scholarly journals Multi-Dimensional Computational Combustion of Highly Dilute, Premixed Spark-Ignited Opposed-Piston Gasoline Engine Using Direct Chemistry With a New Primary Reference Fuel Mechanism

2017 ◽  
Author(s):  
Anshul Mittal ◽  
Sameera D. Wijeyakulasuriya ◽  
Dan Probst ◽  
Siddhartha Banerjee ◽  
Charles E. A. Finney ◽  
...  
Keyword(s):  
Chemical Kinetics ◽  
Gasoline Engine ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Chemical Mechanism ◽  
Detailed Chemical Kinetics ◽  
Detailed Chemistry ◽  
Primary Reference

This work presents a modeling approach for multidimensional combustion simulations of a highly dilute opposed-piston spark-ignited gasoline engine. Detailed chemical kinetics is used to model combustion with no sub-grid correction for reaction rates based on the turbulent fluctuations of temperature and species mass fractions. Turbulence is modeled using RNG k-ε model and the RANS-length scales resolution is done efficiently by the use of automatic mesh refinement when and where the flow parameter curvature (2nd derivative) is large. The laminar flame is thickened by the RANS viscosity and a constant turbulent Schmidt (Sc) number and a refined mesh (sufficient to resolve the thickened turbulent flame) is used to get accurate predictions of turbulent flame speeds. An accurate chemical kinetics mechanism is required to model flame kinetics and fuel burn rates under the conditions of interest. For practical computational fluid dynamics applications, use of large detailed chemistry mechanisms with 1000s of species is both costly as well as memory intensive. For this reason, skeletal mechanisms with a lower number of species (typically ∼100) reduced under specific operating conditions are often used. In this work, a new primary reference fuel chemical mechanism is developed to better correlate with the laminar flame speed data, relevant for highly dilute engine conditions. Simulations are carried out in a dilute gasoline engine with opposed piston architecture, and results are presented here across various dilution conditions.

A predictive combustion model for one-dimensional gasoline engine simulation

2020 ◽  
pp. 146808742094590
Author(s):  
Yoshihiro Nomura ◽  
Seiji Yamamoto ◽  
Makoto Nagaoka ◽  
Stephan Diel ◽  
Kenta Kurihara ◽  
...  
Keyword(s):  
Gasoline Engine ◽  
Early Stage ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Operating Conditions ◽  
Combustion Model ◽  
One Dimensional ◽  
Turbulent Reynolds Number ◽  
Proposed Model ◽  
Wide Range

A new predictive combustion model for a one-dimensional computational fluid dynamics tool in the multibody dynamics processes of gasoline engines was developed and validated. The model consists of (1) a turbulent burning velocity model featuring a flame radius–based transitional function, steady burning velocity that considers local quenching using the Karlovitz number and laminarization by turbulent Reynolds number, as well as turbulent flame thickness and its quenching model near the liner wall, and (2) a knock model featuring auto-ignition by the Livengood–Wu integration and ignition delay time obtained using a full-kinetic model. The proposed model and previous models were verified under a wide range of operating conditions using engines with widely different specifications. Good agreement was only obtained for combustion characteristics by the proposed model without requiring individual calibration of model constants. The model was also evaluated for utilization after prototyping. Improved accuracy, especially of ignition timing, was obtained after further calibration using a small amount of engine data. It was confirmed that the proposed model is highly accurate at the early stage of the engine development process, and is also applicable for engine calibration models that require higher accuracy.

