Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Mechanical and Aerospace Engineering

Committee Chair

Mridul Gautam.


The transportation sector is the second largest energy-consuming sector in the United States. With heavy-duty vehicles comprising 20% of the sector and petroleum products being used as 93% of the sector's fuel, alternatives fuels continue to be investigated to offset petroleum usage. Natural gas is increasingly being considered as a fuel source due to its abundance in the Marcellus Shale Formation. Compressed natural gas (CNG) is a promising energy source for dual-fuel combustion. It appears to benefit the environment and the economy. With the ability to reduce oxides of nitrogen (NOx) emissions, carbon dioxide (CO2) emissions, and particulate matter (PM) emissions, dual-fuel operation is environmentally viable. CNG costs less than petroleum derived diesel and would enable the United States to reduce its dependence on oil imports. Thus, dual-fuel operation promises to be economically practical.;Dual-fuel operation reduces the amount of diesel fuel used during combustion and replaces it with an energy-equivalent amount of CNG. CNG is injected into the intake air stream during the intake stroke of the dual-fuel converted diesel engine's four-stroke cycle. CNG is utilized as the main energy source while diesel fuel is direct injected to initiate the ignition process due to its compression ignition characteristics. The objective of this work was to investigate dual-fuel combustion characteristics and resultant emissions to determine if the partial replacement of diesel fuel with CNG is an applicable technology in the transportation industry. To fulfill this objective, a dual-fuel capable 2005 Mercedes OM-460LA 12.8 liter engine outfitted with in-cylinder pressure and exhaust emissions measurement capabilities was operated at steady-state conditions. Combustion characteristics and resultant emissions were compared between the dual-fuel and diesel operations. To certify a dual-fuel conversion kit with the Environmental Protection Agency's (EPA's) Clean Alternative Fuel Conversion Program, research and development work was also completed on a 2005 Mack AC-460P 12.0 liter engine. Exhaust emissions were collected over steady-state and transient conditions. In-use operation cost comparisons and fuel efficiencies between dual-fuel operation and diesel-only operation were completed with the certified conversion kit.;The combustion characteristics that most affected emission formations were decreased combustion efficiencies (. 39.9%) and decreased maximum in-cylinder gas temperatures (. 15.2%). With the dual-fuel conversion kit meeting certification requirements, NOx emissions decreased for steady-state (10.1%) and transient (7.29%) operations while PM emissions increased for steady-state (14.2%) operation and decreased for transient (27.4%) operation. CO2 emissions decreased for steady-state (8.87%) and transient (7.81%) operations while carbon monoxide (CO) emissions increased for steady-state (754%) and transient (836%) operations. Non-methane hydrocarbon (NMHC) emissions increased for steady-state (34.4%) and transient (59.3%) operations while methane hydrocarbon (MHC) emissions were prominent due to the combustion of CNG for steady-state (4.05 g/bhp-hr) and transient (7.95 g/bhp-hr) operations. The reduction of CO2 emissions is outweighed by the increase in MHC emissions due to a GWP increase of 35% for the steady-state SET and 85.2% for the transient FTP.;Dual-fuel operation yielded operation cost savings of {dollar}17,932/year based on a 2.27-year return of investment timeframe. Though brake specific fuel consumption (BSFC) increased (. 24.2%) and miles per gallon (MPG) efficiencies decreased (. 18.1%), dual-fuel operation still yielded desirable cost savings due to the low price of CNG. Dual-fuel operation cost savings proved to be most effective when the vehicle was operated on highways and accumulated high yearly mileages. The dual-fuel conversion kit successfully showed compliance with the EPA's emissions standards and marketable cost savings.