H2, O2, CO, and CO2, which are common to all hydrocarbon fuels. Sub-mechanisms are then added for small hydrocarbons, such as methane (CH4), formaldehyde (CH2O), and methanol (CH3OH), followed by fuels with two C atoms, and then by those with three C atoms. This is continued until the model size reaches that of the fuel being studied. Recent fuel mechanisms have been produced for fuels characteristic of gasoline, diesel fuels, and biofuels with as many as 16 to 18 carbon atoms (e.g., primary reference fuels, n-alkane, and methyl stearate, respectively). The numbers of chemical species and elementary reactions in a kinetic model increase rapidly with increased fuel molecule size:
A model for hydrogen oxidation includes about 10 chemical species and 30 elementary reactions,
A model for methane requires about 30 chemical species and 300 reactions, and
A mechanism for n-cetane (n-C16H34) includes more than 1,200 species and 7,000 chemical reactions (Westbrook et al., 2009).
Starting with these core reactions and building on additional reactions for more complex fuels, each kinetic-model developer builds his or her own “house of cards” (Frenklach, 2007) that is similar to, but still not the same as, every other mechanism for the same fuels. For reaction rates with much less sensitivity than the above reactions, rates can vary much more widely from model to model. There is no real value in these differences from one model to another, but there is no motivation for convergence either. In the meantime, these multiple reaction mechanisms continue to exist, slowing the overall rate of progress in the direction of developing realistic reaction mechanisms for new, larger, and more practical fuel components. In addition, nonexperts who need usable and reliable kinetic mechanisms are confused and find it difficult to make choices from these multiple sources of models.
Experience with GRIMech (see Appendix A in this report) illustrates that it is possible for the combustion community to accept and thrive in a common, highly validated, and thorough reaction mechanism environment, but experience also has shown that when financial support for that kinetic model ended, the concept of a combustion community collective kinetic model disappeared.
It should be noted that, like many other features of a cyberinfrastructure, the chemical kinetic part would consist of a fairly complicated task in data management, visualization, and computer science in general, as well as in combustion kinetics. Large archives of experimental results would be needed as sources of model-validation data, and it would be necessary to provide such data in some sort of common data structure to