A novel method for high-efficiency methanol compression-ignition engine based on onboard fuel reforming strategy: Experimental study

This study proposes a novel methanol compression-ignition engine system that utilizes an onboard fuel reforming strategy to enhance combustion efficiency and reduce emissions. The system integrates a methanol-reforming subsystem, which partially converts methanol into dimethyl ether (DME) and steam at a reforming temperature around 573 K, with a reverse reactivity controlled compression-ignition (R-RCCI) engine subsystem. By premixing the high-reactivity reformed products with the intake air and directly injecting the remaining methanol into the cylinder, precise control over the ignition and combustion processes is achieved. Experimental results demonstrate that stable methanol reforming is achieved at a reforming temperature of 573 K, with a DME mole fraction of up to 37 % in the reformed products. Engine tests reveal that the optimal fuel energy distribution combines 200–250 J/cycle of premixed reformed fuel and 250–350 J/cycle of directly injected methanol at the indicated mean effective pressure (IMEP) of 4.2–5.5 bar. The first-stage combustion is predominantly controlled by the premixed reformed products, while the subsequent stage is characterized by the diffusion combustion of directly injected methanol. The effects of intake temperature and injection timing on the combustion process exhibit behavior contrary to that observed in conventional RCCI combustion. When the injection timing is −6 °CA ATDC and the intake temperature is 407 K, the methanol-reforming R-RCCI engine achieves a maximum indicated thermal efficiency of 53.8 % with near-zero soot emissions.