Particulate Emissions Characterization of a GDI Engine, 03-R8157

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Principal Investigators
Michael Hedge
Imad Khalek
Jess Gingrich

Inclusive Dates:  06/10/10 – 10/10/10

Background - With the increased implementation of the gasoline direct injection (GDI) engine, particulate matter (PM) emissions have become a source of concern for the gasoline industry. In general, GDI engines have elevated PM emissions caused by non-homogenous mixing and the presence of localized rich fuel-to-air mixtures in addition to liquid fuel in the combustion chamber. This is particularly relevant because the Euro 5 light-duty emissions standard has a 0.005 g/km limit on PM emissions from GDI-equipped vehicles and the U.S. Tier II Bin V standard is 0.01 g/mile for all diesel vehicles, with expectations that future regulations will constrain gasoline-fueled engines. Furthermore, particle number (PN) is anticipated as being the next regulation hurdle for manufacturers to overcome and will be included in Euro 6 regulations. The proposed limit is 6x1011 particles per kilometer over the European Urban Driving Cycle. Previous work has been successful in utilizing exhaust gas recirculation (EGR), both uncooled and cooled, to reduce PM mass and other regulated emissions while improving fuel economy. However, there is limited published research on the topic of characterization of PM size and PN as it relates to GDI engines utilizing cooled EGR as an emissions control strategy.

Approach - A small displacement, turbocharged GDI engine was operated at a variety of steady-state conditions with differing levels of EGR to characterize total (solid plus volatile) and solid particle emissions with respect to size, number, and soot or black carbon mass. Cooled external and uncooled internal EGR were both investigated to provide further insight into the role of bulk temperature on PM formation. Limited work was performed on the effect of enrichment on PM emissions with and without cooled external EGR. All emissions were measured on an engine-out basis, and no catalyst was present in the exhaust system. A Horiba Mexa 7100DEGR gas exhaust analyzer was used to measure carbon dioxide, carbon monoxide, oxygen, total hydrocarbons, nitric oxide and nitrogen dioxide in engine exhaust. Soot mass was measured with an AVL microsoot sensor (MSS), and particle size and number were measured with an TSI engine exhaust particle sizer (EEPS). Solid particle size and number measurements were facilitated with the use of a solid particle sampling system (SPSS).

Accomplishments - Success of the project depended on the ability to significantly reduce particulate mass and size and identify meaningful trends in the data to help explain and characterize particulate matter formation. The completion of this investigation has shown that high EGR levels with the test engine resulted in significant reduction of particle number and soot mass at a variety of operating conditions. Moreover, brake specific soot mass was reduced by 60 percent or more at every operating test point and solid particle number by at least 40 percent at most conditions, whereas reductions in total particle number had a higher dependence on engine speed. The data generated provided consistent trends that will be very useful in characterizing and furthering the understanding of particulate matter emissions from GDI engines. Furthermore, a SAE paper was submitted — with the potential for more to be authored — as a result of this research that should be of interest to the automotive research and development community. This project added significantly to SwRI's knowledge and expertise in particulate emissions formation and characterization from GDI engines as well as providing insight into emissions control strategies that might be viable for clients to meet future regulations.

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