Emissions characterization of paired gaseous jets in a pilot-ignited natural-gas compression-ignition engine

Heavy-duty engines must meet strict emission standards and retain high fuel efficiency. This thesis examines a new type of fuel injector nozzle for a pilot-ignited direct-injection natural gas engine. The nozzle uses paired jets that increase mixing with air during combustion, which aims to reduce the amount of particulate matter (PM) formed. Tests were performed for different speeds and loads and over engine parameter sweeps (including timing, EGR, EQR, and diesel pilot mass) to compare the effects on the emissions to a single-hole nozzle. Low-PM strategies and morphology of the soot were compared as well. Contrary to expectations, the tests showed large increases in CO and PM from all the paired nozzles at all modes compared to the single-holed injector. Changing speed and load did not affect the relative emissions so further tests were only done with the paired nozzle that had the least emissions. The engine parameter sweeps at mid speed, high load (B75) showed similar emission patterns for the paired-hole nozzle and the single-hole nozzle. This suggests that the reasons for the high emissions lie in the characteristics of the jets, which are not changed much under normal HPDI operation. Injecting the natural gas before the pilot injection reduced PM. Late post-injection of some of the gas reduced PM by 50% without increasing other emissions for both injector types. Apparently, these strategies could work for other HPDI injectors. Compared to the reference injector, the paired-hole nozzle produced larger soot aggregates and larger numbers of particles but soot primary particle size showed different trends at different conditions. Soot fractal dimensions were the same and consistent with conventional diesel soot. CFD simulations showed that fuel packets moved through a richer high PM and CO forming zone during combustion for the paired nozzle. This high sooting zone had to be avoided either by further mixing or less mixing to avoid the high emissions produced. The results presented here were developed on a single-cylinder engine. While trends are expected to be similar to those from an equivalent multi-cylinder engine, emission levels and fuel consumption are not directly comparable to production multi-cylinder engines.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat