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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%).

The effects of operating parameters (speed, load, spark-timing, EGR, and end of fuel injection timing [EOI]) on engine-out, regulated (total HC, NOx, and CO) and speciated HC emissions have been investigated for a 1.83 L direct-injection, spark-ignition (DISI) engine. As the EOI is varied over the range from high to low stratification with other engine parameters held constant, the mole fractions of all regulated emissions vary sharply over relatively small (10-20 crank angle degrees [CAD]) changes in EOI, suggesting that emissions are very sensitive to the evaporation, mixing, and motion of the stratified fuel cloud prior to ignition. The contribution of unburned fuel to the HC emissions decreases while the olefinic partial oxidation products increase as the fuel stratification increases, increasing the smog reactivity of the HC in the exhaust gas by 25%.

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.