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• The ignition delay times of natural gas mixtures diluted in CO 2 were measured. • The OXY-NG model was proposed for the natural gas oxy-fuel combustion and validated by the experimental data in the pressure range of 1–260 bar. • As the equivalence ratio increases, the ignition delay times of natural gas with CO 2 dilution increase at the pressure of 2 bar, whereas those decrease at the pressure of 250 bar. • The chaperon effects of CO 2 related to H + O 2 (+M) ⇔ HO 2 (+M) promote the ignition at fuel-rich conditions but inhibit the ignition at fuel-lean condition. Pressurized oxy-fuel combustion has attracted considerable attention as an efficient technology with lower emissions. Natural gas, which primarily consists of methane, ethane, and propane, is a widely used fossil fuel owing to its safety and low cost. The auto-ignition of 90 %methane/9 %ethane/1 %propane mixture diluted in CO 2 or N 2 were investigated using a shock tube at temperatures of 1280–1645 K, pressures of 2 and 10 bar, and equivalence ratios of 0.5–2.0 in this study. An updated model named OXY-NG can accurately predict the ignition delay times, species yields, and laminar flame speeds of natural gas mixtures in oxy-fuel and air combustion modes. The ignition delay times increased as the equivalence ratios increased related to the recombination of CH 3 radicals at 2 bar but decreased as the equivalence ratios increased owing to reactions involving HO 2 at 250 bar. The diluent CO 2 has inhibitory effects on ignition compared with N 2 , and these effects were minor under high pressure and fuel-rich conditions when diluted in CO 2. The effects on natural gas mixture ignition owing to chemical and physical properties of CO 2 are discussed in detail. [ABSTRACT FROM AUTHOR]

Ultra-lean combustion (usually Φ < 0.3) has attracted much attention for its low emission and high efficiency. Propane is a key fuel to characterize the chemical kinetics from small to large hydrocarbons as well as the main content of liquefied petroleum gas. In this study, the ignition delay times of propane with nearly 90%Ar dilution were measured for the equivalence ratios of 0.3, 0.1, and 0.05 at the pressures of 1 atm and 10 atm in a shock tube. The OXYMECH 2.0 model, which was developed for the oxy-fuel combustion and conventional combustion of C 1 ‒C 3 alkanes, was modified and evaluated by the ignition delay times of propane in ultra-lean conditions. The modified model was used to analyze the effects of the equivalence ratio on the ignition of propane with different diluents (CO 2 and Ar) at different pressures. The ignition can be increasingly improved by decreasing the equivalence ratio to 0.05 under atmospheric pressure and the inhibiting effects of CO 2 are very weak at the equivalence ratio below 0.05. The ignition improvement by reducing the equivalence ratio at high pressure is weaker than that at atmospheric pressure and the inhibiting effects of CO 2 on the ignition are evident in either super-lean or ultra-lean mixtures at high pressure. The effects of superabundant air in ultra-lean combustion on the ignition of propane consist of the dilution and oxidation effects and are analyzed in detail. [ABSTRACT FROM AUTHOR]

