Leonel O. Arellano

Surface-Stabilized Fuel Injectors With Sub-Three PPM NOx Emissions for a 5.5 MW Gas Turbine Engine

ALZETA Corporation has developed surface-stabilized fuel injectors for use with lean premixed combustors which provide extended turndown and ultralow NO x emission performance. These injectors use a patented technique to form interacting radiant and blue-flame zones immediately above a selectively perforated porous metal surface. This allows stable operation at low reaction temperatures. A previous ASME paper (IJPGC2002-26088) described the development of this technology from the proof-of-concept stage to prototype testing. In 2002 development of these fuel injectors for the 5.5 MW turbine accelerated. Additional single-injector rig tests were performed which also demonstrated ultralow emissions of NO x and CO at pressures up to 1.68 MPa (16.6 atm) and inlet temperatures up to 670°K (750°F). A pressurized multi-injector sector rig test was conducted in which two injectors were operated simultaneously in the same geometric configuration as that expected in the engine combustor liner. The multi-injector package was operated with various combinations of fired and unfired injectors, which resulted in low emissions performance and no adverse affects due to injector proximity. To date sub-3 ppm NO x emissions with sub-10 ppm CO emissions have been obtained over an operating range of 0.18-1.68 MPa (1.8-16.6 atm), inlet temperatures from 340 to 670K (186-750°F), and adiabatic flame temperatures from 1740 to 1840K (2670-2850°F). A full scale multi-injector engine simulation is scheduled for the beginning of 2003, with engine tests beginning later that year.

Comparison of Trip-Strip/Impingement/Dimple Cooling Concepts at High Reynolds Numbers

Modern industrial combustor liners employ various cooling schemes such as, but not limited to, impingement arrays, trip-strips, and film cooling. With an increasing demand for a higher turbine inlet temperatures and lower emissions, there is less air available to cool the combustor liner. To ensure the required liner durability without compromising engine performance more innovative cooling schemes are required. In the present work, three different cooling concepts, i.e., strip-strips, jet array impingement and dimples, operating at unusually high flow conditions were investigated. There is very little data available in the open literature for the aforementioned cooling schemes in the indicated Reynolds Number range (ReDh >60,000). The wall flow friction characteristics as well as the local heat transfer were measured. The heat transfer coefficients were obtained using a transient liquid crystal technique. The test configurations consisted of a 90° trip-strip surface (only one side turbulated), a fixed staggered array with varying impingement hole sizes, and a fixed staggered dimple pattern. For the Reynolds numbers investigated (26,000< ReDh <360,000), the jet-impingement cooling provided the highest average heat transfer enhancement followed by the trip-strip channel, and then by the dimpled channel. In terms of the overall thermal performance, the dimpled channel tends to stand out as the most effective cooling scheme. This is consistent with findings from other investigators at lower Reynolds numbers.Copyright

Full-Scale Demonstration of Surface-Stabilized Fuel Injectors for Sub-Three ppm NOx Emissions

ALZETA Corporation has developed surface-stabilized fuel injectors for use with lean premixed combustors which provide extended turndown and ultra-low NOx emission performance. These injectors use a patented technique to form interacting high-flow and low-flow flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures. This technology has been given the product name nanoSTAR™. Previous work involved the development of nanoSTAR technology from the proof-of-concept stage to prototype testing. Rig testing of single injectors and of two injectors simulating a sector of an annular combustion liner have been completed for pressure ratios up to 17 and combustion air inlet temperatures up to 700 K (800°F). This paper presents results from the first ever full-scale demonstration of surface-stabilized fuel injectors. An annular combustion liner, fitted with twelve nanoSTAR injectors was successfully tested up to a pressure ratio of 12 and combustion air inlet temperature of 700 K (800°F). NOx emissions were 2 ppm with CO emissions of 3 ppm both corrected to 15% O2 . The combustion system exhibited excellent temperature uniformity around the annular combustor outlet with a maximum pattern factor of 0.16 and engine-appropriate radial profiles.© 2004 ASME

Use of an Extractive Laser Probe for Time-Resolved Mixture Fraction Measurements in a 9 ATM Gas Turbine Fuel Injector

This paper describes the use of a high velocity extractive sampling probe in a gas turbine fuel injector operating at 9 atm. This instrument has the ability to measure the temporal and spatial fluctuations of the mixture fraction. Knowledge of the fuel-air mixing characteristics is necessary to further decrease levels of pollutant emissions such as nitrogen oxides (NOx), and to sustain stable combustion. The extractive probe resolves temporal fluctuations due to the high flow rate through the sampling probe. The residence time of the sample gas in the sampling probe is sufficiently short so that axial diffusion on the relevant time scale can be ignored. Measurements were taken at two operating points: one at a stable low-emissions condition, and one at a condition where pressure oscillations in the combustor were high. At the second operating point, it was found that the frequencies of the pressure oscillations coincided with the frequencies of fluctuation in air-fuel ratio resolved by the probe.© 2001 ASME

