Detonation cell Size Data for Dimethyl-ether Air Mixtures

Peter Diakow Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada Synopsis Dimethyl-ether (C2H6O) a common hydrocarbon is increasingly being used as a transportation fuel and as an aerosol propellant, very limited explosion safety data is available for this fuel. Experiments were performed to determine the detonation characteristics of dimethyl-ether air mixtures as a function of composition, initial temperature and combustion initiation. Introduction Dimethyl-ether is currently used primarily as an aerosol propellant in the place of CFC propellants and as a replacement for propane in liquefied petroleum gas (LPG). There is increasingly more interest in dimethyl-ether as a transportation fuel. Because of its high cetane number and very low emissions during combustion it is especially well suited for compression ignition engine applications. As these applications are developed an infrastructure to transport and store the fuel will have to be developed. Or alternatively, expand the existing infrastructure currently used for propane which has similar properties. Very little explosion safety data is currently available for DME. Mogi et al. [1] performed experiments in two different combustion tubes where they measured detonation velocity and pressure for DME-air mixtures at atmospheric pressure and temperature within the detonability limits. Ng et al. [2] measured the detonation cell size of DME-oxygen mixtures at 298K. They observed a multi-cellular detonation structure for all compositions at low initial pressure. This paper reports experimental results for DME-air mixtures at 298K and 373K. Methods and Results Experiments were performed in a 6.2m long, 10cm inner-diameter heated detonation tube, as seen in figure 1, to determine the detonation characteristics of dimethyl-ether (DME) air mixtures. The detonation velocity and pressure were measured, and cell size was obtained using the soot foil technique. Modeling of equilibrium detonation characteristics were carried out along with kinetic modeling of the steady one-dimensional detonation structure to compare with experimental detonation properties. The measured detonations velocities closely match the calculated ChapmanJouget (CJ) detonation values. DME-air denotations showed a double-cell pattern for all compositions as seen in figure 2. From the kinetic modeling it is evident that DME-air detonations undergo two-stage heat release, on the fuel rich side, as seen in figure 3, which explains the double cell pattern observed. The detonation composition limits were found to be slightly wider at