Combustion and Flame最新文献

Shock-tube experiments at elevated pressures between 2.0 and 2.7 bar were carried out to study H-atom abstractions between D atoms and selected ether compounds: dimethyl ether (DME), diethyl ether (DEE), dimethoxymethane (DMM), and methyl propyl ether (MPE). D-atom resonance absorption spectrometry (D-ARAS) behind reflected shock waves was used to monitor the consumption of D atoms. To study the bimolecular reactions between D atoms and the specific ether, gas mixtures of the selected ether compound and C₂D₅I diluted in argon (bath gas) were prepared; C₂D₅I was used as a precursor for D atoms. This innovative approach using Dual ARAS (D-ARAS and H-ARAS) allows the distinct detection of precursor decay followed by H-atom abstraction reactions and ether decay followed by H-atom release. For the study of the reaction D + DME → HD + products, the experiments covered a temperature range of 940–1050 K; for the reaction D + DEE → HD + products, the temperature range was 980–1260 K; for the reaction D + DMM → HD + products, the temperature range was 930–1300 K; and for the reaction D + MPE → HD + products, the temperature spans a range of 1000–1350 K. Experimentally determined rate coefficients have been expressed by the following Arrhenius equations:

k_total(D+DME)(T) = 1.9×10⁻¹⁰ exp (−31.4 kJ/mol / RT) cm³s⁻¹,

k_total(D+DEE)(T) = 1.7×10⁻¹⁰ exp (−22.4 kJ/mol / RT) cm³s⁻¹,

k_total(D+DMM)(T) = 2.7×10⁻¹⁰ exp (−27.3 kJ/mol / RT) cm³s⁻¹,

and k_total(D+MPE)(T) = 5.1×10⁻¹⁰ exp (−31.5 kJ/mol / RT) cm³s⁻¹.

The experimental results show an uncertainty of ±30 % and were supplemented by transition-state theory (TST) calculations based on molecular properties and energies from computations at the G4 level of theory. TST computations were conducted for H-atom abstraction from various types of primary and secondary carbon bonds. Bond-specific reaction rate-coefficient expressions were derived from theory and compared with experimental results to establish correlations between molecular structure and reactivity.

Understanding the fundamental characteristics of high-pressure cool flames is crucial for the development of advanced and efficient low-temperature combustion engine technologies. The pressure dependency of multi-oxygen addition branching reactions in low-temperature chemistry significantly influences the dynamics, structure, and reactivity of cool flame. This study investigates the non-premixed cool flame of diethyl ether (DEE) at elevated pressures. The results show that pressure rise promotes low-temperature chemistry and significantly extends the extinction limit of cool flame. It is found that the cool flame heat release rate is correlated with the product of pressure and the square root of the pressure-weighted strain rate, $Q\sim \sqrt{aP}·P$, which is different from that of hot flames, $Q\sim \sqrt{aP}$. The radical index concept for atmospheric cool flames is extended to high-pressure cool flames allowing to decouple the mass and thermal transports from the chemical kinetics term to evaluate the fuel reactivity at elevated pressures. The radical index shows that the low-temperature reactivity of DEE is enhanced with the pressure and is higher than n-dodecane by a factor of 19, 18.3, and 16.4 for 1, 3, and 5 atm, respectively. Kinetic analysis reveals that pressure rise results in QOOH stabilization and promotions of the second O₂ addition and the chain-branching reaction pathway for multiple OH radical productions.

RP-3 kerosene is currently the primary jet fuel used in China. However, limited attention has been paid to development of surrogate models that can predict formations of aromatics during RP-3 oxidation in a detailed way, such as by species mole fraction profiles. The present study aims to enrich the experimental database by measuring species mole fraction profiles, particularly focusing on aromatic intermediates, and propose a new surrogate model with a detailed kinetic model to enhance predictive accuracy for these intermediates. Oxidation experiments of real RP-3 kerosene were conducted using an atmospheric flow reactor at temperatures ranging from 800 to 1150 K and equivalence ratios of 0.5 and 2.0. The mole fraction profiles of species including oxygen, major products, important small molecular intermediates and several primary aromatic intermediates were measured using online gas chromatography (GC) and gas chromatography-mass spectrometry (GC–MS). Based on the chemical composition and fundamental physical properties of RP-3 kerosene, a surrogate consisting of 55.0 % n-undecane, 18.7 % trans-decalin, 19.8 % p-xylene and 6.5 % tetralin (by weight) was formulated. A detailed kinetic model of the surrogate was developed and validated against the measured data. Compared to the surrogate models proposed in the previous studies, the current model demonstrates superior predictive capabilities in forecasting the generation of major aromatic intermediates. According to the rate of production (ROP) analysis for the model, benzene generation is associated with three components: decalin, p-xylene and n-undecane. Decalin exhibits the highest contribution to benzene formation under both lean and rich conditions. Toluene predominantly originates from p-xylene, while indene and naphthalene are primarily produced by tetralin. These findings emphasize the significance of decalin as a representative bicyclic cycloalkane component and tetralin as a representative indane/tetralin component in establishing a surrogate for RP-3 fuel to enhance prediction of aromatic intermediates. Furthermore, validation through experimental data from the literature including species mole fraction profiles and ignition delay times confirms the broad applicability of this model.

