An increasing number of alternative vehicle fuel and powertrain options are evolving for both light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) to combat climate change and degraded air quality. Electricity, hydrogen, substitute natural gas, renewable gasoline, and renewable diesel are examples of alternative fuels, while internal combustion engines, fuel cell engines, plug-in battery engines, hybrids, plug-in hybrids, and electrical drivetrains are examples of components comprising powertrains. With such a diverse set of options for LDVs and HDVs, a systematic evaluation of the options that meet environmental goals at a minimum cost is required.

Using linear programming with fuel pathway and vehicle costs, emission constraints, realistic growth scenarios for travel and technology, and fuel feedstock availability, a methodology is developed (“Transportation Rollout Affecting Cost and Emissions, TRACE”) to assess combinations of fuel and vehicle pathways. Each pathway has an associated efficiency, cost, and emission of greenhouse gases (GHGs) and criteria air pollutants (CAPs). Techno-economic data from the literature and Wright’s Law project the cost of infrastructure to produce, distribute, and dispense fuel, and to produce vehicles through 2050.

The results from a Reference Case, comprised of business-as-usual fossil fuel and internal combustion vehicles (ICVs), projects costs of $1.43 trillion. For current LDV regulations in California, the optimization suggests adoption of ICVs fueled by renewable gasoline in the early years with many plug-in hybrid electric vehicles, a large population of zero-emission battery electric vehicles starting in 2030, and significant plug-in fuel cell electric vehicle (PFCEV) adoption in 2050. For all modeled HDV vocations (linehaul, drayage, refuse, and construction), TRACE projects ICVs fueled by renewable diesel until 2045, after which hybrids and PFCEVs are adopted for all vocations except refuse. This LDV and HDV rollout is projected to cost $1.28 trillion by 2050, 10% less than the Reference Case. Significant factors affecting results include battery costs, change in vehicle miles traveled, and zero-emissions vehicles (ZEV) constraints. For cases with proactive ZEV inducements, plug-in FCEVs displace ICVs while satisfying the long range and short fueling attributes provided today by ICVs, reducing GHGs an additional 18% and CAPs up to an additional 40%.

The depletion of fossil fuels and the urgency of reducing greenhouse gas emissions demonstrate a pressing need for alternative energy sources. Currently, natural gas consumption is a major contributor to global warming, not only due to the carbon dioxide emissions in the combustion products but also due to natural gas leakage in the mining, transmission and storage facilities. Therefore, replacing the pipeline natural gas with renewable gas can decrease greenhouse gas emissions as well as reduce dependence on fossil fuels. This dissertation investigated the feasibility of blending renewable gases (i.e., biogas, hydrogen), into existing natural gas transmission and distribution pipelines from the perspective of fuel properties and combustion performance of residential appliances.

The fuel interchangeability technical barriers and challenges were first investigated, including fuel properties, flowrate control, flame performance, etc.. Moreover, the source of reddish hydrogen flame color was also investigated experimentally. The results indicated that hydrogen cracking and embrittlement could be a concern influencing flame appearance. A multi-fuel blending system was fabricated under this dissertation to generate fuel mixtures of various percentages. Burner configurations of existing residential burners were investigated, and representative self-aspirating burners were selected to conduct fuel interchangeability testing on different fuel classes. Monitored combustion performance included ignition behaviors, blowoff/flashback limits, emissions (CO, UHCs, NO, NO2, N2O, NH3, etc.), efficiency, burner temperature, combustion noise, etc.. It was found that CO and UHCs emissions and the risk of flame blow-off increase significantly when the CO2 percentage in the fuel exceeds 5 vol%. Self-aspirating burners were found to have distinct H2 tolerance levels with a limiting factor of the flashback, which is more inclined to occur at ignition conditions. This limited the H2 injection limits below 20 vol%. At a low level of H2 addition to natural gas, most of the combustion performance of the tested self-aspirating devices didn’t differ much and some of them were improved, which shows a positive sign for natural gas replacement with renewable hydrogen for self-aspirating flames

In anticipation of increased use of hydrogen as a means of decarbonizing future power generation in combined heat and power plants, studies are underway to understand how hydrogen impacts operability and emissions from existing low emission gas turbines. In the current study, a full-scale annular combustor is used to study how added hydrogen to methane can be used strategically to extend low emissions operation at lower loads.

