Analysis of an Extended Ionization Equilibrium in the Post-Flame Gases for Spark Ignited Combustion

2004 ◽  
Author(s):  
A. Ahmedi ◽  
F. Mauss ◽  
B. Sunde´n
Keyword(s):  
Initial Conditions ◽  
Chemical Species ◽  
Chemical Kinetic ◽  
Constant Volume ◽  
Chemical Mechanism ◽  
Thermal Ionization ◽  
Combustion Model ◽  
Ionization Degree ◽  
Pressure History ◽  
Temperature And Pressure

Constant volume combustion is studied, using a zero-dimensional model, which is a wide-ranging chemical kinetic simulation that allows a closed system of gases to be described on the basis of a set of initial conditions. The model provides an engine- or reactor-like environment in which the engine simulations allow for a variable system volume and heat transfer both to and from the system. The combustion chamber is divided into two zones as burned and unburned ones, which are separated by a thin adiabatic flame front in the combustion model used in this work. A detailed chemical mechanism is applied in each zone to calculate the temperature and pressure history. Equilibrium assumptions have been adopted for the modeling of the thermal ionization, in which Saha’s equation was derived for singly ionized molecules. The investigation is focused on the thermal ionization and electron attachment of 13 chemical species by solving a set of 6 chemical reactions dynamically, the equilibrium calculation using Saha’s equation is performed in a post process, using the temperature and pressure history from the previous model. The experiments that were used for the validation of this model were performed in constant-volume bomb. The outputs generated by the model are temperature profiles, species concentration profiles, ionization degree and an electron density for each zone. The model also predicts the pressure cycle and the ion current. The results from the simulation show good agreement with the experimental measurements and literature data.

Chemical Kinetic Study on Reaction Pathway of Anisole Oxidation at Various Operating Condition

2020 ◽  
Author(s):  
Shrabanti Roy ◽  
Omid Askari
Keyword(s):  
Kinetic Study ◽  
Equivalence Ratio ◽  
Initial Conditions ◽  
Reaction Pathway ◽  
Chemical Kinetic ◽  
Chemical Mechanism ◽  
Experimental Result ◽  
Alternative Source ◽  
Stirred Reactor ◽  
Constant Volume Combustion Chamber

Abstract Biofuels are considered as an alternative source of energy which can decrease the growing consumption of fossil fuel, hence decreasing pollution. Anisole (methoxybenzene) is a potential source of biofuel produced from cellulose base compounds. It is mostly available as a surrogate of phenolic rich compound. Because of the attractive properties of this fuel in combustion, it is important to do detail kinetic study on oxidation of anisole. In this study a detail chemical mechanism is developed to capture the chemical kinetics of anisole oxidation. The mechanism is developed using an automatic reaction mechanism generator (RMG). To generate the mechanism, RMG uses some known set of species and initial conditions such as temperature, pressure, and mole fractions. Proper thermodynamic and reaction library is used to capture the aromaticity of anisole. The generated mechanism has 340 species and 2532 reactions. Laminar burning speed (LBS) calculated through constant volume combustion chamber (CVCC) at temperature ranges from 460–550 K, pressure of 2–3 atm and equivalence ratio of 0.8–1.4 is used to validate the generated mechanism. Some deviation with experimental result is observed with the newly generated mechanism. Important reaction responsible for LBS calculation, is selected through sensitivity analysis. Rate coefficient of sensitive reactions are collected from literature to modify and improve the mechanism with experimental result. The generated mechanism is further validated with available ignition delay time (IDT) results ranging from 10–20 atm pressure, 0.5–1 equivalence ratio and 870–1600 K temperature. A good agreement of results is observed at different operating ranges. Oxidation of anisole at stoichiometric condition and atmospheric pressure in jet stirred reactor is also used to compare the species concentration of the mechanism. This newly generated mechanism is considered as a good addition for further study of anisole kinetics.

