Oxygenate screening on a heavy-duty diesel engine and emission characteristics of highly oxygenated oxymethylene ether fuelOME1

Abstract

Oxygenated fuel components are known to reduce soot emissions in diesel engines significantly while having little effect on NOx emissions. Several compounds were mixed with diesel fuel and tested for their emission characteristics on a 1.8 l heavy duty diesel engine. The C1-oxygenate dimethoxy methane (OME1) which contains no C–C bonds in its molecular structure was found to have the best effect on the reduction of soot and particle number emissions. OME1 belongs to the group of oxymethylene ethers (OMEn) and has the molecular structure CH3–O–(CH2–O)n–CH3 while n=1. For further investigations, a pure OME1-fuel with cetane number 48 was used which contained OME1 and additives to enhance viscosity, lubricity and cetane number. Engine testing including aftertreatment with a Pt coated oxidation catalyst (DOC) proved the soot-NOx trade-off to vanish completely even at stoichiometric operation. CO and most unburned fuel emissions were efficiently reduced by the DOC. The emission of formaldehyde and methane was measured using FTIR spectrometry. No CH2O emissions could be detected. Near stoichiometric conditions, a growing output of methane was observed, which was not converted in the DOC. This can be explained with the high share of methyl groups, which react to methane with other radicals. As OME1 shows low cetane number (CN), high volatility and weak viscosity and lubricity, the characterization of the less volatile OMEn with n=3…5 and CN > 90 is recommended. These are expected to show similar emission characteristics and might have a smaller potential of methane formation.