The effects of hydrogen in low loading conditions are studied with a numerical approach validated with experimental data conducted by Southwest Research Institute. A chemical reactor network was developed and validated with a prior study involving use of a piloted model combustor. The reactor network was then applied to a full-scale, Solar Turbines 130 combustor tested with various blends of hydrogen and methane for different scaled load conditions and different pilot to main fuel splits.

The validated reactor network was used in combination with a statistically designed simulation matrix to derive a design tool. The tool was used to estimate other performance features including CO emissions near LBO and the impacts of ambient humidity and the presence of higher hydrocarbons typically found in natural gas. The developed model indicates with an increase in hydrogen, an increase in ethane, an increase in pilot flow, and an increase in load, the combustor system has an improvement in stability. The suggested controllable factors for extending operation are increasing the hydrogen composition of the fuel, as well as increasing the fuel flow allocation to the pilot stream.

Risk of significant climate change continues to rise while degraded air quality persists in certain regions of the world. Zero emission vehicles provide one technological solution to these environmental issues. In the near term, forestry residue biomass could be a major resource for the production of these fuels (electricity and hydrogen) in the near term. Given that these biomass supplies are limited, their effective utilization is important if the maximum benefits are to be realized. This dissertation seeks to understand the optimal utilization of these forestry resources in California for fueling zero emission vehicles with a focus on the 2030 timeframe. Various biomass energy conversion plant designs were modeled in detail to understand the differences in energy efficiency, cost, and pollutant emissions. The remaining steps in the supply chain were modeled in varying levels of detail depending on the level of detail available in the literature.

The application of stationary fuel cells was observed to be integral to maximizing energy efficiency and minimizing levelized costs for many of the plant designs. The least cost supply chain for producing fuels for zero emission vehicles on a per mile basis is through production of liquid hydrogen that is liquefied using advanced liquefaction processes and stationary fuel cells at larger scale biomass energy conversion plants. However, hydrogen liquefaction significantly degrades the performance of the integrated biomass gasification plant unless advanced liquefaction processes and/or stationary fuel cells are utilized. A conflict between costs and environmental impacts exists where the largest biomass energy conversion plants exhibit the lowest levelized costs but also have the highest emission rates of NOx, PM2.5, and fossil fuel based GHGs with one exception, the integrated biomass gasification combined cycle design at high roadside feedstock costs. Although the highest offset of GHGs from the displacement of gasoline consumption is through the production of electricity from forestry biomass for plug-in electric vehicles, the production of hydrogen for fuel cell electric vehicles provides the lowest cost per unit of offset GHGs from the displacement of gasoline consumption.

Comprehensive computational models are developed to explore the application of flameless combustion for two significant components of a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid power system: an off-gas burner, and an eductor. Flameless combustion, a regime in which fuel reacts with a high temperature low oxygen content oxidizer, is appropriate for these applications given a characteristically low stable adiabatic flame temperature and reduced pollutant emissions.

In this study, the operation of an off-gas burner and an eductor in the non-traditional flameless combustion regime are explored and investigated. For the off-gas burner application, highlight while alternatives to flameless combustion, such as porous media and catalytic off-gas burner designs, have produced promising results for the stable conversion of diluted SOFC off-gases, the systems are complex and expensive. For the eductor application, the high temperature recycled anode off-gas is mixed with low-oxygen content fuel. Facilitating these optimal conditions within the eductor promotes removal of oxygen in the mixed gas stream, thereby eliminating or reducing the size of an expensive catalytic oxidizer between the eductor and the SOFC inlet. The present research involves developing chemical kinetic models and computational fluid dynamic (CFD) models, simulating operation in the flameless combustion regime, and performing statistical analyses of the results to determine statistically significant design factors. Numerical modeling using chemical reactor networks (CRNs) was validated based on literature data and then used to analyze the associated chemical kinetics for flameless combustion within each component. Higher dimensional modeling, performed using updated CFD models, incorporated both the CRN results as well as important turbulent combustion and physics.