Combined Back-Side Cooled Combustor Liner and Variable Geometry Injector Technology

The need to evolve next-generation ultra-lean premixed systems with advanced air management and improved liner cooling strategies have led Solar to develop a pre-production combustion system for its C50 class engine. The system uses an Augmented Backside Cooled/Thermal Barrier Coated (ABC/TBC) combustor and Variable Geometry injectors. The technology reduces both NOx and CO emissions, while improving part-load cycle efficiency.The ABC/TBC combustor technology eliminates quenching of the reaction at the walls typically found in combustors using film-cooling techniques. Eliminating this quenching effect is not only conducive to reducing CO emissions, but it also enables the operation of the combustor primary zone at low temperatures to produce minimum thermal NOx. Coupled with a set of variable geometry injectors, the system manages air more effectively to extend the combustor operating range under which emissions and stability limits are maintained. The injectors enable the control of air entering the combustor as a function of engine load and ambient temperature. Such ability reduces the need to bleed high-pressure compressor air at part-load, thus enhancing the engine cycle efficiency.The pre-production combustion system is currently undergoing field evaluation to assess long-term durability, characterize system performance, and develop optimum control algorithms. The development methodology and experience for this system is discussed in this paper.Copyright

Development and Demonstration of Engine-Ready Surface-Stabilized Combustion System

Alzeta Corporation has developed surface-stabilized fuel injectors for use in lean-premixed low-emissions combustion systems. These injectors use a patented technique to form interacting high-flow and low-flow flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures conducive for preventing high NOx formation. Solar Turbines and Alzeta had previously worked together to evaluate single-injector and full-scale proof-of-concept test hardware. This paper presents results of a combustion system developed for evaluation on an engine. The next-generation hardware has evolved to include a pilot to handle low engine speeds, and flow circuits have been adjusted to meet low-pressure drop requirements. Screening tests of the full-scale system have been completed at simulated engine conditions in a full-scale rig. Single-digit NOx and CO emissions have been achieved without encountering combustion-driven instabilities. The combustion system demonstrated adequate power turndown with the assistance of the pilot module, and studies to predict the service life of burners have been initiated.Copyright

Surface-Stabilized Fuel Injectors With Sub-Three ppm NO

ALZETA Corporation has developed surface-stabilized fuel injectors for use with lean premixed combustors which provide extended turndown and ultra-low NOx emission performance. These injectors use a patented technique to form interacting radiant and blue-flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures. A previous ASME paper (IJPGC2002-26088) described the development of this technology from the proof-of-concept stage to prototype testing. In 2002 development of these fuel injectors for the 5.5 MW turbine accelerated. Additional single-injector rig tests were performed which also demonstrated ultra-low emissions of NOX and CO at pressures up to 1.68 MPa (16.6 atm) and inlet temperatures up to 670 °K (750 °F). A pressurized multi injector ‘sector rig’ test was conducted in which two injectors were operated simultaneously in the same geometric configuration as that expected in the engine combustor liner. The multi-injector package was operated with various combinations of fired and unfired injectors, which resulted in low emissions performance and no adverse affects due to injector proximity. To date sub-3 ppm NOx emissions with sub-10 ppm CO emissions have been obtained over an operating range of 0.18 to 1.68 MPa (1.8 to 16.6 atm), inlet temperatures from 340 to 670 °K (186 to 750 °F), and adiabatic flame temperatures from 1740 to 1840 °K (2670 to 2850 °F). A full scale multi-injector engine simulation is scheduled for the beginning of 2003, with engine tests beginning later that year.Copyright

Development of Surface-Stabilized Fuel Injectors With Sub-Three PPM NO

ALZETA Corporation has developed surface-stabilized fuel injectors for use with lean premixed combustors which provide extended turndown and ultra-low NOx emission performance. These injectors use a patented technique to form interacting radiant and blue-flame zones immediately above a selectively-perforated porous metal surface. This allows stable operation at low reaction temperatures. This technology is a successful extension of ALZETA’s line of proven Pyromat™ SB metal fiber burners. A proof-of-concept injector in a full-pressure test rig at NETL in Morgantown, West Virginia achieved sub-3 ppm NOx emissions with concurrent single-digit CO emissions, both corrected to 15% O2 . Operating conditions ranged between inlet pressures of 182.4 kPa (1.8 atm) and 1236.2 kPa (12.2 atm), inlet temperatures between 86° C (186° F) and 455° C (850° F) and calculated adiabatic flame temperatures between 1466° C (2670° F) and 1593° C (2900° F). Testing with prototype fuel injectors in test rigs at Solar Turbines last year yielded similar results. In May of 2001, a Solar Saturn 1 MW gas-turbine engine was operated to 95% load with a surface-stabilized injector. Programs are moving forward to adapt these injectors to the Solar Turbines Taurus 60 and Titan 130 engines. Engine tests are scheduled to begin in 2003.Copyright