Title: Characterization of Dimethyl Ether (DME) Spray Using ECN Spray D under Engine-Relevant Conditions

This research experimentally investigates the spray vaporization of high-pressure dimethyl ether (DME) using a single-hole research in- jector focusing on nominal operating conditions of Spray A from the Engine Combustion Network (ECN). DME is a synthetic alternative to diesel fuel, offering both high reactivity and potential reductions in particulate emissions. Because DME only features half of the energy density of diesel fuel, a specifically designed fuel system with a high mass flow rate to meet the energy delivery requirements is needed. The unique physical properties of DME, including higher vapor pressure and lower viscosity, introduce challenges like cavitation and unique evaporation characteristics that deviate from typical diesel fuel. These features are likely to lead to differences in fuel mixing and combus- tion. This study aims to provide detailed experimental data on DME spray characteristics under engine-like conditions, helping the devel- opment of predictive CFD models for optimal injector and combustion chamber design. High-pressure sprays injected via an ECN Spray D injector are analyzed using high-speed diffuse-back illumination ex- tinction imaging (DBI-EI) to measure the liquid phase of the sprays and shadowgraphy imaging to measure the vapor penetration. DME injections show slower penetration when compared to more conven- tional liquid fuels, namely n-dodecane. This delayed injection might indicate cavitation and the role of an evacuated injector tip prior to injection. To confirm this aspect of the empty sac, the injection rate profile was tested using the Musculus and Kattke jet model. Subse- quently, the vapor-liquid equilibrium at the liquid length was analyzed, revealing the distinct mixing nature of DME that DME liquid pene- tration 40% past the predicted vapor-liquid equilibrium distance. This research will provide comprehensive datasets on liquid/vapor mixing, which are crucial for developing reliable spray and combustion model- ing tools.