Effects of water on combustion kinetics at high pressure

The effect of water on reaction mechanisms in high pressure combustion has been studied theoretically using the quantum chemical BAC-MP4 method combined with the Peng-Robinson equation of state to treat non-ideal gas effects. Transition state structures involving additional water molecules have been calculated using the BAC-MP4 method for the water gas shift reaction CO+H 2 O→CO 2 +H 2 going via the formic acid, HCOOH, intermediate. The resulting transition states can be stabilized due to water solvation effects. The magnitude of the Gibbs energy changes due to solvation were calculated using the Peng-Robinson equation of state. The results indicate large lowerings of the activation energies for the reaction when additional water molecules are included in the reaction mechanism. Also, we find that the transition state structures possess significant ionic character which leads to substantial stabilization due to the presence of surrounding water molecules. The temperature and pressure dependence of these effects are discussed with respect to the chemical mechanisms in combustion processes.