Unimolecular Rate Expression for Cyclohexene Decomposition and Its Use in Chemical Thermometry under Shock Tube...

Area of Science:

• Chemical Kinetics
• Combustion Science
• Reaction Mechanism Analysis

Background:

• The reverse Diels-Alder decomposition of cyclohexene is critical for combustion simulations.
• Accurate kinetic and physical data, especially temperature, are increasingly needed for practical applications.
• Existing rate expressions derived from various experimental methods show discrepancies.

Purpose of the Study:

• To review and analyze methods for deriving rate expressions for cyclohexene decomposition.
• To identify the source of discrepancies between different experimental studies.
• To provide implications for accurate temperature determination in shock tube experiments.

Main Methods:

• Review of comparative rate single-pulse shock tube studies.
• Analysis of direct shock tube studies and high-pressure flow experiments.
• Examination of unimolecular decomposition and isomerization processes.
• Investigation of potential non-Arrhenius behavior and radical-induced reactions.

Main Results:

• Rate constants from direct shock tube and high-pressure flow studies are larger than those from comparative rate studies.
• Non-Arrhenius behavior was ruled out as the cause of discrepancies.
• Radical-induced decomposition, particularly H atom addition, is identified as a likely source of inflated rate constants.
• The internal standard method requires careful application, with radical inhibitors recommended.

Conclusions:

• Radical-induced reactions significantly affect the measured rate constants for cyclohexene decomposition.
• The presence of H atoms can lead to overestimation of true rate constants.
• Methodological improvements, including the use of radical inhibitors, are necessary for accurate kinetic data.
• Findings have implications for reliable temperature determination in shock tube experiments.