Nadezhda A. Slavinskaya

Reduced Reaction Mechanisms for Methane and Syngas Combustion in Gas Turbines

Two reduced reaction mechanisms were established that predict reliably for pressures up to about 20 bar the heat release for different syngas mixtures including initial concentrations of methane. The mechanisms were validated on the base of laminar flame speed data covering a wide range of preheat temperature, pressure, and fuel-air mixtures. Additionally, a global reduced mechanism for syngas, which comprises only two steps, was developed and validated, too. This global reduced and validated mechanism can be incorporated into CFD codes for modeling turbulent combustion in stationary gas turbines.

On Model Design of a Surrogate Fuel Formulation

Calculations of evaporation characteristics (distillation curve, two-phase diagram, and critical points) of surrogates are described in detail. The efficiency of some surrogate blends, represented in literature, in reflecting the evaporation characteristics was analyzed. Based on the analysis, the chemical capabilities of surrogate models are not linked to their abilities to reflect the phase-equilibrium properties of real fuel. It is shown that model design of practical fuels must include the phase-equilibrium and distillation curve calculations. A surrogate mixture was selected, which closely matches the boiling-point curve and two-phase diagram for jet-A. Next, physical properties of reference fuel were taken into consideration: combustion enthalpy, formation enthalpy, molar weight, approximate formula (carbon per hydrogen ratio), sooting tendency index, critical point, two-phase diagram, and distillation curve.

A Detailed and Reduced Reaction Mechanism of Biomass-Based Syngas Fuels

In the present work, the elaboration of a reduced kinetic reaction mechanism is described, which predicts reliably fundamental characteristic combustion properties of two biogenic gas mixtures consisting mainly of hydrogen, methane, and carbon monoxide, with small amounts of higher hydrocarbons (ethane and propane) in different proportions. From the in-house detailed chemical kinetic reaction mechanism with about 55 species and 460 reactions, a reduced kinetic reaction mechanism was constructed consisting of 27 species and 130 reactions. Their predictive capability concerning laminar flame speed (measured at To =323 K, 373 K, and 453 K, at p = I bar, 3 bars, and 6 bars for equivalence ratios ϕ between 0.6 and 2.2) and auto ignition data (measured in a shock tube between 1035 K and 1365 K at pressures around 16 bars for ϕ=0.5 and 1.0) are discussed in detail. Good agreement was found between experimental and calculated values within the investigated parameter range.

Towards surrogate reaction model development

The present paper describes the proposed strategy of fuel model design based on identification of chemical and physical criteria for the selection of initial formula of the reference fuel. The first 8 criteria established and studied in previous papers so far are combustion enthalpy, formation enthalpy, molecular weight, C/H-ratio, sooting tendency index, critical point, two-phase diagram, and distillation curve. With these criteria established, the following candidate formula of the kerosene surrogate blend is defined and optimized to adequately mimic the properties of the real fuel: 10% n-propylcyclohexane, 13% iso-octane, 20% n-dodecane, 23% 1-methylnaphthalene, and 32% n-hexadecane. In this work, the ignition delay time has been studied as the next optimization criterion. To keep the model size small, the core reaction mechanism — the skeletal kinetics of n-heptane and iso-octane combustion including aromatics formation, developed earlier — is extended by n-propylcyclohexane, 1-methylnaphthalene, n-dodecane, and n-hexadecane sub-models. The lumped mechanisms for larger n-alkanes are constructed in a similar way to that for n-decane. The n-propylcyclohexane oxidation sub-model is derived from a skeletal mechanism for the low and high temperature cyclohexane oxidation. Reactions for 1-methylnaphthlene oxidation are included in the sub-mechanism for the formation of aromatics up to 5 ringed molecules. The mechanism includes 189 species and 1125 reactions. The proposed sub-models and overall mechanism are validated against experimental data obtained in shock tubes and in jet stirred reactor.s The simulations of ignition delay data for all hydrocarbons and their mixtures, i.e. for kerosene, are in good agreement with the measured data.Copyright

Skeletal Mechanism for C2H4 Combustion With PAH Formation

A semi-detailed kinetic mechanism with 100 species and 816 reactions for ethylene combustion including PAH formation was elaborated. The model includes the C2 H5 OH sub mechanism combustion as well. This mechanism has in view to be the base of further kinetic schemes of practical fuels (reference fuels). The mechanism was reduced to a skeletal model with 72 species and 580 reactions. The elaborated models were validated on experimental data bases of heat release as well as formation of polyaromatic hydrocarbons and soot in laminar premixed C2 H4 , C2 H4 / C2 H5 OH flames taken from literature. The calculated ignition delay times, laminar flame speeds, as well as temporal profiles of small and large aromatics and also soot particles are in good agreement with experimental data obtained for pressures 1 – 5 bar, temperatures T0 = 1100 – 2300 K, fuel/oxygen equivalence ratio φ = 0.5 – 2.Copyright

