Reduced Reaction Mechanism Research Articles

Numerical Simulation of Gaseous Detonation Performance and Wall Reflection Effect of Acetylene-Rich Fuel

The efficient utilization of energy in rich fuel detonation processes and the effective control method of soot are important topics in combustion research. In this paper, we numerically study the detonation wave behavior of acetylene–air systems in rich fuel condition by using a reduced reaction mechanism. The non-stiff terms of the governing equations are solved explicitly using the gas kinetic scheme, and the stiff terms are solved implicitly. Our results show that the acetylene pyrolysis is the dominant reaction process. The oxidation reaction is exploited to initiate the reaction induction process, providing the required energy to overcome the potential energy barrier. The secondary detonation structure is due to the stable interaction of the transverse waves and the combined action of the vinyl reaction system, thus effectively improve the energy release rate and providing a powerful solution for the fuel-rich high-energy release of advanced heat engines. The area of the unreacted pocket increases with the acetylene concentration, resulting in an irregular wave-front and detonation cell. The reflected shock wave impacting on the wall induces the secondary reaction of the detonation products. The concentration of polycyclic aromatic hydrocarbons decreases significantly and regenerates near the wall. Our approach provides an effective tool for controlling detonation soot and the preparation of carbon particles.

A new acid gas destruction kinetic model for reaction furnace of an industrial sulfur recovery unit: A CFD study

• Developing a reduced reaction mechanism for acid gas combustion. • Simulating detailed full-scale reaction furnace with new reduced kinetic model. • Predicting accurate results in terms of temperature profile and chemical species. • Vectorwall and co-directional diffuser showed the lowest radiative heat flux. • Common checkerwall and co-directional diffuser showed the highest H2S efficiency. A new reduced kinetic model is developed for the simulation of acid gas destruction in the industrial reaction furnace of sulfur recovery units. The proposed CFD model includes the reactions of the new kinetic mechanism, steady laminar flamelet model, and fine details of industrial furnace geometry related to the burner, choke ring, checkerwall, and exhaust pipe holder. The mean relative error in predicting H 2 S conversion using CFD, coupled with our new kinetic model, is about 9.48% when compared with the industrial data. The influences of two types of burners and the checkerwalls on the thermohydrodynamics behaviors of the reaction furnace are investigated. The reactor equipped with Vectorwall and co-directional diffuser shows the lowest radiative heat flux (RHF) and favorable outlet temperature to protect the tube sheets, while the one with conventional checkerwall and co-directional diffuser shows the highest H 2 S conversion efficiency in the furnace.

Generation of skeletal and reduced reaction mechanisms for bio-derived syngas generated from biomass gasification – Experimental and numerical approach

Skeletal and reduced reaction mechanisms replicate the behavior of full reaction mechanism within the band/regime of optimization criteria and provide specific computational advantages for resource-intense multi-physics domain analysis. The current work reports on the development of skeletal and reduced mechanisms for bio-derived Producer gas and Hydrogen-rich Syngas by using GRI Mech 3.0 mechanism. The mechanisms are generated adopting graph-based approach, and timescale analysis are validated for laminar flame speed based on experiments in the equivalence ratios regime of 0.6–1.6 adopting a flame tube apparatus built in-house to mimic a freely propagating double infinity domain premixed reactor. Extending the analysis, the reduced/skeletal mechanisms are numerically validated for ignition delay time, major species profile, and volumetric heat release rate with validity established within the 5% tolerance limit. The current work is a first of its kind to propose optimized mechanism for compositions typical of bio-derived Producer gas and Syngas.

A Reduced Reaction Mechanism for Diesel/2-Methyltetrahydrofuran Dual-Fuel Engine Application

A Reduced Reaction Mechanism for Diesel/2-Methyltetrahydrofuran Dual-Fuel Engine Application

A New Reduced Reaction Mechanism of the Surrogate Fuel for Rp-3 Kerosene

A New Reduced Reaction Mechanism of the Surrogate Fuel for Rp-3 Kerosene

An experimental and kinetic modeling study on the low-temperature oxidation, ignition delay time, and laminar flame speed of a surrogate fuel for RP-3 kerosene

