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Hydrogen is seen as a sustainable energy carrier for transportation because it can be generated using renewable energy sources and it is a favorable fuel for clean vehicle powertrains. Hydrogen internal-combustion engines have been identified as a cost-effective consumer of hydrogen in the near term to aid in the development of a large-scale hydrogen infrastructure. Current research on hydrogen internal-combustion engines is directed by a series of efficiency and emissions targets defined by the US Department of Energy including a peak brake thermal efficiency of 45% and nitrogen oxide emissions of less than 0.07 g/mile. A high-efficiency hydrogen direct-injection engine was developed at Argonne National Laboratory to take advantage of the combustion characteristics of hydrogen. The engine employs a lean control strategy with turbocharging for power density comparable with that of gasoline engines. The injection strategy was optimized through collaborative three-dimensional computational fluid dynamics and experimental efforts to achieve mixture stratification that is beneficial for both a high efficiency and low nitrogen oxide emissions. The efficiency maps of the hydrogen engine demonstrate a peak brake thermal efficiency of 45.5% together with nitrogen oxide maps showing emissions of less than 0.10 g/kW h in much of the operating regime. In order to evaluate the driving-cycle nitrogen oxide emissions, the engine maps were fed into a vehicle simulation assuming a midsize sedan with a conventional (non-hybrid) powertrain. With a 3.0 l hydrogen engine, nitrogen oxide emissions from a Urban Dynamometer Driving Schedule cycle are 0.017 g/mile which fulfills the project goal and are even sufficiently low to meet the Super-Ultra-Low-Emissions Vehicle II emissions specification. The city or highway fuel economy, normalized to gallons of gasoline, is 32.4/51.5 mile/gal(US) for a combined average of 38.9 mile/gal(US), exceeding the 2016 Corporate Average Fuel Economy standard. Further vehicle simulations were performed to show the effect of engine downsizing. With a smaller 2.0 l engine, nitrogen oxide emissions increase to 0.028 g/mile, which still exceeds the US Department of Energy target together with the benefit of a fuel economy improvement to 45.4 mile/gal(US) (combined).

This chapter provides an overview on the use of hydrogen as a fuel for internal combustion engines. First, pros and cons are discussed for using hydrogen to fuel internal combustion engines versus fuel cells. Then, the properties of hydrogen pertinent to engine operation are briefly reviewed, after which the present state-of-the-art of hydrogen engines is discussed.Ongoing research efforts are highlighted next, which primarily aim at maximizing engine efficiency throughout the load range, while keeping emissions at ultra-low levels. Finally, the challenges for reaching these goals and translating lab results to production are discussed. KeywordsHydrogen, internal combustion engine, efficiency, port fuel injection, direct injection, transportation, vehicles, sustainable Introduction H 2 -ICE vs. fuel cellThe interest in hydrogen as an energy carrier or buffer is explained in detail throughout this book. A lot of research effort has gone into the development of the hydrogen-fueled fuel cells for stationary or transport applications as also discussed elsewhere. Fuel cells are attractive for their high efficiency potential throughout the load range with their high efficiency at part Page 2 load operation being of particular interest to transportation applications. Furthermore, they are relatively quiet and only emit water vapor as the reaction product. Much less attention has been devoted to internal combustion engines (ICEs) using hydrogen as fuel. The ICE is often readily dismissed as a future prime mover, for its low efficiency (particularly at part load), and pollutant emissions. However, as discussed in this chapter, because of hydrogen's unique properties, it is possible to substantially increase the ICE's efficiency when operated on hydrogen. When using high temperature oxidation of fuel to produce power, i.e. combustion, the formation of oxides of nitrogen (NO and NO 2 , collectively termed NO X ) is possible, which is a disadvantage compared to the low temperature oxidation in fuel cells.Again, the unique properties of hydrogen allow the emission of NO X to be ultra-low if adequate measures are taken, as explained below.More importantly, ICEs have the very interesting feature of being able to operate on different fuels. This "flex-fuel" ability is an advantage for introducing hydrogen vehicles to the marketplace. First, this can assist with the gradual build-up of a hydrogen fueling infrastructure, and secondly, this can alleviate the on-board storage challenge, with a second fuel (e.g. gasoline) essentially serving as a "range extender". The much lower cost of a hydrogen-fueled ICE compared to a fuel cell is another advantage that can help with setting up demonstration fleets etc., with the HyNor project vehicle fleet being a prime example (see http://hynor.no). The lower cost not only applies to the ICE itself, but also to the fuel: the ICE can handle lower purity hydrogen without any problems.The hydrogen-fueled ICE has thus been recognized as being a compelling bridging technology to introduce h...

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While the transportation field is mostly characterized by the use of liquid fuels, gaseous fuels like hydrogen and natural gas have shown high thermal efficiency and low exhaust emissions when used in internal combustion engines (ICEs). In particular, high-pressure direct injection of a gaseous fuel within the cylinder overcomes the loss of volumetric efficiency and allows stratifying the mixture around the spark plug at the ignition time. Direct injection and mixture stratification can extend the lean flammability limit and improve efficiency and emissions of ICEs. Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model. Nevertheless, the numerical simulation of a high-pressure gas jet is not a simple task. At high injection pressure, immediately downstream of the nozzle exit the flow is supersonic, the gas is under-expanded, and a large series of shocks occurs due to the effect of compressibility. To simulate and capture these phenomena, grid resolution, computational time-step, discretization scheme, and turbulence model need to be properly set. The research group on hydrogen ICEs at Argonne National Laboratory has been extensively working on validating numerical results on gaseous direct injection and mixture formation against PIV and PLIF data from an optically accessible engine. While a good general agreement was observed, simulations still could not perfectly predict the mixing of fuel with the surrounding air, which sometimes led to significant under-prediction of fuel dispersion. The challenge is to correctly describe the gas dynamic phenomena of under-expanded gas jets. To this aim, x-ray radiography was performed at the Advanced Photon Source (APS) at Argonne to provide high-detail data of the mass distribution within a high-pressure gas jet, with the main focus on the under-expanded region. In this paper, the numerical simulation of high-pressure (100 bar) injection of argon in a cylindrical chamber is performed using the computational fluid dynamic (CFD) solver Fluent. Numerical results of jet penetration and mass distribution are compared with x-ray data. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm directed along the injector axis, is chosen as a canonical case for modeling validation. A sector (90°) mesh, with high resolution in the under-expanded region, is used and the assumption of symmetry is made. Results show good agreement between CFD and x-ray data. Gas dynamics and mass distribution within the jet are well predicted by numerical simulations.

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