Impact of Fuel Injector Design and Operating Pressure on PM Emissions from a PFI Engine

Yan  Chang, University of Michigan-Ann Arbor

PM emissions have been shown to be a health hazard and have been a concern for diesel engines and GDI engines for a long time. Although PM emissions from PFI engines are significantly less than from diesel and GDI engines, PFI PM emissions may also receive more attention as increasingly stringent limits on particulate mass and number are imposed. PFI is currently the most widely used injection system for gasoline engines in the world and this proven technology still retains potential to further reduce fuel consumption and emissions. Gasoline PFI’s robust mixture preparation process tolerates a wider range of fuel properties and offers significant cost advantages over systems with high-pressure direct injection. This study investigates the impact of fuel injector design and operating pressure on PM emissions from a PFI engine during steady-state operation.

The engine used in this study was a 3.6 L 6 cylinder PFI engine. The effect of injector design and injection pressure on PM mass, number, size distribution and nanostructure during steady-state operation were investigated. Three different sets of injectors were compared: 1^st set of 4 holes injectors, 2^nd set 6 holes injectors, and 3^rd set of 4 holes injectors with special injection path. For each set of injectors, the engine was run at a variety of operating conditions, ranging from low load to full load and from low speed to high speed. Gravimetric PM measurements were accomplished using a Sierra Instruments BG-3 partial flow dilution tunnel, a filter conditioning chamber, and a Sartorius M5P microbalance. PM number and size distribution for each condition were obtained by using a TSI Scanning Mobility Particle Sizer Spectrometer. Also, smoke number for each operating condition was investigated with an AVL smoke meter. Thermophoretic sampling and transmission electron microscopy (TEM) was used to investigate the nanostructure of primary particles and particle aggregates.

It was found that the 3^rd set of injectors are best at reducing PM number on this engine and at specific operating conditions. PM mass at steady state is very low for all injectors tested and depends largely on the engine operating condition. 6 bar fuel injection pressure reduces PM mass compared to 4 bar. Increasing engine load and speed increases PM aggregate size and produces more ordered nanostructure, while low-load and low-speed conditions produce particles with more amorphous nanostructure.

Authors’ list:

Yan Chang, Shounak Bapat, Chenxi Sun, Jinhuai Lu, Michael Gross, Michael Mosburger, Andre Boehman, Stanislav V. Bohac