Propyl Oxymethylene Ether–Ignited Natural Gas Dual Fuel Reactivity Controlled Compression Ignition—A Low Carbon Pathway for High Efficiencies and Low Emissions

Abstract

Abstract. Climate change concerns persisting with petroleum-based fuels and their propensity to produce high NOx and soot emissions have led researchers to investigate renewable low-carbon fuels to power medium- and heavy-duty vehicles. The ease of synthesis and the highly oxygenated nature of oxymethylene ethers (OMEs with chemical structure: R-O-(CH2O)n-R’, where R and R’ are alkyl groups) have positioned them as a viable low soot-producing, low-carbon alternative to diesel. Previous investigations have shown that methyl-terminated OMEs, such as polyoxymethylene dimethyl ether (POMDME), can be used to ignite natural gas, virtually eliminating soot emissions while retaining the very low engine-out NOx emissions possible with diesel–natural gas dual fuel low temperature combustion (LTC). Substituting methyl groups with higher alkyl groups (e.g., propyl or butyl groups) to terminate these OMEs have shown an improvement in diesel blending properties while maintaining higher oxygen content and cetane number than diesel. In this study, the combustion characteristics of diesel and propyl oxymethylene ether (also known as P-1-P) were experimentally compared on a single cylinder engine. Engine performance and emissions were measured at different loads for pure diesel and pure P-1-P before proceeding to dual fuel RCCI of natural gas. P-1-P–natural gas LTC experiments were performed at a constant load of 10 bar IMEPg and engine speed of 1339 rev/min. At this speed–load condition, the effect of engine operating parameters such as P-1-P injection timing, intake pressure, and rail pressure, on engine performance and emissions with P-1-P – natural gas dual fuel RCCI, was characterized with a specific focus on identifying pathways for improving fuel conversion efficiencies without significant penalties in engine-out emissions or engine stability. The optimum efficiency-emissions tradeoff was achieved at a boost pressure of 1.75 bar, rail pressure of 1000 bar and 90% PES. An IFCE of ∼47% was observed at that operating condition, while maintaining ISCO and ISHC emissions ∼5 and 11 g/kWh, respectively. ISNOx emission was around 0.05 g/kWh, and smoke emissions in the range of 0.001 FSN were measured using an AVL smokemeter.