scholarly journals Experimental investigation of oscillatory heat release mechanisms and stability margin analysis in lean -premixed combustion

2005 ◽  
Author(s):  
Don H. Ferguson
Keyword(s):  
Experimental Investigation ◽  
Heat Release ◽  
Stability Margin ◽  
Premixed Combustion ◽  
Lean Premixed Combustion ◽  
Release Mechanisms ◽  
Lean Premixed ◽  
Margin Analysis

Nonlinear combustion instability analysis of a bluff body burner based on the flame describing function

2021 ◽  
pp. 095441002110440
Author(s):  
Yipin Lu ◽  
Yinli Xiao ◽  
Juan Wu ◽  
Liang Chen
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Premixed Combustion ◽  
Single Frequency ◽  
Describing Function ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Flame Describing Function ◽  
Frequency Harmonic

Lean premixed combustion is a common form of combustion organization in power equipment and propulsion systems. In order to understand the dynamic characteristics of lean premixed flame and predict and control its combustion instability, it is necessary to obtain its flame describing function (FDF). Based on the open source CFD toolbox, OpenFOAM, the dynamic K-equation model, and the finite rate Partially Stirred Reactor (PaSR) model were used to perform large eddy simulations (LES) of lean premixed combustion, and the response of the unsteady heat release rate to single-frequency harmonic disturbances was studied. The response of the unsteady heat release rate was characterized by the FDF, and the response of the unsteady heat release rate to the two-frequency harmonic disturbance was studied. The results show that the quantitative heat release rate response and flame dynamics have very proper accuracy. In the single-frequency harmonic disturbance, as the forcing frequency increases, the curling behavior of the flame surface and the instantaneous vortex structure change; the nonlinear kinematics effect is manifested by the entrainment of the vortex. At lower forcing frequencies, the heat release response changes linearly with the increase of forcing amplitude; at intermediate frequencies, the heat release response exhibits obvious nonlinear behavior; at high frequencies, the heat release response to amplitude changes decreases. The introduction of the second harmonic disturbance will significantly reduce the response range of the total heat release rate and make the combustion more stable.

Simplified Models for NOx Production Rates in Lean-Premixed Combustion

1994 ◽  
Author(s):  
David G. Nicol ◽  
Philip C. Malte ◽  
Robert C. Steele
Keyword(s):  
Laboratory Data ◽  
Chemical Reactor ◽  
Premixed Combustion ◽  
Empirical Correlations ◽  
Simplified Models ◽  
Reactor Modeling ◽  
Lean Premixed Combustion ◽  
Co Concentration ◽  
Lean Premixed ◽  
Recent Laboratory

Simplified models for predicting the rate of production of NOx in lean-premixed combustion are presented. These models are based on chemical reactor modeling, and are influenced strongly by the nitrous oxide mechanism, which is an important source of NOx in lean-premixed combustion. They include 1) the minimum set of reactions required for predicting the NOx production, and 2) empirical correlations of the NOx production rate as a function of the CO concentration. The later have been developed for use in an NOx post-processor for CFD codes. Also presented are recent laboratory data, which support the chemical rates used in this study.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Numerical Simulation of Turbulent Combustion Flows for Coaxial Jet Cluster Burner

2013 ◽  
Author(s):  
Keita Yunoki ◽  
Tomoya Murota ◽  
Keisuke Miura ◽  
Teruyuki Okazaki
Keyword(s):  
Turbulent Combustion ◽  
High Efficiency ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Gas Temperature ◽  
Lean Premixed Combustion ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Lean Premixed ◽  
Multiple Holes

We have developed a burner for the gas turbine combustor, which was high efficiency and low environmental load. This burner is named the “coaxial jet cluster burner” and, as the name indicates, it has multiple fuel nozzles and holes in a coaxial arrangement. To form lean premixed combustion, this burner mixes fuel and air in the multiple holes rapidly. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing. However, the combustion field coexisting with premixed and non-premixed combustion is complicated. The phenomena that occur in the combustion field should be understood in detail. Therefore, we have developed the hybrid turbulent combustion (HTC) model to calculate the form in which non-premixed flame coexists with premixed flame. Turbulent flow has been simulated using a large eddy simulation (LES) with a dynamic sub grid scale (SGS) model coupled with the HTC model. These models were programmed to a simulation tool based on the OpenFOAM library. However, there were unclear points about their applicability to an actual machine evaluation and the predictive precision of CO concentration which affects burner performance. In this study, we validate the HTC model by comparing its results with measured gas temperature and gas concentration distributions obtained with a coaxial jet cluster burner test rig under atmospheric pressure. In addition, we analyze the CO generation mechanism for the lean premixed combustion in the burner.

Direct Numerical Simulation of Partial Fuel Stratification Assisted Lean Premixed Combustion for Assessment of Hybrid G-Equation/Well-Stirred Reactor Model

2021 ◽  
Author(s):  
Chao Xu ◽  
Muhsin Ameen ◽  
Pinaki Pal ◽  
Sibendu Som
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Initial Conditions ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Lean Premixed Combustion ◽  
Fuel Stratification ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
Flame Structures

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames, and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that conventional triple flame structures are prevalent during the initial stage of flame kernel growth. Both premixed and non-premixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis reveals the effects of flame stretch and fuel pyrolysis on the flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for PFS-assisted lean operation in the LES context. The G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the non-premixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

Development of a Natural Gas-Fired, Ultra-Low NOx Can Combustor for an 800 KW Gas Turbine

1991 ◽  
Author(s):  
K. O. Smith ◽  
A. C. Holsapple ◽  
H. K. Mak ◽  
L. Watkins
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Premixed Combustion ◽  
Experimental Results ◽  
Nox Emissions ◽  
Variable Geometry ◽  
Lean Premixed Combustion ◽  
Full Load ◽  
Primary Zone ◽  
Lean Premixed

The experimental results from the rig testing of an ultra-low NOx, natural gas-fired combustor for an 800 to 1000 kw gas turbine are presented. The combustor employed lean-premixed combustion to reduce NOx emissions and variable geometry to extend the range over which low emissions were obtained. Testing was conducted using natural gas and methanol. Testing at combustor pressures up to 6 atmospheres showed that ultra-low NOx emissions could be achieved from full load down to approximately 70% load through the combination of lean-premixed combustion and variable primary zone airflow.

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