Fuel Combustion Chemistry

Diethyl carbonate (DEC) is a common component of the liquid electrolyte in lithium ion batteries (LIBs). As such, understanding DEC combustion chemistry is imperative to improving chemical kinetic modeling of LIB fires. To this end, a comprehensive experimental study was conducted to collect ignition delay times, CO time histories, and laminar flame speeds during DEC combustion. Ignition delay times were collected using a heated shock tube at real fuel–air conditions for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0) near atmospheric pressure and for temperatures between 1182 and 1406 K. Another shock tube was used to collect CO time histories using a laser absorption diagnostic. These experiments were conducted for the same equivalence ratios, but highly diluted in argon and helium (79.25% Ar + 20% He) at an average pressure of 1.27 atm and a temperature range of 1236–1669 K. Finally, a heated constant-volume vessel was used to collect laminar flame speeds of DEC at an initial temperature and pressure of 403 K and 1 atm, respectively, for equivalence ratios between 0.79 and 1.38. The results are compared with different mechanisms from the literature. Good agreement is seen for the ignition delay time and flame speed measurements. However, significant deviations are observed for the CO time histories. A detailed discussion of the chemical kinetics is presented to elucidate the important reactions and direct future modeling efforts. Full article

The structural parameters of five bituminous coals were analyzed by using X-ray diffraction and attenuated total reflection–Fourier transform infrared spectroscopy. The combustion behavior of coal was investigated by using a thermogravimetric analyzer under air conditions. Furthermore, the relationships between combustion parameters and the coal structure were established. The results show that bituminous coals contain crystalline and amorphous carbon. The aromaticity, interlayer spacing, average stacking height, aliphatic chain length, and the hydrocarbon-generating potential varied with the different bituminous coals. The coal samples exhibited similar weight changes during the combustion process, and the combustion parameters increased with increments in heating rate. The maximum combustion rate and activation energy increased with declining interlayer spacing and hydrocarbon-generating potential and increasing aromaticity, average stacking height, and aliphatic chain length. The bituminous coal for the utilization of combustion should have high aromaticity, a degree of graphitization, crystalline, long aliphatic chain length, and weak hydrocarbon-generating potential. Full article

Coal spontaneous combustion (CSC) is a disaster that seriously threatens safe production in coal mines. Revealing the mechanism of CSC can provide a theoretical basis for its prevention and control. Compared with experimental research is limited by the complexity of coal molecular structure, the quantum chemical calculation method can simplify the complex molecular structure and realize the exploration of the mechanism of CSC from the micro level. In this study, toluene and phenylacetaldehyde were used as model compounds, and the quantum chemical calculation method was adopted. The reaction processes of the methyl and aldehyde groups with oxygen were investigated with the aid of the Gaussian 09 software, using the B3LYP functional and the 6-311 + G(d,p) basis set and including the D3 dispersion correction. On this basis, the generation mechanisms of CO and CO₂, two important indicator gases in the process of CSC, were explored. The calculation results show that the Gibbs free energy changes and enthalpy changes in the two reaction systems are both of negative values. Accordingly, it is judged that the reactions belong to spontaneous exothermic reactions. In the reaction processes, the activation energy of CO is less than that of CO₂, indicating that CO is formed more easily in the above-two reaction processes. In addition, the variations in concentrations of important oxidation products (CO and CO₂) and main active functional groups (such as methyl, carboxyl and carbonyl) with temperature were revealed through a low-temperature oxidation experiment. The experimental results verify the accuracy of the above quantum chemical reaction path. Moreover, it is also found that the generation mechanisms of CO and CO₂ in coal samples with different metamorphic degrees are different. To be specific, for low-rank coal (HYH), CO and CO₂ mainly come from the oxidation of alkyl side chains; for high-rank coal (CQ), CO is produced by the oxidation of alkyl side chains, and CO₂ is attributed to the inherent oxygen-containing structure. Full article

