The pre-chamber dominated diffusion combustion: Toward heavy-duty hydrogen engines

Abstract

Achieving high power density remains a major challenge for heavy-duty hydrogen engines, hindered by issues like knocking and backfire associated with premixed combustion. This study proposed a novel pre-chamber concept termed the combustion-assisted fuel supply chamber (CAFSC) to enable diffusion combustion, thereby mitigating knocking risks and enhancing power density. All hydrogen is supplied by low-pressure direct injection into the CAFSC, while air is introduced through the manifold. Ignition within the CAFSC generates pressure that drives the fuel into the main chamber (MC), inducing diffusion combustion. Experiments conducted on an optical constant volume combustion chamber (CVCC) confirmed the feasibility of the CAFSC-dominated diffusion combustion process and investigated the effects of global equivalence ratio (Φ_G), nozzle diameter (d), and nozzle number (n). Key findings demonstrate that the CAFSC approach achieves stable and controllable heat release. Crucially, combustion duration (t_dur) and ignition delay (t_delay) are significantly shorter than conventional passive pre-chambers (PPC) and exhibit minimal sensitivity to variations in Φ_G. Furthermore, appropriately increasing d and n reduces t_dur and t_delay while improving the burnt fuel ratio (BFR). The optimized configuration (n = 3, d = 6 mm) achieved a BFR comparable to PPC (97.9 %) while significantly accelerating combustion. However, an excessively large total connecting area induces unstable flame front development. The CAFSC presents a viable pathway towards high-power-density, knock-free hydrogen engines through controllable diffusion combustion.