Vaporization and gas-phase combustion of electrosprayed heptane in a small chamber

A model is formulated of the vaporization and gas-phase combustion of a dilute spray of electrically charged droplets of heptane with a coflow of preheated air in a mesoscale combustion chamber. The model includes an Eulerian/Lagrangian treatment of the gas and the droplets, an equilibrium vaporization submodel, and a single step mechanism for the combustion of heptane vapor. The effects of the inlet air temperature, the fuel flow rate and the overall equivalence ratio are investigated. Two combustion modes are described for globally lean systems. When rapid vaporization leads to a kernel of high fuel vapor concentration, combustion may begin before the fuel diffuses in the air coflow, in a layer of intense reaction that locally depletes the oxygen and leaves behind a region of high temperature fuel vapor surrounded by a diffusion flame. When the vaporization rate and the maximum fuel vapor concentration are decreased by increasing the size of the droplets or the inlet velocity of the air, combustion occurs in a lifted lean premixed flame after the fuel has fully vaporized and mixed with the air coflow. Ignition and extinction conditions are discussed. The degree of accuracy that can be expected from the single step reaction mechanism is also discussed.