The Combustion of Lean Mixtures of Methane and Air—A Kinetic Investigation

1986 ◽  
Vol 108 (4) ◽  
pp. 336-342 ◽  
Author(s):  
M. Hanna ◽  
G. A. Karim
Keyword(s):  
Combustion Process ◽  
Kinetic Scheme ◽  
Reaction Rates ◽  
Chemical Kinetic ◽  
Energy Utilization ◽  
Wide Range ◽  
Lean Mixtures ◽  
The Times ◽  
Combustion Processes ◽  
Detailed Chemical

The combustion of lean mixtures of methane, representing natural gas, in air is examined analytically employing a detailed chemical kinetic scheme involving 14 species and made up of 32 reaction steps that proceed simultaneously. The changes with time in the concentrations of the major relevant reactive species are determined throughout, right from the commencement of the preignition reactions to the time of achieving near equilibrium conditions. The results of such an approach to the combustion process are considered over a wide range of temperature (1200 K–2200 K) and equivalence ratios (from 0.20 to the stoichiometric value). Information is then presented in relation to some important combustion parameters that included the ignition delay, overall reaction rates and the times needed for completing the combustion process. Some guidelines are suggested for effecting eventually improved energy utilization and reduced environmental pollution from combustion processes involving lean mixtures of methane and air.

An Analytical Examination of the Partial Oxidation of Rich Mixtures of Methane and Oxygen

1992 ◽  
Vol 114 (2) ◽  
pp. 152-157 ◽  
Author(s):  
G. A. Karim ◽  
A. S. Hanafi
Keyword(s):  
Partial Oxidation ◽  
Equivalence Ratio ◽  
Kinetic Scheme ◽  
Reaction Rates ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Wide Range ◽  
Rich Mixtures ◽  
Detailed Chemical

The uncatalyzed partial oxidation of rich mixtures of methane and oxygen is examined analytically, primarily with the view of hydrogen and/or synthesis gas (hydrogen plus carbon monoxide) production while employing a detailed chemical kinetic scheme of 108 simultaneous reactions and 28 species. The role of various operating conditions in establishing the yield of hydrogen and other products, the corresponding ignition delay periods and reaction rates is examined over a wide range of temperature, equivalence ratio and pressure. Correlations in terms of simple overall Arrhenius expressions are also provided.

Use of Detailed Chemical Kinetics to Study HCCI Engine Combustion With Consideration of Turbulent Mixing Effects

2002 ◽  
Vol 124 (3) ◽  
pp. 702-707 ◽  
Author(s):  
S.-C. Kong ◽  
R. D. Reitz
Keyword(s):  
Chemical Kinetics ◽  
Turbulent Mixing ◽  
Combustion Process ◽  
Reaction Rates ◽  
Detailed Chemical Kinetics ◽  
Wide Range ◽  
Hcci Engines ◽  
Heavy Duty Diesel ◽  
Flame Chemistry ◽  
Detailed Chemical

Detailed chemical kinetics was used in an engine CFD code to study the combustion process in HCCI engines. The CHEMKIN code was implemented in KIVA such that the chemistry and flow solutions were coupled. The reaction mechanism consists of hundreds of reactions and species and is derived from fundamental flame chemistry. Effects of turbulent mixing on the reaction rates were also considered. The results show that the present KIVA/CHEMKIN model is able to simulate the ignition and combustion process in three different HCCI engines including a CFR engine and two modified heavy-duty diesel engines. Ignition timings were predicted correctly over a wide range of engine conditions without the need to adjust any kinetic constants. However, it was found that the use of chemical kinetics alone was not sufficient to accurately simulate the overall combustion rate. The effects of turbulent mixing on the reaction rates need to be considered to correctly simulate the combustion and heat release rates.

Simplified Descriptions of Cool-Flame Chemistry

2015 ◽  
Vol 229 (4) ◽  
Author(s):  
Forman A. Williams
Keyword(s):  
Chemical Kinetic ◽  
Essential Elements ◽  
Chemical Processes ◽  
Normal Alkanes ◽  
Alkyl Radicals ◽  
Future Developments ◽  
Large Numbers ◽  
Flame Chemistry ◽  
Combustion Processes ◽  
Detailed Chemical

AbstractCorrect detailed chemical-kinetic descriptions of the consequences of the additions of oxygen molecules to alkyl radicals involve large numbers of elementary steps. The resulting complexity of the system of equations needed to describe combustion processes often taxes computational capabilities. Simplified descriptions of the chemical kinetics that retain essential elements of the results therefore can be useful for a number of purposes, even though they fail to include many of the chemical processes. Such simplified descriptions for combustion processes are presented here for certain normal alkanes. Their potential utility and prospects for future developments are discussed.

