Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Mechanical and Aerospace Engineering

Committee Chair

Hailin Li

Committee Co-Chair

Nigel N Clark

Committee Member

David L McKain

Committee Member

Scott W Wayne


Natural gas (NG) is a promising alternative fuel to reduce exhaust emissions of greenhouse gases (GHG), particulate matter (PM) and nitrogen oxides (NOx) from heavy-duty (HD) vehicles. Past HD NG vehicle research has focused on the fuel consumption and exhaust emission of PM and NOx. Recent global warming concerns have raised interest in methane emissions from NG vehicles. However, there is currently no model available to estimate the methane emissions from HD NG vehicles. There is also a need to project the methane emissions of HD NG vehicles in 2035.;This research developed a scenario based estimation model for methane emissions of the heavy-duty transportation sector. The methane emissions sources considered include: tailpipe; crankcase; dynamic ventilation; fueling tank; and fueling stations. The main work conducted includes (1) processing experimental data and developing model input data; (2) estimating the population scenarios of the HD transportation sector in 2035, including HD NG vehicles and NG fuel stations; (3) developing operation characteristics for each type of vehicle; (4) developing a 2035 methane emissions and fuel consumption scenario; (5) developing, coding, and demonstrating the methane emissions estimation model; (6) estimating the methane emissions of the HD transportation sector in 2035. In this research, the methane emissions and fuel consumptions measured were statistically analyzed and characterized to fuel specific methane emissions (FSME) and distance specific fuel consumption for idle activity and three driving activities noted as city, arterial, and highway operation activities. The idle activity had methane emissions and fuel consumption characterized to FSME and time specific fuel consumption. With an input of the vehicle population and operation characteristics, the model was able to estimate the total fuel consumed and total methane emissions associated with tailpipes, crankcases, dynamic ventilation, on-board fuel storage tanks, and refueling stations. The total methane emissions and fuel consumption were further processed to calculate the FSME.;The estimation model was validated using the stasis scenario developed in this research. The model was validated by comparing the estimated FSME output with the input and verifying calculations. The contribution of tailpipes, crankcases, and fuel stations to the methane emissions of HD spark ignition (SI) CNG vehicles were 33.2%, 59.4%, and 7.4%, respectively, for the stasis scenario, representing current vehicle technology. The validated model was applied to estimate the methane emissions in the HD transportation sector with the high, medium and low methane emissions and fuel consumption scenarios. It was concluded that the total methane emissions estimated using the high, medium, and low scenarios were 46.8%, 20.5%, and 6.9%, respectively, of the stasis scenario. The reduced methane emissions were the comprehensive impact of the expected reduction in fuel consumption and FSME. The contribution of each source to the total methane emissions will be presented and discussed. Such a model can also be used to estimate the emissions of other pollutants with the input of fuel specific emissions data, vehicle operation characteristics, and emissions.