A NOx Prediction Scheme for Lean-Premixed Gas Turbine Combustion Based on Detailed Chemical Kinetics

1996 ◽  
Vol 118 (4) ◽  
pp. 765-772 ◽  
Author(s):  
W. Polifke ◽  
K. Do¨bbeling ◽  
T. Sattelmayer ◽  
D. G. Nicol ◽  
P. C. Malte
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Concentration Field ◽  
Operating Conditions ◽  
Chemical Mechanism ◽  
Reacting Flow ◽  
Oxides Of Nitrogen ◽  
Detailed Chemical Kinetics ◽  
Nox Formation ◽  
Lean Premixed

The lean-premixed technique has proven very efficient in reducing the emissions of oxides of nitrogen (NOx) from gas turbine combustors. The numerical prediction of NOx levels in such combustors with multidimensional CFD codes has only met with limited success so far. This is to some extent due to the complexity of the NOx formation chemistry in lean-premixed combustion, i.e., all three known NOx formation routes (Zeldovich, nitrous, and prompt) can contribute significantly. Furthermore, NOx formation occurs almost exclusively in the flame zone, where radical concentrations significantly above equilibrium values are observed. A relatively large chemical mechanism is therefore required to predict radical concentrations and NOx formation rates under such conditions. These difficulties have prompted the development of a NOx postprocessing scheme, where rate and concentration information necessary to predict NOx formation is taken from one-dimensional combustion models with detailed chemistry and provided—via look-up tables—to the multidimensional CFD code. The look-up tables are prepared beforehand in accordance with the operating conditions and are based on CO concentrations, which are indicative of free radical chemistry. Once the reacting flow field has been computed with the main CFD code, the chemical source terms of the NO transport equation, i.e., local NO formation rates, are determined from the reacting flow field and the tabulated chemical data. Then the main code is turned on again to compute the NO concentration field. This NOx submodel has no adjustable parameters and converges very quickly. Good agreement with experiment has been observed and interesting conclusions concerning superequilibrium O-atom concentrations and fluctuations of temperature could be drawn.

High-Speed Spectrally Resolved Imaging Studies of Spherically Expanding Natural Gas Flames Under Gas Turbine Operating Conditions

2019 ◽  
Author(s):  
Pradeep Parajuli ◽  
Tyler Paschal ◽  
Mattias A. Turner ◽  
Eric L. Petersen ◽  
Waruna D. Kulatilaka
Keyword(s):  
Natural Gas ◽  
Flame Front ◽  
Gas Turbines ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Initial Pressure ◽  
Flame Speed ◽  
Operating Conditions ◽  
Important Species

Abstract Natural gas is a major fuel source for many industrial and power-generation applications. The primary constituent of natural gas is methane (CH4), while smaller quantities of higher order hydrocarbons such as ethane (C2H6) and propane (C3H8) can also be present. Detailed understanding of natural gas combustion is important to obtain the highest possible combustion efficiency with minimal environmental impact in devices such as gas turbines and industrial furnaces. For a better understanding the combustion performance of natural gas, several important parameters to study are the flame temperature, heat release zone, flame front evolution, and laminar flame speed as a function of flame equivalence ratio. Spectrally and temporally resolved, high-speed chemiluminescence imaging can provide direct measurements of some of these parameters under controlled laboratory conditions. A series of experiments were performed on premixed methane/ethane-air flames at different equivalence ratios inside a closed flame speed vessel that allows the direct observation of the spherically expanding flame front. The vessel was filled with the mixtures of CH4 and C2H6 along with respective partial pressures of O2 and N2, to obtain the desired equivalence ratios at 1 atm initial pressure. A high-speed camera coupled with an image intensifier system was used to capture the chemiluminescence emitted by the excited hydroxyl (OH*) and methylidyne (CH*) radicals, which are two of the most important species present in the natural gas flames. The calculated laminar flame speeds for an 80/20 methane/ethane blend based on high-speed chemiluminescence images agreed well with the previously conducted Z-type schlieren imaging-based measurements. A high-pressure test, conducted at 5 atm initial pressure, produced wrinkles in the flame and decreased flame propagation rate. In comparison to the spherically expanding laminar flames, subsequent turbulent flame studies showed the sporadic nature of the flame resulting from multiple flame fronts that were evolved discontinuously and independently with the time. This paper documents some of the first results of quantitative spherical flame speed experiments using high-speed chemiluminescence imaging.

scholarly journals Evaluation of Reduced Kinetics in Simulation of Gasified Biomass Gas Combustion

