Evaluation of the efficiency and the drive cycle emissions for a hydrogen direct-injection engine

Abstract

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).