Date of Award
Fall 2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
Adam Dempsey
Second Advisor
Casey Allen
Third Advisor
John Borg
Abstract
Methane the primary component of natural gas, has 80 times the global warming potential of CO2. As a result methane emissions regulations have rapidly increased in recent years. This posses a challenge for heavy duty spark ignited (SI) natural gas engine OEMs, in efforts to reduce methane and other criteria pollutant emissions such as NOx. Heavy duty natural gas engine OEMs are pushing engine efficiency and reducing emissions by running higher compression ratios and leaner air fuel ratios. This reduces fuel consumption and combustion temperature which decreases NOx emissions, but tends to increase methane emissions. Unfortunately, lean high compression ratio engines present combustion challenges as SI engines are subject to knock and misfire. These phenomena are exacerbated in lean high compression ratio combustion regimes and can not only damage engine components, but also hurt emissions performance. To mitigate these challenges, current heavy-duty natural gas engine manufacturers often utilize passive prechamber igniters also known as a turbulent jet igniter (TJI). Passive prechambers are used to increase in-cylinder turbulence and speed up the combustion process, allowing them to burn much faster than a traditional open chamber spark plugs. This can both increase combustion stability and allow prechamber igniters to avoid end gas auto-ignition, which is the primary cause of engine knock. However, it is unclear how methane and NOx emissions are impacted by passive prechamber spark plugs. This project will aim to quantify the effects of passive prechamber and traditional open chamber ignition systems on lean burn fumigated natural gas engine emissions and performance. The Marquette University engine research lab will operate a fumigated single cylinder heavy duty C9.3b engine with both a traditional spark plug and passive prechamber ignition system. During testing the natural gas engine will be subject to both a lambda sweep and combustion phasing sweep. The information gathered from these experiments will then be used to quantify the drawbacks and advantages of passive prechamber igniters when compared to their traditional SI counterpart, to better understand emission and operating stability at lean high compression ratio combustion conditions.