For the aforementioned applications, an increase in temperature and/or pressure promoted key reactions for producing and sustaining flameless combustion. Optimal design criteria for inlet mass flow rates for the off-gas burner application, and inlet stream temperatures for the eductor reactor application, are established utilizing a systematic method and significant statistical analysis tools. Insight from chemical kinetic modeling is essential for exploring the practical limits of the flameless combustion regime as they are uniquely tied to application-specific operating conditions such as residence time, temperature, pressure, and reactant composition.

California’s transportation and power generation sectors emit more than 50 percent of the state’s greenhouse gas (GHG) emissions. The state GHG emission mitigation goals include reducing GHG emissions to 1990 levels by 2020. Additionally, to improve air quality throughout the state, aggressive criteria pollutant emission standards have been established for both sectors. Transitioning from fossil fuels to renewable fuels is one strategy to meet these environmental goals. Landfills and wastewater treatment plants are a source for the production of alternative fuels like renewable natural gas (RNG) and hydrogen (H2) which could then be used in either sector. To evaluate this strategy, the impact on GHG and criteria pollutant emissions, and on air quality resulting from the production and use of RNG in zero or near-zero emission medium-duty vehicles (MDV) and heavy-duty vehicles (HDV) are analyzed. The research reveals that (1) RNG produced from biogas is the most cost effective strategy to utilize the limited resource of biogas available in California even though H2 is the most attractive fuel, (2) the transportation sector is the more effective sector for the use of RNG fuel, (3) MDV and HDV outfitted with commercially available near-zero emission CNG engines with RNG results in substantial reductions in both GHG and criteria pollutant emissions, and significantly improves air quality than the use of H2 in LDV, and (4) the reductions in GHG and criteria pollutant emissions and improvements in air quality exceed those achieved with the MDV and HDV populations envisioned by the State Implementation Plan (SIP).

For California and other parts of the world to move towards a net-zero-emission grid, potentially a 100% renewable grid, complementary technologies to support renewable solar and wind integration need to be clearly established. Specifically, the integration of variable and intermittent solar and wind renewable generation requires resources that can respond dynamically to changes in the net load in order to ensure stable grid performance. Zero-emission vehicles (ZEVs), encompassing battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs), are uniquely positioned to (1) support variable renewable generation and provide benefits to the grid while, at the same time (2) reducing emissions from the transportation sector. Due to their disproportionately large contribution to air pollution and greenhouse gas (GHG) emissions, targeting heavy-duty vehicles (HDVs) is essential if reduction goals are to be met. This work assesses the feasibility of heavy duty ZEVs (HD-ZEVs), selecting California as the example. From a technical standpoint, more than half of Class 3-7 vehicle miles travelled (VMT) can be met with heavy-duty BEV product in development today without trip modification. Class 8 trucks have a much lower BEV feasibility due to their longer trip distances and heavy-duty FCEV product becomes more likely. The challenge becomes providing carbon-free fuel, namely renewable electricity for HD-BEVs, and renewable hydrogen for HD-FCEVs. This study assesses the fuel supply chain impact of HD-ZEV deployment on GHG emissions and air quality for the year 2050. HD-BEVs relying on uncoordinated charging can increase peak load demand and hinder the target of achieving zero GHG emissions from the electric grid. Intelligent charging of HD- BEVs and renewable hydrogen production for HD-FCEVs are both effective methods for utilizing otherwise curtailed renewable generation for the support of a zero or near-zero emissions electric grid. This study also finds that moving towards an 80% reduction in GHG emissions from HDVs through ZEV adoption has the co-benefit of significantly reducing ozone and PM2.5 concentrations in key regions of California. In comparison, reducing grid emissions from an 80% reduction to a 100% clean electric grid has a significantly smaller, but not trivial, impact in criteria air pollutant concentrations.

