Formation and degradation of hydrocarbons in high-temperature reactions
Horst Hippler
Karlsruhe, Germany
Simple hydrocarbons are intensively used in many technical processes, e.g. as fuel in combustion, as propellant for engines, or as starting material in high temperature synthesis of solid pyrolytic carbon. Although these important technical processes are controlled by high temperature elementary reactions of hydrocarbons, the knowledge of their kinetic and thermodynamic data is rather scarce. This holds in particular for radical reactions, which lead to the formation and/or degradation of large hydrocarbon molecules. Generally, the formation of aromatic hydrocarbons is discussed to initiate the formation of soot and the deposition of solid pyrolytic carbon of different structure and texture. Complex reaction mechanisms and transport equations of various types characterize the competition of the processes involved.
This was the first International Bunsen Discussion Meeting on high temperature reactions. The aim of this Discussion Meeting was the analysis of the relation between elementary processes of the high temperature systems and macroscopic overall observables. The meeting has been concentrated on the following topics:
(i) Reactions of unsaturated hydrocarbon radicals
(ii) Decomposition of aromatic molecules
(iii) Analysis of complex chemical systems
(iv) From elementary reactions to macroscopic observables
New experiments and theoretical simulations have been compared and the practical relevance for reaction kinetics in general has been illustrated. In this special issue of PCCP, several papers presented at the discussion meeting are published. A broad range of experimental and theoretical investigations has been covered.
The following report on a forum discussion at the Bunsen Discussion Meeting on “completeness and reliability of chemical reaction models” has to be considered to be of particular importance. Today, large amounts of information are available however, they are scattered over different sources and are not properly evaluated. Most importantly, the majority of these data cannot be applied directly to practical problems – they have to be “transformed” into useful models. Such models, however, cannot be created by a simple “compilation” of the data. Chemical reaction model building is a time-consuming activity that requires expert knowledge. This has led to the conclusion, that a new approach for data handling and evaluation is required. Model building has to be converted into science, the methodology has to be automated, and the results have to be made available in a prompt and convenient form for the user. According to the suggestion of Michael Frenklach (Berkeley) and others, the concept of “Process Informatics” was born.
The “Process Informatics Model” must have two principal components: a database and a collection of tools:
The database (virtual or real) should represent the complete set of knowledge available in a given field. In the field of combustion for instance, it must contain experimental data, on both combustion systems and on elementary reactions, collected in flow reactors, shock tubes, flames etc., molecular properties determined from quantum chemical calculations, reaction rates obtained from reaction-rate theories, and so on.
The tools should be of two general kinds: those enabling the collection, transfer, organization, display, and mining of the data as well as enabling scientific collaboration among all participants, i.e. computer science tools, and those enabling processing and analysis of the data along with assembly of the data into models, i.e. scientific and numerical tools. Scientific and numerical computer tools are required to enable processing and analysis of the data along with assembly of the data into models.
This new approach represents a shift in the paradigm of the scientific method – building reaction models in a consistent and systematic way by a process that incorporates all the data available and includes all members of the scientific community. In other words, the scientific community builds the Process Informatics System and Process Informatics builds the community.
Horst Hippler (Karlsruhe)
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