Rate Of Production Analysis Research Articles

Chemiluminescence during the high-temperature pyrolysis and oxidation of ammonia

Chemiluminescent emissions from NH2*, NH*, NO*, and OH* during the pyrolysis and oxidation of ammonia (NH3) are quantitatively characterized to gain insight into their reaction mechanisms. Time profiles of light emitted from high-temperature reactions of NH3/Ar and NH3/O2/Ar mixtures have been measured behind reflected shock waves at temperatures of 2300–2600 K and pressures of 1.6–1.9 bar in a high-repetition-rate shock tube. The emission intensities have been calibrated based on the well-characterized OH* chemiluminescence in a hydrogen-oxygen system and converted to photon emission rates for quantitative comparison with kinetic simulations. A kinetic model describing the pyrolysis and oxidation of ammonia and reactions of excited species has been constructed by combining the reaction mechanisms proposed in recent modeling studies. With only modest updates of the thermodynamic functions and the rate constants for the formation and quenching of excited species, the observed chemiluminescence profiles could be reasonably reproduced, with a few exceptions. The rate of production analysis indicates that NH2* is produced by the reaction of NH3 with H as well as thermal excitation of NH2, that the energy transfer reactions from 3N2 to NH and NO are responsible for the formation of NH* and NO*, respectively, and that the formation of OH* is competitively contributed by the reactions of H with N2O, 3N2 with OH, and NH with NO. Remaining discrepancies between the experiment and modeling are noted, and potential directions for further model improvement are discussed.

Performance and Emission Optimisation of an Ammonia/Hydrogen Fuelled Linear Joule Engine Generator

This paper presents a Linear Joule Engine Generator (LJEG) powered by ammonia and hydrogen co-combustion to tackle decarbonisation in the electrification of transport propulsion systems. A dynamic model of the LJEG, which integrates mechanics, thermodynamics, and electromagnetics sub-models, as well as detailed combustion chemistry analysis for emissions, is presented. The dynamic model is integrated and validated, and the LJEG performance is optimised for improved performance and reduced emissions. At optimal conditions, the engine could generate 1.96 kWe at a thermal efficiency of 34.3% and an electrical efficiency of 91%. It is found that the electromagnetic force of the linear alternator and heat addition from the external combustor and engine valve timing have the most significant influences on performance, whereas the piston stroke has a lesser impact. The impacts of hydrogen ratio, oxygen concentration, inlet pressure, and equivalence ratio of ammonia-air on nitric oxide (NO) formation and reduction are revealed using a detailed chemical kinetic analysis. Results indicated that rich combustion and elevated pressure are beneficial for NO reduction. The rate of production analysis indicates that the equivalence ratio significantly changes the relative contribution among the critical NO formation and reduction reaction pathways.

Experimental and kinetic modeling study on the oxidation and laminar combustion characteristics of natural gas

The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO2 and H2O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions.

Experimental and kinetic model studies on the low- to moderate-temperature oxidation of N-methyl pyrrole in a jet-stirred reactor

N-methyl pyrrole (NMP) is an important nitrogenous heterocyclic compound in bio-oils produced from biomass conversion. NMP can be used as surrogate model compound to clarify the combustion chemistry of nitrogenous fuels and NOX formation mechanism. The low- to moderate-temperature oxidation experiments of NMP are carried out in atmospheric pressure jet-stirred reactor for 0.5% NMP/oxygen/Argon mixtures at different equivalence ratios (0.5, 1.0, and 2.0) over the temperature range of 760 – 1030 K. More than twenty species, including reactants, nitrogen-containing species, and oxygenated products, are measured using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). A detailed and comprehensive kinetic model for NMP oxidation is developed for the first time based on the pyrrole oxidation model developed by Pelucchi et al. and Chen et al.. Simulated results show that the present model can reasonably reproduce the experimental results. Rate of production analysis indicates that the H-abstraction reactions on the methyl group dominate in NMP oxidation at all equivalence ratios. NMP oxidation produces C4 and C5 nitrogen-containing compounds including pyridine and pyrrole. These species are found to be products of the primary reactions of NMP, and their formation pathways can be explained satisfactorily by the present model. The present work provides a basis to further understand the oxidation characteristics of nitrogen-containing heterocyclic fuels.