The low-temperature oxidation (under the conditions of the initial pressure of 0.1 MPa, equivalence ratio of 0.5 and 1.0, temperature range of 550–1100 K), ignition delay times (under the conditions of the equivalence ratio of 0.5, 1.0, 1.5, initial pressure of 0.1, 0.3 MPa, temperature range of 1000–1700 K) and laminar flame speeds (under the conditions of the initial temperature of 400, 420, 450, 480 K, equivalence ratio of 0.7–1.4 and pressure of 0.1, 0.3 MPa) of RP-3 kerosene and its surrogate fuel (including 14% n-decane/10% n-dodecane/30% isohexadecane/36% methylcyclohexane/10% toluene, by mole fraction) were experimental tested in the jet-stirred reactor, shock tube, and constant volume combustion bomb, respectively. The results show that the low-temperature oxidation, ignition delay times, and laminar flame speeds of the surrogate fuel are in good agreement with those of RP-3 kerosene. Meanwhile, through the reaction class-based global sensitivity analysis, decoupling methodology, and multi-objective genetic algorithm, the reduced reaction mechanism of the surrogate fuel (including 181 species and 872 reactions) was established. The results show that this reduced reaction mechanism can well predict the low-temperature oxidation, ignition delay times, and laminar flame speeds of RP-3 kerosene and the surrogate fuel.

Experimental Investigation of Ethanol Oxidation and Development of a Reduced Reaction Mechanism for a Wide Temperature Range

Experimental Investigation of Ethanol Oxidation and Development of a Reduced Reaction Mechanism for a Wide Temperature Range

Construction of reduced oxidation mechanisms of polyoxymethylene dimethyl ethers (PODE1–6) with consistent structure using decoupling methodology and reaction rate rule

Due to high oxygen content and lack of CC bond, polyoxymethylene dimethyl ethers (PODEn) have become desired fuel additives to simultaneously reduce nitrogen oxides (NOx) and soot emissions. However, there is a vacancy of reduced reaction mechanisms to describe the long-chain PODEn (n>3) combustion for engine simulations. This study aims at the construction of reduced mechanisms for the series of PODE1–6 with a consistent structure based on the decoupling methodology and reaction rate rule. First, the reduced mechanisms of PODE1–2 are constructed using the reaction class-based global sensitivity analysis and the decoupling methodology. In the reduced mechanisms of PODE1–2, the skeletal fuel-related sub-mechanism is integrated with a detailed H2/CO/C1 sub-mechanism and a reliable reduced C2–C3 sub-mechanism. Then, due to the similar molecular structure, the skeletal fuel-specific sub-mechanisms of the long-chain PODE3–6 are constructed based on the benchmark fuel of PODE2. The kinetic parameters of the reactions in the skeletal fuel-specific sub-mechanism of PODE3–6 are obtained using the modified linear lumping method and the reaction rate rule assumption. Through the approach proposed in this study, the reduced mechanisms of long-chain PODEn can be effectively constructed based on the chemistry of short-chain PODEn, especially for PODE5–6 with no available detailed mechanisms so far. The final reduced mechanism for the complete series of PODE1–6 only consists of 92 species and 389 reactions. To validate the predictions of the reduced mechanism, extensive comparisons are carried out including ignition delay times in shock tubes, major species concentrations in jet-stirred reactors, and laminar flame speeds and flame species concentrations in premixed laminar flames. Moreover, the measurements of homogeneous charge compression ignition (HCCI) engines fueled with PODE2–4 and PODE3–6 are used for the validations of in-cylinder pressure, heat release rate, and emissions. The overall performance of the reduced mechanism of PODE1–6 is satisfactory under wide operating conditions. This present approach can also be extended to build compact-size reduced mechanisms for the fuels with similar molecular structures, even though no detailed mechanism is available.

Large eddy simulation of premixed hydrogen-rich gas turbine combustion based on reduced reaction mechanisms

This study numerically investigates the combustion characteristics in a swirl burner for CO-H2 syngas by large eddy simulation. Firstly, experimental data are used to verify the applicability of the Boivin mechanism and the Sandia mechanism. The simulation results show that the Boivin mechanism predicts a more reasonable flame structure. Then, Syngas25, Syngas45, and Syngas100 (composed of 25%, 45%, and 100% H2 by volume, respectively) are set to numerically investigate the effect of hydrogen addition ratio on combustion characteristics by using the dynamic Smagorinsky model and the partially stirred reactor model. The detailed simulation data shows that the addition of hydrogen greatly influences the flame structure and flow field; with an increase in hydrogen addition, the flame length shortens, the temperature rises, and flashback caused by combustion induced vortex breakdown occurs. Furthermore, the precessing vortex core cannot exist stably in Syngas100, though it can be clearly observed in other cases.

Reduced Reaction Mechanisms for Ethanol under Ultra-lean Conditions in Internal Combustion Engines.

