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Temperature Dependence of laminar burning velocity in Ammonia/Dimethyl Ether-air Premixed Flames

Journal of Thermal Science 2022年第1期31卷 189-197页

作者： CAI Tao ZHAO Dan Department of Mechanical Engineering College of EngineeringUniversity of CanterburyChristchurch 8041New Zealand

The combustion of ammonia(NH3)has attracted wide interest in fuel vehicle engines,marine engines,and power generators to mitigate carbon dioxide emissions.Unfortunately,the relatively low laminar flame speed presents a technical barrier for this renewable fuel to be used in practice.This work is concerned with numerical examining the effects of elevating inlet temperature on the laminar burning velocity of NH3/air flames with various contents of dimethyl ether(DME)using ID freely propagating flame calculations,and to shed light on the flame enhancement mechanism.For this,the mechanism is first validated by comparing the numerical predictions with experimental data.Results show that increasing the inlet temperature has a positive effect on the laminar burning velocity of pure NH3/DME/air flames.It is revealed that elevating inlet temperature contributes to a higher adiabatic flame temperature,which is beneficial to the overall chemical reaction rate.Furthermore,the thermal diffusivity of the binary mixture is observed to increase substantially as well.Further kinetic and sensitivities analyses reveal that the inlet temperature has a minimal effect on the reaction pathway,leading to the relative importance of the dominant chain branching over terminating reaction steps to be varied negligibly.The present work confirms that the flame speed enhancement with increasing inlet temperature is primarily the synergetic result of the thermal and diffusion effects,rather than the chemical effect.

关键词： ammonia dimethyl ether laminar burning velocity temperature dependence kinetic analyses

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Applying machine learning techniques to predict laminar burning velocity for ammonia/hydrogen/air mixtures

Energy and AI

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Energy and AI 2023年第3期13卷 207-218页

作者： Cihat Emre Ustun Mohammad Reza Herfatmanesh Agustin Valera-Medina Amin Paykani School of Physics Engineering and Computer ScienceUniversity of HertfordshireHatfieldAL109ABUnited Kingdom College of Physical Sciences and Engineering Cardiff UniversityCardiffCF243AAUnited Kingdom

Ammonia utilisation in internal combustion engines has attracted wide interest due to the current trend toward decarbonisation,as ammonia is a zero-carbon fuel with different combustion properties to hydrocarbons.The laminar burning velocity(LBV)is a fundamental property of fuels with a significant effect on the combustion processes and accurate calculations and measurements of the LBV over a wide range of fuel blends,pressures and flow conditions is a time-consuming,complicated procedure.The main goal of the current study is to predict the LBV of NH_(3)/H_(2)/air mixtures using a hybrid machine learning(ML)approach based on a training dataset consisting of both the experimental LBV values and additional data obtained from numerical simulations with a detailed kinetic model.Initial ML model training data is collected from existing experimental LBV in the literature for NH_(3)/H_(2)/air mixtures.Then,synthetic data is generated using one-dimensional(1D)simulations to reduce data inhomogeneity and increase accuracy of the ML model.In total,24 different ML algorithms are tested to find the best model both for the experimental and the hybrid dataset.The results suggest that both Gaussian Process Regression(GPR)and Neural Networks(NNs)can be utilised to predict LBV of NH_(3)/H_(2)/air mixtures with reasonable accuracy.The hybrid ML model achieved a coefficient of determination of R^(2)=0.998.Finally,hybrid ML model hyperparameters are optimised to achieve a coefficient of determination of R^(2)=0.999.It was also found that ML can speed up LBV computation from 9500 to 27000 times compared to 1D simulations with a reduced mechanism.

关键词： Machine learning Ammonia Hydrogen laminar burning velocity Combustion

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Measurements of laminar burning Velocities of Alternative Fuels:Application in Transport and Aerospace

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Journal of Thermal Science 2023年第2期32卷 503-512页

作者： RICHTER Sandra BRAUN-UNKHOFF Marina NAUMANN Clemens German Aerospace Center(DLR) Institute of Combustion TechnologyDepartment of Chemical Kinetics and AnalyticsStuttgart 70569Germany

The laminar burning velocity belongs to the fundamental combustion properties of fuels being a measure for their heat release,flame length,as well as reactivity and combustion stability,and thus,may impact the design of burners and combustion chambers.Also,these experimental data are needed for the validation and optimization within the construction and development of detailed chemical kinetic reaction mechanisms.Within this study,an overview of the different applications of fuel characterization regarding the specific area of interest(road transport,aviation,and aerospace)will be given.Depending on the application,effects of different molecular characteristics on the laminar burning velocity are evaluated:the presence of oxygen atoms and the grade of branching in a specific fuel molecule as well as the difference in the type of a chemical bond,here,single and double bonds.Examples of alternative fuels being discussed in the present study are:(Ⅰ)oxymethylene ether(OMEn)in the field of road transport;(Ⅱ)a paraffinic Alcohol-to-Jet fuel as sustainable aviation fuel;and(Ⅲ)mixtures of ethane or ethene with nitrous oxide as green propellants for rocket propulsion applications.

