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The effect of diluents on the laminar burning velocity of the premixed methane–air–diluent flames was numerically studied using the Chemkin package. The mechanisms of dilution, thermal-diffusion, and chemical effects of diluents on the laminar burning velocity were analyzed quantitatively at different dilution ratios for different diluents. Results show that the laminar burning velocity is decreased in the order from helium, argon, nitrogen, and carbon dioxide. In the case of N2, the thermal-diffusion and chemical effects can be negligible and the decrease of the laminar burning velocity is largely caused by the dilution effect. The dilution, thermal-diffusion, and chemical effects of CO2 suppress the laminar burning velocity, where the dilution effect plays a dominant effect among them. For helium and argon diluents, the chemical effect can be negligible and the thermal-diffusion effect enhances the laminar burning velocity. Therefore, the dilution effect has a much larger suppression effect on decreasing the laminar burning velocity to counteract the thermal-diffusion effect of helium and argon. An empirical formula of the laminar burning velocity that takes into account the adiabatic flame temperature and thermal diffusivity is obtained. Good correlations between the laminar burning velocity and mole fraction of H + OH at the position of the maximum mole fraction of the H radical in the flame are also demonstrated. The laminar burning velocity has the same tendency with the product of thermal-diffusion and chemical reaction terms as a function of the dilution ratio for different diluents. The adiabatic flame temperature plays a dominant influence on the laminar burning velocity, and thermal diffusivity has a secondary influence on methane–air–diluent flames.

Modulating the morphology and chemical composition is an efficient strategy to enhance the catalytic activity for water splitting, since it is still a great challenge to develop a bifunctional catalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) over a wide pH range. Herein, Pd/ NiFeO x nanosheets are synthesized with tightly arranged petal nanosheets and uniform mesoporous structure on nickel foam (NF). The porous 2D structure yields a larger surface area and exposes more active sites, facilitating water splitting at all pH values. The overpotential of Pd/NiFeO x nanosheets for OER is only 180, 169, and 310 mV in 1 m KOH, 0.5 m H 2 SO 4 , and 1 m phosphate-buffered saline (PBS) conditions at 10 mA cm −2 current density, as well as excellent HER activity with ultralow overpotential in a wide pH range. When using porous Pd/NiFeO x nanosheets as bifunctional catalysts for water splitting, it just required a cell voltage of 1.57 V to reach a current density of 20 mA cm −2 with nearly 100% faradic efficiency in alkaline conditions, which is much lower than that of benchmark Pt/CǁRuO 2 (1.76 V) couples, along with the improving stability benefiting from the good corrosion resistance of the inner NiFeO x nanosheets.

Ignition delay times of n-butanol/oxygen diluted with argon were measured behind reflected shock waves. Experiments were carried out in the temperature range 1200−1650 K, at 2 and 10 atm, and at equivalence ratios of 0.5, 1.0, and 2.0. Correlations of ignition delay times were constructed on the basis of measured data through multiple linear regression. A modified kinetic model for the oxidation of n-butanol at high temperature was developed, based on previous models by adding and modifying some key reactions. The modified model shows good prediction of the measured data under all measured conditions. This model was also validated against jet-stirred reactor (JSR) data obtained from the literature, and fairly good agreement was observed. A fair improvement on the simulation of aldehydes (acetaldehyde and butyraldehyde) was found compared to the original model. Finally, reaction pathway and sensitivity analysis indicate that the H-abstraction reactions play a dominant role in the consumption of n-butanol, while unimolecular decomposition reactions become more important with increasing temperature. High-level accurate investigation of the rate constants of H-abstraction reactions and unimolecular decomposition reactions is required to further improve n-butanol oxidation kinetics.

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