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This paper describes a system for minimizing NOx emissions in gas turbines. The system uses an optimization technique implemented on a portable computer. No hardware changes are necessary in the combustion system. The system was developed for an LM6000 Dry Low Emissions (DLE) engine. However, it can be applied across the board on any LM series DLE engine manufactured by the Industrial Aero-derivatives (IAD) division of GE Power Systems (GEPS).Copyright © 2000 by ASME

Computational Combustion Dynamics has been used extensively at General Electric Company for combustion applications. This paper demonstrates an application of Advanced Combustion Code to GE’s lean premixed dry low NOx emissions LM2500 and LM6000 gas turbine combustors. A methodology for anchoring the Double Annular Counter-Rotating Swirler (DACRS) exit conditions to Laser Doppler Velocity data from a reacting single cup experiment is described. The DACRS exit velocity profiles and turbulence parameters are inlet boundary conditions for the annular combustor simulation. Since over 80 per cent of the total air enters the combustor via the premixers, inaccuracies in these boundary conditions have a significant impact on the predicted flame shape, liner temperatures and emissions. The paper shows comparisons between measured and predicted velocity in a rectangular duct equipped with a single DACRS. The k-ε turbulence model and the two-step eddy break up/eddy dissipation combustion models are used to predict the reacting flow field of the natural gas/air flame. The inlet velocity profiles are developed first to match the LV data and the observed flame impingement location at nominal settings of the inlet turbulence parameters. The sum square error between measured and predicted velocity is used as the optimization function. Next, a design of experiment computational study is conducted to determine the inlet turbulence length scale and kinetic energy in order to further improve the data match. The eddy break up model is shown to be more robust than the eddy dissipation model. The eddy dissipation model resulted in slow combustion rates, and high fuel and carbon monoxide emissions.

Lower Emissions have become key characteristics of most new gas turbine engines over the last several years. The ‘lean premixed’ approach has been used in the development of the Dry Low Emissions (DLE) technology. The LM6000 and the LM2500 combustors employ a triple dome design with staging of fuel and air flows to achieve lean-premixed operation from light-off to full power. This technology permits the operator to run with reduced emissions of NOx as well as CO and UHC over a wide load setting. Emissions goals of 25 ppm have been successfully met at site rating conditions for the entire family of LM DLE products. The DLE combustor operates on the mid dome at light-off, the inner and the outer domes are brought on progressively, as the engine is loaded. The combustor utilizes a small quantity of air for dome and liner cooling as most of the combustor air is mixed with fuel in the premixers. Backside cooling enhancements permit the reduction of film cooling, which can cause quenching of CO oxidation reactions. Combustion acoustics are controlled by the use of passive devices on the exterior of the engine as well as by fuel staging within premixers and by the use of a control system which senses and alters the combustor operation to limit acoustics. The DLE technology meets the emissions and reliability needs of the industry with limited package modifications. This paper describes the DLE technology, developed to meet the needs of the industry. Critical design features including the Double Annular Counter-Rotating Swirler (DACRS) premixer, the triple annular dome design, the heat shield design and the staging sequence are discussed, in addition to the field experience gained on the LM2500 and LM6000 DLE models.Copyright © 1998 by ASME

An experimental program was conducted to develop premixer concepts for use in GE’s aero-derivative Marine and Industrial gas turbine engines such as the LM 1600, 2500 and 6000. These engines operate typically at pressure ratios up to 30:1. Extensive tests in 1 and 2 cup test combustors were carried out to evaluate the Double Annular Counter-Rotating Swirler (DACRS) premixers at test conditions representative of the above mentioned engines. These tests also help establish combustor design parameters. Single digit NOx emissions were measured at engine operating conditions with the DACRS II and III premixers. Premixer interactions and their effects on Lean Blow Out were also studied.Copyright © 1994 by ASME