Investigation of the Combustion Mechanism of a Fuel Droplet Cloud by Numerical Simulation

The combustion mechanism of a fuel droplet cloud was studied by numerical simulation. We investigated how the flame front speed and combustion products changed depending on the equivalence ratio and initial temperature. Modeling was performed using the KIVA-III software package, a three dimensional analysis software used mainly for internal combustion engine applications. The computational domain was a horizontal 1x1x100 cell sector of a spherical combustion chamber and the fuel was n-decane.

Results showed that when all the fuel droplets were assumed to have evaporated, the flame front speed increased from 28 cm/s to 152 cm/s as the equivalence ratio increased. The maximum flame front speed was reached at ϕ=1.1, beyond which it decreased (at richer overall equivalence ratios). With a constant equivalence ratio, the flame front speed decreased near the outside region, because the unburned gas was compressed by the expanding burned gas. When the initial fuel temperature was decreased, the flame front speed was lower than when all fuel droplets were evaporated. The case when the fuel density distribution had a discontinuity in the computational domain was also calculated to simulate a mixture stratification technique. This resulted in a significant reduction of NOx, and the flame front speed was affected by the perturbation.