Gas jet structure effects on fuel concentrations and flames in a hydrogen low-pressure direct-injection spark-ignition engine

This study aims to find the impact of the nozzle shape of a side-mounted, 3.5-MPa pintle injector on hydrogen concentration and flame development in a low-pressure direct-injection spark ignition (H2LPDI) engine. To this end, endoscopic high-speed imaging of gas jet laser shadowgraph and flames as well as spark-induced breakdown-spectroscopy (SIBS) method are applied to one of the inline four cylinders of H2LPDI engine. Two engines with endoscopic access are used: one motored engine for high-speed laser shadowgraph imaging of gas jet development and the other combustion engine for SIBS-based spark gap <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> </mml:math> measurements and high-speed hydrogen flame imaging. The gas jet visualisation showed that a nozzle with a narrower jet spreading angle leads to more turbulent jet boundaries and the jet axis being directed more towards the piston. Due to higher axial momentum, the narrower spreading angle nozzle also caused enhanced jet penetration across the in-cylinder tumble flow. This jet development pattern resulted in locally leaner hydrogen mixtures near the centrally mounted spark plug at the time of ignition, evidenced by a higher difference between spark gap λ and global λ. As a result, the flame size was measured smaller at any fixed combustion stage. For both nozzle types, the injection timing was also varied between 150 and 120 °CA bTDC but there was no significant difference measured in spark gap <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> </mml:math> and flame size compared to that associated with the nozzle type.