scholarly journals Conversion of Liquid to Gaseous Fuels for Lean Premixed Combustion

1995 ◽  
Author(s):  
B. Stoffel ◽  
L. Reh
Keyword(s):  
Diesel Oil ◽  
Premixed Combustion ◽  
Liquid Fuels ◽  
Fuel Vapor ◽  
Main Process ◽  
Lean Premixed Combustion ◽  
Gaseous Fuels ◽  
Lean Combustion ◽  
Wide Range ◽  
Lean Premixed

The lean premixed combustion of gaseous fuels is an attractive technology to attain very low NOx emission levels in gas turbine engines. If liquid fuels are converted to gaseous fuels by vaporization, they also can be used in premix gas burners and similar low NOx emissions are achievable. Experiments were carried out in a test rig in which the three main process steps of liquid fuel combustion (vaporization of fuel, mixing of air and fuel vapor and combustion reaction) can be performed successively in three separate devices and examined independently. A wide range of liquid fuels (methanol, ethanol, heptane, gasoline, rape oil methyl ester and two diesel oil qualities) was vaporized in an externally heated tube in the presence of superheated steam. These fuel vapors were led to a Pyrocore® radiant burner operating in fully premixed mode at atmosperic pressure. For all fuels without bound nitrogen, NOx levels below 15 mg/m3 at 3% O2 in the dry exhaust gas (2.5 ppm at 15% O2) were measured at lean combustion conditions. However, the nitrogen particularly bound in higher boiling fuels like diesel oil was converted completely to NOx under these conditions. The fuel bound nitrogen (FBN) proved to be the major source of NOx when burning vaporized diesel oil.

Characterizing Combustion of Synthetic and Conventional Fuels in a Toroidal Well Stirred Reactor

2013 ◽  
Author(s):  
Shazib Z. Vijlee ◽  
John C. Kramlich ◽  
Ann M. Mescher ◽  
Scott D. Stouffer ◽  
Alanna R. O’Neil-Abels
Keyword(s):  
Aromatic Compounds ◽  
Chemical Reactor ◽  
Synthetic Jet ◽  
Premixed Combustion ◽  
Liquid Fuels ◽  
Jet Fuels ◽  
Synthetic Fuels ◽  
Lean Premixed Combustion ◽  
Stirred Reactor ◽  
Lean Premixed

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of the performance envelopes and emissions characteristics relative to the behavior of conventional fuels. In this study, experiments in a toroidal well-stirred reactor (TWSR) are used to study lean premixed combustion temperature and extinction behavior for several fuels including simple alkanes, synthetic jet fuels, and conventional JP8. A perfectly stirred reactor (PSR) model is used to interpret the observed behavior. The first portion of the study deals with jet fuels and synthetic jet fuels with varying concentrations of added aromatic compounds. Synthetic fuels contain little or no natural aromatic species, so aromatic compounds are added to the fuel because fuel system seals require these species to function properly. The liquid fuels are prevaporized and premixed before being burned in the TWSR. Air flow is held constant to keep the reactor loading roughly constant. Temperature is monitored inside the reactor as the fuel flow rate is slowly lowered until extinction occurs. The extinction point is defined by both its equivalence ratio and temperature. The measured blowout point is very similar for all four synthetic fuels and the baseline JP8 at aromatic concentrations of up to 20% by volume. Since blowout is essentially the same for all the base fuels at low aromatic concentrations, a single fuel was used to test the effect of aromatic concentrations from 0 to 100%. PSR models of these complex fuels show the expected result that behavior diverges from an ideal, perfectly premixed model as the combustion approaches extinction. The second portion of this study deals with lean premixed combustion of simple gaseous alkanes (methane, ethane, and propane) in the same TWSR. These simpler fuels were tested for extinction in a similar manner to the complex fuels, and behavior was characterized similarly. Once again, PSR models show that the TWSR behaves similar to a PSR during stable combustion far from blowout, but as it approaches blowout and becomes less stable a single PSR no longer accurately describes the TWSR. This work is a step towards developing chemical reactor networks (CRNs) based on computational fluid dynamics (CFD) of the simple gaseous fuels in the TWSR. Ultimately, CRNs are the only realistic way to accurately perform detailed chemical modeling of the combustion of complex liquid fuels.

