Geometrical Limitation for Detonation Propagation

Solid curves - calculated data, 373 K dashed curves - calculated data, 

The same diagram presents detonation limit values calculated with the help of the ZND model using detailed kinetics and taking into account the impulse losses [27]. The diagrams of detonations in a H2 + air mixture with the diluents (CO2 and H2O) have a peninsular shape, the narrow part of which corresponds to the minimum quantity of the diluent necessary for detonation suppression in a tube of such a diameter. 

The calculated and measured data obtained at 298 K initial temperature are in good agreement. The solid curves show the data calculated at 373 K. The model correctly predicts the expansion of the detonation boundaries as the temperature increases as well as a more efficient retardation in hydrogen-air mixtures diluted with CO2 than when the mixture is diluted with water steam. 

It is a known fact that in small diameter tubes, the detonation propagates within narrower concentration limits. Examples of concentration limits for H2 + O2 + N2 mixtures detonating in 14-16 mm diameter tubes are given in Fig. 7.22. The same diagram presents the detonation propagation boundaries found by extrapolation for tubes of infinite diameter. 

Real measurements in wide tubes were taken in [28] the detonation limits in H2 + air mixtures were measured in a 0.3-m diameter tube at room temperature and 0.1 MPa. In [28] an experimental investigation of the critical conditions for 

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Fig. 7.26 Geometrical limits for detonation propagation (1) in ducts and initiation (2) in the space after the diffraction d - characteristic size of tube or duct a - detonation cell size...

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