Sooting tendency of isopropanol-butanol-ethanol (IBE)/diesel surrogate blends in laminar diffusion flames

Recent advancements in metabolic engineering have demonstrated the cost-effective production of isopropanol-butanol-ethanol (IBE) from switchgrass biomass. As such, IBE is seen as a viable future fuel to transition the transportation sector towards renewable biofuels. In this study, an atmospheric co-flow diffusion flame burner was used to examine the sooting tendency of IBE when mixed with a diesel surrogate for blend ratios varying from 0% to 100% by volume. Experimental measurements of soot volume fraction were obtained by implementing a color-ratio pyrometry technique and reporting the variation of sooting tendency in terms of the Yield Sooting Index (YSI). Measurements demonstrated soot formation and hence YSI decreased nonlinearly with increasing IBE content. To gain further insight into the kinetics affecting soot formation, numerical modeling studies were carried out using laminarSMOKE++ and a comprehensive kinetic mechanism with soot chemistry. From a reaction path and rate of production analysis, IBE demonstrated that it can perturb OH and HO2 radical pools and enhance CO and CO2 reactive channels from IBE oxygenated intermediates to suppress the formation of soot precursors. Studies were also extended to examine the role of CO2 dilution on soot formation. It was shown that further soot reduction can be attained by lowering the rate of overall soot formation kinetics, perturbing reaction intermediates leading to soot formation by the depletion of H-atom radical pool, while enhancing the oxidation through enhanced OH-radical production.

Construction and validation of a reduced mechanism in a diesel engine fueled with 2-methylfuran-diesel

The addition of 2-methylfuran into diesel has been studied extensively to deal with the fossil energy crisis and reduce pollutant emissions. However, the chemical reaction mechanism of the engine combustion model related to 2-methylfuran is rarely reported. In this study, a reduced 2-methylfuran chemical reaction mechanism was developed by the directed relation graph with error propagation, reaction path analysis, sensitivity analysis and rate of production analysis. Then it was coupled with a diesel mechanism, and the pre-exponential factor A of the Arrhenius equation was adjusted for specific reactions to finally forma reduced 2-methylfuran-diesel mechanism containing 55 species and 190 reactions for application in combustion modeling under engine related conditions. Based on the experimental data in the literature, the predicted ignition delay time and species mole fractions by the mechanism were validated. Also, the three-dimensional simulation data was compared with the test data of cylinder pressure and heat release rate from a single-cylinder diesel engine under different working conditions. The simulation results of the mechanism with certain stability and accuracy are basically consistent with the experimental data and can be used to analyze the characteristics of 2-methylfuran-diesel combustion on diesel engines.

Combustion of Salicornia bigelovii Pyrolysis Bio-oil and Surrogate Mixtures: Experimental and Kinetic Study

Pyrolysis bio-oil (PBO), a renewable and sustainable alternative energy source, is gaining significant importance. PBOs are polar, viscous, and acidic in nature, which restrict their direct utilization. The blending of PBOs with fossil-based fuels in combustion processes can potentially reduce net carbon emissions. The utilization of PBOs in combustion systems warrants an understanding of their combustion chemistry, which serves as the motivation for this study. In this study, pyrolysis of a saltwater halophyte, Salicornia bigelovii, was performed to obtain PBO. Based on the PBO composition, a blend of pyrrole, furfural, and toluene was prepared as a surrogate. The combustion chemistry of a three-component surrogate comprising oxygen- and nitrogen-containing compounds is studied for the first time. To understand the gas-phase combustion chemistry of the PBO surrogate, experiments were performed in a jet-stirred reactor (JSR) at atmospheric pressure and a residence time of 2 s in the temperature range of 780–960 K (ϕ = 0.25). Also, the PBO surrogate was blended in the ratios of 10 and 20% (by wt) with a toluene/iso-octane (80/20 mol/mol) mixture and investigated to mimic the combustion of PBO with hydrocarbons. A detailed chemical kinetic mechanism was compiled using different sub-mechanisms for surrogate components. NUIGMech1.2 was used as the base mechanism. Fuel-reactant species and 17 product species were identified to understand the combustion chemistry of PBO surrogate and its blends. Furthermore, rate of production analysis was performed to understand the pathways vital for forming intermediates. In addition, the thermal stability of PBO was studied in a thermogravimetric analyzer in the temperature range of 105–750 °C in oxygen and nitrogen atmospheres. The mass loss and derivative mass loss profiles were acquired, different stages of the reactions were identified under the oxygen atmosphere, and the apparent kinetic parameters were determined via the Friedman method.

