Conventionally, turbulent burning velocity models are compared by showing the model-predicted ST/SL0 ratios in an ST/SL0 - u′/SL0 plane, where ST and SL0 are the turbulent and laminar burning velocities, respectively, with u′ being the turbulence intensity. Such a method applies to only those models which take u′ or u′/SL0 as the only variable of ST or of ST/SL0.
In order to analyze and compare most recent models in which turbulence and flame spatial scales (or length scales) are also taken into account because of their importance in combustion, this paper showed the model-predicted ST/SL0 ratios as contours in three planes (Re-Da, ηκ/η0 - u′/SL0 and L/η0 - u′/SL0, where Re, Da, L, ηκ and η0 are the Reynolds number, Damköhler number, turbulence integral scale, Kolmogorov scale and laminar flame preheat zone thickness, respectively); these planes are usually used in discussing the flame structure. The obtained planes showing contours of the model-predicted ST/SL0 ratios were referred to as burning velocity diagrams of the models. As a burning velocity diagram shows not only detailed ST/SL0 ratios under different u′/SL0 ratios but also those under different ratios of L/η0, as well as the overall characteristics of the model (such as the flame quenching limit, etc.) at the same time, it gives a thorough representation of the model. Therefore, comparison of different models on the basis of their respective burning velocity diagrams can take account of the influences of turbulence and flame spatial scales in addition to the influences of the u′/SL0 ratios. Five models proposed by different authors were shown as diagrams respectively. Based on the diagrams obtained and with an emphasis put on a model proposed by the authors previously, these models were discussed and compared with recent experimental results on (1) ST/SL0 ratios under the same turbulence characteristics and the same mixture properties; (2) flame quenching limit and; (3) relation between turbulent burning velocity and flame structure.