Experimental and computational investigations of hydrogen safety, dispersion and combustion for transportation applications

Hydrogen is an energy carrier that can be produced from a variety of sources, offering one of the viable solutions to the increasing demands for clean and sustainable energy. Compared to the conventional fuels, hydrogen has distinct properties that need to be properly accounted for during its safer storage and delivery as well as more efficient and cleaner utilization. The broader objective of this study is to contribute to the scientific knowledge necessary to overcome key technical barriers to the widespread implementation of hydrogen in transportation applications. Specifically, lower flammability limit of hydrogen is first measured with an enhanced experimental setup and then supported with a theoretical analysis in order to provide safety guidelines for hazardous conditions. Small and large hydrogen releases are computationally investigated under different conditions corresponding to potential accidental release scenarios. This involves quantifying the relative roles of buoyancy, diffusion and momentum during hydrogen transient mixing in air and the associated flammable zones in a simple geometry. The numerical predictions are extended to a practical geometry in which high pressure unsteady hydrogen leaks occur due to a catastrophic failure of a storage tank in a typical mobile hydrogen unit. Additionally, the combustion, performance and emission characteristics of a hydrogen-powered internal combustion engine are simulated by incorporating fuel-specific sub-models into a quasi-dimensional model, which is subsequently validated against independent data and utilized to quantify the effect of exhaust gas recirculation on emissions of oxides of nitrogen. Such reasonably fast and accurate predictive tools are essential to effectively design and optimize hydrogen engines for higher efficiency and near-zero emissions in the automotive industry --Abstract, page iii

A Computational Study on Performance, Combustion and Emission Characteristics of a Hydrogen-Fueled Internal Combustion Engine

Hydrogen is an alternative fuel that is considered to be one of the viable solutions to the increasing demands of clean and secure energy. Internal combustion engines fueled by hydrogen have the potential for higher power and efficiency with lower emissions when compared to gasoline. In the present study, advanced engine simulations were used to study the performance, combustion and emission characteristics of a hydrogen-fueled engine. Hydrogen fuel-specific combustion models were used to account for the distinctive characteristics of hydrogen combustion when compared to that of gasoline. The simulation results matched well with the already-published experimental data under similar engine operational conditions. NOx emissions were found to increase drastically after an equivalence ratio of 0.5 due to high combustion temperatures. EGR was found to be an effective way to reduce NOx emissions but compromised engine power and efficiency

Detailed Simulations of the Transient Hydrogen Mixing, Leakage and Flammability in Air in Simple Geometries

During an accidental release, hydrogen disperses very quickly in air due to a relatively high density difference. A comprehensive understanding of the transient behavior of hydrogen mixing and the associated flammability limits in air is essential to support the fire safety and prevention guidelines. In this study, a buoyancy diffusion computational model is developed to simultaneously solve for the complete set of equations governing the unsteady flow of hydrogen. A simple vertical cylinder is considered to investigate the transient behavior of hydrogen mixing, especially at relatively short times, for different release scenarios: (i) the sudden release of hydrogen at the cylinder bottom into air with open, partially open, and closed tops, and (ii) small hydrogen jet leaks at the bottom into a closed geometry. Other cases involving the hydrogen releases/leaks at the cylinder top are also explored to quantify the relative roles of buoyancy and diffusion in the mixing process. The numerical simulations display the spatial and temporal distributions of hydrogen for all the configurations studied. The complex flow patterns demonstrate the fast formation of flammable zones with implications in the safe and efficient use of hydrogen in various applications

Development and Integration of Engine Simulation Projects into the Mechanical Engineering Curriculum At Missouri S&T

The main objective of this paper was to report the development of instructional engineering projects and necessary tutorials that utilize the GT-POWER software for engine simulations in combustion-related courses at Missouri S&T as part of the Partners for the Advancement of Collaborative Engineering Education (PACE) program. Students teamed up to perform modeling of engine performance and emission characteristics so that they could learn state-of-the art engine technology and explore innovative design procedures routinely employed by the leading automotive companies. The projects included understanding and comparison of simple hand calculations using typical textbook assumptions with detailed and complicated software calculations. Such projects would help to bridge the gap between the theoretical and simple concepts learned by students in the classroom and the practical and advanced skills desired by industry. Various tools available for studying engine combustion fueled by alternative fuels were also introduced

Computational Modeling, Validation, and Utilization for Predicting the Performance, Combustion and Emission Characteristics of Hydrogen IC Engines

Hydrogen-fueled internal combustion engines are considered to be more efficient and cleaner alternatives to their fossil-fueled counterparts. Reasonably fast and accurate predictive computational tools are essential for practical design, control and optimization of hydrogen engines. to serve for this broader purpose, a computational model, which has been widely used for gasoline and diesel engines, is investigated for its capability to simulate hydrogen engines. Specifically, fuel-specific sub-models are first incorporated by properly accounting for hydrogen\u27s distinct properties such as flame speed and burn rate. the accuracy of the model is then assessed by validating it in comparison to independent experimental data. Finally, it is utilized to quantify the environmental impact of exhaust gas recirculation. with these improvements, the present predictive model is shown to capture the measured engine performance and emission data well under different operating conditions. in particular, the variations of peak in-cylinder pressure, heat release rate, brake power, brake thermal efficiency, exhaust temperature, and NOx emissions are predicted close to the measured values. with the addition of a proportional-integral-derivative controller to the engine model, exhaust gas recirculation level is varied, resulting in nearly an order of magnitude reduction in NOx emissions during the present simulations

Hydrogen Safety in Accidental Release Scenarios [abstract]

Only abstract of poster available.Track II: Transportation and BiofuelsWith the intensified energy and environmental concerns, hydrogen is considered to be one of the viable solutions to the increasing demands for clean and secure energy. The transition from fossil fuels to such technologies involves challenges that must be overcome for widespread public use/acceptance. Safety issues need to be fully addressed by developing proper codes and standards that are critical for the design and operation of hydrogen-powered systems. Fire safety of hydrogen applications is generally provided by experience from other traditional fuels whose properties are drastically different from those of hydrogen. As part of a broader project to establish the first hydrogen fueling station and hydrogen-powered commuter service in the state of Missouri, the transient behavior of hydrogen mixing and the associated flammability limits in air are investigated to support the fire safety and prevention guidelines. Advanced computer simulations are developed and utilized to gain a comprehensive understanding of the unsteady mixing, leakage, and flammability of hydrogen under simple and practical conditions. Different hydrogen accidental release scenarios were studied and compared with that of traditional fuels like methane and ethane. The observed complex temporal and spatial distributions of hydrogen demonstrate the fast formation of flammable zones. These results have implications in the safe and efficient use of hydrogen in various applications (e.g., fuel cells) as well as the ventilation of hydrogen accidental leakage in closed and partially closed environments (e.g., parking garage, storage facilities, road tunnel) and other supplementary infrastructure

Hydrogen Safety: A Focus on Power Generation Applications

Hydrogen has the potential to provide clean and secure energy. It can be used to power internal combustion engines or fuel cells. Although hydrogen has long been used in various industrial processes, some myths persist that it is an intrinsically dangerous fuel. This article discusses hydrogen’s unique properties and outlines some guidelines for its safe use in many applications