Tailoring Engine Piston for Carbon-Neutral Polyoxymethylene Dimethyl Ethers: From Diesel Comparison to Fuel-Specific Co-Optimization

Polyoxymethylene dimethyl ethers (PODE) is a promising carbon-neutral synthetic fuel for reducing emissions in compression ignition engines. This study employed a progressive optimization from operating parameters alone to co-optimization with operating and geometric parameters to improve engine performance, and the coupling among fuel properties, injection strategies, and piston geometry is elucidated by comparing the combustion and emission characteristics of diesel and PODE. Compared to diesel, the high oxygen content and superior atomization of PODE promote rapid combustion and lower exhaust losses, albeit with larger heat transfer losses that limit net thermal efficiency gains. Consequently, the optimization priority shifts from enhancing mixture preparation for diesel to managing flame/wall interactions for PODE. From parameter-only tuning to co-optimization, diesel adopts a lower injection pressure to alleviate the fast combustion rate, paired with a shrunken bowl bottom pocket to compensate for the lower spray momentum; PODE prioritizes a lower injection pressure and an elevated side pocket to mitigate flame/wall interactions and suppress heat transfer losses. Under co-optimization, PODE achieves a 2.1% improvement in thermal efficiency and a 14.3% reduction in nitrogen oxides (NOx) relative to parameter-only optimization; both gains are more pronounced than those for diesel. These insights provide a theoretical basis for designing high-efficiency engines with carbon-neutral fuels.