2013 ◽  
Author(s):  
Xiaoxiang Zhang ◽  
Nur Farizan Munjat ◽  
Jeevan Jayasuriya ◽  
Reza Fakhrai ◽  
Torsten Fransson
Keyword(s):  
Gas Turbine ◽  
Chemical Kinetics ◽  
Cfd Simulation ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Turbulent Flame Speed ◽  
Operation Conditions ◽  
Simulation Results ◽  
Gas Turbine Combustion

It is essentially important to use appropriate chemical kinetic models in the simulation process of gas turbine combustion. To integrate the detailed kinetics into complex combustion simulations has proven to be a computationally expensive task with tens to thousands of elementary reaction steps. It has been suggested that an appropriate simplified kinetics which are computationally efficient could be used instead. Therefore reduced kinetics are often used in CFD simulation of gas turbine combustion. At the same time, simplified kinetics for specific fuels and operation conditions need to be carefully selected to fulfill the accuracy requirements. The applicability of several simplified kinetics for premixed Gasified Biomass Gas (GBG) and air combustion are evaluated in this paper. The current work is motivated by the growing demand of gasified biomass gas (GBG) fueled combustion. Even though simplified kinetic schemes developed for hydrocarbon combustions are published by various researchers, there is little research has been found in literature to evaluate the ability of the simplified chemical kinetics for the GBG combustion. The numerical Simulation tool “CANTERA” is used in the current study for the comparison of both detailed and simplified chemical kinetics. A simulated gas mixture of CO/H2/CH4/CO2/N2 is used for the current evaluation, since the fluctuation of GBG components may have an unpredictable influence on the simulation results. The laminar flame speed has an important influence with flame stability, extinction limits and turbulent flame speed, here it is chosen as an indicator for validation. The simulation results are compared with the experimental data from the previous study [1] which is done by our colleagues. Water vapour which has shown a dilution effect in the experimental study are also put into concern for further validation. As the results indicate, the reduced kinetics which are developed for hydrocarbon or hydrogen combustion need to be highly optimized before using them for GBG combustion. Further optimization of the reduced kinetics is done for GBG and moderate results are achieved using the optimized kinetics compared with the detailed combustion kinetics.

Modeling of Emissions in a Laboratory Swirl Combustor

2015 ◽  
Author(s):  
Viswanath R. Katta ◽  
William M. Roquemore
Keyword(s):  
Chemical Kinetics ◽  
Numerical Study ◽  
Flame Structure ◽  
Detailed Chemical Kinetics ◽  
Swirl Combustor ◽  
Detailed Chemistry ◽  
Hydrocarbon Emission ◽  
Recirculation Zones ◽  
Fuel Mixtures ◽  
Detailed Chemical

A swirl-stabilized combustor utilizes recirculation zones for stabilizing the flame. The performance of such combustors could depend on the fuel used as the cracked fuel products may enter the recirculation-zones and alter their characteristics. A numerical study is conducted for understanding the effects of fuel variation on the combustion and unburned-hydrocarbon-emission characteristics of a laboratory swirl combustor. A time-dependent, detailed-chemistry CFD model UNICORN is used. Six binary fuel mixtures formulated with n-dodecane and n-heptane, m-xylene, iso-octane or hexadecane are considered. A semi-detailed chemical-kinetics model (CRECK-0810) involving 206 species and 5652 reactions for the combustion of these fuels is incorporated into UNICORN code. Calculations are performed for a fuel-lean condition, which represents cruise operation of an aircraft. Combustor flows simulated with different fuel mixtures yielded nearly the same flowfields and flame structures. Production of the intermediate cracked fuel species that are key for the final flame structure and emissions seems to be independent of the fuel used. This finding could greatly simplify the detailed chemical kinetics used for obtaining cracked products. As the cracked fuel species are completely consumed with in the flame zone, no emissions are observed at the combustor exit for the considered fuel-lean condition.