On surrogate fuel formulation

Calculations of evaporation characteristics (distillation curve, two-phase diagram, critical points) of surrogates are described in detail. The efficiency of some surrogate blends, represented in literature, in reflecting the evaporation characteristics was analysed. Based on the analysis, the chemical capabilities of surrogate models are not linked to their abilities to reflect the phase equilibrium properties of real fuel. It is shown, that blending of pure hydrocarbons must begin with the phase equilibrium and distillation curve calculations. A surrogate mixture was selected which closely matches the boiling-point curve and two phase diagram for Jet-A.Copyright

Kinetic Surrogate Model for GTL Kerosene

This paper present results of kinetic model formulation for synthetic Gas-To-Liquid (GTL) kerosene. The input formula of surrogate (IFS) is determined from the optimization of a set of criteria: enthalpy of formation, density, C/H ratio, viscosity, sooting tendency index, two phase diagram, distillation curve, and ignition delay and cetane number (CN). The proposed surrogate consists of 17% of 2,7-dimethyloctane, 32% of 2-methyldecane, 15% of n-propylcyclohexane and 36% of n-decane. Due to the lack of data for branched 2,7-dimethyloctane (i-C10H22) and monoparaffin 2methyldecane (i-C11H24), the simplified surrogates composed of n-decane, npropylcyclohexane and iso-octane has been suggested and used as a reference model. Then the chemical kinetic models for both lowand high-temperature regimes for a iC10H22 and i-C11H24 have been developed on the basis of the previously-developed kinetic model for C1-nC10 oxidation. The oxidation mechanisms have been tested on experimental data from literature and on the measured ignition delay times performed in a shock tube for two isomers of i-C10H22 under the conditions: p5 = 16-17 atm, T5 = 6501500K and  = 1. The obtained kinetic sub-models have been gradually introduced in the simplified reference model. The experimental data for ignition delay of GTL kerosene have been modeled using these simplified surrogates and results have been compared. The influence of the brunched alkanes on the combustion characteristics of the GTL kerosene has been discussed.

Enhancement of a Detailed Mechanism of Propene

Propene (C3 H6 ) is an important constituent of practical hydrocarbons fuels and an important intermediate in the combustion of these fuels. Furthermore, synthetic gases such as biogenic gas mixtures not only consist of hydrogen, methane, and carbon monoxide, but also of small amounts of higher hydrocarbons, in different proportions, including propene. In the present work, a detailed propene sub-model was constructed starting from an in-house reaction model (DLR-LS) shown previously to describe major combustion properties including PAH and soot formation for several different fuel air flames. The predictive capability of the detailed propene submodel concerning laminar flame speed and ignition delay time of different propene-oxygen mixtures will be discussed. These data are needed to describe the heat release and to predict the possibility of a flashback. From these comparisons, it is concluded that the extended propene sub-model is capable to predict combustion properties of propene-oxygen gas mixtures.Copyright

CHEMICAL KINETIC MODELING IN COAL GASIFICATION PROCESSES: AN OVERVIEW.

Coal is the fuel most able to cover world deficiencies in oil and natural gas. This motivates the development of new and more effective technologies for coal conversion into other fuels. Such technologies are focused on coal gasification with production of syngas or gaseous hydrocarbon fuels, as well as on direct coal liquefaction with production of liquid fuels. The benefits of plasma application in these technologies is based on the high selectivity of the plasma chemical processes, the high efficiency of conversion of different types of coal including those of low quality, relative simplicity of the process control, and significant reduction in the production of ashes, sulphur, and nitrogen oxides. In the coal gasifier, two-phase turbulent flow is coupled with heating and evaporation of coal particles, devolatilization of volatile material, the char combustion (heterogeneous/porous oxidation) or gasification, the gas phase reaction/oxidation (homogeneous oxidation) of gaseous products from coal particles. The present work reviews literature data concerning modelling of coal gasification. Current state of related kinetic models for coal particle gasification, plasma chemistry and CFD tools is reviewed.Copyright

Evaluation of the Chemical Interaction of Exhaust Gases of Methane / Oxygen Propelled Liquid Rocket Engines with the Atmosphere

It is known that during a launch of a rocket the interaction of the exhaust gases of rocket engines with the atmosphere cause local depletion of the ozone layer. In order to study these chemical processes in detail a chemical reaction mechanism of methane oxidation appropriate for high and low pressure conditions and the network of chemical reactors available in CHEMICAL WORKBENCH software have been successfully developed to simulate pressure, temperature, and velocity field in the convergent-divergent rocket nozzle and in the exhaust-jet. A detailed chemical kinetic model for high pressure CH4/O2-combustion developed earlier has been improved for the low pressure and low temperature methane combustion and augmented with sub-models for NOX, O3 and Polyaromatic Hydrocabons (PAHs) chemistry. The main model improvements are related to the pressure dependent reactions. The model has been validated for operating conditions of 0.02 atm < p < 100 atm, 300 K < T < 1800 K and 0.5 < Ф < 3.0. The simulations performed have demonstrated that active radicals in the exhaust gases of a methane/oxygen propelled liquid rocket engine intensify the nitrogen compound production as well as the ozone consumption in the jetatmosphere mixing layer. Additionally, the simulation results reveal that the temperature and pressure conditions in the combustion chambers of methane/oxygen propelled rocket engines considerably reduce the production of PAH.