A Real-Time Pressure Wave Model for Predicting Engine Knock

2019 ◽  
Author(s):  
Ruixue C. Li ◽  
Guoming G. Zhu
Keyword(s):  
Pressure Wave ◽  
Time Pressure ◽  
Initial Conditions ◽  
Evaluation Criteria ◽  
Maximum Amplitude ◽  
Wave Model ◽  
Chemical Kinetic ◽  
Combustion Model ◽  
Pressure Oscillations ◽  
Engine Knock

Abstract This paper proposes a control-oriented pressure wave model, utilizing outputs of a reaction-based two-zone engine combustion model developed earlier, to accurately predict the key knock characteristics. The model can be used for model-based knock prediction and control. An in-cylinder pressure wave model of oscillation magnitude decay is proposed and simplified to describe pressure oscillations due to knock combustion, and the boundary and initial conditions of the pressure wave model at knock onset are provided by the two-zone reaction-based combustion model. The proposed pressure wave model is calibrated using experimental data, and the chemical kinetic-based Arrhenius integral (ARI) and maximum amplitude of pressure oscillations (MAPO) are used as the evaluation criteria for predicting knock onset and intensity, and the knock frequency is studied with the fast Fourier transform (FFT). The calibrated model is validated for predicting knock onset timing, knock intensity and frequency. Simulation results are compared with the experimental ones to demonstrate the capability of predicting engine knock characteristics by the proposed model.

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.

Numerical Simulation of Flame Spray Pyrolysis Process for Nanoparticle Productions: Effects of 2D and 3D Approaches

2014 ◽  
Author(s):  
Dirceu Noriler ◽  
Maximilian J. Hodapp ◽  
Rodrigo K. Decker ◽  
Henry F. Meier ◽  
Florian Meierhofer ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Quantitative Difference ◽  
Flame Temperature ◽  
Chemical Species ◽  
Temperature Fields ◽  
Test Facility ◽  
Combustion Model ◽  
Flame Spray ◽  
Grid Convergence Index ◽  
2D And 3D

Nanoparticle production in flames was modeled in an Eulerian-Lagrangean framework, considering droplet evaporation and fuel combustion to predict the flame chemical species concentration and the flame temperature fields by means of Computational Fluid Dynamics (CFD). A mathematical model was carried out considering two-way coupling between the gas phase and the droplets. For the combustion model, the eddy dissipation concept model was applied, taking into account the droplets vaporization, the chemical reaction mechanisms, and the chemistry-turbulence interaction. 2D axisymmetric and 3D approaches were investigated in standard operations conditions. The initial conditions for the droplet sizes and droplet velocities were taken in experiment test facility by means of Laser-Diffraction. The grid independence study was made according to the Grid Convergence Index (GCI) methodology for both approaches. The droplets mass evaporated, temperature and velocities profiles were used to compare the 2D and 3D results. The results show similar behavior for both approaches, however, with some quantitative difference. The 2D approach showed lower temperature resulted by a larger mass fuel not evaporated and unburned.

Engine Knock Prediction Using Multi Zone Model for Spark Ignition Engines

2006 ◽  
Author(s):  
A. Ahmedi ◽  
O. Stenla˚a˚s ◽  
B. Sunde´n ◽  
R. Egnell ◽  
F. Mauss
Keyword(s):  
Flame Front ◽  
Compression Ratio ◽  
Chemical Kinetic ◽  
Chemical Mechanism ◽  
Combustion Model ◽  
Zone Model ◽  
Chemical Kinetic Model ◽  
Engine Knock ◽  
Si Engines ◽  
Detailed Chemical

Autoignition in SI engines is an abnormal combustion mode and may lead to engine knock in SI engines. Knock may cause damage and it is a source of noise in engines. It limits the compression ratio of the engine and a low compression ratio means low fuel conversion efficiency of the engine. In this paper a multi zone model based on an existing two zone model Hajireza et al., [1 and 12] and Stenla˚a˚s et al., [30] is developed and validated against the experimental results. The validation is done by using the same detailed chemical mechanism consisting of 141 species and about 1405 reactions under the same conditions. The model is a zero dimensional model capable of simulating a full engine cycle. The two zone combustion model consists of a burned and an unburned zone, separated by a thin adiabatic flame front. The multi zone model differs in the handling of the burned gas. In the multi zone case a number of burned zones are present. The number of zones is decided by the temperature difference between the flame front and the last generated burned zone. The detailed chemical mechanism is taken into account in each zone, while the propagating flame front is calculated from the Wiebe function. Each zone is assumed to be a homogeneous mixture with a uniform temperature, mole and mass fractions of species. The spatial variation of the pressure is neglected, i.e., it is assumed to be the same in the whole combustion chamber at every instant of time. Autoignition is handled by the chemical kinetic model. As the unburned zone is assumed homogeneous the effect of auto ignition is a single pressure peak. The model is not designed to predict the pressure oscillations seen in engine knock.