Biogas Combustion and Chemical Kinetics for Gas Turbine Applications

2008 ◽  
Author(s):  
Saeed Jahangirian ◽  
Abraham Engeda
Keyword(s):  
Gas Turbine ◽  
Chemical Kinetics ◽  
Laminar Flame ◽  
Biogas Production ◽  
Agricultural Waste ◽  
Detailed Chemical Kinetics ◽  
Fuel Blends ◽  
Reduced Mechanism ◽  
Turbine Design ◽  
Detailed Chemical

Biogas is produced from anaerobic digestion of biodegradable materials such as agricultural waste, animal waste, and municipal solid waste and its main constituents are CH4 and CO2. A review of biogas production and benefits as well as its combustion as an alternative gas turbine fuel is presented. To further understand the characteristics of biogas combustion, a detailed chemical kinetics study of biogas is conducted using the GRI-Mech 3.0 and the San Diego detailed mechanisms and a reduced mechanism in a counterflow configuration. Ignition delays and laminar flame speeds of some gaseous fuel blends which simulate biogas are calculated. Effects of the concentration of each species in the blend are discussed as well as its chemical contribution in the biogas combustion. Approximate analytical correlations are extracted from these results for quantitative predictions. Results of this study will provide valuable data both for gas turbine manufacturers and for biogas producers to modify the gas turbine design for biogas and to figure out how much cleaning and upgrading is required for biogas turbines.

Ignition Delay Time and Laminar Flame Speed Calculations for Natural Gas/Hydrogen Blends at Elevated Pressures

2012 ◽  
Author(s):  
Marissa Brower ◽  
Eric Petersen ◽  
Wayne Metcalfe ◽  
Henry J. Curran ◽  
Marc Füri ◽  
...  
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Chemical Kinetics ◽  
Ignition Delay ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Hydrogen Addition

Applications of natural gas and hydrogen co-firing have received increased attention in the gas turbine market, which aims at higher flexibility due to concerns over the availability of fuels. While much work has been done in the development of a fuels database and corresponding chemical kinetics mechanism for natural gas mixtures, there are nonetheless few if any data for mixtures with high levels of hydrogen at conditions of interest to gas turbines. The focus of the present paper is on gas turbine engines with primary and secondary reaction zones as represented in the Alstom and Rolls Royce product portfolio. The present effort includes a parametric study, a gas turbine model study, and turbulent flame speed predictions. Using a highly optimized chemical kinetics mechanism, ignition delay times and laminar burning velocities were calculated for fuels from pure methane to pure hydrogen and with natural gas/hydrogen mixtures. A wide range of engine-relevant conditions were studied: pressures from 1 to 30 atm, flame temperatures from 1600 to 2200 K, primary combustor inlet temperature from 300 to 900 K, and secondary combustor inlet temperatures from 900 to 1400 K. Hydrogen addition was found to increase the reactivity of hydrocarbon fuels at all conditions by increasing the laminar flame speed and decreasing the ignition delay time. Predictions of turbulent flame speeds from the laminar flame speeds show that hydrogen addition affects the reactivity more when turbulence is considered. This combined effort of industrial and university partners brings together the know-how of applied, as well as experimental and theoretical disciplines.

Prediction of Ultra-Lean SI Engine Performance by QD-Combustion Model With an Improved Laminar Flame Speed

2020 ◽  
Author(s):  
Ratnak Sok ◽  
Jin Kusaka ◽  
Kyohei Yamaguchi
Keyword(s):  
Gasoline Engine ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Flame Speed ◽  
Combustion Model ◽  
Lean Mixture ◽  
Turbulent Flame Speed

