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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Ignition of Lean Methane-Based Fuel Blends at Gas Turbine Pressures

[+] Author and Article Information
Eric L. Petersen1

Mechanical, Materials & Aerospace Engineering, University of Central Florida, P.O. Box 162450, Orlando, FL 32816petersen@mail.ucf.edu

Joel M. Hall, Schuyler D. Smith, Jaap de Vries

Mechanical, Materials & Aerospace Engineering, University of Central Florida, P.O. Box 162450, Orlando, FL 32816

Anthony R. Amadio, Mark W. Crofton

Space Materials Laboratory, The Aerospace Corporation, El Segundo, CA 90245

1

Corresponding author.

J. Eng. Gas Turbines Power 129(4), 937-944 (Jan 02, 2007) (8 pages) doi:10.1115/1.2720543 History: Received July 17, 2006; Revised January 02, 2007

Abstract

Shock-tube experiments and chemical kinetics modeling were performed to further understand the ignition and oxidation kinetics of lean methane-based fuel blends at gas turbine pressures. Such data are required because the likelihood of gas turbine engines operating on $CH4$-based fuel blends with significant $(>10%)$ amounts of hydrogen, ethane, and other hydrocarbons is very high. Ignition delay times were obtained behind reflected shock waves for fuel mixtures consisting of $CH4$, $CH4∕H2$, $CH4∕C2H6$, and $CH4∕C3H8$ in ratios ranging from 90/10% to 60/40%. Lean fuel/air equivalence ratios $(ϕ=0.5)$ were utilized, and the test pressures ranged from 0.54 to $30.0atm$. The test temperatures were from $1090K$ to $2001K$. Significant reductions in ignition delay time were seen with the fuel blends relative to the $CH4$-only mixtures at all conditions. However, the temperature dependence (i.e., activation energy) of the ignition times was little affected by the additives for the range of mixtures and temperatures of this study. In general, the activation energy of ignition for all mixtures except the $CH4∕C3H8$ one was smaller at temperatures below approximately$1300K$$(∼27kcal∕mol)$ than at temperatures above this value $(∼41kcal∕mol)$. A methane/hydrocarbon–oxidation chemical kinetics mechanism developed in a recent study was able to reproduce the high-pressure, fuel-lean data for the fuel/air mixtures. The results herein extend the ignition delay time database for lean methane blends to higher pressures $(30atm)$ and lower temperatures $(1100K)$ than considered previously and represent a major step toward understanding the oxidation chemistry of such mixtures at gas turbine pressures. Extrapolation of the results to gas turbine premixer conditions at temperatures less than $800K$ should be avoided however because the temperature dependence of the ignition time may change dramatically from that obtained herein.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

Figure 1

Sample endwall pressure and CH* chemiluminescence traces and definition of ignition delay time: (a) lower pressure experiment; and (b) higher pressure experiment

Figure 2

Ignition delay times for methane-only Mixture 1 at lower pressure. Comparison is with the correlation of Petersen (7) (Eq. 1) and correlation of current data.

Figure 3

Results for CH4-only Mixture 2 at two different average pressures: 10.8atm and 19.9atm. Comparison is with correlation of Petersen (7) (Eq. 1) and correlation of current data.

Figure 4

Ignition delay times for the methane/hydrogen blends in comparison to the methane-only data at similar pressures

Figure 5

Ignition delay times for the methane/ethane blends in comparison to the methane-only data at similar pressures

Figure 6

Measured ignition delay times for the methane/propane blend in comparison to the methane-only data at similar pressures

Figure 7

Ignition–time sensitivity spectra for two target conditions. Reactions shown are those with the largest sensitivity coefficients of the current model (32): for Mixture 2 (CH4/Air, ϕ=0.5). Sensitivity to the H+O2 chain branching step is shown for comparison.

Figure 8

Numerical simulations for fuel-lean, pure-CH4/air mixtures at elevated pressure. Models include GRI-Mech 3.0 (22), RAMEC (24), and that adopted by the current study (32): (a) Mixture 2, CH4/Air, ϕ=0.5, 19.9atm; and (b) Mixture 1 from Petersen (8), CH4∕O2∕Ar, ϕ=0.4, 50atm.

Figure 9

Comparison between model (32) and experiment for mixtures of methane and hydrogen in air (Mixtures 3 and 4)

Figure 10

Comparison between model (32) and experiment for mixtures of methane and ethane in air (Mixtures 5 and 6)

Figure 11

Model and experiment at low-pressure, high-temperature conditions. As expected, both the model adopted herein (32) and GRI-Mech 3.0 agree favorably with the data and each other at conditions where the latter model was formulated.

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