Experimental and kinetic modeling studies of phenyl acetate pyrolysis at atmospheric pressure

Phenyl acetate (CH3COOC6H5, PA) shares a similar aryl acetate group with vitamin E acetate, which is thought to be responsible for producing pulmonary toxic ketene in e-cigarettes. Hence, PA is reported to be a model compound of vitamin E acetate in producing ketene. To better understand the pyrolysis chemistry of vitamin E acetate, pyrolysis of PA in a jet-stirred reactor was investigated by using synchrotron vacuum ultraviolet photoionization mass spectrometry at atmospheric pressure and at temperature range of 700 – 1025 K. Several key products such as acetylene, ethylene, carbon monoxide, formaldehyde, carbon dioxide, vinyl acetylene, 1,3-butadiene, 1,3-cyclopentadiene, benzene, phenol, etc., and especially, ketene, were identified and measured. By extending the phenyl formate pyrolysis model, a detailed PA pyrolysis model containing 735 species and 3365 reactions was constructed and validated against the current experimental results of PA pyrolysis. Rate of production analysis and sensitivity analysis show that the main reaction pathways of PA pyrolysis are the unimolecular decomposition forming phenol and ketene, followed by the C–CH3 bond cleavage forming phenoxycarbonyl and methyl. The corresponding products of these two reactions and of the subsequent reactions, including phenol, ketene and carbon monoxide, etc., are demonstrated to be the key products in PA pyrolysis. Toxic aromatic compounds, such as benzene, toluene and ethylbenzene, etc., also have relatively high mole fractions in PA pyrolysis.

An experimental and kinetic modeling study of auto-ignition and flame propagation of ethyl lactate/air mixtures, a potential octane booster

Spark ignition engines are one of the main technologies in the transport sector. The improvement and optimization of the fuels used to empower these engines are of vital importance, both for economic and environmental reasons. In particular, one of the main issues of spark ignition engines is the knock phenomenon; new formulations of fuels are being studied in order to overcome this problem. In this study, a possible innovative anti-knock, octane booster additive is considered: ethyl lactate. This molecule is almost unknown in combustion literature, as it has been used only as green solvent and food additive. The first experimental results under combustion conditions are presented, together with a kinetic mechanism. Two set-ups have been employed: a rapid compression machine, to measure ignition delay times, and an innovative spherical bomb, OPTIPRIME, to obtain laminar flame speeds. The results are encouraging for the expected application and the mechanism shows good performance. Ignition delay times at all conditions are well predicted by the mechanism and, when compared to ethanol, they are longer, implying a greater anti-knock capability. A rate of production analysis has been performed, where the unimolecular reaction leading to ethylene and lactic acid has been proved to be quite important at high temperatures and lean conditions. For laminar flame speeds, the agreement between model and experiments is good, with some discrepancies at lean conditions and high pressures. Compared to ethanol, at rich and stoichiometric conditions ethyl lactate flame speeds are slightly slower except at lean conditions, indicating that under some conditions this molecule could provide better performances than ethanol as an octane booster additive.

Experimental and kinetic modeling study on auto-ignition properties of ammonia/ethanol blends at intermediate temperatures and high pressures

The auto-ignition properties of ammonia (NH3)/ethanol (C2H5OH) blends close to engine operating conditions were investigated for the first time. Specifically, the ignition delay times (IDT) of ammonia/ethanol blends were measured in a rapid compression machine (RCM) at elevated pressures of 20 and 40 bar, five C2H5OH mole fractions from 0% to 100%, three equivalence ratios (ϕ) of 0.5, 1.0 and 2.0, and intermediate temperatures between 820 and 1120 K. The measurements reveal that ethanol can drastically promote the reactivity of ammonia, e.g., the auto-ignition temperature with merely 1% C2H5OH in fuel decreases accordingly around 110 K at 40 bar as compared to that of neat ammonia. Moreover, the promotion efficiency of ethanol is higher than hydrogen and methane with a factor of 5 and 10 under the same condition. Different dependences of IDT on the equivalence ratio were observed with different ethanol fractions in the blends, i.e., the IDTs of the 5%, 10% and 100% C2H5OH in fuel decrease with an increase of ϕ, but an opposite trend was observed in the mixture with 1% C2H5OH. A new chemical kinetic mechanism for NH3/C2H5OH mixtures was developed and it is highlighted that the addition of cross-reactions between the two fuels is necessary to obtain reasonable simulations. Basically, the newly developed mechanism can reproduce the measurements of IDT very well, whereas it overestimates the reactivity of the stoichiometric and fuel-rich mixture with 1% C2H5OH in fuel. The sensitivity, reaction pathway, as well as rate of production analysis indicated that the ethanol addition to ammonia fuel blends provides key interaction pathways and enriches the O/H radical pool which further promotes the auto-ignition process.

