Search Results

This paper examines the issues concerning particulate matter (PM) emissions measurement at the 3 mg/mi level proposed as the future LEV III standard. These issues are general in nature, but are exacerbated at the low levels contemplated for upcoming emissions standards. They are discussed in the context of gasoline direct injection (GDI) engines, where they can have an important impact on the continued development of this technology for improved fuel economy. GDI particulate emissions, just as engine-out diesel PM, contain a high fraction of soot. But the total PM mass is significantly lower than from diesel engines, and there can be significant variations in emissions rate and apparent PM composition between cold-start and running emissions. PM emissions levels depend on sampling method and location. As a result, there can be substantial differences in PM sampled and diluted directly at the exhaust pipe, as opposed to measurements from a dilution tunnel.

Concentrations of individual species in the engine-out exhaust gas from a gasoline-fueled (101.5 or 91.5 RON), direct-injection, compression-ignition (HCCI) engine have been measured by gas chromatography over the A/F range 50 to 230 for both stratified and nearly homogeneous fuel-air mixtures. The species identified include hydrocarbons, oxygenated organic species, CO, and CO2. A single-cylinder HCCI engine (CR = 15.5) with heated intake charge was used. Measurements of the mass and size distribution of particulate emissions were also performed. The 101.5 RON fuel consisted primarily of five species, simplifying interpretation of the exhaust species data: iso-pentane (24%), iso-octane (22%), toluene (17%), xylenes (10%), and trimethylbenzenes (9%).

Particulate emissions are reported for a 0.31 L single cylinder engine fitted with an air forced direct injection system. Trends in number, size, and mass of engine out particle emissions are examined as a function of injection timing, spark timing, and EGR. Injection timing determines to a large degree the nature of the combustion, with early injection leading to homogeneous like combustion and late injection producing stratified charge combustion. As fuel injection is retarded, at a fixed lean air to fuel ratio, PM emissions decline to a minimum at an injection time well within the compression stroke, after which they rapidly increase. In the heavily stratified regime, the PM increase can be attributed to a growing number of rich zones that occur in the progressively more inhomogeneous fuel mixture. At fixed injection timing, advancing the spark causes a general increase in particle emissions.