Combustion process optimization for oxymethylene ether fuels in a heavy-duty application

Synthetic fuels are a promising possibility to close the gap between future transport requirements like CO2-neutral mobility, pollution and cruising range. For the latter, the internal combustion engine benefits from the high energy density of liquid fuels, especially in heavy-duty applications. Previous publications have shown that oxymethylene ethers (OMEn) suit well for the use in diesel engines. Their molecular structure is CH3 O(-CH2 O)n CH3 with n ranging from 0 to 6. Due to their high oxygen content of 35 wt. % for OME0 (also known as DME) up to 49.5 wt. % for OME6 and the lack of C-C bonds in the molecule, the usage of these fuels leads to lowest soot and particulate raw exhaust emissions. This allows completely new degrees of freedom for the application and design of the combustion process with the aim to improve efficiency and to reduce nitrogen oxide emissions. This talk deals with the 3D-CFD optimization of the piston bowl shape for OME1 combustion at a constant compression ratio and the subsequent experimental investigations with two of the optimized pistons. The reference piston has an ω-bowl shape with step, one of the optimized pistons has a larger step volume by reducing the bowl diameter and the other piston has an ω-bowl without a step. The used injection system is adapted with a volumetric nozzle flow rate with a factor of 2.5 to com-pensate both the lower heating value of OME1 and the operation at lowered rail pressures. The results show a good accordance to the tendencies predicted by CFD simulation. The ω-bowl piston without a step leads to a little worse efficiency, but a higher reduction potential of NOx. The ω-bowl piston with step leads to lowered NOx emissions and still good indicated efficiency. With in-creased EGR levels, so that the air/fuel equivalence ratio λ = 1.25, the CO emissions are rising and indicated efficiency becomes lower for all pistons. All pistons showed lowest soot levels while the optimized bowl shapes led to a reduction in particle numbers.     «

Synthetic fuels are a promising possibility to close the gap between future transport requirements like CO2-neutral mobility, pollution and cruising range. For the latter, the internal combustion engine benefits from the high energy density of liquid fuels, especially in heavy-duty applications. Previous publications have shown that oxymethylene ethers (OMEn) suit well for the use in diesel engines. Their molecular structure is CH3 O(-CH2 O)n CH3 with n ranging from 0 to 6. Due to their high oxy...     »