Droplet Size Effects on NOx Formation in a One-Dimensional Monodisperse Spray Combustion System

Abstract

A one-dimensional monodisperse aerosol spray combustion facility is described and experimental results of post-flame NO/NOx emissions are presented. Four different hydrocarbon fuels were studied: isopropanol, methanol, n-heptane, and n-octane. The results indicate an optimum droplet size in the range of 43-58 microns for minimizing NO/NOx production for all of the test fuels. This NOx behavior is associated with droplet interactions and the transition from diffusive type of spray burning to that of a prevaporized and premixed case. Decreasing the droplet size results in a trend of increasing droplet interactions, which suppresses temperatures and reduces NOx. This trend continues until prevaporization effects begin to dominate and the system tends towards the premixed limit. The occurrence of the minimum NOx point at different droplet diameters for the different fuels appears to be governed by the extent of prevaporization of the fuel in the spray and is consistent with theoretical calculations based on each fuel’s physical properties.