Ignition delay experiments for gas phase n-nonane/air mixtures have been performed behind reflected shock waves over a wide temperature range of 684–1448 K, pressures of 2.0–15.0 atm, and equivalence ratios of 0.5, 1.0, and 2.0. Ignition delay times were determined using electronically excited CH emission and reflected shock pressure signals monitored at the sidewall of the shock tube. A negative-temperature-coefficient (NTC) behavior of n-nonane/air ignition was observed at temperatures of 800–950 K. Dependence of ignition delay time upon temperature, pressure, and equivalence ratio was investigated systematically. High temperature (T > 1000 K) results show that the effect of equivalence ratio on ignition delay times is different at low and high pressures. In the NTC region, ignition delay times are highly sensitive to equivalence ratio and pressure. The present ignition data are in satisfactory agreement with predictions of two widely used chemical kinetic mechanisms. Sensitivity and reaction pathway analyses reveal that the dominating reactions affecting ignition delay times and reaction pathways during ignition process for n-nonane/air are quite different at high and low temperatures. Comparison of n-nonane/air ignition delay times with those of other larger n-alkanes (n-heptane, n-octane, n-decane, n-dodecane, and n-tetradecane) indicates that the length of n-alkanes chain influences little on ignition delay times of n-alkanes. The present results are useful for understanding ignition characteristics of n-nonane and providing experimental data to validate chemical kinetic mechanisms for n-nonane.

Ignition delay times of n-nonane and n-undecane in 4% oxygen/argon have been measured behind reflected shock waves in a heated shock tube at temperatures of 1168–1600 K, pressures of 2, 10, and 20 atm, and equivalence ratios of 0.5, 1.0, and 2.0. Ignition delay times are determined by using CH* emission and pressure signals monitored at the sidewall. Results show that ignition delay times of two fuels decrease as the temperature or pressure increases, and a decrease in equivalence ratio results in a shorter ignition delay time. For fuel-lean and stoichiometric mixtures, n-nonane has ∼25%–35% longer ignition delay times than n-undecane. For fuel-rich mixtures, ignition delay times of two fuels are very close. Correlations for ignition delay times of two fuels as a function of temperature, pressure, and equivalence ratio are formulated through regression analysis. The experimental data are in good agreement with shock tube data available, and the trends of experimental data were captured well by the predictions from the LLNL and JetSurF mechanisms under conditions studied. Comparison of ignition delay times for nine n-alkanes from propane to n-undecane reveals that the n-alkanes have the similar ignition delay behavior and their ignition delay times are close to each other. Reaction path analyses and sensitivity analyses are performed to investigate the consumption of fuels and identify the important reactions in the ignition process. To our knowledge, we provide the first ignition delay time data for n-undecane at elevated pressures, and our measurements for n-nonane are at a broader range of conditions than previous studies. Current results contribute toward understanding the ignition characteristics of n-nonane and n-undecane, and they provide validation targets for corresponding kinetic mechanisms.

Autoignition properties of diethoxymethane/O2/Ar mixtures were systematically investigated using a shock-tube facility under various ignition conditions, including reflected shock pressures of 2−10 × 105 Pa, temperatures of 1065–1370 K, and equivalence ratios of 0.5, 1.0 and 2.0. Ignition delay times were determined by measuring the time interval between electronically excited CH∗ emission and reflected shock pressure signals monitored at shock-tube sidewall. An empirical correlation for ignition delay times as a function of temperature, pressure and equivalence ratio was deduced by linear regression analysis. A chemical kinetic mechanism describing the high-temperature oxidation of diethoxymethane was proposed. The theoretical predictions match experimental results quite well. Sensitivity and reaction pathway analyses were employed to identify dominant reactions and fuel consumption paths during the ignition process. To our knowledge, we are the first one to present the ignition delay time measurements of gas-phase diethoxymethane.