• The ignition delay times of CH 4 /C 3 H 8 mixtures in ratios from 90/10% to 70/30% diluted in CO 2 were measured at pressures of 1.75 and 10 atm. • The addition of propane promotes the ignition significantly in the C 3 H 8 proportion range from 0 to 30% in both cases of CO 2 and N 2 , but has slight effects on the ignition with the C 3 H 8 proportion more than 30%. • The fast increase of the methyl radicals in the initial stage is through C 3 H 8 (+M) ⇔C 2 H 5 + CH 3 (+M) owing to the easier breaking of C-C bonds in propane, which enhances CH 3 + HO 2 ⇔OH + CH 3 O, consequently promoting the ignition. • The effects of CO 2 on the promoting influence of C 3 H 8 addition are slight. • H + O 2 (+M) ⇔HO 2 (+M) suppresses the ignition at the fuel-lean condition but promotes the ignition in stoichiometric and fuel-rich conditions at 10 atm. Pressurized oxy-fuel combustion has gained great interest owing to its low emission and high efficiency. Methane and propane are important composition of natural gas, which is a clean fossil fuel and widely utilized for combustion applications including gas turbines. In this work, the auto-ignition properties of CH 4 /C 3 H 8 mixtures in ratios from 90/10% to 70/30% diluted in CO 2 were measured at pressures of 1.75 and 10 atm; equivalence ratios of 0.5, 1.0, and 2.0; and temperatures in the range of 1240–1520 K in a shock tube. Four key reactions in the Oxymech 2.0 model were updated and the modified model shows reasonable performance in both the ignition delay time and the laminar flame speed predictions in O 2 /N 2 and O 2 /CO 2 atmospheres. Two kinetic models (NUIG 1.0 and AramcoMech 3.0) were evaluated by present data and the laminar flame speed from the literature. The results of the experiment and calculation show that the addition of propane promotes the ignition significantly in the C 3 H 8 proportion range from 0 to 30% in both cases of CO 2 and N 2 , but has slight effects on the ignition with the C 3 H 8 proportion more than 30%. The effects of CO 2 on the promoting effects of C 3 H 8 addition are slight. The ignition delay times increase with the equivalence ratio at 1.75 atm but no statistical difference is observed between the measured data of different equivalence ratios at 10 atm. The influence of C 3 H 8 addition and the equivalence ratio on the ignition delay of CH 4 /C 3 H 8 mixtures was also analyzed in detail. [ABSTRACT FROM AUTHOR]

Super lean (usually Φ < 0.5) and ultra-lean (usually Φ < 0.3) combustion are regarded as promising combustion techniques owing to high fuel economy and low emission. Ethane is one of the key components of natural gas. In the present study, the ignition delay times (IDTs) of ethane/oxygen/argon mixture were measured behind reflected shock waves at three equivalence ratios of 0.5, 0.1, 0.05, two pressures of 1.68, 9.0 atm, and in the temperature range of 1120 – 1351 K. The OXYMECH2.0, proposed in our previous works, is modified in the present study by updating several elementary reactions. The modified OXYMECH is validated by ethane IDTs of super lean combustion measured in the present study, in high CO 2 atmospheres and O 2 /Ar atmospheres from the literature as well as laminar flame speeds (LFSs) under O 2 /N 2 and O 2 /CO 2 atmospheres. Aramco3.0, San Diego, NUIGMech0.9, and CRECK-GB models are also evaluated by ethane IDTs measured in the present study, the results show that modified OXYMECH, NUIGMech0.9, and CRECK-GB models provide equally accurate predictions for experiments. The NUIG Mech0.9 and CRECK-GB are further evaluated using the ethane IDTs in high CO 2 atmospheres and experimental LFSs of ethane under O 2 /N 2 and O 2 /CO 2 atmospheres, the results show that modified OXYMECH has good performance in predicting IDTs and LFSs of ethane. The detailed comparisons of IDTs and LFSs prediction between modified OXYMECH and CRECK-GB models are conducted. The effects of superabundant air, which is the air excess with equivalence ratio decreases from Φ 1 to Φ 2 , on the ignition in super lean combustion consist of the dilution and oxidation effects, which are studied in the present study in detail. It is very interesting that the dilution effects promote the ignition while the oxidation effects inhibit the ignition at Φ < 0.3 and P = 9.0 atm. [ABSTRACT FROM AUTHOR]