Experimental and kinetic modeling studies of low- to moderate-temperature oxidation of 2-furfuryl alcohol in a jet-stirred reactor

2-Furfuryl alcohol, a promising platform chemical, and alternative fuels or additives, is produced from the hydrogenation of furfural. However, the low- to moderate-temperature oxidation study of 2-furfuryl alcohol is scarce up to now. The present study first performed the oxidation experiments in a jet-stirred reactor at the equivalence ratios of 0.5, 1.0, and 2.0. The oxidation species were identified and measured by the synchrotron vacuum ultraviolet photoionization mass spectrometry. No negative-temperature-coefficient behavior was observed. A detailed kinetic model was developed to better understand the consumption of 2-furfuryl alcohol and the formation of oxidation products. The present model can well reproduce the experimental results. Based on the rate of production analysis, H-abstraction reactions on hydroxymethyl group forming hydroxyl(2-furyl)methyl radical are the dominant pathways. Besides, the formation and consumption of main products, such as furfural, furan, acrolein, acetaldehyde, etc., are also discussed. Fuel radicals control the formation of furfural. Furan has multiple formation sources, such as the H-addition reactions on 2-furfuryl alcohol, furfural, and 2-hydroxyfuran. Acrolein is produced by the H-addition reaction on 2-hydroxyfuran and OH-addition reactions on furan. Also, the present work compares and discusses peak concentration for major oxidation products of 2-furfuryl alcohol and 2-methyl furan under the same simulated condition. 2-Furfuryl alcohol oxidation produces a higher concentration of furfural, furan, and acrolein than that of 2-methyl furan. OH on hydroxymethyl group promotes the H-abstraction reactions on the side chain and inhibits the OH-addition reaction on the furan ring.

A case study on laminar flame propagation of flame synthesis precursors using spherically propagating flame: Tetramethylsilane and its alkane counterpart

In this work, the spherically propagating flame method was applied to the measurements of laminar flame propagation for the flame synthesis precursors. The laminar burning velocities of a typical precursor of silica nanoparticles, i.e. tetramethylsilane (TMS, Si(CH3)4), were measured, and a comparative study was carried out on its hydrocarbon counterpart, neopentane. The laminar burning velocities of the two fuels were measured at the initial pressure of 1 atm, initial temperature of 323 K and equivalence ratios of 0.7–1.5. The results show that the laminar burning velocities of TMS are much higher than those of neopentane, showing remarkable fuel molecular structure effects. Kinetic models of TMS and neopentane combustion were constructed and validated against the new experimental data in this work. Based on the rate of production analysis and sensitivity analysis, the critical pathways in the flames of TMS and neopentane were revealed. The fictitious diluent gas method was adopted to provide insight into the fuel molecular structure effects on the laminar burning velocities of TMS and neopentane. It is concluded that the relatively high adiabatic flame temperature of TMS is the driven force of the rapid laminar flame propagation of TMS compared with neopentane, while the chemical effect also promotes the laminar flame propagation of TMS, especially under near stoichiometric conditions.

A shock tube experiment and an improved high-temperature diisopropyl ketone model by Bayesian optimization

