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Liquefied petroleum gas (LPG), like many other alternative fuels, has witnessed increased adoption in the last decade, and its use is projected to rise as stricter emissions regulations continue to be applied. However, much of its use is limited to dual fuel applications, gaseous phase injection, light-duty passenger vehicle applications, or scenarios that require conversion from gasoline engines. Therefore, to address these limitations and discover the most efficient means of harnessing its full potential, more research is required in the development of optimized fuel injection equipment for liquid port and direct injection, along with the implementation of advanced combustion strategies that will improve its thermal efficiency to the levels of conventional fuels.

Internal combustion engines will continue to be the leading power-train in the heavy-duty, on-highway sector as technologies like hydrogen, fuel cells, and electrification face challenges. Natural gas (NG) engines offer several advantages over diesel engines including near zero particle matter (PM) emissions, lower NOx emissions, lower capital and operating costs, availability of vast domestic NG resources, and lower CO2 emissions being the cleanest burning of all hydrocarbons (HC). The main limitation of this type of engine is the lower efficiency compared to diesel counterparts. Addressing the limitations (knock and misfire) for achieving diesel-like efficiencies is key to accomplishing widespread adoption, especially for the US market. With the aim to achieve high brake thermal efficiency (BTE), three (3) computational fluid dynamics (CFD) optimized pistons with three different compression ratios (CR) have been tested.

Liquefied petroleum gas (LPG), whose primary composition is propane, is a promising candidate for heavy-duty vehicle applications as a diesel fuel alternative due to its CO2 reduction potential and high knock resistance. To realize diesel-like efficiencies, spark-ignited LPG engines are proposed to operate near knock-limit over a wide range of operating conditions, which necessitates an investigation of fuel-engine interactions that leads to end-gas autoignition with propane combustion. This work presents both experimental and numerical studies of stoichiometric propane combustion in a spark-ignited (SI) cooperative fuel research (CFR) engine. Engine experiments are initially conducted at different compression ratio (CR) values, and the effects of CR on engine combustion are characterized.

Natural Gas used in high-efficiency engines holds promise as a low-cost intermediate solution to reduce Greenhouse Gases and particulate matter. However, to achieve high engine efficiencies, engines need to be operated at increased Brake Mean Effective Pressures (BMEP), which is limited by destructive, engine damaging knock. Alternatively, if controlled, the same End-Gas Autoignition (EGAI) process responsible for knock can boost efficiencies and consume unburned methane while leveraging low-cost traditional exhaust aftertreatment technologies, such as a three-way catalyst, to minimize environmental impact. For this reason, this work has developed a method to detect the presence of EGAI and to determine its onset location (or crank angle).

Research on alternative fuels has made significant progress as demands for cleaner and more efficient engine operation intensifies. Liquefied petroleum gas (LPG) can offer a potential alternative fuel route in the Diesel fuel dominated heavy-duty transportation sector due to its low cost, high anti-knock limit relative to gasoline, and reduced emission levels. In this work, experimental investigations are performed to study the effects of LPG compositions on performance, emissions, and combustion behavior of a spark-ignited (SI) cooperative fuel research (CFR) engine under stoichiometric conditions. Four LPG blends (chemically pure propane, a representative US blend, HD-5, and a representative European blend) representing the present LPG market are chosen. The impact of fuel composition is studied under different compression ratios (CR), ranging from 7:1 to 10:1 with one-unit increments, and at constant engine speed, intake manifold air pressure (IMAP) and 50% burn crank angle (CA50).

This study presents experimental and numerical examination of directly injected (DI) propane and iso-octane, surrogates for liquified petroleum gas (LPG) and gasoline, respectively, at various engine like conditions with the overall objective to establish the baseline with regards to fuel delivery required for future high efficiency DI-LPG fueled heavy-duty engines. Sprays for both iso-octane and propane were characterized and the results from the optical diagnostic techniques including high-speed Schlieren and planar Mie scattering imaging were applied to differentiate the liquid-phase regions and the bulk spray phenomenon from single plume behaviors. The experimental results, coupled with high-fidelity internal nozzle-flow simulations were then used to define best practices in CFD Lagrangian spray models.

In this work two different Parametric Emissions Monitoring System (PEMS) models are developed, an algebraic, semi-empirical model and a neural network model. The semi-empirical model is based on general relationships between oxides of nitrogen (NOx) emissions and engine parameters. The neural network model utilizes a similar set of input parameters, but relies on the neural network code to determine the relationships between input parameters and measured NOx emissions. Two sets of data are used for model development. The first set is composed of typical engine parametric variations and is used to train the models. The second set is used to test the models and is composed of changes to engine operation associated with engine degradation, termed Operations and Maintenance (O&M) issues.

An investigation into applying a tracer gas method for determining trapping efficiency to 4-stroke engines is carried out. The experimental errors are identified and analyzed. The errors include incomplete cylinder reaction, exhaust instability, and inconsistent exhaust sampling. Tracer gas global kinetic mechanisms are reviewed and used as a means for tracer gas selection. The tracer gases investigated are nitrous oxide (N2O) and monomethylamine (CH3NH2). As a benchmark the oxygen tracer technique is analyzed, where oxygen is used as the tracer. Test results from a GM 5.7 l, 8 cylinder, 4-stroke engine are presented that include measurement of the experimental errors and the trapping efficiency. Of the tracers considered, N2O is determined to be optimal for the engine tested.