Effect of Injection Timing on Combustion, NO_x, Particulate Matter and Soluble Organic Fraction Composition in a 2-Stroke Tier 0+ Locomotive Engine

The effects of injection timing on combustion, NO_x, PM mass and composition from a 2-stroke turbocharged Tier 0+ locomotive diesel engine are investigated in this study. Results provide insight into how injection timing affects combustion and emissions in this family of engine and identifies areas of potential future emissions reduction. For a range of injection timings at a medium load (notch 5) operating condition, the majority of PM mass is insolubles (81–89%), while the soluble component of PM (SOF) accounts for a smaller fraction (11–19%) of total PM mass. The SOF is 66–80% oil-like C₂₂-C₃₀₊ hydrocarbons, with the remainder being fuel-like C₉-C₂₁ hydrocarbons. A heat release analysis is used to calculate mass fraction burned curves and elucidates how injection timing affects combustion. Retarding injection timing retards combustion phasing, decreases peak cylinder pressure and temperature, and increases expansion pressure and temperature. Results show that insolubles and fuel-like hydrocarbons increase, and oil-like hydrocarbons decrease with later injection timing. Analysis suggests that insolubles and fuel-like HC increase due to lower peak combustion temperature, while oil-like HC, which are distributed more widely throughout the cylinder, decrease due to higher expansion temperatures. The net result is that total PM mass increases with retarded combustion phasing, mostly due to increased insolubles. Considering the high fraction of insoluble PM (81–89%) at all injection timings tested at notch 5, steps taken to reduce PM elemental carbon should be the most effective path for future reductions in PM emissions. Further reductions in oil consumption may also reduce PM, but to a smaller extent.