(528b) Intensity and Efficiency of Idealized Spray-Fed Adiabatic Chemical Reactors

We revisit liquid-fed steady-flow chemical reactor theory, providing new results for the combustion intensity and corresponding efficiency of well-stirred adiabatic chambers fed with a prescribed polydispersed spray. Liquid fuel evaporation is presumed to be rate-controlling and occur via a non-quasi-steady(non-QS) gas-phase energy/mass diffusion-controlled rate law in the prevailing gaseous environment. As a byproduct, we calculate the complete droplet size distribution (DSD-) function exiting the chamber, along with its associated dimensionless moments (shape factors)---all potentially of interest for the design of downstream components.

In this instructive asymptotic limit, two decisive dimensionless parameters dictate the steady-state performance of spray combustors; viz., a: 1) Damkohler-like number (ratio of the mean residence time of the chemically reacting mixture in the combustion space, to the reference value of the vaporization lifetime of a SMD- droplet produced by the injector(s)), and 2) non-QS parameter (which increases with gas density and fuel volatility). Illustrative results are generated/displayed here for log-normal feedstream DSDs over a realistic range of spreads.

As discussed, our deliberately idealized mathematical model can be generalized in many ways, but even our present results set instructive bounds to the achievable performance of real spray combustors at high pressures.