Abstract
●Peripheral direct injection improves uniformity in the midstream of the combustion chamber.●Peripheral direct injection can control local fuel enrichment in the combustion dead zone.●Side direct injection is more robust in indicating the improvement of thermal efficiency.●Peripheral/side direct injection achieve lower unburned NH3 emissions at α+45° and β−45°.
To enhance thermal uniformity and mitigate combustion dead zones, this study proposes the implementation of peripheral direct injection. To elucidate the differences between peripheral direct injection and side direct injection, a three-dimensional numerical simulation model was developed. After validating the reliability of the turbulence model, combustion model, and mesh discretization, the analysis was conducted on a quantitative basis. In the case of side direct injection, the localized concentration of thermal stress compromises the coherence of flame propagation. Moreover, the localized fuel enrichment, constrained by the relatively narrow space within the combustion chamber and the flammability limits and quenching distance of fuels, results in substantial incomplete combustion losses. Under peripheral direct injection, the issue of vortex enrichment on one side of the combustion chamber is alleviated. Compared to side direct injection, peripheral direct injection reduces incomplete combustion losses by >50%. In side direct injection, the downward displacement of the nozzle position leads to an increasing concentration of hydrogen downstream, which gradually shifts to one side. In contrast, peripheral direct injection further enhances mixture homogeneity. Therefore, two direct injection positions, SDI1 and PDI3, are recommended. Both side direct injection and peripheral direct injection achieve significant reductions in unburned NH3 emissions at injection angles of α+45° and β-45°.