An experimental investigation into the soot particle emissions at early injection timings in a single-cylinder research diesel engine

Engine experiments were performed to examine the effect of early-injection on smoke emissions and engine performance under typical low temperature combustion (LTC) and reactivity controlled compression ignition (RCCI) operating conditions. On that basis, the influence of exhaust gas recirculation (EGR), intake pressure, fuel properties and fuel injection strategy on the engine-out soot emissions at early injection timings was also assessed. At last, the morphology, nanostructure characteristics of exhaust soot particles were analyzed. The test results showed when the injection timing was advanced before -30 degrees crank angle after top dead center (CA ATDC) and earlier, the fuel spray impinged onto the piston crown surface, and a part of fuel entered into the squish zone and expanded to reach the cylinder liner wall and entered into the crevice volume, leading to a continuous increase in soot emissions, the peak smoke emission was found to occur at -55 degrees CA ATDC. By adopting fuels with high volatilities and a RCCI fuel delivery strategy, soot emissions can be effectively reduced at early timings. Most of the high-resolution transmission electron microscopy (HRTEM) images of the sampled soot particles showed small spherical particles with a wide range of size distribution connected, and onion-like fringe arrangement was found in most of the images. As the fuel injection timing was retarded from -55 degrees to -35 degrees CA ATDC, the samples exhibited more highly organized carbon nanostructures; the fringe tortuosity and separation distance increased, while the fringe length decreased. The formation of more ordered arrangement of graphene layers led to significant resistance to oxidation.

Automated summary

Engine experiments were conducted to study the impact of early injection on smoke emissions and performance, and the influence of EGR, intake pressure, fuel properties and injection strategy on soot emissions at early timings was assessed. The morphology and nanostructure characteristics of exhaust soot particles were also analyzed. The findings showed that using fuels with high volatilities and a RCCI fuel delivery strategy can effectively reduce soot emissions at early injection timings.