Experimental Study of NOx Formation in Lean, Premixed, Prevaporized Combustion of Fuel Oils at Elevated Pressures

2007 ◽  
Author(s):  
P. Gokulakrishnan ◽  
M. J. Ramotowski ◽  
G. Gaines ◽  
C. Fuller ◽  
R. Joklik ◽  
...  
Keyword(s):  
Natural Gas ◽  
Ignition Delay ◽  
Pilot Scale ◽  
Combustion Characteristics ◽  
Premixed Combustion ◽  
Fuel Oil ◽  
Liquid Fuels ◽  
Nox Formation ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Dry low Emissions (DLE) systems employing lean, premixed combustion have been successfully used with natural gas in combustion turbines to meet stringent emissions standards. However, the burning of liquid fuels in DLE systems is still a challenging task due to the complexities of fuel vaporization and air premixing. Lean, Premixed, Prevaporized (LPP) combustion has always provided the promise of obtaining low pollutant emissions while burning liquid fuels such as kerosene and fuel oil. Because of the short ignition delay times of these fuels at elevated temperatures, the autoignition of vaporized higher hydrocarbons typical of most practical liquid fuels has proven difficult to overcome when burning in lean, premixed mode. To avoid this autoignition problem, developers of LPP combustion systems have focused mainly on designing premixers and combustors that permit rapid mixing and combustion of fuels before spontaneous ignition of the fuel can occur. However, none of the reported works in the literature has looked at altering fuel combustion characteristics in order to delay the onset of ignition in lean, premixed combustion systems. The work presented in this paper describes the development of a patented low-NOx LPP system for combustion of liquid fuels which modifies the fuel rather than the combustion hardware in order to achieve LPP combustion. In the initial phase of the development, laboratory-scale experiments were performed to study the combustion characteristics, such as ignition delay time and NOx formation, of the liquids fuels that were vaporized into gaseous form in the presence of nitrogen diluent. In phase two, an LPP combustion system was commissioned to perform pilot-scale tests on commercial turbine combustor hardware. These pilot-scale tests were conducted at typical compressor discharge temperatures and at both atmospheric and high pressures. In this study, vaporization of the liquid fuel in an inert environment has been shown to be a viable method for delaying autoignition and for generating a gaseous fuel stream with characteristics similar to natural gas. Tests conducted in both atmospheric and high pressure combustor rigs utilizing swirl-stabilized burners designed for natural gas demonstrated operation similar to that obtained when burning natural gas. Emissions levels were similar for both the LPP fuels (fuel oil #1 and #2) and natural gas, with any differences ascribed to the fuel-bound nitrogen present in the liquid fuels. Extended lean operation was observed for the liquid fuels as a result of the wider lean flammability range for these fuels compared with natural gas. Premature ignition of the LPP fuel was controlled by the level of inert gas in the vaporization process.

NOx Behavior for Lean-Premixed Combustion of Alternative Gaseous Fuels

2015 ◽  
Author(s):  
K. Boyd Fackler ◽  
Megan Karalus ◽  
Igor Novosselov ◽  
John Kramlich ◽  
Philip Malte
Keyword(s):  
Natural Gas ◽  
Heat Loss ◽  
High Intensity ◽  
Combustion Temperature ◽  
Premixed Combustion ◽  
Nox Emission ◽  
Fuel Composition ◽  
Lean Premixed Combustion ◽  
Gaseous Fuels ◽  
Lean Premixed

Gaseous fuels other than pipeline natural gas are of interest in high-intensity premixed combustors (e.g., lean-premixed gas turbine combustors) as a means of broadening the range of potential fuel resources and increasing the utilization of alternative fuel gases. An area of key interest is the change in emissions that accompanies the replacement of a fuel. The work reported here is an experimental and modeling effort aimed at determining the changes in NOx emission that accompany the use of alternative fuels. Controlling oxides of nitrogen (NOx) from combustion sources is essential in non-attainment areas. Lean-premixed combustion eliminates most of the thermal NOx emission, but is still subject to small, though significant amounts of NOx formed by the complexities of free radical chemistry in the turbulent flames of most combustion systems. Understanding these small amounts of NOx, and how their formation is altered by fuel composition, is the objective of this paper. We explore how NOx is formed in high-intensity, lean-premixed flames of alternative gaseous fuels. This is based on laboratory experiments and interpretation by chemical reactor modeling. Methane is used as the reference fuel. Combustion temperature is maintained the same for all fuels so that the effect of fuel composition on NOx can be studied without the complicating influence of changing temperature. Also, the combustion reactor residence time is maintained nearly constant. When methane containing nitrogen and carbon dioxide (e.g., landfill gas) is burned, NOx increases since the fuel/air ratio is enriched in order to maintain combustion temperature. When fuels of increasing C/H ratio are burned leading to higher levels of carbon monoxide (CO) in the flame, or when the fuel contains CO, the free radicals made as the CO oxidizes cause the NOx to increase. In these cases, the change from high-methane natural gas to alternative gaseous fuel causes the NOx to increase. However, when hydrogen is added to the methane, the NOx may increase or decrease, depending on the combustor wall heat loss. In our work, in which combustor wall heat loss is present, hydrogen addition deceases the NOx. This observation is compared to the literature. Additionally, minimum NOx emission is examined by comparing the present results to the findings of Leonard and Stegmaier.

