Spray and combustion characteristics of PODE fuel under high-pressure high-temperature compression ignition engine conditions: A review

Polyoxymethylene dimethyl ethers (PODEn/OMEx) are increasingly recognized as promising low-emission alternatives or blending components for petroleum diesel, supported by favorable physicochemical characteristics and a strong potential to reduce particulate matter and greenhouse-gas emissions while improving energy security through fuel diversification. This review synthesizes evidence from approximately 300 studies to evaluate PODE across the full value chain, encompassing feedstock options, production routes, techno-economic considerations, catalytic synthesis pathways, and the chemical-kinetic understanding of combustion. Particular emphasis is placed on how PODE's defining properties, high oxygen content, absence of C–C bonds, and elevated cetane number translate into distinct spray and combustion behavior in compression-ignition engines. Compared with conventional diesel, variations in density, viscosity, volatility, and surface tension shape atomization quality, spray penetration, droplet size, and mixing processes, which in turn influence ignition, heat-release characteristics, combustion efficiency, and emissions formation. The review integrates experimental diagnostics (including optical studies), computational fluid dynamics, and mechanistic analyses to consolidate current knowledge and identify critical gaps that limit technological readiness, particularly material compatibility concerns associated with fuel polarity and the need for injection-system optimization to ensure long-term durability and stable spray patterns. By consolidating these opportunities and challenges under realistic operating conditions, this work provides a coherent framework to guide future research on tailored combustion strategies and engine designs, supporting the broader adoption of PODE-based fuels in cleaner, more efficient transportation energy systems.