Sum over Histories Representation for Kinetic Sensitivity Analysis: How Chemical Pathways Change When Reaction Rate...

Area of Science:

• Chemical kinetics
• Computational chemistry
• Combustion science

Background:

• Understanding chemical reaction mechanisms is crucial for predicting system behavior.
• Traditional methods like static flux analysis lack explicit time dependence in pathway analysis.
• Quantifying the sensitivity of kinetic observables to parameters is essential for model validation and uncertainty quantification.

Purpose of the Study:

• To develop and apply a novel sum over histories representation for analyzing the sensitivity of kinetic observables.
• To investigate how kinetic parameters, such as rate coefficients, influence chemical pathway probabilities over time.
• To identify critical reactions and pathways that dominate the sensitivity of species concentrations in combustion systems.

Main Methods:

• Developed a sum over histories (SoH) representation for chemical kinetics.
• Decomposed species concentrations into probabilities of distinct chemical pathways.
• Analyzed the time-dependent impact of kinetic parameters on pathway probabilities.
• Applied the method to H2 combustion to study species concentration sensitivities.

Main Results:

• The SoH method explicitly incorporates time dependence in pathway analysis.
• Sensitivities of observables were linked to how kinetic parameters affect pathway probabilities.
• Identified rate-limiting steps and branching reactions as major contributors to large sensitivities.
• Demonstrated the method's utility in H2 combustion with varying rate coefficients.

Conclusions:

• The sum over histories representation provides a powerful tool for sensitivity analysis in chemical kinetics.
• This approach enhances understanding of reaction mechanisms by highlighting critical pathways and parameters.
• The findings are valuable for improving kinetic models and reducing uncertainties in combustion simulations.