Semester

Fall

Date of Graduation

2025

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Nigel N. Clark

Committee Member

Gregory J. Thompson

Committee Member

W. Scott Wayne

Committee Member

Derek R. Johnson

Committee Member

Rakesh K. Gupta

Committee Member

Ralph D. Nine

Abstract

The transition toward zero-emission transportation requires a stronger understanding of particulate matter (PM) emitted from heavy-duty engines. While mass-based PM regulations have successfully reduced emissions, particle size and number, particularly within the sub-micrometer (PM1) range remain unregulated in the United States despite links to adverse health effects. Populations in close proximity to bus routes, often lower socioeconomic populations, are especially impacted by these emissions due to higher exposure levels. This dissertation addresses this gap by analyzing size-resolved and number-based PM emissions from transit bus technologies including diesel, diesel-hybrid, and compressed natural gas (CNG) engines. Measurements were obtained under representative duty cycles using the West Virginia University Transportable Heavy-Duty Emissions Testing Laboratory, producing detailed characterization of PM emissions from heavy-duty vehicles that continue to operate in many regions around the world.

The analysis characterizes how particle number emissions vary across operating modes and duty cycles, with particular attention to nucleation- and accumulation-mode behavior and Ultrafine Particle (UFP) emissions. Cycle-resolved statistics, geometric mean diameters, and size distributions are evaluated for each technology and fuel type, with repeatability checks confirming the robustness of the data. Comparisons highlight how hybridization, fuel choice, vehicle weight, and engine operation shape particle emissions, especially UFPs. These findings provide important context for both historical emissions trends and present-day exposure concerns.

To extend and complement the experimental results, computational fluid dynamics (CFD) models were developed to simulate near-tailpipe exhaust dilution and plume evolution. The modeling framework captures mixing and dispersion processes that influence particle number and size distribution as emissions interact with ambient air and compares these results with certification-style dilution tunnel methods. Together, experimental and modeling work offer new insight into the characteristics of particle emissions from heavy-duty transit buses and establish a foundation for future studies linking emissions to exposure, health outcomes, regulatory decisions, and the transition to zero-emission vehicles.

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