Investigating OME3-diesel droplet evaporation, combustion dynamics, and soot characterization

Abstract

The combustion behavior of fuel droplets plays a crucial role in controlling emissions and combustion efficiency in internal combustion engines. Droplet heating, evaporation, and burning characteristics strongly influence ignition delay, combustion duration, and soot formation. Oxymethylene ethers (OMEs), particularly oxymethylene ether-3 (OME₃), have attracted interest as drop-in diesel alternatives due to their high oxygen content and clean combustion potential. This study experimentally investigates the combustion of a single fuel droplet suspended on a thermocouple and exposed to a controlled environment at 500 °C and atmospheric pressure. Four fuels were examined: neat diesel and diesel blends containing 20, 40, and 60 vol% OME₃. High-speed imaging was used to analyze ignition delay, combustion duration, and flame luminosity, complemented by scanning electron microscopy (SEM) of collected particulates. Increasing OME₃ content significantly reduced ignition delay (by ∼ 65–70% for D40-O60) while increasing combustion duration by ∼ 25–30%. Flame luminosity decreased markedly, indicating suppression of macroscopic soot. This behavior is primarily attributed to the high oxygen content of OME₃, which promotes oxidation pathways that limit soot precursors formation. SEM analysis revealed a shift toward finer particles, with sub-micrometer particle counts increasing from ∼ 120 mm⁻² to ∼ 340 mm⁻². These results demonstrate that reduced flame luminosity does not necessarily correspond to lower particulate emissions but instead reflects a shift toward ultrafine particle formation. Overall, OME₃ modifies combustion behavior by reducing visible soot while increasing ultrafine particle number density, highlighting a critical trade-off in oxygenated fuel performance.