Chemical kinetics models for ethanol under ultra-lean engine conditions were evaluated to couple with CFD multidimensional simulations of a spark-assisted homogeneous charge compression ignition (HCCI) rotary engine. Five reduced reaction sets proper for CFD simulations and two detailed reaction mechanisms for comparison were tested by simulating ignition delay times, laminar flame speeds, and a single-cycle HCCI engine with virtual piston dimensions. The simulated results of the new mechanism with 188 reactions were well-fitted to both experimental ignition delay times for ultra-lean ethanol/air conditions and laminar flame speeds at high pressures. This reaction set resulted in better-simulated ignition delay times at 30 and 40 bar for ultra-lean ethanol/air conditions than other chemical kinetics models. Maximum temperatures and pressures of 2500–2580 K and 280–289 bar, respectively, were observed for hydrous ethanol/air under ultra-lean conditions in HCCI engine. In addition, the simulation results of the HCCI ethanol engine presented high pressure rise rates of 8–26 bar/CAD at 3600 rpm. These results indicated that the engine test should be carried out at 2500 rpm with 2 bar of boost pressure for CFD model calibration with the new optimized reaction mechanism.

Detailed gas-phase kinetics and reduced reaction mechanism for methane pyrolysis involved in CVD/CVI processes

A detailed gas-phase kinetic model consisting of 37 species and 318 reactions is developed for methane pyrolysis involved in the chemical vapour deposition/infiltration (CVD/CVI) processes. The model was used to perform the simulations of CH4 pyrolysis in a hot-wall CVD reactor over a wide range of operating conditions and validated against the experimental data. The overall trend of the concentration profiles of notable species is in good agreement with experimental results. The sensitivity analysis and reaction path flux diagram revealed that CH4 pyrolysis directly proceeds without any induction period. C2 species are the primary intermediates for the formation of acetylene, ethylene, and benzene. Besides, the accuracy of the present model is better than the models available in the literature. The detailed kinetic model was then systematically reduced to a small mechanism comprising 13 species and 29 reactions. The predictions of reduced mechanism also agreed well with the detailed mechanism at low inlet partial pressure (<10 kPa). Although the error in the mole fraction of light species was minimal, the relatively large error for C6H6 species was observed at high inlet partial pressure of CH4.

Large eddy simulation of an ignition sequence and the resulting steady combustion in a swirl-stabilized combustor using FGM-based tabulated chemistry

PurposeThis study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime.Design/methodology/approachThe CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method.FindingsBy comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs.Research limitations/implicationsThe proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement.Practical implicationsThis CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species.Originality/valueThe incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.

Reduced reaction mechanism for natural gas combustion in novel power cycles

Abstract We study the auto-ignition behavior of several natural gas surrogates; in particular, the influence of ethane and propane on the ignition delay time of methane is studied. A rapid compression machine was used to obtain experimental measurements of ignition delay times at two different compression pressures (10 and 15 bar) and a wide range of compression temperatures (904–1151 K), for both stoichiometric and fuel-rich ( ϕ = 2 ) mixtures. The experimental results are compared to homogeneous reactor model simulations (HOMREA). A first set of simulations treats chemical reaction in detail, using the AramcoMech 3.0 reaction mechanism. It was observed that the mechanism predicted the observed ignition delay times well. Experimental results indicate that both ethane and propane have an ignition enhancing effect on the mixture, shortening the ignition delay time. Propane, in particular, appears to have a higher influence compared to ethane at low temperatures. In general, fuel rich mixtures show shorter ignition delay times. These trends are well captured by the AramcoMech 3.0 mechanism showing great agreement with experimental data. To make the chemistry underlying the AramcoMech 3.0 available in a concise form, e.g., for CFD applications or similar, a reduced chemistry scheme was developed (reaction mechanism with 49 species and 332 reactions). Simulations using the reduced model showed a similarly good agreement to which was developed based on the detailed AramcoMech 3.0 reaction mechanism. The experimental results are predicted well by the reduced model, in a similar fashion like the detailed scheme. Furthermore, the reduced reaction mechanism is validated against experimental data found in literature, covering a wide range of conditions. This establishes the reduced model as a useful, computationally efficient substitute for describing the effect of ethane and propane onto the auto-ignition of methane.