Pressurized oxy-fuel combustion is deemed an advanced oxy-fuel combustion technique due to the lower cost and little decrease in the generating efficiency compared to conventional PC system without CO 2 capture. Butane is an important composition of petroleum and natural gas. In this work, the ignition delay times (IDTs) for n-butane and i-butane under O 2 /CO 2 atmospheres were measured in a shock tube at different equivalence ratios (Φ) and pressures. Based on our previous C 1 C 3 model Oxymech2.0 and the C 4 sub-model of Aramco3.0, a chemical kinetic model Oxymech2.0 Plus was updated. Oxymech2.0 Plus was validated by the newly measured IDTs of butane under O 2 /CO 2 atmospheres. The model was also validated by the literature experimental data for IDTs of n-butane and i-butane at O 2 /Ar and O 2 /N 2 atmospheres, laminar flame speeds of n-butane and i-butane in air, and species profiles of n-butane and i-butane pyrolysis. The comparison between Oxymech2.0 Plus and Aramco 3.0 models was also conducted in detailed. The results show that the updated reactions in the study significantly improve the prediction of IDTs, laminar flame speeds and species profiles of butane in O 2 /CO 2 atmospheres. The effects of equivalence ratios and CO 2 on the IDTs of n-butane and i-butane were analyzed. [ABSTRACT FROM AUTHOR]

• Ignition delay times of dimethyl ether/ethane/O 2 /CO 2 mixtures were first provided. • OXYMECH predicts well on the IDTs of the mixtures in O 2 /CO 2 and O 2 /N 2 atmosphere. • IDTs of the mixtures first decrease and then increase as adding DME at 10 atm. • The effect of DME addition and CO 2 on the IDTs of the mixtures were analyzed. The ignition delay times (IDTs) of dimethyl ether (DME)/ethane/O 2 /CO 2 mixtures were measured in a shock tube at pressures of 0.8, 2, and 10 atm; temperatures within the range of 1126–1449 K; equivalence ratio of 0.5; and DME proportions within the range of 0–100%. Four chemical kinetic models named OXYMECH, AramcoMech 3.0, San-Diego 2016 and Wang-DME were validated using the IDTs measured in this work. The results indicate that the OXYMECH predicts well the experimental data under O 2 /CO 2 and O 2 /N 2 atmospheres. At P = 0.8 and 2 atm, T = 1300 K, the increase of the DME proportion inhibits the ignition of the mixtures under O 2 /N 2 and O 2 /CO 2 atmospheres. At P = 10 atm, T = 1300 K, the IDTs of the mixtures firstly decrease when DME proportion increases from 0 to 20%, and then increase when DME proportion increases from 20 to 100% under O 2 /CO 2 atmosphere, while the IDTs of the mixtures increase as the DME proportion increases under O 2 /N 2 atmosphere. The valley-values of the IDTs of the mixtures appear at the certain DME proportion at P = 10 atm, T = 1100 K and 1200 K under O 2 /N 2 and O 2 /CO 2 atmospheres. The analyses of sensitivity and the rate of production were conducted to interpret the effect of DME addition and the properties of CO 2 on the ignition of the DME/C 2 H 6 /O 2 /CO 2 mixtures. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion of fossil fuels based on the Allam cycle has garnered increasing attention owing to its high-power cycle efficiency in carbon capture. The submechanism of ethylene, an important intermediate product in the oxidation of long-chain alkanes, is vital for establishing chemical kinetic models of alkanes for oxy-fuel combustion. In this study, the ignition delay times of C 2 H 4 diluted in CO 2 are measured at pressures of 1 and 10 atm under O 2 /CO 2 atmospheres at three equivalence ratios (0.5, 1.0, and 2.0) in a shock tube. Meanwhile, the ignition delay times of C 2 H 4 / n -C 4 H 10 mixtures and n -C 4 H 10 / i -C 4 H 10 mixtures diluted in CO 2 are measured at pressures of 1 and 10 atm, equivalence ratios of 1.0, and three mixing ratios (1:2, 1:1, and 2:1). The C 2 H 4 submechanism in the Oxymech2.0 Plus model proposed in our previous study is modified by updating some C 2 H 4 -related reactions. The modified Oxymech model, NUIGMECH1.1, and Wang2021 are evaluated based on the present experimental ignition delay times and other experimental results from the literature, including the ignition delay times of C 2 H 4 diluted in both CO 2 and conventional atmospheres, as well as the laminar flame speeds of C 2 H 4 and C 2 H 4 profiles in pyrolysis. The results show that the modified Oxymech model accurately predicts the experimental results. The modified Oxymech model is compared with NUIGMECH1.1 to predict the ignition delay times in CO 2 atmospheres and laminar flame speeds more accurately. The effects of CO 2 on the ignition delay of C 2 H 4 are discussed comprehensively. [ABSTRACT FROM AUTHOR]

