was found in tests of an air-cooled combustion liner. The results were used to further develop HAT cycle modeling efforts. Previous investi-gations on the HAT cycle had largely been limited to systems and model-ing studies.
Duel-Fuel
Combustion
Many gas turbine installations require operation on both liquid and gaseous fuels without affecting op-erability or environmental perfor-mance. Liquid fuels are more difficult to mix and pose difficulties in achieving the homogeneous fuel-air mixture distribution that is needed for low-NO combustion.
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Under a CRADA, NETL and Parker Hannifin evaluated a novel dual fuel pre-mixer concept using a manufacturing technique called “macrolamination.” This technique allows complex internal flow chan-nels to be formed by etching them into thin substrates and bonding the substrates together to form fuel in-jector arrays.
Testing at NETL showed that the Parker Hannifin pre-mixer en-abled comparable environmental performance with both natural gas and type 2 diesel fuel at representa-tive temperatures and pressures.
Stabilizing
Combustion
Dynamics
Combustion oscillations (or dynamics) continues to be a chal-lenging issue for the design of low-emissions combustors. Oscillations often complicate achievement of emissions goals, or limit engine ca-pability for new fuels or new re-quirements. To address this issue, NETL has conducted various re-search projects to identify methods to improve combustion stability. These investigations have identified important time scales that can be modified to improve combustion performance. In partnership with the Pittsburgh Supercomputing Center, NETL has explored the dy-namic structure of turbine flames. The results are being used to under-stand how the dynamic combustion response can be modified to enhance stability. In addition, through an AGTSR award, Virginia Tech has conducted a series of acoustic tests in the NETL facilities that have demonstrated promising methods to evaluate the acoustic response of turbine combustors. Methods to measure both the acoustic and com-bustion responses are vital to en-hance the stability of low-emission combustors and achieve the goals of tomorrow’s advanced combustion systems.
Another promising approach to enhance combustion stability is called “active” dynamics control. Active control pulses the fuel to re-lease heat out-of-phase relative to the oscillation. Through a CRADA, NETL and Solar Turbines recently explored a variation of active com-bustion dynamics control, called periodic equivalence ratio modula-tion (PERM). In applying PERM, adjacent injectors alternately inject fuel at a modulated frequency. This modulation serves to dampen pres-sure pulses from any particular in-jector, while maintaining a desired time-averaged fuel-air ratio (equiva-lence ratio). Testing on a 12-injec-tor engine showed that PERM effectively eliminated a 3-psi peak-to-peak pressure oscillation. Modu-lation was carried out at frequencies from 10 to 100 hertz without notice-able effect on engine performance.
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