Ab initio combustion kinetics

 

The kinetics of combustion processes result from many intermediates and their elementary reactions. CFD-Simulations can use the mechanism of all these reactions (or a reduction of this mechanism) to optimize engines towards less pollutants and more efficiency. For quantitative predictions, we need thermodynamic data for the species and intermediates as well as the rates of the reactions between them. Frequently these data result from a correlation with combustion events - like autoignition delay times.

These data can also be calculated from physical models (see lecture Combustion Chemistry). Doing such calculations for potential biofuels is the goal of this project. The methods are both improved (to capture better the relevant effects) as well as applied to potential and bio-hybrid-fuel molecules that are under development in the fuel science center.

In order to optimize engines and fuels for high efficiency and low emissions, we need to understand the ignition and burning properties of potential new fuels. In tight cooperation with partners working experimentally, we study the elementary kinetics of such fuels with methods based on quantum mechanics and statistical thermodynamics.

  Copyright: © Institute of Technical Thermodynamics, RWTH Aachen University

Together with the Chair of High Pressure Gas Dynamics and the Institute for Combustion Technology, biofuel candidates like butanol [1], butanone [2], dimethoxymethane [3], diethoxymethane [4], and cyclopentanol [5] have been studied in the past.

Presently, we systematically study the family of ethyl esters (as potential e-fuels) and bio-hybrid fuel candidates 1,3-dioxane, 1,3-dioxolane, and their substituted derivatives in the Fuel Science Center. By calculating the bond dissociation energies (BDEs), and the rate constants of the H abstraction and ring opening reactions of the fuel, the detailed mechanism has been developed, which helps to explain the ignition behavior of these fuels. The figure shows a typical transition state of the H-abstraction of 1,3-dioxolane by HO₂ radical.

For the prediction of polycyclic aromatic hydrocarbon (PAH) formation, we collaborate with our project partners in ITV and studied the resonance-stabilized cyclopentadienyl radicals (C5H5, RSR) [8]. The temperature- and pressure-dependent rate coefficients for important reactions involved in the C5H5 PES are calculated. The updated kinetic model helps to reveal the impacts of these RSRs on the PAH formation in a low-pressure cyclopentene counterflow diffusion flame.
We currently investigate the role of smaller PAHs and radicals as soot precursors.

 

Selected Publications on this topic

[1] S. Vranckx, K. A. Heufer, C. Lee, H. Olivier, L. Schill, W. A. Kopp, K. Leonhard, C. A. Taatjes und R. X. Fernandes, Role of Peroxy Chemistry in the High Pressure Ignition of n-Butanol – Experiments and Detailed Kinetic Modelling, Combust. Flame 158, 1444–1455 (2011)

[2] U. Burke, K. A. Heufer, Y. Uygun, H. Olivier, W. Kopp, K. Leonhard, J. Beeckmann und H. Pitsch, A comprehensive experimental and kinetic modeling study of butanone, Combust. Flame 168, 296-309 (2016)

[3] S. Jacobs, M. Döntgen, A. B. S. Alquaity, W. A. Kopp, L. C. Kröger, U. Burke, H. Pitsch, K. Leonhard, H. J. Curran und K. A. Heufer, Detailed kinetic modeling of dimethoxymethane. Part II: Experimental and theoretical study of the kinetics and reaction mechanism, Combust. Flame 205, 522 (2019)

[4] L. C. Kröger, M. Döntgen, W. A. Kopp, D. Firaha und K. Leonhard, Ab initio kinetics predictions for H-atom abstraction from diethoxymethane by hydrogen, methyl, and ethyl radicals and the subsequent unimolecular reactions, Proc. Combust. Inst. 37, 275-282 (2019)

[5] L. Cai, L. Kröger, M. Döntgen, K. Leonhard, K. Narayanaswamy, S. M. Sarathy, K. A. Heufer und H. Pitsch, Exploring the combustion chemistry of a novel lignocellulose-derived biofuel: cyclopentanol. Part I: quantum chemistry calculation and kinetic modelling, Combust. Flame 210, 490-501 (2019)

[6] C. Huang, Y. Zhao, I.S. Roy, B. Chen, N. Hansen, H. Pitsch, and K. Leonhard, Pathway exploration in low-temperature oxidation of a new-generation bio-hybrid fuel 1,3-dioxane, Proc. Combust. Inst. (2023), 10.1016/j.proci.2022.09.057

[7] C. Huang, Y. Zhao, I.S. Roy, L. Cai, H. Pitsch, and K. Leonhard, Effect of methyl substituents, ring size, and oxygen on bond dissociation energies and ring-opening kinetics of five- and six-membered cyclic acetals, Combust. Flame 242, 112211 (2022)

[8] Q. Mao, C. Huang, M. Baroncelli, L. Shen, L. Cai, K. Leonhard, and H. Pitsch, Unimolecular reactions of the resonance-stabilized cyclopentadienyl radicals and their role in the polycyclic aromatic hydrocarbon formation
Proc. Combust. Inst. 38, 729-737 (2021)