Restrictions on the thermodynamic efficiency of the detonation cycle

Abstract

In this study, an attempt was made to comprehensively analyze the detonation cycle by comparing it with the Brayton and Otto cycles with six variants of restrictions on the main thermodynamic characteristics. As a tool, we used a set of necessary and sufficient evaluation criteria introduced by the authors, taking into account equivalent Carnot cycles. It is shown that the thermal efficiency does not give a complete picture of the thermodynamic perfection of a detonation engine. In the considered variants of restrictions, the thermal efficiency of the detonation cycle exceeds (variants 1 and 5 of restrictions) or is equal (variants 3, 4 and 6 of restrictions) to the Otto and Brayton cycles. The exception is the second variant of restrictions (Tmin = const, Tmax = const), when the thermal efficiency of the detonation cycle is 3 % lower than the Otto cycle and 27 % lower than the Brayton cycle. In the first variant of restrictions (ε = const), the detonation cycle exceeds the thermal efficiency of the Otto and Brayton cycles by 1.42 and 1.21 times, and in the fifth variant of restrictions (Tmin = const, ηi = const), by 1.12 times 1.06 times, respectively. At the same time, under these restrictions, the detonation cycle is inferior in terms of the degree of perfection of the actual cycle to the relative theoretical cycle: the relative efficiency of the Otto and Brayton cycles exceeds the detonation cycle by 1.09 times and 1.05 times, respectively, in the first variant, and by 1.11 times and 1.07 times, respectively, in fifth variant of restrictions.In the third case of restrictions (Tmin = const, Tmax = const, ηt = const), the detonation cycle is inferior in some criteria to the Otto cycle (specific volumetric work, indicator and relative efficiency), but surpasses the Brayton cycle in almost all criteria. In the fourth variant of restrictions (Tmin = const, ηt = const), the detonation cycle is less effective in terms of indicator and relative efficiencies than the Otto cycle (by 11 %) and the Brayton cycle (by 6–7 %). And, in terms of specific volumetric work, the detonation cycle exceeds the Brayton cycle by 1.27 times, but is inferior to the Otto cycle by almost 70 %. In the fifth variant of restrictions (Tmin = const, ηi = const), the detonation cycle has the lowest relative efficiency ηr (11 % and 7 % less than the Otto and Brayton cycles, respectively), despite its superiority in thermal efficiency. Under the sixth variant of restrictions (Tmin = const, ηt = const, ηi = const), the detonation cycle exceeds the Otto and Brayton cycles in terms of internal irreversibility criterion β. At the same time, in terms of specific volumetric work, the detonation cycle is 64 % inferior to the Otto cycle, but exceeds the Brayton cycle by 1.29 times.