CCS and Power Systems
Advanced Energy Systems - Hydrogen Turbines
Fundamental Studies to Enable Robust, Reliable, Low Emission Gas Turbine Combustion of High Hydrogen Content Fuels
Performer: Regents of the University of Michigan
Project No: FE0007465
Figure 1. University of Michigan Rapid Compression Facility.
Figure 2. Example Time-Sequence of Images (Recorded with High-Speed Imaging Data Capability) that Documents a Weak/Localized Ignition Event Prior to Complete Combustion.
In Figure 2, notice how non-homogeneous the images are during the time sequence, which is indicative of some localized ignition event occurring at earlier stages before the remainder of the fuel mixture is observed to completely ignite. This localized ignition event is complex and influences the temperature, pressure, and thereby the reaction chemistry of the surrounding fuel mixture, and thus the entire experiment.
Figure 3 shows that the localized ignition event causes the pressure to increase (as the gas mixture temperature increases and more fuel gradually ignites) prior to complete combustion.
The RCF imaging capability provides a powerful diagnostic tool to evaluate fuel mixture behavior that is useful to interpret experimental data and provide insights pertinent to the underlying detailed reaction mechanisms governing ignition/combustion behavior of fuels.
Figure 3. Pressure-Time History in RCF Experiment Where Localized "Weak" Ignition is observed.
In the RCF experiment of Figure 3, a fuel containing 20% H2/80% CO at an equivalence ratio of 0.4 and inert: O2 ratio of 3.76 was initially compressed to about 11 atm and effective temperature of 1004 K.
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Figure 4. Comparison of experimental (solid symbols and error bars with solid lines) and modeling results (open symbol and error bars with dashed lines) for syngas ignition over a range of temperatures and pressures. There is excellent agreement between the experimental and predicted values at all conditions; however, the uncertainties in the syngas reaction chemistry are large at lower pressures as noted by the larger error bars.
Reference: Kalitan, D.M. , Petersen, E.L. et al., 2007. Ignition and Oxidation of Lean CO/H2 Fuel Blends in Air. Journal of Propulsion and Power, 23(6), pp.1291–1303.
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Figure 5. Pressure/temperature ignition maps.
Top panel: results of ignition experiments showing the transition between weak and strong ignition as a function of fixed pressure.
Middle panel: superposition of the H2 /O2 explosion limits with the experimental data of the top panel. Note the close relationship between the transitions between ignition regimes and the explosion limits.
Bottom panel: experimental results from current work and previous ignition studies by Kalitan et al.
Consistent results are seen from different experimental facilities and spanning a broad range of conditions. Together the results indicate the changes in ignition behavior are not random and the relationship of the conditions to the explosion limits may be an indicator for predicting weak ignition behavior.