Combustion and emission responses of methanol-enriched catalytic plastic waste pyrolysis oil in a stationary otto engine

Plastic waste pyrolysis oil (PWPO) offers a waste-to-energy pathway; however, its use in small spark-ignition engines is constrained by fuel-property variability, mixture preparation, and combustion phasing. This study integrated evidence on fuel properties, crank-angle-resolved combustion, indicated performance, cyclic variability, and emissions for PWPO produced using a silica-alumina catalyst containing 0, 5, 10, and 15 vol.% methanol in a 163 cm³ single-cylinder stationary Otto engine at engine speeds of 1,500–4,000 rpm. A 4 × 6 operating matrix was used to compare pressure-volume behavior, pressure-crank-angle development, apparent heat-release rate (HRR), CA10/CA50/CA90 phasing, net indicated mean effective pressure (IMEPₙ), COVIMEP, and gaseous emissions. The response to methanol was distinctly non-monotonic. M10 generally produced the highest IMEPₙ, whereas M5 yielded the lowest speed-averaged CO (3.87 vol.%, 16.9% below PWPO) and M10 yielded the lowest speed-averaged HC (411.7 ppm, 28.1% below PWPO); CO emissions from M10 were 14.2% lower than those from PWPO. Re-examination of the archived burn-phasing data showed that the M10 CA10-CA90 interval was approximately 2.8-5.6% longer than that of PWPO despite earlier CA90, while M10 COVIMEP remained approximately 16-25% under no-load conditions. The evidence therefore supports a trade-off between fuel composition and engine responses rather than a concentration-proportional benefit or statistically validated optimum: moderate methanol reformulation improved pressure development and incomplete-combustion emissions, but did not eliminate cyclic instability.