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The diesel community has used one-equation models for ignition delay in engines for decades. The inverse Arrhenius forms characterizing many of these expressions thus lump together liquid fuel evaporation, mixing of the vapour with the charge and the chemical delay. As a result, correlations apply only to the injector, engine and operating conditions tested. Additionally, they typically exhibit energies or temperatures of activation that can be as much as ten times lower than those obtained in well-mixed, controlled systems that isolate and study the chemical delay. Here the latter system is modelled first, using classical analysis techniques. The result is then extended to the relatively straightforward fluid mechanic environment of a laminar counterflow burner to clarify how both chemistry and mixing can be included in a more general one-equation model. This new model is validated with ignition limit data for ethane or ethene with O2/N2 either premixed or unmixed in the counterflow arrangement and liquid diesel fuel in a pool configuration. Since the overall mixing time in this burner is known a priori, the data can be manipulated to yield global chemical ignition delay activation temperatures for these fuels. As expected, the results are equivalent to those measured in shock tubes and combustion tunnels where reactants are premixed before ignition. [ABSTRACT FROM AUTHOR]