Combustion Quasi-Two Zone Predictive Model for Dual Fuel Engines

1999 ◽  
Author(s):  
G. H. Abd Alla ◽  
H. A. Soliman ◽  
O. A. Badr ◽  
M. F. Abd Rabbo
Keyword(s):  
Predictive Model ◽  
Combustion Process ◽  
Chemical Species ◽  
Kinetic Scheme ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Gaseous Fuel ◽  
Combustion Model ◽  
Dual Fuel ◽  
Dual Fuel Engines

Abstract A quasi-two zone predictive model developed in the present work for the prediction of the combustion processes in dual fuel engines and some of their performance features. Methane is used as the main fuel while employing a small quantity of liquid fuel (pilot) injected through the conventional diesel fuel system. This model emphasizes the effects of chemical kinetics activity of the premixed gaseous fuel on the combustion performance, while the role of the pilot fuel in the ignition and heat release processes is considered. A detailed chemical kinetic scheme consists of 178 elementary reaction steps and 41 chemical species is employed to describe the oxidation of the gaseous fuel from the start of compression to the end of expansion process. The associated formation and concentrations of exhaust emissions are correspondingly established. This combustion model is able to establish the development of the combustion process with time and the associated important operating parameters such as pressure, temperature, rates of energy release and composition. Predicted values for methane operation show good agreement with corresponding previous experimental values over a range of operating conditions mainly associated with high load operation.

scholarly journals Semianalytical Correlations for NOx, CO, and UHC Emissions

1992 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Kinetic Scheme ◽  
Large Data ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Emission Model ◽  
Future Goals ◽  
Unburned Hydrocarbon ◽  
Annular Combustor ◽  
Analytical Approaches ◽  
Detailed Chemical

To meet the future goals of reduced emissions produced by gas turbine combustors, a better understanding of the process of formation of various pollutants is required. Both empirical and analytical approaches are used to provide the exhaust concentrations of pollutants of interest such as NOx, CO, and unburned hydrocarbon with varying degrees of success. In the present investigation, an emission model that simulates the combustor by a number of reactors representing various combustion zones is proposed. A detailed chemical kinetic scheme was used to provide a fundamental basis for the derivation of a number of expressions that simulate the reaction scheme. The model addresses the combined effects of spray evaporation and mixing in the reaction zone. The model validation included the utilization of a large data base obtained for an annular combustor of a modern turbopropulsion engine. In addition to the satisfactory agreement with the measurements, the model provided insight into the regions within the combustor that could be responsible for the excessive formation of emissions. Methods to reduce the emissions may be implemented in light of such information.

A Numerical Study of the Unsteady Effects of Droplet Evaporation and Ignition in Homogeneous Environments of Fuel and Air

1994 ◽  
Vol 116 (3) ◽  
pp. 194-200 ◽  
Author(s):  
P. Samuel ◽  
G. A. Karim
Keyword(s):  
Numerical Study ◽  
Reaction Rates ◽  
Detailed Chemical Kinetics ◽  
Surrounding Environment ◽  
Unsteady Effects ◽  
Combustion Processes ◽  
Effective Reaction ◽  
Detailed Chemical ◽  
Homogeneous Environment ◽  
Effective Reaction Rate

The transient processes of droplet heating, vaporization and ignition in a quiescent heated environment of a homogeneous mixture of air and fuel that is potentially combustible are analyzed. A system of partial differential equations that governs this hybrid diffusional-premixed processes is presented. The equations were solved numerically for an n-heptane droplet vaporizing in a homogeneous environment of methane and air. The effective reaction rate of the oxidation processes was assumed throughout to equal the sum of the reaction rates due to droplet and auxiliary fuels. The gross reaction rates used in the model for the droplet and auxiliary fuels were obtained from curve fitting of reaction rates results obtained from detailed chemical kinetics for the two fuels system. It is to be shown, for example, that the presence of an auxiliary fuel with the air in the surrounding environment of the droplet enhances the rates of the ignition/combustion processes of the droplet.

Three-Dimensional Gas Turbine Combustor Emissions Modeling

1992 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Three Dimensional ◽  
Kinetic Scheme ◽  
Reaction Rates ◽  
Chemical Kinetic ◽  
Emission Model ◽  
Pollutant Formation ◽  
Emissions Modeling ◽  
Pollutant Concentrations ◽  
Mathematical Expressions ◽  
And Performance

An emission model that combines the analytical capabilities of 3-D combustor performance codes with mathematical expressions based on detailed chemical kinetic scheme is formulated. The expressions provide the trends of formation and/or the consumption of NOx, CO, and UHC in various regions of the combustor utilizing the details of the flow and combustion characteristics given by the 3-D analysis. By this means, the optimization of the combustor design to minimize pollutant formation and maintain satisfactory stability and performance could be achieved. The developed model was used to calculate the emissions produced by several engine combustors that varied significantly in design and concept, and operated on both conventional and high density fuels. The calculated emissions agreed well with the measurements. The model also provided insight into the regions in the combustor where excessive emissions were formed, and helped to understand the influence of the combustor details and air admission arrangement on reaction rates and pollutant concentrations.

Semianalytical Correlations for NOx, CO, and UHC Emissions

1993 ◽  
Vol 115 (3) ◽  
pp. 612-619 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Kinetic Scheme ◽  
Large Data ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Emission Model ◽  
Future Goals ◽  
Unburned Hydrocarbon ◽  
Annular Combustor ◽  
Analytical Approaches ◽  
Detailed Chemical

To meet the future goals of reduced emissions produced by gas turbine combustors, a better understanding of the process of formation of various pollutants is required. Both empirical and analytical approaches are used to provide the exhaust concentrations of pollutants of interest such as NOx, CO, and unburned hydrocarbon with varying degrees of success. In the present investigation, an emission model that simulates the combustor by a number of reactors representing various combustion zones is proposed. A detailed chemical kinetic scheme was used to provide a fundamental basis for the derivation of a number of expressions that simulate the reaction scheme. The model addresses the combined effects of spray evaporation and mixing in the reaction zone. The model validation included the utilization of a large data base obtained for an annular combustor of a modern turbopropulsion engine. In addition to the satisfactory agreement with the measurements, the model provided insight into the regions within the combustor that could be responsible for the excessive formation of emissions. Methods to reduce the emissions may be implemented in light of such information.

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