Fuel, Vol.234, 1414-1421, 2018
Neat polyoxymethylene dimethyl ether in a diesel engine; part 2: Exhaust emission analysis
Oxygenated fuels have already shown potential to be used in Diesel engines without major modifications. Polyoxymethylene dimethyl ether (POMDME, short OME) possesses particular characteristics (i.e. no C-C bonds, high cetane number, high potential to reduce greenhouse gases when produced with renewable energy, etc.), which are favourable for combustion in a standard Diesel engine, and offer the possibility to overcome the classical NOx-PM trade off. In order to capture the full potential of this fuel, its combustion characteristics under diesel engine conditions need to be investigated. In the present work, as the second of a two-part paper, the gaseous and particulate emissions of neat OME in a composition of approximately 80% OME3 and 20% OME4 have been studied. Numerous operating conditions have been recorded under globally stoichiometric conditions with simultaneously high EGR rates to evaluate the engine operation, suitable for a three-way catalyst. For the measurement campaign, a heavy duty single cylinder research engine has been used. In addition to standard exhaust gas measurement equipment, emissions have been recorded through fast mass spectrometer calibrated for methane, a particle spectrometer and transmission electron microscopy (TEM) of the solid particles. It is observed that CO and HC show an extreme spike in globally stoichiometric operation. Furthermore, the total HC emissions contain a substantial amount of methane. NOx emissions within the recorded operating conditions show a strong dependence on the applied EGR rate. The particle emissions using OME show high number (compared to the corresponding Diesel case in agglomeration mode) in a size range mainly below 20 nm. TEM imaging combined with an energy dispersive X-ray system revealed that these particles are mostly soot with a few nanometers large metal inclusions.
Keywords:Polyoxymethylene dimethyl ether;OME;POMDME;Stoichiometric diffusion combustion;TEM particle analysis;Oxygenated fuel