The ignition delay times of gas-phase 1,3,5-trimethylbenzene/air mixtures were measured behind reflected shock waves in a heated shock tube facility. The experimental conditions spanned as follows: temperatures of 1080–1560 K, pressures of 1.0–20.0 atm, and equivalence ratios of 0.5, 1.0, and 2.0. Ignition delay times were determined using pressure and CH* emission signals monitored at the sidewall. The increasing temperature or pressure results in decreasing ignition delay time definitely. However, the effect of equivalence ratio on the ignition delay time is complex. Lean mixtures are fastest to ignite at temperatures above 1390 K at 1.0 atm, whereas they are slowest to ignite below 1300 K at 20.0 atm, and the equivalence ratio does not have an evident effect on the ignition time at 5.0 atm. The global activation energy decreases dramatically as the pressure increases at all equivalence ratios. Current results are in good agreement with other shock-tube experimental data, and comparisons of current data to kinetic predictions from two recently published mechanisms are presented. In addition, sensitivity analysis was performed to access the important reactions in the ignition process. To our knowledge, this study provides the first ignition delay time data for 1,3,5-trimethylbenzene at a pressure of 1.0 atm. Present results extend the database for 1,3,5-trimethylbenzene ignition delay time.

Autoignition delay time measurements were performed for dimethoxymethane/oxygen/argon mixtures at pressures of approximately 2, 4, and 10 atm, temperatures of 1103–1454 K, argon/oxygen dilution ratios of 11.25, 23.75, and 48.75, and equivalence ratios of 0.5, 1.0, and 2.0 in a shock-tube facility. Ignition delay times were determined using OH* emission and reflected shock pressure signals monitored at the shock-tube sidewall. The dependence of the ignition delay time upon the temperature, pressure, dilution ratio, and equivalence ratio was characterized. An empirical correlation for the ignition delay times with the experimental parameters was formulated by linear regression of these data. Experimental results were compared to the kinetic modeling predictions of two available chemical kinetic mechanisms to test the performance of mechanisms. Glaude’s mechanism yielded good agreement with the experimental results at 4 and 10 atm but underestimated the ignition delay times at 2 atm. Sensitivity analysis on ignition delay time was conducted, and the dominant reactions during the ignition process were identified. Better predictions on ignition delay times were achieved after modifying the reaction rate of selected small radical reactions. Moreover, fuel reaction pathway analysis was conducted to investigate the consumption of dimethoxymethane.

Ultraviolet–Visible emission from iso-octane combustion was measured behind reflected shock waves. OH∗, CH∗ and C2∗ were recorded as the major intermediate species. When the equivalence ratio increases, the emission intensity ratio of OH∗/CH∗ decreases and that of C2∗/OH∗ increases. Rotational and vibrational temperatures were determined by comparing the measured emission spectra with the simulated ones of CH∗ and C2∗. The rotational temperatures are in good agreement with the calculated adiabatic flame temperatures and the vibrational temperatures are significantly higher. Furthermore, ignition delay times were obtained to provide a database for the validation of the kinetic mechanism.Graphical abstractHighlights► The rotational temperatures are in good agreement with the calculated flame temperatures. ► The emission intensity ratios of OH∗/CH∗ and C2∗/OH∗ are sensitive to the equivalence ratio. ► Ignition delay times provide a database to validate the kinetic mechanism. ► Emission spectrum can be used as a good indicator in combustion systems.

Autoignition delay time measurements were performed for toluene/oxygen/argon mixtures at pressures of approximately 1.0 and 3.0 atm, temperatures of 1312–1713 K, oxygen mole fractions of 1.8–18.0%, and equivalence ratios of 0.5, 1.0, and 2.0 in a shock-tube facility. Ignition times were determined using electronically excited CH* and OH* emissions and reflected shock pressure monitored through the shock-tube sidewall. The dependence of the ignition delay times upon pressure, oxygen mole fraction, and equivalence ratio has been characterized. An empirical correlation for the ignition delay has been deduced by linear regression of the ignition data. Experimental results are compared to simulations of three recent chemical kinetic mechanisms for the oxidation of toluene. The overall trends are captured fairly well by the mechanisms. In addition, the important reaction pathways have been elucidated by both flux and sensitivity analyses. Ultraviolet and visible chemiluminescence of toluene combustion were measured using an intensified charge-coupled device camera coupled with a spectrometer. The transient spectra show remarkably high intensities of OH*, CH*, and C2* electronic emission bands. Rotational and vibrational resolution spectra of OH*, CH*, and C2* were clearly observed behind reflected shock waves. It was found that the peak intensity ratios of OH*/CH* and C2*/CH* are strongly related to the equivalence ratio.

