Flow field characteristics and spatiotemporal NOx distribution from a high-pressure nitrogen jet impinging on a hydrogen premixed flame

During hydrogen combustion in direct-injection hydrogen internal combustion engines (HICE), the impingement of a high-pressure gas jet exerts a significant impact on both flame evolution and NOx formation. Based on a constant-volume vessel (CVV) test rig, this study experimentally and numerically investigates the interaction between a hydrogen-air premixed flame and a high-pressure nitrogen jet to isolate the physical impact of the jet on the premixed flame. Results show that the jet enhances local flame-front propagation velocity (from 5.5 m/s to 45 m/s), and reduces thermal NOx via convective cooling (maximum temperature from ∼ 3200 K to ∼ 1850 K) and dilution (flame front from ∼ 1850 K to ∼ 1500 K), shifting combustion from premixed laminar to diluted turbulent mode. Because the chemical fields cannot be experimentally verified, the NOx-related quantities are treated as indicative and the discussion emphasizes qualitative trends.