Effect of the stagnation plate on PAHs, soot and OH distributions in partially premixed laminar flames fueled with a blend of n-heptane and toluene

Abstract

The stagnant plate influence on spatial distributions of polycyclic aromatic hydrocarbons (PAHs), soot and hydroxyl radical (OH) in the surrogate fuel (80% n-heptane and 20% toluene in volume) partially premixed flame on a McKenna burner were originally investigated in terms of different plate heights above the burner (Hp) and plate temperatures (Tp). Both PAHs and OH distributions were qualitatively measured by laser-induced fluorescence (LIF) and soot volume fraction field was quantitatively measured by two-color laser-induced incandescence (2C-LII). It is found that the LIF intensity of 2&3-ring aromatics (A2&A3) and 4-ring aromatics (A4) and soot volume fraction firstly increase and then reduce when the Hp is set from 35 to 10 mm. The variation tendency transition happens between Hp = 20 and 25 mm. In contrary, OH-LIF intensity gradually decreases as the Hp decreases. On the other hand, the Tp has an opposite effect on the A2&A3-LIF, A4-LIF and soot volume fraction variation tendency at two Hp. At Hp = 15 mm, A2&A3-LIF, A4-LIF and soot volume fraction increase as the Tp increases. However, A2&A3-LIF, A4-LIF and soot volume fraction decrease with the rise of the Tp at Hp = 35 mm. Interestingly, OH-LIF intensity always increases as the Tp rises at any Hp. Therefore, it can be concluded that the PAHs-LIF intensity and soot volume fraction depend on the Hp and Tp, and the maximums of them would be reached at the specific Hp and Tp. While both the Hp and Tp have a monotonic effect on the OH-LIF intensity.