Optical Spray Investigations on OME3-5 in a Constant Volume High Pressure Chamber 2019-24-0234
Synthetic fuels generated with surplus renewable electricity, water and captured CO2, so called E-fuels, offer the possibility to easily store excess energy over long periods of time. Therefore, the ALIGN-CCUS-project seeks to use them for power-generation and as a fuel for the transport-sector.
Polyoxymethylene-dimethyl-ethers (POMDMEs, short: OME) are promising E-fuels for passenger-car applications. Their molecular structure is CH3-O-(CH2O)n-CH3. For passenger-car applications, OME-mixtures with n between 3 and 5 seem most suitable, as the mixture is liquid under normal ambient conditions, offers a high cetane-number and sufficient lubricity. Their high flash-point, low toxicity and good miscibility with conventional diesel-fuel also may ease their market-introduction. The lack of direct C-C-bonds within their molecule and the high oxygen-content lead to very low soot-emissions, thus attenuating the NOx-soot-tradeoff through higher EGR-rates which are required for lowest NOx raw-emissions. However, oxygenated fuels such as OME offer a lower heating value and a different evaporation-behavior compared to conventional diesel-fuel. This leads to differences in spray-formation and ignition-delay.
In order to determine the mixture formation characteristics and the combustion behavior of neat OEM3-5, optical investigations have been carried out in a high-pressure-chamber using shadowgraphy, mie-scatterlight and OH-radiation recordings. Liquid penetration length, gaseous penetration length, lift off length, spray cone angle and ignition delay have been determined and compared to those measured with diesel-fuel at different pressures, temperatures, rail pressures and injection durations. Liquid penetration length for OME3-5-sprays was found to be shorter than that of diesel-fuel. Spray cone angles were smaller at low temperature and larger at high temperature. Lift off length was generally observed to be longer for OME3-5, while gaseous penetration length was similar. Ignition delay was found to be shorter for OME3-5. These results serve as a valuable basis for the optimum design of the combustion process parameters for the application of E-fuels.
Christian Honecker, Marcel Neumann, Sandra Glueck, Markus Schoenen, Stefan Pischinger