| dc.description.abstract | Large bore, natural gas two-stroke engines form a vital backbone of the pipeline
industry. With current green initiatives and governmental pushes to reduce harmful
emissions, such as oxides of nitrogen (NOx) and hydrocarbons (HC), the need to
continually improve the performance of an ageing compressor engine fleet is critical. A
practical way to reduce NOx and HC emissions has been to pursue increasingly lean fuel
to air ratio ignition limits, but lean mixtures are exceptionally hard to ignite and result in
frequent misfires. Misfires produce high levels of harmful emissions, introducing a
multitude of complexities related to engine stability and reliable operation. Building
understanding of why these mixtures are difficult to ignite, or conversely, how to take a
lean mixture and make it easier and more reliable to burn, is critical to enabling more
restrictively lean engine operation.
This study sought to simulate a full crank cycle of the Ajax E-565, a single cylinder, large bore natural gas two-stroke similar to those of the pipeline industry. To
accomplish this, a computational fluid dynamic simulation of the engine was built in
commercial software Converge CFD, then validated against experimentally measured
datasets at a variety of spark timings. After successful validation, the performance
impact of manipulating a low pressure system that delivers fuel directly into the engine
cylinder was studied. This was examined by first lengthening the duration of fuel
injection compared to standard baseline, then shortening the injection. Global
equivalence ratio (ER) was maintained as a constant by varying fuel header pressures to iii
compensate for the altered injection durations. Finally, the best performing injection
parameters were tested at progressively lower fuel header pressures until misfire to
analyze fuel and performance benefits. Overall, the highest cylinder pressure and lowest
fuel consumption was obtained by decreasing the fuel injection period and using higher
fuel injection pressures. Injection pressures should be held as high as possible without
impinging upon the cylinder walls and piston or over-penetrating the scavenging loop
flow field. | en |
