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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%).

A direct comparison is made of time-resolved measurements of diesel PM emissions obtained using laser-induced incandescence (LII), an electrical low pressure impactor (ELPI), and a tapered element oscillating microbalance (TEOM). The measurements were made on two diesel passenger vehicles, one of which was equipped with a diesel particulate filter. Both LII and the ELPI performed well for both vehicles, whereas the TEOM lacked the sensitivity required for the filtered vehicle. We estimate that the LII system used has a limit of detection better than 0.2 mg/mi.

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. The filter media used have high efficiency for small particles found in vehicle exhaust, but they also collect organic matter from the vapor phase with a lower, but nonzero, efficiency. In the past, organic vapor adsorption was usually negligible compared with PM levels from untreated diesel engine exhaust. For vehicles employing a DPF (Diesel Particulate Filter) and emitting very low PM, that is no longer the case. This paper reports measurements of the organic vapor deposition artifact for different filter media, including the two types (TX40 and Teflo) called for by the 2007 regulations for heavy duty diesel engines. The vapor artifact represents a substantial fraction of the 2007 regulatory standard of 10 mg/mi for light duty vehicles.

The trapping and regeneration behaviors of a diesel particulate filter (DPF), including particle size, are examined via engine dynamometer testing. The exhaust system consists of two active lean NOx (ALN) catalysts in series followed by a catalyzed DPF. Forced regenerations are accomplished by injecting diesel fuel into the exhaust in front of the ALN catalysts to generate an exotherm sufficient to induce soot oxidation. Results are reported for two diesel fuels, one with 340 ppm sulfur, and the other with 4 ppm sulfur, and as a function of DPF regeneration temperature. The results show the DPF to be very effective at removing particulate matter, >99% efficiency. The <1% of particles that escape trapping exhibit a size distribution very similar to engine out soot. During regeneration, particle emissions remain well below engine out levels for the low sulfur fuel, but exhibit a temporary nucleation mode of about ten times the engine out level for the high sulfur fuel.

Previous research into Particulate Matter (PM) emissions from a spark-ignition engine has shown that the main factor determining the how PM emissions respond to transient engine operating conditions is the effect of those conditions on intake port processes such as fuel evaporation. The current research extends the PM emissions data base by examining the effect of transient load and speed operating conditions, as well as engine start-up and shut-down. In addition, PM emissions are examined during “real-world” driving conditions - specifically, the Federal Test Procedure. Unlike the previous work, which was performed on an engine test stand with no exhaust gas recirculation and with a non-production engine controller, the current tests are performed on a fully-functional, production vehicle operated on a chassis dynamometer to better examine real world emissions.

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.

The numbers, sizes, and derived mass emissions of particles from a production DISI engine are examined over a range of engine operating conditions. Particles are sampled directly from the exhaust pipe using heated ejector pump diluters. The size distributions are measured using a scanning mobility particle sizer. The numbers and sizes of the emitted particles are reported for stratified versus homogeneous operation and as a function of fuel injection timing, spark timing, engine speed, and engine load. The principal finding is that particle number emissions increase by about a factor of 10 - 40 going from homogeneous to stratified charge operation. The particulate emissions exhibit a strong sensitivity to injection timing; generally particle number and volume concentrations increase steeply as the injection timing is retarded, except over a narrow portion of the range where the trend reverses.

This paper explores the extent to which standard dilution tunnel measurements of motor vehicle exhaust particulate matter modify particle number and size. Steady state size distributions made directly at the tailpipe, using an ejector pump, are compared to dilution tunnel measurements for three configurations of transfer hose used to transport exhaust from the vehicle tailpipe to the dilution tunnel. For gasoline vehicles run at a steady 50 - 70 mph, ejector pump and dilution tunnel measurements give consistent results of particle size and number when using an uninsulated stainless steel transfer hose. Both methods show particles in the 10 - 100 nm range at tailpipe concentrations of the order of 104 particles/cm3.

FTP emissions tests on a passenger vehicle equipped with a 1.8 L IDI turbo-charged diesel engine show that the mass emissions of particles decrease by (36±8)% when 16.6% dimethoxymethane (DMM) by volume is added to a diesel fuel. Particle size measurements reveal log-normal accumulation mode distributions with number weighted geometric mean diameters in the 80 - 100 nm range. The number density is comparable for both base fuel and the DMM/diesel blend; however, the distributions shift to smaller particle diameter for the blend. This shift to smaller size is consistent with the observed reduction in particulate mass. No change is observed in NOx emissions. Formaldehyde emissions increase by (50±25)%, while emissions of other hydrocarbons are unchanged to within the estimated experimental error.