scholarly journals Forecasts and assimilation experiments of the Antarctic ozone hole 2008

2011 ◽  
Vol 11 (5) ◽  
pp. 1961-1977 ◽  
Author(s):  
J. Flemming ◽  
A. Inness ◽  
L. Jones ◽  
H. J. Eskes ◽  
V. Huijnen ◽  
...  
Keyword(s):  
Transport Model ◽  
Initial Conditions ◽  
Stratospheric Ozone ◽  
Satellite Observations ◽  
Ozone Hole ◽  
Chemical Mechanism ◽  
Ozone Monitoring Instrument ◽  
Variable Effect ◽  
Antarctic Ozone ◽  
Antarctic Ozone Hole

Abstract. The 2008 Antarctic ozone hole was one of the largest and most long-lived in recent years. Predictions of the ozone hole were made in near-real time (NRT) and hindcast mode with the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The forecasts were carried out both with and without assimilation of satellite observations from multiple instruments to provide more realistic initial conditions. Three different chemistry schemes were applied for the description of stratospheric ozone chemistry: (i) a linearization of the ozone chemistry, (ii) the stratospheric chemical mechanism of the Model of Ozone and Related Chemical Tracers, version 3, (MOZART-3) and (iii) the relaxation to climatology as implemented in the Transport Model, version 5, (TM5). The IFS uses the latter two schemes by means of a two-way coupled system. Without assimilation, the forecasts showed model-specific shortcomings in predicting start time, extent and duration of the ozone hole. The assimilation of satellite observations from the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), the Solar Backscattering Ultraviolet radiometer (SBUV-2) and the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) led to a significant improvement of the forecasts when compared with total columns and vertical profiles from ozone sondes. The combined assimilation of observations from multiple instruments helped to overcome limitations of the ultraviolet (UV) sensors at low solar elevation over Antarctica. The assimilation of data from MLS was crucial to obtain a good agreement with the observed ozone profiles both in the polar stratosphere and troposphere. The ozone analyses by the three model configurations were very similar despite the different underlying chemistry schemes. Using ozone analyses as initial conditions had a very beneficial but variable effect on the predictability of the ozone hole over 15 days. The initialized forecasts with the MOZART-3 chemistry produced the best predictions of the increasing ozone hole whereas the linear scheme showed the best results during the ozonehole closure.

scholarly journals Simulation of a GOx-GCH4 Rocket Combustor and the Effect of the GEKO Turbulence Model Coefficients

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 341
Author(s):  
Evgeny Strokach ◽  
Victor Zhukov ◽  
Igor Borovik ◽  
Andrej Sternin ◽  
Oscar J. Haidn
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Turbulence Model ◽  
Chemical Kinetic ◽  
Wall Heat Flux ◽  
Combustion Model ◽  
Combustion Chambers ◽  
Separation Parameter ◽  
Kinetic Mechanisms ◽  
Stable Performance

In this study, a single injector methane-oxygen rocket combustor is numerically studied. The simulations included in this study are based on the hardware and experimental data from the Technical University of Munich. The focus is on the recently developed generalized k–ω turbulence model (GEKO) and the effect of its adjustable coefficients on the pressure and on wall heat flux profiles, which are compared with the experimental data. It was found that the coefficients of ‘jet’, ‘near-wall’, and ‘mixing’ have a major impact, whereas the opposite can be deduced about the ‘separation’ parameter Csep, which highly influences the pressure and wall heat flux distributions due to the changes in the eddy-viscosity field. The simulation results are compared with the standard k–ε model, displaying a qualitatively and quantitatively similar behavior to the GEKO model at a Csep equal to unity. The default GEKO model shows a stable performance for three oxidizer-to-fuel ratios, enhancing the reliability of its use. The simulations are conducted using two chemical kinetic mechanisms: Zhukov and Kong and the more detailed RAMEC. The influence of the combustion model is of the same order as the influence of the turbulence model. In general, the numerical results present a good or satisfactory agreement with the experiment, and both GEKO at Csep = 1 or the standard k–ε model can be recommended for usage in the CFD simulations of rocket combustion chambers, as well as the Zhukov–Kong mechanism in conjunction with the flamelet approach.

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