Исследование математической модели каталитического риформинга бензина методами анализа чувствительности

Для изучения одного из важнейших процессов нефтепереработки — каталитического риформинга, требуется детализированная кинетическая модель. При разработке кинетической модели возникает сложность в связи с большим количеством компонентов реакционной смеси и большим количеством стадий химических превращений. Альтернативой могут быть сокращенные механизмы реакций, которые применимы для решения задачи и обеспечивают реалистичное описание процесса. В данной работе для анализа кинетической модели и получения сокращенного механизма реакции используются методы анализа чувствительности математической модели. Применение указанной методики позволяет выявить стадии каталитического риформинга бензина, наименее влияющие на общую динамику изменения концентраций значимых веществ реакции. Исследовано влияние исключения данных стадий на кинетику процесса с химической точки зрения. Предложена редуцированная схема каталитического риформинга бензина с исключением данных стадий. Редуцированная схема обеспечивает вполне удовлетворительное согласие как по профилям температуры, так и по профилям концентраций значимых веществ реакции. A detailed kinetic model is required to study one of the most important oil refining processes known as catalytic reforming. The difficulty arises in connection with a large number of components of the reaction mixture and a large number of stages of chemical transformations in developing the kinetic model. An alternative may be reduced reaction mechanisms that are applicable to solve the problem and provide a realistic description of the process. In this paper, to analyze the kinetic model and to obtain an abbreviated reaction mechanism, the sensitivity analysis methods of the mathematical model are used. The least influential stages of catalytic reforming of gasoline, which do not affect the general dynamics of changes in the concentrations of significant reaction substances are identified using this technique. The effect of eliminating these stages on the kinetics of the process from the chemical point of view is analyzed. A reduced scheme for catalytic reforming of gasoline by excluding these stages is proposed. A reduced scheme provides a quite satisfactory agreement both in temperature profiles and in concentration profiles of significant substances.

Chemical Kinetics Modeling and Analysis of Monomethylamine for Power Plants Selective Non-Catalytic Reduction (SNCR) Systems

A study was performed to investigate monomethylamine (MMA) as an alternative or supplementary reagent for selective non-catalytic reduction (SNCR) of nitrogen oxides (NOx) for power plants especially the coal-fired type. A detailed chemical kinetics mechanism for MMA, related to the SNCR NOx reduction process, was modeled using a simplified plug flow reactor (PFR) approach using the CHEMKIN software. Model validation results were in line with reported experimental results. A model sensitivity analysis showed that the normalized MMA/NO stoichiometric ratio (NSR) and the initial NOx concentration are the most critical parameters that significantly affect MMA-based process performance. Additionally, a reduced reaction mechanism and its mechanism tree for this particular process are proposed, consisting of only 18 reactions and 21 species. Simulation comparisons with three other reagents (ammonia, urea, and cyanuric acid), under similar process conditions, indicate that MMA-based SNCR NOx reduction process has a superior performance at much lower temperatures (under 800 K) than conventional SNCR processes, with the added benefit that it does not suffer from ammonia slip problems. The MMA-based SNCR NOx removal system could be applied in cascade mode with other post-combustion NOx removal approaches to extend NOx control to lower temperatures and eliminate the temperature window limitation and potential ammonia slip of conventional SNCR systems. The cascade design is a perfect solution for coal power plants especially at partial load modes of operation which provides more flexibility in performance for such plants. The results of the simulations in this study show that the potential of MMA for SNCR NOx reduction systems at full-scale power plants has significant merit.

Predicting lubricant oil induced pre-ignition phenomena in modern gasoline engines: The reduced GasLube reaction mechanism

Recent research highlights the influence of the presence of lubricant oil droplets on the combustion process in Direct Injection Spark Ignition (DISI) engines. Lubricant oil is considered to be the main responsible agent for the onset of pre-ignition phenomena, which can escalate highly undesired super-knock events. Moreover, lubricant oil plays a primary role in the generation of very fine soot particle emissions. In the present work, a reduced reaction mechanism is developed for modeling the combustion of gasoline-oil mixtures, allowing one to simulate the variation in ignitability of gasoline-like fuels induced by the presence of lubricant oil. In this study, a single hydrocarbon species, namely n-Hexadecane (n-C16H34), is shown to reproduce lubricant oil chemical and physical characteristics. Great effort has been performed to identify the most significant reaction pathways to reduce the complexity of the chemistry mechanism and the number of variables, while maintaining the important features of detailed mechanisms, for the highest computational efficiency. The proposed reduced mechanism has been validated for a wide range of operating conditions. It is employed for 3D simulations of experimental measurements in which iso-Octane was blended with different percentages of lubricant oil and its surrogates. Operating conditions representative of those of a typical turbocharged DISI engine are considered. The very good agreement obtained in the comparison with the experimental data confirms the effectiveness of the proposed “GasLube” mechanism in reproducing lubricant oil’s influence on ignition propensity of gasoline-like fuels. Furthermore, the 3D numerical simulations allowed a detailed analysis of the ignition phenomenon, providing more insight into the basic processes of lubricant oil induced pre-ignition events in DISI gasoline engines.

