Computational Fluid Dynamics Study of Alternative Nitric-Oxide Emission Mechanisms in a Spark-Ignition Engine Fueled with Hydrogen and Operating in a Wide Range of Exhaust Gas Recirculation Rates for Load Control

Abstract

AbstractNitric oxide (NO) emissions are practically the only ones emitted from spark-ignition (SI), hydrogen-fueled engines, and their reliable prediction is important in engine simulation codes. In this work, the reaction mechanisms of nitric oxide are investigated in such engines during load variation by using a very wide range of exhaust gas recirculation (EGR) rates, up to 47%. For that purpose, a three-dimensional computational fluid dynamics code is applied, which has been developed by the authors and validated for its main sub-models, such as the heat transfer and combustion. The latter one includes the thermal NO mechanism, widely known as “Zeldovich mechanism,” whereas two alternative production paths have been included, viz. through the NNH and N2O species formation in order to improve the numerical predictions. The NNH path has been shown to be favored under lean and low-temperature combustion conditions, especially for hydrogen flames, whereas the N2O path becomes important for lean flames irr...