The Dimethyl ether (DME) kinetic model is significant to understand the DME combustion in the atmosphere containing high CO 2 concentration, such as pressurized oxy-fuel combustion process and exhaust gas recirculation, and design the combustor. In this paper, the ignition delay times (IDTs) of DME were measured in a shock tube under the conditions of equivalence ratios of 0.5, 1 and 1.5, temperature ranges from 1007 K to 1340 K, and pressures of 2 and 11 atm. A detailed kinetic model of DME named as OXYDME was put forward based on the OXY-Aramco model, and was validated by the low and high temperature IDTs, laminar flame speeds, and species profiles measured in this work and those from literatures in atmospheres of O 2 /Ar/CO 2 , O 2 /N 2 , O 2 /N 2 /He/CO 2 and O 2 /CO 2. The OXYDME model was compared with OXY-Aramco, Liu-DME model in detail. The effects of CO 2 on the DME ignition are very weak and not sensitive to the temperature and pressure. The reason for the weak effects of CO 2 is that the chemical effects of CO 2 promote ignition, which counteracts the inhibition effects caused by the physical properties of CO 2. The chaperon effects of CO 2 dominate the chemical effects. Meanwhile, the effects of the reactions with CO 2 are very small. [ABSTRACT FROM AUTHOR]

Understanding the details of pyrrole combustion chemistry in the O 2 /CO 2 atmosphere contributes to developing the strategies for nitrogen oxides (NOx) control during the pressurized oxy-coal combustion (POCC). However, the existing kinetic models for pyrrole oxidation lack multi-dimensional validation, and the ignition delay times (IDTs) of pyrrole in the O 2 /CO 2 atmosphere are still scarce. This study measured the IDTs of pyrrole in O 2 /CO 2 atmospheres at an elevated pressure of 5.2 bar, temperatures from 1271 to 1645 K, and equivalence ratios Φ = 0.5, 1.0, and 2.0 in a shock tube. The results demonstrate that the pyrrole IDTs decrease with decreasing equivalence ratio and the pyrrole mixtures in O 2 /CO 2 atmospheres have longer IDTs than those in O 2 /Ar atmospheres. A pyrrole oxidation kinetic model (HUST pyrrole model) has been developed by updating 19 reactions in our previous model (HUST pyridine model). HUST pyrrole model gives a satisfactory prediction of the IDTs of pyrrole in the O 2 /Ar atmosphere (measured by MacNamara et al.) and O 2 /CO 2 atmosphere (measured in this study) and the profiles of pyrrole, HCN, and NO (measured by Yamamoto et al.). The comparison of the HUST pyrrole model with the Lumbreras model (2001) was conducted by the pyrrole IDTs and profiles of HCN using the sensitivity and flux analysis. The addition of HNCPROP and modification of R665 (C 3 H 3 + O 2 = CH 2 CO + HCO), R1273 (AC 3 H 4 CN + H 2 => ALLYLCN + H), R1251 (PYRLNE = ALLYLCN), R1238 (PYRROLE + H = PYRLYL + H 2), and R1240 (PYRROLE + OH = PYRLYL + H 2 O) in HUST pyrrole model significantly improve the prediction performance for the pyrrole oxidation. The effects of the equivalence ratio and CO 2 on the IDTs for pyrrole oxidation have been analyzed. [ABSTRACT FROM AUTHOR]