The flue evaporation of desulfurization wastewater can solve the problem that it is difficult to remove some heavy metal ions and chloride ions by conventional methods. A large amount of chloride ions in desulfurization wastewater can also promote the catalytic oxidation removal of Hg in the flue gas. The migration character of chloride ions in the flue evaporation process of desulfurization wastewater was studied by using the coal-fired thermal state experimental platform. The concentrations of Hg⁰ and Hg²⁺ in the flue gas at the inlet and outlet of selective catalytic reduction denitration (SCR), electrostatic precipitator (ESP), and wet desulfurization (WFGD) devices were tested, and the synergistic removal of traditional pollutant removal equipment by flue evaporation of desulfurization wastewater was analyzed. The influence of Hg and the effect of the evaporation of desulfurization wastewater at different positions on the removal of Hg in the flue gas were compared and analyzed, and the catalytic mechanism of Hg on the SCR surface was further revealed. The results show that 10% chloride ions enter the flue gas after the desulfurization wastewater evaporates. The content of chlorine elements and evaporation temperature influence the evaporation of desulfurization wastewater. The mechanism of SCR catalytic oxidation of Hg⁰ was explored; oxygen atoms have catalytic oxidation effects on Hg⁰ at different positions in the V₂O₅ molecule in SCR; and chloride ions can enhance the catalytic oxidation of Hg⁰ by V₂O₅. The intermediate product HgCl is generated, which is finally converted into HgCl₂. The oxidation efficiency of Hg⁰ in electrostatic precipitation (ESP) is increased from 3% to 18%, and the removal efficiency of Hg is increased from 5% to 10%. The removal efficiency of Hg²⁺ in WFGD is basically maintained at approximately 85%. In addition, a small amount of Hg²⁺ was restored to Hg⁰ in WFGD. The removal efficiency of Hg⁰ in the flue gas of evaporative desulfurization wastewater before SCR is 65%, and the removal efficiency of gaseous Hg is 62%. When the evaporative desulfurization wastewater before ESP, the synergistic removal efficiency of Hg⁰ is 39%, and the gaseous Hg removal efficiency is 39%, and the removal efficiency of Hg is 40%. Evaporation of the desulfurization wastewater before SCR was more conducive to the coordinated removal of Hg by the device. Full article

The performance of rotating detonation engines (RDEs) is theoretically better than that of traditional aero engines because of self-pressurization. A type of swirl injection scheme is introduced in this paper for two-phase detonation. On the one hand, experiments are performed on continuous rotating detonation of ternary “kerosene, hydrogen and oxygen-enriched air” mixture in an annular combustor. It is found that increasing the mass fraction of hydrogen can boost the wave speed and the stability of detonation waves’ propagation. One the other hand, characteristics of kerosene–hot air RDE is investigated for engineering application. Some unstable phenomena are recorded, such as changes of the number of detonation waves, low-frequency oscillations, and sporadic detonation. Full article

To understand the effect of hydrogen addition on the laminar burning velocity (LBV) of ethanol–air mixtures, experiments were conducted in a constant volume combustion chamber with the high-speed schlieren photography technique. The experiments were carried out under the equivalence ratios (ERs) of 0.7–1.4, an initial temperature of 400 K, an initial pressure of 0.1 MPa, and hydrogen fractions of 30% and 90% by volume, respectively. The effects of ER, initial temperature, initial pressure, and hydrogen fractions on the LBV were investigated. Moreover, adiabatic flame temperature (AFT), heat release rate (HRR), flow rate sensitivity analysis, and ROP (rate of production) analysis were also performed. Results showed that LBV increased with increasing hydrogen addition and temperature but decreased with increasing pressure. The hydrogen addition significantly increased the HRR of ethanol–hydrogen–air flames. The sensitivity analysis showed that R5 (O₂ + H = O + OH) significantly influenced the LBV. Full article