An Experimental Kinetics Study of Isopropanol Pyrolysis and Oxidation behind Reflected Shock Waves

Abstract

Isopropanol has potential as a future bio-derived fuel and is a promising substitute for ethanol in gasoline blends. Even so, little has been done in terms of high-temperature chemical kinetic speciation studies of this molecule. To this end, experiments were conducted in a shock tube using simultaneous CO and H2O laser absorption measurements. Water and CO formation during isopropanol pyrolysis was also examined at temperatures between 1127 and 2162 K at an average pressure of 1.42 atm. Species profiles were collected at temperatures between 1332 and 1728 K and at an average pressure of 1.26 atm for equivalence ratios of 0.5, 1.0, and 2.0 in highly diluted mixtures of 20% helium and 79.5% argon. Species profiles were also compared to four modern C3 alcohol mechanisms, including the impact of recent rate constant measurements. The Li et al. (2019) and Saggese et al. (2021) models both best predict CO and water production under pyrolysis conditions, while the AramcoMech 3.0 and Capriolo and Konnov models better predict the oxidation experimental profiles. Additionally, previous studies have collected ignition delay time (τign) data for isopropanol but are limited to low pressures in highly dilute mixtures. Therefore, real fuel–air experiments were conducted in a heated shock tube with isopropanol for stoichiometric and lean conditions at 10 and 25 atm between 942 and 1428 K. Comparisons to previous experimental results highlight the need for real fuel–air experiments and proper interpretation of shock-tube data. The AramcoMech 3.0 model over predicts τign values, while the Li et al. model severely under predicts τign. The models by Capriolo and Konnov and Saggese et al. show good agreement with experimental τign values. A sensitivity analysis using these two models highlights the underlying chemistry for isopropanol combustion at 25 atm. Additionally, modifying the Li et al. model with a recently measured reaction rate shows improvement in the model’s ability to predict CO and water profiles during dilute oxidation. Finally, a regression analysis was performed to quantify τign results from this study.

Experimental Kinetics Study on Diethyl Carbonate Oxidation

“…Under pyrolysis conditions, as seen in the authors' previous study, the CO formation from DEC pyrolysis occurs primarily via (the reaction numbers and the names of the molecules and radicals correspond to those in the TAMU model): course of the experiment, and where the profile of the species followed experimentally typically depends on a limited set of reactions and the accuracy of their reaction coefficients. This discrepancy in the models' performance between global kinetics data and kinetics measurements has been observed recently in the authors' work on various alcohols [25,36,46]. In the authors' opinion, since the global kinetics data are accurately reproduced, the CO profiles presented herein should be the main focus of this discussion section to provide ways to improve the model.…”

“…With these analogies in mind, similar pressure and temperature uncertainties were observed. In terms of IDT, this uncertainty in temperature translates to ±20% uncertainty for IDT [25]. Again, to generate 1 atm test pressures, 0.25 mm thick polycarbonate diaphragms paired with a downstream cutter were used.…”

“…Significant pressure rise due to combustion was observed and can also be used to define ignition. Because of this, an endwall definition for IDT is appropriate, as the changing conditions during combustion artificially accelerate IDTs at the sidewall location [25,35]. Pressure traces at the sidewall and endwall locations as well as a OH* trace from a representative experiment is given in Figure 2 to illustrate the IDT definition in the present study.…”

Laminar Flame Speed, Ignition Delay Time, and CO Laser Absorption Measurements of a Gasoline-like Blend of Pentene Isomers

“…The experiments were conducted within two shock tubes made of stainless steel: the HPST to measure OH* and CH*, and the AST to measure CO timehistory profiles. Details on dimensions and methods can be found in Cooper et al 35 In both vessels, the driver and driven sections are separated by a single diaphragm of 0.25 mm thickfilm polycarbonate to generate pressures around 1.3 atm behind the reflected shock. To measure the incident-shock velocities, four (HPST) and five (AST) piezoelectric pressure transducers detect the shock passage along the end section of each apparatus.…”

An Experimental and a Kinetic Modelling Study of Ethanol/Acetone/Ethyl Acetate Mixtures

“…Ethanolgasoline blended fuel can increase the compression ratio to achieve a higher combustion efficiency and to increase engine output torque [7,8]. An ethanol-gasoline fuel mixture can reduce HC, CO, and NOx emissions [9,10]. Moreover, an acetone and a gasoline fuel mixture can significantly improve engine performance.…”