Ignition delay times for n-decane/O2/Ar mixtures were measured behind reflected shock waves using endwall pressure and CH* emission measurements in a heated shock tube. The initial postshock conditions cover pressures of 0.09–0.26MPa, temperatures of 1 227–1 536 K, and oxygen mole fractions of 3.9%–20.7% with an equivalence ratio of 1.0. The correlation formula of ignition delay dependence on pressure, temperature, and oxygen mole fraction was obtained. The current data are in good agreement with available low-pressure experimental data, and they are then compared with the prediction of a kinetic mechanism. The current measurements extend the kinetic modeling targets for the n-decane combustion at low pressures.

Time resolved spectroscopy was applied to a real time investigation of chemical reaction of quercetin (5.0 × 10− 5 mol L− 1) with various concentrations of sodium hydroxide (from 5.0 × 10− 3 to 1.0 mol L− 1). The UV–vis absorption spectra acquired first reveal that there was an intermediate product with an absorption band centered at 427 nm formed during the reaction. The rates of chemical changes for quercetin in basic medium are also first obtained by the present work. The transient spectral information obtained is valuable for understanding the molecular mechanism of the reaction between quercetin and sodium hydroxide.

•A novel combining rule is introduced to calculate the potentials of hetero-nuclear dimers from the homo-nuclear dimers.•Together with the Tang-Toennies potential model, this rule can tell if the result is converged or not.•When the sizes of the interacting atoms are very different, the result is converged after several rounds of iterations.•The converged results are in excellent agreement with experiments.An iterative procedure is introduced to make the results of some simple combining rules compatible with the Tang-Toennies potential model. The method is used to calculate the well locations Re and the well depths De of the van der Waals potentials of the mixed rare gas systems from the corresponding values of the homo-nuclear dimers. When the “sizes” of the two interacting atoms are very different, several rounds of iteration are required for the results to converge. The converged results can be substantially different from the starting values obtained from the combining rules. However, if the sizes of the interacting atoms are close, only one or even no iteration is necessary for the results to converge. In either case, the converged results are the accurate descriptions of the interaction potentials of the hetero-nuclear dimers.

Autoignition delay time measurements were performed for gas-phase RP-3/air mixtures behind reflected shock waves at temperatures of 650–1500 K, pressures of 1–20 atm, and equivalence ratios of 0.2, 1.0, and 2.0. Ignition delay times were determined using electronically excited CH∗ and/or OH∗ emissions and reflected shock pressure monitored through the shock tube sidewall. The dependence of the ignition delay times upon temperature, pressure and equivalence ratio has been investigated at high temperatures. Correlation expressions for the ignition delay under different equivalence ratios and pressures have been deduced separately. The global activation energy for RP-3/air varies significantly as the ignition pressure changes. A negative temperature coefficient (NTC) effect for RP-3 at 10 atm was observed in the temperature range of 750–850 K. Current results were compared with available Jet-A ignition data, showing good agreement with previous results of Jet-A. Based on the composition identification of RP-3, a mixture of 88.7% n-decane and 11.3% 1,2,4-trimethylbenzene by mole has been proposed as a surrogate for RP-3. Surrogate mechanism simulations were performed by using the mechanism proposed by Peters et al. (2009). The simulations show good agreement with the experimental data over wide ignition conditions. Sensitivity analyses were carried out to identify the important reactions in the ignition process and to explain the experimental phenomena. Current work provides a fundamental database for the development and validation of surrogate kinetic models for RP-3 jet fuel.