Ignition delay times (IDTs) for di-isopropyl ketone (DIPK) were measured at pressures of 6 and 10 atm, equivalence ratios (ϕ) of 0.5, 1.0, and 2, and over a temperature range of 1100 - 1500 K. In the DIPK sub-model proposed by Barari et al., DIPK⇔IC3H7+IC3H7CO (R2) was erroneously written as DIPK⇔IC3H7+ IC4H7O and the consumption paths of dimethyl ketene (DMK) are missing. A DIPK sub-model was proposed on the basis of Barari model by correcting these errors, reassigning the rate coefficients of the DIPK unimolecular decomposition reactions (R1, R2), H-abstraction reactions by O˙H (R3, R4), fuel radical isomerization reaction (R5), and β-scission decomposition reactions (R5-R10) using the analogy method, and adopting the theoretical calculations of the H-abstraction reactions by H˙, C˙H3, and HO˙2 (R11-R16) provided by Allen et al.. The rate coefficients of R1-R10 were globally optimized by the Bayesian optimization algorithm using the experimental IDTs and profiles of DIPK and DMK. The optimized model well predicts not only the IDTs and profiles of DIPK and DMK, but also the laminar flame speeds and the profiles of many intermediates (propyne, propylene, and methyl ketene) and small species (H2, CO, CH4) during the pyrolysis of DIPK. The calculation using the method of Chen et al. shows that no optimized reaction violates the collision limit. The sensitivity and rate of production analysis were used to discuss the DIPK unimolecular decompositions, DIPK H-abstraction reactions, DIPK radicals isomerization and β-scission reactions, and the optimization of the DIPK sub-model.

Molecular beam mass spectrometry study on plasma-assisted low-temperature oxidation of ethylene

The chemical kinetics of plasma-assisted low-temperature oxidation of ethylene (C2H4) is explored by molecular beam mass spectrometry and kinetic modeling. In the experiments, a dielectric barrier discharge (DBD) flow reactor coupled with photoionization and electron ionization molecular beam mass spectrometry (PI-MBMS/EI-MBMS) is employed to provide detailed speciation information, including ions, radicals, and molecules in C2H4/O2/Ar systems (∼340 K, 30 Torr). A series of hydrocarbons and oxygenated intermediates including ethenol, methyl hydroperoxide, ethyl hydroperoxide, diacetylene, vinylacetylene, and hydroxyacetaldehyde is detected for the first time in this system. A kinetic mechanism that contains both combustion and plasma reaction networks is developed. The path fluxes of fuel consumption and oxygenates formation are obtained based on the rate of production analysis. Based on our experimental observations and modeling analysis, new insights into the kinetics of C2H4/O2/Ar plasmas are provided. The fuel is mainly consumed through OH addition, dissociation after e/Ar* collision, reactions with O/O(1D), and dissociative ionization. H abstraction reactions that are favored in alkane plasmas contribute little to the fuel consumption of ethylene. Formation pathways of C1 oxygenates are mainly initiated by CH3 produced by O/O(1D) reactions with fuel, and the subsequent pathways of OH/H addition to the fuel are responsible for the formation of most C2 oxygenates. Oxygen addition-elimination reactions of C2H4OH isomers are the sources of ethenol formation. The concentration profiles for some of the species under different oxygen mole fractions are measured. The two distinct patterns of species mole fraction profiles with increasing oxygen concentrations indicate the different dominating formation pathways, namely oxidation pathways and non-oxidation pathways. And the competition between oxidation effects and plasma effects is displayed by the non-monotonic mole fractions profiles of oxidation products.

Experimental and kinetic model studies on the pyrolysis of 2-furfuryl alcohol at two reactors: Flow reactor and jet-stirred reactor

2-Furfuryl alcohol, derived from non-edible biomass, is the significant component of bio-oil in the pyrolysis of lignocellulose biomass and a potential alternative fuel or fuel additive. To better optimize the pyrolysis model of lignocellulose to improve the properties of pyrolysis bio-oil and further understand the combustion characteristics of 2-furfuryl alcohol, the pyrolysis experiments were performed in a flow reactor at 30 Torr for T = 1006 – 1339 K and 760 Torr for T = 850 – 1131 K, and in a jet-stirred reactor at 760 Torr for T = 750 – 1050 K. The pyrolysis products, including radicals (methyl, propargyl, allyl, and cyclopentadienyl), isomers (furfural/2-ethyl furan, furan/vinyl ketene, and allene/propyne), and aromatics (benzene, toluene, indene, etc.) were identified and measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A comprehensive kinetic model for 2-furfuryl alcohol pyrolysis was developed and was validated against the experimental data in the present and previous work. Rate of production analysis indicated that the C–O bond dissociation reaction, H-abstraction reactions on the hydroxymethyl group, and the H-addition reactions on the furan-ring controlled the consumption of 2-furfuryl alcohol and the formation of primary pyrolysis products like 2-methyl furan, 2-ethyl furan, furfural, and furan. In addition, the OH-addition reaction on the furan-ring had a certain contribution to the consumption of 2-furfuryl alcohol, while the contribution of H-shift reactions was negligible. The present work systematically compared the effects of methyl, ethyl, and hydroxymethyl groups on the decomposition of furanic fuels and the formation of major products. The results showed that the substituent groups can reduce the decomposition temperature of the fuels, especially the ethyl and hydroxymethyl groups. The alkyl substituent group can promote the formation of small hydrocarbons, of which the mole fraction increased with the length of the carbon chain increasing. The hydroxymethyl group facilitated the formation of oxygenated products.

