Preliminary development of a Dome combustion chamber dedicated to hydrogen direct injection engines

Abstract

The imperative to reduce greenhouse gas emissions is compelling the road transport industry to explore various solutions in addition to electrification. A pivotal step in this direction involves adopting low-carbon footprint fuels such as hydrogen, ammonia, and e-fuels for vehicles powered by internal combustion engines. Hydrogen classifies itself as a promising candidate for spark-ignited internal combustion engines (ICEs) due to its high laminar burning velocity, wide ignitability range in terms of equivalence ratio, and increased resistance to auto-ignition. However, it also exhibits a very low minimum ignition energy, increasing the likelihood of pre-ignition events during engine operation. Therefore, the design of the combustion system and operational strategy must be tailored to achieve stable and efficient hydrogen combustion across various loads and engine speeds. This article introduces a Dome-shaped combustion chamber designed specifically for hydrogen combustion targeting high specific performance. The Dome is integrated into a robust four-valve flat cylinder head at the central position facilitating the placement of both the medium pressure hydrogen injector and a spark plug specifically designed for H₂ operation near the cylinder axis, in cooperation with a straightforward piston design. Preliminary test results obtained at 2000 rpm × 16 bars of IMEP on a 500cc single cylinder engine are reported. Variations in equivalence ratios and spark timings demonstrated robust and excellent combustion stability until an equivalence ratio of 0.40 and achieved a gross indicated thermal efficiency of 46%. Subsequently, the 3D-CFD simulations were carried out at 2000 rpm × 16 bar, incorporating the hydrogen injection and combustion modeling. The CFD results demonstrated a satisfactory agreement with the experimental results in terms of in-cylinder pressure and apparent heat release rates. Finally, the CFD simulations are utilized to evaluate the potential high load performance of the Dome engine at 6000 rpm of engine speed, emphasizing the effect of a split injection strategy.