Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner

Abstract

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15-100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700K and 1900K. Once aflame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was tised.

Influence of Burner Material, Tip Temperature, and Geometrical Flame Configuration on Flashback Propensity of H2-Air Jet Flames

“…In most of UCI's previous work, a quartz enclosure was used as a strategy to stabilize the flame on top of the burner tube [23]. In most of UCI's previous work, a quartz enclosure was used as a strategy to stabilize the flame on top of the burner tube [23].…”

“…This unique method was introduced to simulate a typical practical gas turbine control strategy [23]. The AFT is held constant in each EB experiment.…”

“…In more recent work, though not considering BLF, Kedia and Ghoniem [22] studied the effect of flame holder material on combustion dynamics. Shaffer et al [23] also proposed a relationship between flashback propensity and the thermal conditions near the burner rim. Manuscript received July 3.…”

“…Recent work has been conducted independently by UCI and TUM examining these issues [23,25]. In all cases, thermal coupling between the flame and burner rim has been found to be very important for the onset of FB.…”

Experimental Investigation of the Effects of Central Fuel Injectors on Premixed Swirling Flames

“…Several authors [8][9][10] stated that the behaviour of fuel mixture can be significantly different than that of individual constituents. Syred et al 11,17 showed considerable difference in flashback blowoff limits when increasing the hydrogen content of the fuel, whilst demonstrating that these limits could be correlated with the inlet tangential velocity level..…”