关键词： laminar burning velocity alternative sustainable fuels road transport aviation fuels green propellants

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Effect of CO_(2) dilution on laminar burning velocities,combustion characteristics and NO_(x) emissions of CH_(4)/air mixtures

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International Journal of Coal Science & Technology 2023年第5期10卷 119-136页

作者： Wenlong Dong Longkai Xiang Jian Gao Bingbing Qiu Huaqiang Chu School of Energy and Environment Anhui University of TechnologyMa'anshan 243002People's Republic of China Key Laboratory for Power Machinery and Engineering of Ministry of Education(MOE) Shanghai Jiao Tong UniversityShanghai 200240People's Republic of China

The laminar combustion characteristics of CH_(4)/air premixed flames with CO_(2) addition are systemically studied.Experimental measurements and numerical simulations of the laminar burning velocity(LBV)are performed in CH_(4)/CO_(2)/Air flames with various CO_(2) doping ratio under equivalence ratios of 1.0–1.4.GRI 3.0 mech and Aramco mech are employed for predicting LBV,adiabatic flame temperature(AFT),important intermediate radicals(CH_(3),H,OH,O)and NO_(x) emissions(NO,NO_(2),N2O),as well as the sensitivity analysis is also conducted.The detail analysis of experiment and simulation reveals that as the CO_(2) addition increases from 0%to 40%,the LBVs and AFTs decrease monotonously.Under the same CO_(2) doping ratio,the LBVs and AFTs increase first and then decrease with the increase of equivalence ratio,and the maximum of LBV is reached at equivalence ratio of 1.05.The mole fraction tendency of important intermediates and NO_(x) with equivalence ratio and CO_(2) doping ratio are similar to the LBVs and AFTs.Reaction H+O_(2)⇔O+OH is found to be responsible for the promotion of the generation of important intermediates and NO_(x) under the equivalence ratios and CO_(2) addition through sensitivity analysis.The sensitivity coefficients of elementary reactions that the increasing of CO_(2) doping ratio promotes or inhibits formation of intermediate radicals and NO_(x) decreases.

关键词： CO_(2)dilution laminar burning velocity Adiabatic flame temperature Sensitivity analysis

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Measurement of laminar burning velocities and Markstein lengths near rich propane/air flammability limits under microgravity conditions

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Journal of Beijing Institute of Technology 2011年第4期20卷 466-471页

作者：胡俊任坦 Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of EducationSchool ofAerospace EngineeringBeijing Institute of Technology

A small cubic closed vessel with schlieren measurement technique combined with high-speed video camera were used to study limit flame properties under microgravity conditions at atmospheric pressure and room temperature.The rich flammability limit of C3H8/air was determined to be 9.2% C3H8.Stretched flame propagation speeds,stretched laminar burning velocities and unstretched laminar burning velocities near rich C3H8/air flammability limits were measured at different equivalence ratios.Outwardly propagating spherical flames were used to study the sensitivities of the flame propagation speeds and laminar burning velocities to flame stretch using Markstein lengths.Unstretched laminar burning velocity at rich flammability limit was determined to be 1.09cm/s.Lewis numbers were less than unity in rich C3H8/air and negative Markstein lengths were concluded.Absolute values of Markstein lengths were found to decrease linearly with equivalence ratios increase.

关键词： laminar burning velocity Markstein lengths rich flammability limit flame stretch

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Study on the flame propagation and gas explosion in propane/air mixtures

Study on the flame propagation and gas explosion in propane/...

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第五届全国强动载效应及防护学术会议暨复杂介质/结构的动...

作者：刘庆明 ZhangYun-ming NiuFang LiLei State Key Lab of Explosion Science and Technology Beijing Institute of Technology

The characteristics of flame propagations and gas explosions in propane/air mixtures were studied in a 1.16 m explosion chamber with two quartz glass windows of 250 mm diameter.The outward propagations of the spherical flame were recorded by the Schlieren system and high speed motion analysis system.The pressure and temperature histories of the explosion process were measured by pressure sensors and platinum-rhodium thermal couples of 0.02 mm diameter mounted on the wall of the experimental chamber.The instabilities of the propane air flame with different equivalence ratio flame were observed and the critical radii of flame instability onset were obtained.The laminar burning velocities of propane air mixture were obtained by analyzing the experimental results of Schlieren system by using outwardly propagating spherical method.The variation of laminar burning velocity with equivalence ratio was studied Pressure and temperature responses of the gas explosion were obtained and analyzed.The variations of the maximum overpressure and the maximum temperature with equivalence ratio were obtained and discussed. In propane/air mixture with an equivalence ratio near 1.8,two explosions take places.

关键词： laminar burning velocity flame instability gas explosion

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