Large-Bore Locomotive Engines – Numerical Simulations of Natural Gas/Diesel Dual-Fuel Operation

Abstract

Abstract US DOE has identified hard-to-decarbonize sectors like rail, marine, and aviation as candidates for sustainable low carbon fuels. Along with diesel or biodiesel, hydrogen or natural gas can be burned in a dual-fuel setup. In this paper, numerical simulations of natural gas and diesel dual-fuel combustion in a large-bore rail engine are discussed. The numerical results are investigated to determine best practices that guide future simulations with different fuels. Previous experimental results of a single cylinder Wabtec engine at four different operating conditions; from pure diesel up to 80% natural gas energy-based substitution rate, were used for validation. Natural gas is port injected while diesel is directly injected into the cylinder. First, previous numerical work involving large-bore diesel engines is covered. Then, for every case, the temporal pressure and temperature boundary conditions at the intake and exhaust ports, in addition to the diesel rate of injection, are discussed. The boundary conditions are generated using 1D engine models and the rate of injection are extracted from data of a similar injector with different nozzle flow. The results investigate the effect of turbulence model and grid size on computational results. Global in-cylinder pressure, heat release rate, and combustion phasing in addition to local flame-wall interactions are investigated to determine the best grid and turbulence model setups. The results show that RSM turbulence model provides better results than RNG k-ε turbulence model. In addition, a finer grid is required as substitution rate increases to account for increased mixed-mode combustion. Finally, potential additional challenges in modeling Hydrogen/Diesel dual-fuel combustion in locomotive engines are discussed.