection regarding particulate emissions, advantages for port fuel injection are reported in majority of published investigations; however, significantly high particulate number emissions were also observed for port fuel injection. The work presented here focuses on the particulate formation mechanisms during dynamic engine load changes. Experiments are performed at both warm and cold engine conditions. Parameters such as injection timing, engine load, and the intensity of charge motion are varied in order to evaluate possible optimization measures regarding particulate number. Furthermore, different injectors with varying spray targeting are tested. Particulate formation mechanisms during dynamic load changes are analysed using high-speed video endoscopy; therefore, optical access to both the intake channel and the combustion chamber is set up. The optical access within the intake manifold towards the intake valves allows for the observation of the interaction of air flow and fuel spray. The endoscopic access to the combustion chamber facilitates the localization of particulate number sources by means of soot luminosity. By combining a parameter study with high-speed imaging techniques, a profound understanding of the underlying mechanisms leading to particulate number emissions is acquired.