A multi-component surrogate mechanism of diesel from indirect coal liquefaction for diesel engine combustion and emission simulations

Diesel from indirect coal liquefaction (DICL) is a kind of extremely promising alternative fuel to alleviate the oil security problem caused by excessive dependence on imported oil and reduce the pollutant emission. However, the mechanism of diesel from indirect coal liquefaction is very few, and the numerical simulation of combustion and emission characteristics of diesel from indirect coal liquefaction is even less. Therefore, a reduced mechanism of DICL, entailing 178 components and 650 reactions, was put forward to research the combustion and emission characteristics of engines fueled with DICL under different loads in this work. n-Hexadecane (HXN) mechanism and 2,2,4,4,6,8,8-heptamethylnonane mechanism (HMN) were respectively considered as representative species of straight-chain paraffin and branched alkane in surrogate model. Firstly, direct relation graph and direct relation graph with error propagation were used in turn. Then, sensitivity analysis coupled with rate of production analysis has been used to further reduce the detail 2,2,4,4,6,8,8-heptamethylnonane mechanism. After that, the skeleton mechanism of n-hexadecane and the reduced polycyclic aromatic hydrocarbon (PAH) mechanism were combined with the simplified HMN mechanism to develop a novel multi-component mechanism of HXN-HMN-PAH. Brute-force sensitivity analyses were respectively conducted at different temperatures to find out these key reactions that have great effects on the ignition delay times (IDTs). Then, the optimizations of the reduced mechanism were made based on the ignition delay times of the experimental datum and the detail mechanism. A proportion of 71.5% HXN and 28.5% HMN by mole fraction was determined according to the properties of practical DICL. Furthermore, the optimized mechanism was employed to verify experimental values including the ignition delay times, the species concentrations on jet-stirred reactors (JSR) and the laminar flame speeds. Eventually, the mechanism was coupled into computational fluid dynamic (CFD) to perform multi-dimensional numerical simulation validation in a directed injection compression ignition (DICI) engine under different loads.

Experimental and kinetic modeling study of the homogeneous chemistry of NH3 and NOx with CH4 at the diluted conditions

Homogeneous oxidation of CH4/NH3/NO/NO2 mixtures in the temperature range from 600 to 1200 K was investigated in this work. Seven gas mixtures were designed to reveal the influence of CH4 and NO/NO2 ratio during the reaction process. The experiments were carried out in a laminar flow reactor at atmospheric pressure. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used to achieve comprehensive detection of major products and critical hydrocarbon, carbonyl and nitrogenous intermediates. An improved kinetic model, which incorporates a detailed C1-C2/NOx/NH3 sub-mechanism was developed to complement the experiments. In general, the experimental results are in good agreement with prediction of the kinetic model. Rate of production analysis and sensitivity analysis were performed to interpret the experimental observations. The results show that in the oxidation of NH3/NOx mixtures, the NO/NO2 ratio can affect the conversion of NO through the reaction NH2 + NO2 = H2NO + NO. In the presence of CH4, the oxidation reactivity of NH3/NOx mixture is significantly promoted. As the added amount of CH4 increases, the production of H2O is enhanced while N2 formation is inhibited. Beside, the addition of CH4 also promotes the production of carbonyl and nitrogenous species. In the oxidation of CH4/NH3/NOx mixtures, the change of NO2/NO ratios only has little effect on the formation of major products and intermediates.

Construction of a Chemical Kinetic Model of Five-Component Gasoline Surrogates under Lean Conditions.

