New research has unveiled significant advancements in hydrogen internal combustion engine (HICE) design, demonstrating that optimized piston geometries combined with tailored injection strategies can dramatically boost thermal efficiency and curtail nitrogen oxide (NOx) emissions. The study, which involved both numerical investigations and experimental validation, provides a critical pathway for developing more efficient and environmentally friendly hydrogen-fueled powertrains, a key focus for the renewable energy sector.

The investigation centered on two novel piston bowl designs—a right-concave piston and a left-concave piston—analyzing their interaction with hydrogen jets during mixture formation and combustion. The right-concave piston exhibited a stronger and larger-scale tumble, facilitating superior hydrogen diffusion within the combustion chamber. While early injection timings with this design resulted in relatively uniform mixture distribution and comparable indicated thermal efficiency (ITE) and NOx emissions to conventional flat-top pistons, its inherent design advantages suggest potential for further optimization.

Conversely, the left-concave piston initially showed inferior ITE and higher emissions under a single injection strategy. However, its performance was significantly transformed with the implementation of an optimized dual injection strategy. This innovative approach enhanced mixture stratification, leading to a notable increase in thermal efficiency and a substantial reduction in NOx emissions. This finding underscores the critical role of precise fuel delivery timing and stratification in achieving optimal hydrogen combustion.

Hydogen's properties, including its fast combustion rate, wide combustible limit, and rapid diffusion, make it an ideal zero-carbon alternative to traditional fossil fuels in ICEs. While HICEs offer near-zero carbon emissions, managing NOx formation remains a challenge due to high combustion temperatures. Thermal NOx, which forms above 1800 K, is the primary concern. The study's success in reducing NOx, particularly with the dual injection strategy, aligns with the industry's goal of achieving near-zero emissions, especially when the air-fuel ratio (lambda, λ) exceeds 2.5, where NOx emissions typically drop to negligible levels. Current HICEs can achieve over 35% thermal efficiency, with lean burn conditions pushing this above 40%, and some advanced concepts even targeting over 70%.

This research builds upon ongoing efforts to mitigate issues like pre-ignition and knock in HICEs, which are often addressed through stratified combustion, delayed injection, or Miller cycle applications. By demonstrating that specific piston geometries can synergistically interact with injection strategies, the study offers a more integrated solution to these challenges, paving the way for more robust and commercially viable hydrogen engine technologies. The validation of numerical outputs with experimental data reinforces the practical applicability of these findings for future engine development and design.