Aiming to reduce criteria air pollutant and greenhouse gas emissions, several initiatives have been announced throughout the world to incorporate zero emission buses into public transit agencies within the next 15 years. One example is the California Air Resources Board “Innovative Clean Transit Regulation” with the goal to transform the statewide transit bus fleet by 2040 with zero emission buses. In response, transit authorities face decisions between multiple bus technologies, each with different strengths and weaknesses as well as infrastructure requirements. Furthermore, because the performance of new bus technologies depends on the operating conditions of each transit agency, the results from demonstration projects are not typically applicable to another district.

This dissertation addresses the use of Life Cycle Assessment (LCA) to compare different zero-emission bus (ZEB) technologies for transit districts in the State of California. For LCAs conducted to date, the focus has been on one-on-one bus technology comparisons rather than a combination of bus technologies integrated into bus fleets (mixed fleet). This dissertation extends the traditional LCA approach by using Multi-Objective Linear Programming (MOLP) to identify the optimal ZEB technology mix.

The novelty of this extended LCA is the use of a consistent framework across multiple powertrain types with the same operating conditions. The fleet optimization incorporates essential aspects of a fleet operation such as operational constraints, route length, required infrastructure, and cost. Additionally, a Multi-Criteria Decision Analysis (MCDA) is incorporated to evaluate parameter weighting in the optimization problem, thereby creating an optimization solution that considers real constraints and priorities from stakeholders, users, and regulatory agencies.

The combination of these capabilities (LCA, MOLP, and MCDA) provides a comprehensive tool, including a variety of energy supply chains, which can inform transit agencies in the design of an electric bus fleet comprised by a mix of available and emerging ZEB technologies.

Carbon emissions from the combustion of fossil fuels are a concern within the power generation sector. As a result, while natural gas is currently plentiful, strategies for using fuels derived from renewable sources (i.e., alternative fuels) must still be pursued if a reduction in carbon signature is to be achieved. Many of these potential fuels contain some level of hydrogen. The combustion of high hydrogen content fuels reduces carbon-containing pollutants. However, NOx emissions are still an inevitable result of fuel/air combustion. Hence, lean premixed combustion of hydrogen-rich fuels has been implemented along with a precise control of combustion temperatures to achieve a reduction in all pollutant species. This technology is well established for gas turbines operating on natural gas, while the combustion of alternative fuels faces additional challenges. Hydrogen-rich fuels are particularly prone to flashback.

Boundary layer flashback of a premixed jet flame has been investigated experimentally under turbulent flow conditions at elevated pressures and temperatures (i.e., 3 to 8 atm and 300 to 600 K). The data presented in this study are for hydrogen fuel at various Reynolds numbers, which are representative of gas turbine premixer conditions and are significantly higher than results currently available in the literature. Three burner heads constructed of different materials (stainless steel, copper, and zirconia ceramic) were used to evaluate the effect of tip temperature, a parameter found to be an important factor in triggering flashback. This study adds insight towards understanding of boundary layer flashback at high pressures. To confirm the accuracy and consistency of the results, similar experiments were conducted at the same operating conditions for a commercially available injector from a micro turbine combustor. In addition, this study characterizes flashback systematically by developing a comprehensive non-dimensional model which takes into account all effective parameters in boundary layer flashback propensity. The model developed using the high pressure test rig is able to predict flashback tendencies for the new data as well as the existing data in the literature, including a commercial gas turbine engine and can thus serve as a design tool for identifying when flashback is likely to occur for a given geometry and condition.