Application of comprehensive kinetic models

The duration of the compression stroke in the calculated times (Table 6.14) corresponded to approximately 50 ms, signifying that autoignition occurred after top dead centre, as observed experimentally. The choice of bdc as the initial condition is essential to permit the development of spontaneous combustion during the course of the compression stroke as the gas pressure and temperature increase. This definition of the time for ignition differs from that given by, (i) the admission of reactants to a hot, closed reaction vessel, (ii) the end of compression in an RCM, or (iii) the passage of a shock through the reactants in a shock tube. 

It is not easy to rationalize these times for ignition shown in Table 6.14 with the research octane number for each fuel, even in the context of a broad correlation based on RON = 60-70, 70-80, 80-90 or 90-100. Moreover, isomers of similar structure that exhibit a similar RON do not show a similar degree of correspondence in the calculated ignition delay. Before any further assessment of these data is made, it would be desirable also to have experimentally measured ignition delays for these single component fuels under high pressure conditions, as in an RCM or shock tube. 

Most of the numerical modelling discussed in this section has been 

Research octane numbers for selected alkane fuels and predicted times of ignition [239] 

As discussed in Section 6.6, numerical analyses can be used with some success to simulate the chemical features of low-temperature hydrocarbon oxidation. However, there is progress yet to be made on a number of fronts by both experimentalists and numerical modellers. The kinetics and mechanism of certain classes of compounds, such as the alkenes and aromatics, have not been investigated fully in the low-temperature region, the information on aromatic compounds being particularly sparse (Chapter 1). By contrast, there is much better understanding of the low-temperature oxidation of alkanes. Following Section 1.4.1, the reactivity of alkanes arises within the mechanistic structure 

---