Abstract A quasi-dimensional (QD) simulation model is a preferred method to predict combustion in the gasoline engines with reliable results and shorter calculation time compared with multi-dimensional simulation. The combustion phenomena in spark ignition (SI) engines are highly turbulent, and at initial stage of the combustion process, turbulent flame speed highly depends on laminar burning velocity SL. A major parameter of the QD combustion model is an accurate prediction of the SL, which is unstable under low engine speed and ultra-lean mixture. This work investigates the applicability of the combustion model for evaluating the combustion characteristics of a high-tumble port gasoline engine operated under ultra-lean mixture (equivalence ratio up to ϕ = 0.5) which is out of the range of currently available SL functions initially developed for a single component fuel. In this study, the SL correlation is improved for a gasoline surrogate fuel (5 components). Predicted SL data from the conventional and improved functions are compared with experimental SL data taken from a constant-volume chamber under micro-gravity condition. The SL measurements are done at reference conditions at temperature of 300K, pressure of 0.1MPaa, and at elevated conditions whose temperature = 360K, pressure = 0.1, 0.3, and 0.5 MPaa. Results show that the conventional SL model over-predicts flame speeds under all conditions. Moreover, the model predicts negative SL at very lean (ϕ ≤ 0.3) and rich (ϕ ≥ 1.9) mixture while the revised SL is well validated with the measured data. The improved SL formula is then incorporated into the QD combustion model by a user-defined function in GT-Power simulation. The engine experimental data are taken at 1000 RPM and 2000 RPM under engine load IMEPn = 0.4–0.8 MPa (with 0.1 increment) and ϕ ranges are up to 0.5. The results shows that the simulated engine performances and combustion characteristics are well validated with the experiments within 6% accuracy by using the QD combustion model coupled with the improved SL. A sensitivity analysis of the model is also in good agreement with the experiments under cyclic variation (averaged cycle, high IMEP or stable cycle, and low IMEP or unstable cycle).

scholarly journals Empirical investigation of spark-ignited flame-initiation cycle-to-cycle variability in a homogeneous charge reciprocating engine

2017 ◽  
Vol 19 (5) ◽  
pp. 491-508 ◽  
Author(s):  
Philipp Schiffmann ◽  
David L Reuss ◽  
Volker Sick
Keyword(s):  
Mass Fraction ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Operating Conditions ◽  
Strain Rate Tensor ◽  
Flame Velocity ◽  
Fuel Mass ◽  
Markstein Number ◽  
Fuel Mass Fraction ◽  
Homogeneous Charge

This experimental study investigates the flame-initiation period variability in the spark-ignited homogeneous charge third-generation transparent combustion chamber optical engine. The engine was operated with lean, rich, and stoichiometric, propane and methane, with and without nitrogen dilution. These operating conditions were chosen to systematically change the unstretched laminar flame velocity and the Markstein number. Traditional pressure measures, apparent heat release analysis, particle image velocimetry, and OH* flame imaging were used to generate over 400 metrics for 750 cycles at each of the 34 tests at 11 operating conditions. A multivariate statistical analysis was used to identify the parameters important to the variability of the crank angle at 10% fuel mass fraction burned but could not reveal physical mechanisms or cause and effect. The analysis here revealed that the combustion-phasing cycle-to-cycle variability is established by the time of the notional laminar-to-turbulent flame transition that occurs by 1% mass burn fraction, measured here from the flame image growth. Both the Markstein number and stretched laminar flame speed were found to be important. The velocity magnitude and direction were found to correlate with fast and slow 10% fuel mass fraction burned as found in early literature. It was also revealed that the shear strength, a property of the strain rate tensor at the scales resolved here (1 mm), deserves further investigation as a possible effect on 10% fuel mass fraction burned.

Quasidimensional Modeling of Diesel Combustion Using Detailed Chemical Kinetics

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Aron P. Dobos ◽  
Allan T. Kirkpatrick
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Chemical Kinetics ◽  
Computational Cost ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Detailed Chemical Kinetics ◽  
Air Mixing ◽  
Primary Reference ◽  
Detailed Chemical

This paper presents an efficient approach to diesel engine combustion simulation that integrates detailed chemical kinetics into a quasidimensional fuel spray model. The model combines a discrete spray parcel concept to calculate fuel-air mixing with a detailed primary reference fuel chemical kinetic mechanism to determine species concentrations and heat release in time. Comparison of predicted pressure, heat release, and emissions with data from diesel engine experiments reported in the literature shows good agreement overall, and suggests that spray combustion processes can be predictively modeled without calibration of empirical burn rate constants at a significantly lower computational cost than standard multidimensional (CFD) tools.

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