Laser based investigations were performed on a prototype 4th generation DLE (dry low emission) burner under atmospheric pressure conditions to study the effects of changing burner geometry on the flame. In a full burner configuration, a divergent conical section termed the Quarl is located after the burner exit for expanding the flow area and holding the flame. The planar laser-induced fluorescence (PLIF) of OH radicals together with the flame chemiluminescence imaging were employed to study the flame characteristics under the conditions with and without Quarl using CH4 as fuel to understand the influence of Quarl on the flame. When there is no Quarl, the flame has more freedom to expand at the burner exit and with an increase in the global equivalence ratio (ϕ), the width of the flame increases and the total extension of the flame shortens. For all the global ϕ considered here, the total extension of the flame is shorter under the condition without Quarl in comparison to the one with Quarl. For a richer global ϕ (ϕ ≥ 0.46) the outer recirculation zones (ORZs) are not observed under the condition with Quarl, but are observed without Quarl along with the inner recirculation zone. Without Quarl conditions, equivalence ratios (ϕ) of the concentrically arranged three sections of the burner: an outer Main section, an intermediate section (Pilot) and a central pilot body or pre-chamber combustor, termed the RPL (Rich-Pilot-Lean) sections were altered. The results show that at a constant global ϕ, with an increase in the RPL ϕ and the Pilot ϕ, the flame shortens and expands radially as well as the flame stabilization zone that is produced after the burner exit moves further downstream. At a richer global ϕ, the ORZ is observed along with the inner recirculation zone of the flame. Otherwise, with an increase in global ϕ, the changes in the flame shape, in the flame fluctuation and in the flame stabilization position follow similar trends as for increasing the Pilot ϕ and the RPL ϕ. Additionally, combustion emissions were obtained to observe the effects on NOX level for different operating conditions with and without Quarl.

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