Stability and Liftoff of a N2-in-H2 Jet Flame in a Vitiated Co-flow at Atmospheric Pressure

Abstract

<p>The stability and liftoff characteristics of a nitrogen (N<sub>2</sub>) diluted hydrogen (H<sub>2</sub>) jet flame in a vitiated co-flow are investigated experimentally with particular attention focused on regimes where multiple stabilization mechanisms are active. Information gleaned from this research is instrumental for informing modeling approaches in flame transition situations when both autoignition and flame propagation influence combustion characteristics. Stability regime diagrams which outline the conditions under which the flame is attached, lifted, blown-out, and unsteady are experimentally developed and explored. The lifted regime is further characterized in determining liftoff height dependence on N<sub>2</sub> dilution, jet velocity, and co-flow equivalence ratio (or essentially, co-flow temperature). A strong sensitivity of liftoff height to N<sub>2</sub> dilution, jet velocity, and co-flow equivalence ratio is observed. Liftoff heights predicted by Kalghatgi’s correlation are unable to capture the effects of N<sub>2</sub> dilution on liftoff height for the heated co-flow cases. A uniquely formulated Damköhler number, where the chemical time scale is based on flame propagation rather than autoignition, was therefore developed which acceptably captures the effects of jet velocity, nitrogen dilution and environment temperature on liftoff height. Satisfactory agreement between the correlation results indicate that stabilization is dominated by propagation, and prior studies with similar flames, such as the research of Muñiz and Mungal (1997) indicate that the propagating flame is likely tribrachial.</p>

Effect of Pressure, Environment Temperature, Jet Velocity and Nitrogen Dilution on the Liftoff Characteristics of a N2-in-H2 Jet Flame in a Vitiated Co-flow

“…Berkeley's Vitiated Co-flow Burner (VCB) [1] has been redesigned and built in the interior of a pressure chamber in adding functionality for investigating the pressure effect on lifted N 2 -in-H 2 flames. An illustration of Berkeley's VCB is depicted in Fig.…”

“…Hydrogen (H 2 ) is an attractive stationary gas turbine fuel because its products of combustion do not contain carbon monoxide or Carbon Dioxide (CO 2 ) [1]. H 2 can be produced by reforming natural gas or by gasifying coal and when burned, the generation of power from fossil fuels in this manner is known as pre-combustion Carbon Capture and Sequestration (CCS).…”

“…Therefore, the knowledge base which led to the state of the art in gas turbine combustors is restricted to a single fuel. H 2 , however, differs markedly in its combustion properties from natural gas (greater energy density by mass, reduced autoignition delay times, wide flammability limits, high flame speeds [1]). A key research flame beneficial for developing knowledge which is critical for optimizing stationary gas turbine combustor performance with H 2 is the lifted flame.…”

“…Many explanations of the flame stabilization mechanism of turbulent lifted jet flames are available [1,2,3] which are utilized in this research in understanding lifted H 2 jet flame stability. Peters [4] explains that quenching near the nozzle due to excessive local strain rates precedes liftoff.…”

“…Experimental liftoff height results from prior work at atmospheric pressure motivated the development of a liftoff height correlation [1]. The correlation based on the Damköhler number, Dα, and the same correlation is applied in this research in assessing its applicability with pressure as an additional parameter.…”