Characterization of dimethyl ether (DME) combustion using ECN Spray D injector under engine-relevant conditions

This study experimentally examines dimethyl ether (DME) spray combustion under engine-relevant conditions utilizing a single-hole research injector “Spray D” from the Engine Combustion Network (ECN). DME is a promising substitute for diesel fuel, due to its high cetane number and low level of particulate emissions, but also because it is manageable to produce DME with low lifecycle carbon emissions. Using an optically accessible chamber, DME sprays injected through an ECN Spray D injector (0.189 mm diameter) are examined using a range of advanced optical and laser diagnostic techniques. High-speed (50 kHz) diffuse back-illumination extinction imaging (DBI-EI) is utilized to assess both the spray liquid phase and any soot formation. High-speed 355 nm-planar laser-induced fluorescence (PLIF) and line-of-sight OH* chemiluminescence imaging are also performed in a quasi-simultaneous manner to evaluate the low- and high-temperature reactions during different ignition stages as well as under steady-state combustion. The PLIF measurements show formaldehyde (CH 2 O) as a low-temperature product or Polycyclic aromatic hydrocarbons (PAHs) where soot formation may occur at higher temperature. At regular oxidizing environments ranging from 12% to 21% O 2 , we observe no PAH and soot formation from DME, rendering the CH 2 O PLIF measurements unaffected by PAHs. The two-stage ignition process demonstrates the formation and consumption of CH 2 O, followed by increased OH* production under varying oxygen concentrations and temperatures. Consistent with a lower cetane number, the high-temperature ignition delay of DME is found to be slightly longer than that of n-dodecane, accompanied by a longer lift-off length. Under a 0% O 2 environment created to study fuel pyrolysis, mild PAH and soot formation of DME was observed, in contrast to the oxidative experiments where soot was not detectible. This research aims to enhance the global understanding of DME spray combustion by providing comprehensive datasets on low- and high-temperature ignition and combustion processes, as well as soot formation, which may be used to advance computational models specific for DME.