The requirements for improving the efficiency of internal combustion engines and reducing emissions have promoted the development of new combustion technologies under extreme operating conditions (e.g., lean combustion), and the ignition and combustion characteristics of fuels are increasingly becoming important. A chemical kinetic reduced mechanism consisting of 115 species and 414 elementary reactions is developed for the prediction of ignition and combustion behaviors of gasoline surrogate fuels composed of five components, namely, isooctane, n-heptane, toluene, diisobutylene, and cyclohexane (CHX). The CHX sub-mechanism is obtained by simplifying the JetSurF2.0 mechanism using direct relationship graph error propagating, rate of production analysis, and temperature sensitivity analysis and CHX is mainly consumed through ring-opening reactions, continuous dehydrogenation, and oxygenation reactions. In addition, kinetic parameter corrections were made for key reactions R14 and R391 based on the accuracy of the ignition delay time and laminar flame velocity predictions. Under a wide range of conditions, the mechanism’s ignition delay time, laminar flame speed, and the experimental and calculated results of multi-component gasoline surrogate fuel and real gasoline are compared. The proposed mechanism can accurately reproduce the combustion and oxidation of each component of the gasoline-surrogate fuel mixture and real gasoline.

Experimental and kinetic modeling study of di-n-propyl ether and diisopropyl ether combustion: Pyrolysis and laminar flame propagation velocity

To explore the fuel isomeric effect on ether combustion characteristics, pyrolysis, and laminar flame propagation of di-n-propyl ether (DPE) and diisopropyl ether (DIPE) were investigated. A new kinetic model of DIPE was developed based on our recent DPE model [Fuel 298 (2021) 120797]. The pyrolysis experiments were carried out in two jet-stirred reactors at near-atmospheric pressure with good agreement on the measurements using synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography/mass spectrometry. The decomposition profile of DIPE showed a faster trend than that of DPE, which can be attributed to the faster alcohol elimination reaction of DIPE. The dominant roles of alcohol elimination reaction and H-abstraction reactions in fuel consumption explain the production of fuel-specific oxygenated species, i.e. n-propanol and propanal in DPE and i-propanol, acetaldehyde and acetone in DIPE. The laminar burning velocities of DPE and DIPE were also measured in a high-pressure constant-volume cylindrical combustion vessel at the initial temperature of 373 K and pressures of 1–10 atm. It was found that the linear DPE propagated faster than DIPE with the branched structure under all investigated conditions. Rate of production analysis and sensitivity analysis were also performed to elucidate the key radicals and reactions responsible for the remarkable reactivity of isomeric fuels. Fuel structures have a great influence on the distribution of radical pools, resulting in the easy formation of active radicals in DPE flames such as vinyl and ethyl and stable radicals in DIPE flames like methyl and allyl. The successive decomposition reactions of these dominant radicals promote the DPE flame and inhibit the DIPE flame propagation respectively, which explains the higher laminar burning velocities and reactivity of DPE than that of DIPE. Furthermore, the present model was also examined against the literature data, including pyrolysis and oxidation in the jet-stirred reactor and flow reactor.

Study on oxidation and pyrolysis of carbonate esters using a micro flow reactor with a controlled temperature profile. Part I: Reactivities of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate

Carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are widely used as electrolyte solvents in a lithium-ion battery (LIB) and are considered as one of potential fire causes. This study investigates a difference in gas-phase reactivities of DMC, EMC and DEC. Species measurements for oxidation (equivalence ratio of 1.0) and pyrolysis of DMC and DEC at maximum wall temperatures of Tw,max = 700–1300 K and atmospheric pressure were performed using a gas chromatograph connected to a micro flow reactor with a controlled temperature profile (MFR). Measured mole fractions of C2H4 and CO2 in the DEC case started increasing at a low temperature (Tw,max = 750 K), while those of CH4 and CO2 in the DMC case started increasing at an intermediate temperature (Tw,max = 1050 K). Gas-phase reactivities of the three carbonate esters were found to be DMC < EMC ≈ DEC through observation of their weak flames. Computational species and heat release rate profiles of DEC showed a three-stage reaction: thermal decomposition, oxidation of decomposition products to CO and CO oxidation to CO2. This three-stage reaction of DEC is distinct from the one driven by low-temperature oxidation observed with n-heptane and DME in earlier studies. Rate of production analysis indicated that principal fuel consumption reactions of DMC were H-atom abstraction reactions and that of DEC was a thermal decomposition reaction producing C2H4. Based on reaction path analysis of DEC oxidation, initial-stage reactions produced few active radicals at the low temperature region. The reactivity difference between DMC and DEC is, therefore, mainly driven by the difference in the primary fuel consumption reactions that relies on fuel molecular structure. Considering the existence of ethyl ester group in EMC, a dominant EMC consumption reaction would be similar to DEC.