Gaseous Emissions Results from a Three-Cup Flametube Test of a Third-Generation Swirl-Venturi Lean Direct Injection Combustion Concept

This paper summarizes the development of lean direct injection (LDI) combustor technology at, or in collaboration with, the NASA Glenn Research Center. These configurations differ mainly in fuel-air mixing strategy. The paper reviews the NOx performance and operability characteristics of multiple LDI configurations tested at NASA Glenn

A Second Generation Swirl-Venturi Lean Direct Injection Combustion Concept

A low-NO (sub x) aircraft gas turbine engine combustion concept was developed and tested. The concept is a second generation swirl-venturi lean direct injection (SV-LDI) concept. LDI is a lean-burn combustion concept in which the fuel is injected directly into the flame zone. Three second generation SV-LDI configurations were developed. All three were based on the baseline 9-point SV-LDI configuration reported previously. These second generation configurations had better low power operability than the baseline 9-point configuration. Two of these second generation configurations were tested in a NASA Glenn Research Center flametube; these two configurations are called the at dome and 5-recess configurations. Results show that the 5-recess configuration generally had lower NO (sub x) emissions than the flat dome configuration. Correlation equations were developed for the flat dome configuration so that the landing-takeoff NO (sub x) emissions could be estimated. The flat dome landing-takeoff NO (sub x) is estimated to be 87-88 percent below the CAEP/6 standards, exceeding the ERA project goal of 75 percent reduction

Flashback propensity of gas mixtures

In this study, experimental measurements of flashback propensity of hydrogen (H2)-carbon monoxide (CO) mixtures, which are the primary constituents of syngas fuels, are described. The effects of H2 concentration, diluents and swirl on the flashback propensity of H2-CO flames are discussed. For boundary layer type flashback, the critical velocity gradient (gF) values of 5 to 95%, 15 to 85%, and 25 to 75% H2-CO mixtures somewhat agree with the scaling relation [special characters omitted] and yield an average c value of 0.038. At a lower SL 2/α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher S L2/α ratio. For a given Ubulk, the %F at which the combustion induced vortex breakdown (CIVB) flashback occurs decreases with the increase in H2 concentration in fuel mixtures. The more swirl, the more stabilized the recirculation zone and flame. For a given U bulk, the %F at which the CIVB flashback occurs increases with the increase of swirl number. The 6 vane swirler (swirl number S = 0.71) stabilized flame is more prone to CIVB flashback than the 12 vane swirler (swirl number S = 0.97) stabilized flame. The flashback of 25% H2 - 75% CO mixture with 12 vane swirler (swirl number S = 0.97) occurs at 14.4 to 15.2% fuel; on the other hand, the same composition with 6 vane swirler (swirl number S = 0.71) stabilized flame flashback occurs at the 11.2 to 12.8% fuel. The flashback map for actual syngas compositions derived from different source of coal is different due to the presence of diluents in the mixtures. Diluents play a vital role to map the flashback regimes for both the swirler stabilized flames. Lignite coal derived syngas compositions went up to 33 to 35% fuel at which the flashback occurs. The strong swirled flow produces a more stabilized reaction zone (OH concentration) just after the swirler. The 12 vane swirler (swirl number S = 0.97) produce a more OH concentration (1 through 4 sequence images) after the flow separation as compared to the 6 vane swirler (swirl number S = 0.71)

Flame Stability of Methane and Syngas Oxy-Fuel Steam Flames

Oxy-fuel combustion has been used previously in a wide range of industrial applications. Oxy-combustion is carried out by burning a hydrocarbon fuel with oxygen instead of air. Flames burning in this configuration achieve higher flame temperatures, which present opportunities for significant efficiency improvements and direct capture of CO2 from the exhaust stream. In an effort to better understand and characterize the fundamental flame characteristics of oxy-fuel combustion, this research presents the experimental measurements of flame stability of CH4/O2and syngas (H2–CO)/O2 flames. Effects of the H2 concentration, fuel composition, exhaust gas recirculation ratio, firing inputs, and burner diameters on the flame stability of these fuels are discussed. Effects of exhaust gas recirculation, i.e., CO2 and H2O (steam) acting as diluents on burner operability, are also presented. The roles of firing input on flame stability are then analyzed. For this study, it was observed that many oxy-flames did not stabilize without exhaust gas recirculation because of their higher burning velocities. In addition, the stability regime of all compositions was observed to decrease as the burner diameter increased. A flashback model is also presented, using the critical velocity gradient (gF) values for CH4–O2–CO2 flames. The scaling relation [gF = c(SL2/α)] for different burner diameters was obtained for various diameter burners. The paper shows that results correlated linearly with a scaling value of c = 0.0174

Effects of Syngas Composition on Combustion Induced Vortex Breakdown (CIVB) Flashback in a Swirl Stabilized Combustor

Flame flashback attributed to combustion induced vortex breakdown (CIVB) is a major design challenge for swirl stabilized burner combustors. This paper presents an experimental investigation of combustion induced vortex breakdown (CIVB) flashback propensity for flames yielded from Hydrogen (H2)–Carbon Monoxide (CO) fuel blends and actual synthesized gas (syngas) mixtures. A two-fold experimental approach, consisting of a high definition digital imaging system and a high speed PIV system, was employed. The main emphasis was on the effect of concentration of different constituents in fuel mixtures on flashback limit. In addition, the effect of Swirl Number on flashback propensity was discussed. The percentage of H2 in fuel mixtures played the dominant role when CIVB flashback occurred. For a given air mass flow rate, the mixture containing a higher percentage of H2underwent flashback at much leaner conditions. Flashback maps for actual syngas fuel compositions showed a distinct behavior when various concentrations of diluents were introduced in the mixture. For the two major diluents tested, carbon dioxide (CO2) and nitrogen dioxide (NO2), CO2 was more dominant. The effect of Swirl Number on the flashback propensity was also tested and showed a decrease with an increase in Swirl Number. The final portion of this paper also provides an analysis of flow field of reacting flames which revealed complex vortex–chemistry interactions leading to vortex breakdown and flashback. Based on the experimental results a parametric model similar to Peclet Number approach was developed employing a flame quenching concept. A value of the quench parameter, Cquench was obtained from the correlation of flow Peclet Number and flame Peclet Number, which was observed to be dominated by the fuel composition rather than Swirl Number