Mixing and combustion of methanol and ethanol high-pressure sprays

Time-resolved liquid and vapor mixing and combustion of methanol and ethanol from high-pressure sprays are measured by employing simultaneous high-speed diffuse-back illumination extinction imaging (DBI-EI), Rayleigh scattering, and OH* chemiluminescence. The experiments are performed in a constant-volume vessel at 22.8 kg/m 3 and 800–1200 K. Methanol exhibits a longer liquid length and slightly faster vapor penetration than ethanol. Methanol liquid droplets suspected to be nanometer-scale, invisible to the DBI-EI diagnostic, are observed via scattering several millimeters downstream of the extinction-measured liquid length. On the other hand, the DBI-EI technique appears suitable for measuring ethanol liquid length at these conditions. A 1-D adiabatic jet mixing model and vapor–liquid equilibrium approximations shed insights on differences in mixing and evaporation. Methanol is shown to be the most sensitive to perturbations from equilibrium. The alcohols require relatively little mixing to approach near-stoichiometric conditions and are thus weakly sensitive to ambient oxygen levels, but fail to ignite below 1000 K ambient temperature, at least 200 K higher than needed for typical diesel-representative hydrocarbons such as n-dodecane. Instead, they require strong mixing to reach sufficient temperatures for ignition to counteract the strong evaporative cooling effects. The effect of 5% EHN is mild under these conditions, as it was estimated to lower the ignition temperature threshold by 40 K at most.