NOx Behavior for Lean-Premixed Combustion of Alternative Gaseous Fuels

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
K. Boyd Fackler ◽  
Megan Karalus ◽  
Igor Novosselov ◽  
John Kramlich ◽  
Philip Malte ◽  
...  
Keyword(s):  
Natural Gas ◽  
Heat Loss ◽  
High Intensity ◽  
Combustion Temperature ◽  
Premixed Combustion ◽  
Nox Emission ◽  
Fuel Composition ◽  
Lean Premixed Combustion ◽  
Gaseous Fuels ◽  
Lean Premixed

Gaseous fuels other than pipeline natural gas are of interest in high-intensity premixed combustors (e.g., lean-premixed gas turbine combustors) as a means of broadening the range of potential fuel resources and increasing the utilization of alternative fuel gases. An area of key interest is the change in emissions that accompanies the replacement of a fuel. The work reported here is an experimental and modeling effort aimed at determining the changes in NOx emission that accompany the use of alternative fuels. Controlling oxides of nitrogen (NOx) from combustion sources is essential in nonattainment areas. Lean-premixed combustion eliminates most of the thermal NOx emission but is still subject to small, although significant amounts of NOx formed by the complexities of free radical chemistry in the turbulent flames of most combustion systems. Understanding these small amounts of NOx, and how their formation is altered by fuel composition, is the objective of this paper. We explore how NOx is formed in high-intensity, lean-premixed flames of alternative gaseous fuels. This is based on laboratory experiments and interpretation by chemical reactor modeling. Methane is used as the reference fuel. Combustion temperature is maintained the same for all fuels so that the effect of fuel composition on NOx can be studied without the complicating influence of changing temperature. Also the combustion reactor residence time is maintained nearly constant. When methane containing nitrogen and carbon dioxide (e.g., landfill gas) is burned, NOx increases because the fuel/air ratio is enriched to maintain combustion temperature. When fuels of increasing C/H ratio are burned leading to higher levels of carbon monoxide (CO) in the flame, or when the fuel contains CO, the free radicals made as the CO oxidizes cause the NOx to increase. In these cases, the change from high-methane natural gas to alternative gaseous fuel causes the NOx to increase. However, when hydrogen is added to the methane, the NOx may increase or decrease, depending on the combustor wall heat loss. In our work, in which combustor wall heat loss is present, hydrogen addition deceases the NOx. This observation is compared to the literature. Additionally, minimum NOx emission is examined by comparing the present results to the findings of Leonard and Stegmaier.

A Novel Low NOx Lean, Premixed, and Prevaporized Combustion System for Liquid Fuels

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
P. Gokulakrishnan ◽  
M. J. Ramotowski ◽  
G. Gaines ◽  
C. Fuller ◽  
R. Joklik ◽  
...  
Keyword(s):  
Natural Gas ◽  
Ignition Delay ◽  
Pilot Scale ◽  
Combustion Characteristics ◽  
Premixed Combustion ◽  
Liquid Fuels ◽  
Combustion System ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Combustion Systems

Dry low emission (DLE) systems employing lean, premixed combustion have been successfully used with natural gas in combustion turbines to meet stringent emission standards. However, the burning of liquid fuels in DLE systems is still a challenging task due to the complexities of fuel vaporization and air premixing. Lean, premixed, and prevaporized (LPP) combustion has always provided the promise of obtaining low pollutant emissions while burning liquid fuels, such as kerosene and fuel oil. Because of the short ignition delay times of these fuels at elevated temperatures, the autoignition of vaporized higher hydrocarbons typical of most practical liquid fuels has been proven difficult to overcome when burning in a lean, premixed mode. To avoid this autoignition problem, developers of LPP combustion systems have focused mainly on designing premixers and combustors that permit rapid mixing and combustion of fuels before spontaneous ignition of the fuel can occur. However, none of the reported works in the literature has looked at altering fuel combustion characteristics in order to delay the onset of ignition in lean, premixed combustion systems. The work presented in this paper describes the development of a patented low NOx LPP system for combustion of liquid fuels, which modifies the fuel rather than the combustion hardware in order to achieve LPP combustion. In the initial phase of the development, laboratory-scale experiments were performed to study the combustion characteristics, such as ignition delay time and NOx formation, of the liquid fuels that were vaporized into gaseous form in the presence of nitrogen diluent. In the second phase, a LPP combustion system was commissioned to perform pilot-scale tests on commercial turbine combustor hardware. These pilot-scale tests were conducted at typical compressor discharge temperatures and at both atmospheric and high pressures. In this study, vaporization of the liquid fuel in an inert environment has been shown to be a viable method for delaying autoignition and for generating a gaseous fuel stream with characteristics similar to natural gas. Tests conducted in both atmospheric and high pressure combustor rigs utilizing swirl-stabilized burners designed for natural gas demonstrated an operation similar to that obtained when burning natural gas. Emission levels were similar for both the LPP fuels (fuel oils 1 and 2) and natural gas, with any differences ascribed to the fuel-bound nitrogen present in the liquid fuels. An extended lean operation was observed for the liquid fuels as a result of the wider lean flammability range for these fuels compared to natural gas.

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.

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