This book offers gas turbine users and manufacturers a valuable resource to help them sort through issues associated with combustion instabilities. In the last ten years, substantial efforts have been made in the industrial, governmental, and academic communities to understand the unique issues associated with combustion instabilities in low-emission gas turbines. The objective of this book is to compile these results into a series of chapters that address the various facets of the problem. The Case Studies section speaks to specific manufacturer and user experiences with combustion instabilities in the development stage and in fielded turbine engines. The book then goes on to examine The Fundamental Mechanisms, The Combustor Modeling, and Control Approaches.

This paper details the development of a thermoacoustic model and associated dynamic analysis. The model describes the results obtained in a gas fueled experimental combustion program carried out at UTRC. The contents of the paper are (a) the development of a thermoacoustic model composed of acoustic and heat release components, (b) the dynamic analysis of the resulting non-linear model using harmonic balance methods to compute linear stability boundaries and the amplitudes of oscillations and (c) the calibration of the model to experimental data.

We present results of experiment with two distinct extremum-seeking adaptive algorithms for control of combustion instability suitable for reduction of acoustic pressure oscillations in gas turbine over large range of operating conditions. The algorithms consists of a frequency tracking Extended Kalman Filter to determine the in-phase component, the quadrature component, and the magnitude of the acoustic mode of interest, and a phase shifting controller with the controller phase tuned using an extremum-seeking algorithms. The algorithms are also applicable for control of oscillations of systems whose oscillation frequency and optimal control phase shift depends on operating conditions, and which are driven by strong broad-band disturbance. The algorithms have been tested in combustion experiments involving full-scale engine hardware and during simulated fast engine transients.

The increasingly strict regulation for pollutant emissions has recently led engine manufacturers to develop combustors that meet various regulatory requirements. Lean-premixed combustion appears to be the most promising technology for practical systems at the present time. In lean-premixed combustion, the fuel and air are premixed upstream of the combustor to avoid the formation of stoichiometric regions. The combustor is operated with excess air to reduce the flame temperature; consequently, thermal NOx is virtually eliminated. Unsteady flow oscillations, also referred to as combustion instability, have emerged as a common problem, and hindered the development of lean-premixed combustors. These oscillations may reach sufficient amplitudes to interfere with engine operation, and in extreme cases, lead to failure of the system due to excessive structural vibration and heat transfer to the chamber. The book is organized in two parts: an extensive bibliographic review of combustion instabilities and the motivation of this work in part 1; and the study about a new diagnostic methodology for thermoacoustic instability detection and future control in part 2.

This is the first book in the literature to cover the development and testing practices for liquid rocket engines in Russia and the former Soviet Union.Combustion instability represents one of the most challenging probelms in the development of propulsion engines. A famous example is the F-1 engines for the first stage of the Saturn V launch vehicles in the Apollo project. More than 2000 full engine tests and a vast number of design modifications were conducted to cure the instability problem.This book contains first-hand information about the testing and development practices for treating liquid rocket combustion-instability problems in Russia and the former Soviet Union. It covers more than 50 years of research, with an emphasis placed on the advances made since 1970.The book was prepared by a former R&D director of the Research Institute of Chemical Engineering, NIICHIMMASH, the largest liquid rocket testing center in the world, and has been carefully edited by three well-known experts in the field.

Modern, low NOx emitting gas turbines typically utilize lean pre-mixed (LPM) combustion as a means of achieving target emissions goals. As stable combustion in LPM systems is somewhat intolerant to changes in operating conditions, precise engine tuning on a prescribed range of fuel properties is commonly performed to avoid dynamic instabilities. This has raised concerns regarding the use of imported liquefied natural gas (LNG) and natural gas liquids (NGL's) to offset a reduction in the domestic natural gas supply, which when introduced into the pipeline could alter the fuel BTU content and subsequently exacerbate problems such as combustion instabilities. The intent of this study is to investigate the sensitivity of dynamically unstable test rigs to changes in fuel composition and heat content. Fuel Wobbe number was controlled by blending methane and natural gas with various amounts of ethane, propane and nitrogen. Changes in combustion instabilities were observed, in both atmospheric and pressurized test rigs, for fuels containing high concentrations of propane (> 62% by vol). However, pressure oscillations measured while operating on typical "LNG like" fuels did not appear to deviate significantly from natural gas and methane flame responses. Mechanisms thought to produce changes in the dynamic response are discussed.

This paper describes ongoing testing of an adaptive control method to suppress high frequency thermo-acoustic instabilities like those found in lean-burning, low emission combustors that are being developed for future aircraft gas turbine engines. The method called Adaptive Sliding Phasor Averaged Control, was previously tested in an experimental rig designed to simulate a combustor with an instability of about 530 Hz. Results published earlier, and briefly presented here, demonstrated that this method was effective in suppressing the instability. Because this test rig did not exhibit a well pronounced instability, a question remained regarding the effectiveness of the control methodology when applied to a more coherent instability. To answer this question, a modified combustor rig was assembled at the NASA Glenn Research Center in Cleveland, Ohio. The modified rig exhibited a more coherent, higher amplitude instability, but at a lower frequency of about 315 Hz. Test results show that this control method successfully reduced the instability pressure of the lower frequency test rig. In addition, due to a certain phenomena discovered and reported earlier, the so called Intra-Harmonic Coupling, a dramatic suppression of the instability was achieved by focusing control on the second harmonic of the instability. These results and their implications are discussed, as well as a hypothesis describing the mechanism of intra-harmonic coupling. Kopasakis, George and DeLaat, John C. and Chang, Clarence T. Glenn Research Center NASA/TM-2004-213198, AIAA Paper 2004-4028, E-14698