Development and validation of a reduced chemical kinetic model for used vegetable oil biodiesel/1-Hexanol blend for engine application

In this study, a compact kinetic model consisting of 588 reactions and 139 species is proposed for 1-Hexanol and used vegetable oil (UVO) biodiesel blend for simulating internal combustion (IC) engines. Suitable modifications were made to the pre-exponential factor to ascertain predictive performance comparable to the investigational results. This reduced reaction model was validated with experimental data from the published work for laminar flames speed, ignition delay and species mole fractions. The reduced mechanism and the experimental results are comparable within a factor of 1.3–2.5. A zero-dimensional single zone model was employed for simulating internal combustion engine conditions with the reduced mechanism using Cantera software and the results are analogous and as expected from the simulation study. The reduced reaction mechanism could be utilized by the researchers working on alternative fuels to simulate and study the combustion of used vegetable oil/1-Hexanol blend in an engine using computational fluid dynamics (CFD) modeling software.

Generation of reduced reaction mechanisms for heterogeneous flows in nozzles

Generation of reduced reaction mechanisms for heterogeneous flows in nozzles

A new skeletal mechanism for diesel-n-butanol blends combustion in engine

A new skeletal mechanism consisting of 116 species and 433 reactions for diesel-n-butanol blends combustion in engine is proposed in this study. Starting from a detailed chemical kinetics considering high-temperature and low-temperature reaction pathways of n-butanol, a reduced reaction mechanism was built using directed relation graph with error propagation and sensitivity analysis (DRGEPSA), computational singular perturbation (CSP) and reaction pathway analysis (RPA) methods. Then, it was further combined with a reduced diesel surrogate fuel chemical reaction mechanism of n-heptane/toluene with the NOx and soot formation kinetics embedded. After optimizing the reaction rate constants of selected reactions in the coupled mechanism based on sensitivity analysis, the final n-heptane/toluene-n-butanol skeletal mechanism for diesel-n-butanol blend oxidation was generated and validated against ignition delay time, laminar flame speed and premixed flame species profiles, and a good prediction was presented. In addition, the current mechanism was coupled into the KIVA3V2-CANTERA to simulate the combustion and emissions characteristics of an engine fueled with B00, B20 and B40 (0 vol%, 20 vol% and 40 vol% n-butanol blended with diesel). It is indicated that the in-cylinder pressure, heat release rate and NOx and soot emission of diesel/n-butanol blend can be well reproduced by the newly developed skeletal mechanism with a reliable accuracy.

A reduced reaction mechanism of biodiesel surrogates with low temperature chemistry for multidimensional engine simulation

A reduced biodiesel mechanism composed of 156 species and 589 reactions is reduced from an original complex mechanism (3299 species and 10806 reactions) based on MD, MD9D, and n-heptane as the surrogates. The mechanism reduction is conducted using the path flux analysis method, which considers multiple reaction path generations in the analysis of species interactions, and isomer lumping. Calculations of homogeneous auto-ignition and perfectly stirred reactor (PSR) combustion on a variety of reaction states, including pressures from 1 to 100 atm and equivalence ratios from 0.5 to 2, are the basis of the reduction. The initial temperatures are from 700 to 1800 K for the auto-ignition, and the inlet temperature is 300 K for the PSR. These reaction states cover the high-pressure and low-temperature operating conditions of future engines using advanced combustion technologies characterized by fuel–air premixing and auto-ignition. The fidelity of the resulting reduced mechanism with low-temperature chemistry is examined using a variety of applications. Close agreements between the reduced and original mechanisms are obtained in the predictions of ignition delay, history of mixture temperature, and species mole fraction during homogeneous auto-ignition and the temperature profile in PSR. The reduced mechanism, further integrated with a nitrogen oxides chemistry and a two-step soot model, is implemented into the KIVA/CHEMKIN program for the 3D simulation of biodiesel spray combustion. The predicted liquid and vapor penetrations agree with the experimental data in a non-reactive biodiesel spray simulation, indicating an accurate estimation of biodiesel physical properties. In the simulation of biodiesel spray combustion, predicted spatial distributions of hydroxyl radical and soot also agree with the corresponding experimental data.