Particle Size Distribution Measurements of Neat and Water-Emulsified Oxymethylene Ethers in a Heavy-Duty Diesel Engine

Diesel-fueled compression ignition engines display a distinct trade-off in particulate matter (PM) and nitrogen oxide (NOX) emissions due to the nature of diffusive combustion. The modification of fuel properties has drawn much attention since these methods offer additional potential to reduce emissions. Oxygenated fuels are reported to greatly diminish particle emissions while water emulsification of regular diesel causes a significant decrease in NOX. However, recent studies indicate that these fuel-based approaches may lead to an increase in nanoparticle emissions, which are known to be more dangerous to human health than large particles. This has raised the question about whether current engine technology is prone to nanoparticle formation.In this work, the authors present a detailed study on combustion and emission performance of the oxygenate fuel Oxymethylene Ether (OMEn, the mixture contains neat OME with chain length n = 2 − 6). In a novel approach, a single-cylinder heavy-duty diesel engine was fueled with both neat and water-emulsified OME to combine the two fuel-based methods in order to simultaneously reduce both NOX and particle emissions to a great extent. Particular emphasis was put on the particle size distribution (PSD) of emitted PM to elaborate a potentially severe drawback of these fuel-based approaches. In the process, hydrogenated vegetable oil (HVO) was used as the diesel reference fuel. The findings are summarized as such: PSD measurements of OME2-6 reveal similar particle diameters in mid-load operation and a shift to smaller particles at unfavorable engine operations compared to HVO. Water-emulsified OME2-6 reduces NOX by roughly 2-3% with a one percent increase in water concentration while maintaining a nearly constant combustion efficiency. Adverse effects on nanoparticle formation by water emulsification were not observed.