The soot formation characteristics of laminar nitrogen-diluted n-butylcyclohexane and n-butylbenzene diffusion flames were experimentally and numerically investigated at pressures from 2 to 7 bar. In the experiment, laser-induced incandescence (LII), time-resolved LII, and color-ratio pyrometry were used to measure soot volume fraction, soot particle diameter, and flame temperature. The results show that n-butylbenzene has a significantly higher soot propensity than n-butylcyclohexane. The soot growth and oxidation in both flames are enhanced with increasing pressure. The difference is that the promotion effect of pressure on the soot formation in the n-butylcyclohexane flame continues to weaken as the pressure increases, while this phenomenon does not occur in n-butylbenzene flames. Within the studied pressure range, the mean particle sizes (Dp_mean) in n-butylcyclohexane and n-butylbenzene flames show a good linear relationship with pressure. The pressure dependence of Dp_mean in n-butylbenzene flames is stronger than that of n-butylcyclohexane flames at pressures between 2 and 6 bar. The experiment and simulation results indicate that the enhancement of the promotion effect of pressure on the soot formation in the n-butylbenzene flame may be due to the combined effect of an increase in the soot surface reactivity and an increase in the number density of soot particles. The reaction pathway analysis suggests that the stepwise dehydrogenation reactions of cyclohexene are the main source of benzene formation in n-butylcyclohexane flames and pyrene is mainly formed via the reaction between indenyl and benzyl radicals in n-butylbenzene flames.

Olefins are important components in gasoline fuels as well as essential intermediates in the combustion of carbon-based fuels and oxy-fuels. Therefore, it is essential to investigate the oxidation chemistry of olefins, especially of long-chain olefins, to gain a deeper insight into the combustion of these fuels. 1-Decene is an important industrial chemical product and is often regarded as one of the representatives of long-chain olefins. This work investigated the low-temperature oxidation of 1-decene in a jet-stirred reactor with atmospheric pressure, temperature range of 700 – 900 K and equivalence ratio of 1.0. Twelve main oxidation species were detected and measured, by gas chromatography-mass spectrometry, including carbon dioxide, ethylene, ethane, acrolein, 1,3-butadiene, 1-butene, 1-pentene and benzene, etc. Based on previous reports, a detailed low-temperature oxidation kinetic model of 1-decene was developed and validated against the experimental data and literature data. In the model of 1-decene, the rate of production analysis revealed that the majority of 1-decene was consumed by H-abstractions to generate the primary radicals and OH-addition reaction onto C(1) to generate 1-decanol-2-yl radical. Sensitivity analyses show that H₂O₂ (+ M) = OH + OH (+ M) was the most sensitive reaction to promote 1-decene consumption. The decomposition of hydrogen peroxide was the main source of the hydroxyl radical. Simulation results indicate that ignition delay time of 1-decene is higher than that of n-decane in the low-temperature at equivalence ratios of 0.5 – 2.0 and pressure of 20, 40 bar.

A viable strategy to improve ammonia (NH₃) combustion stability is blending ammonia with high-reactivity fuels. Propane (C₃H₈) is the prevalent component in liquefied petroleum gas (LPG), emerging as a compelling choice for co-firing with ammonia in various practical applications. The ignition delay times (IDTs) of stoichiometric NH₃/C₃H₈ mixtures in Ar dilution (90 %) with varying C₃H₈ fractions (X_C3H8) of 0–30 % were conducted at pressures of 1.75 and 10 bar, and temperatures ranging from 1305 to 1890 K in a shock tube. The NH₃-C₃H₈ model was developed based on the NH₃ model optimized by Li et al., the C₃H₈ submodel in the NUIG 1.1 model, and some new cross-reactions were considered in the NH₃-C₃H₈ model. The NH₃-C₃H₈ model was extensively validated against IDTs measured in this work as well as laminar flame speeds (LFSs) and species profiles (SPs) of NH₃/C₃H₈ from the literature. The comparison of the prediction performance between the NH₃-C₃H₈ model and the M-NUIG model was conducted for ignition, flame propagation, and NH₃ consumption. The effects of the cross-reactions on IDTs, LFSs, and SPs of NH₃/C₃H₈ were studied in detail by the sensitivity analysis and rate of production (ROP) analysis using the NH₃-C₃H₈ model. The newly added C/N cross-reactions play an important role in the prediction of the IDTs, LFSs, and SPs of NH₃/C₃H₈ combustion.