Deflagration-to-Detonation Transition in Stochiometric Propane–Hydrogen–Air Mixtures

Abstract

Hydrocarbon–hydrogen blends are often considered as perspective environmentally friendly fuels for power plants, piston engines, heating appliances, home stoves, etc. However, the addition of hydrogen to a hydrocarbon fuel poses a potential risk of accidental explosion due to the high reactivity of hydrogen. In this manuscript, the detonability of stoichiometric C3H8–H2–air mixtures is studied experimentally in terms of the run-up time and distance of deflagration to detonation transition (DDT). The hydrogen volume fraction in the mixtures varied from 0 to 1. Three different configurations of detonation tubes were used to ensure the DDT in the mixtures of the various compositions. The measured dependences of the DDT run-up time and distance on the hydrogen volume fraction were found to be nonlinear and, in some cases, nonmonotonic with local maxima. Blended fuel detonability is shown to increase sharply only at a relatively large hydrogen volume fraction (above 70%), i.e., the addition of hydrogen to propane in amounts less than 70% vol. does not affect the detonability of the blended fuel significantly. The observed nonlinear/nonmonotonic dependences are shown to be the manifestation of the physicochemical properties of hydrogen-containing mixtures. An increase in the hydrogen volume fraction is accompanied by effects leading to both an increase and a decrease in mixture sensitivity to the DDT. Thus, on the one hand, the increase in the hydrogen volume fraction increases the mixture sensitivity to DDT due to an increase in the laminar flame velocity and a decrease in the self-ignition delay at isotherms above 1000 K and pressures relevant to DDT. On the other hand, the mixture sensitivity to DDT decreases due to the increase in the speed of sound in the hydrogen-containing mixture, thus leading to a decrease in the Mach number of the lead shock wave propagating ahead of the flame, and to a corresponding increase in the self-ignition delay. Moreover, for C3H8–H2–air mixtures at isotherms below 1000 K and pressures relevant to DDT, the self-ignition delay increases with hydrogen volume fraction.

Fast Deflagration-to-Detonation Transition in Helical Tubes

“…The geometric parameters of all structural elements of SDT-2 and SDT-1, except for the helical tube section and the length of the measuring section, differ insignificantly. Thus, following the results of [51][52][53][54][55][56], the distance between the last turn of the Shchelkin spiral and the first coil of the helical tube in SDT-2 is reduced to 100 mm, whereas that of the SDT-1 is 150 mm. The Shchelkin spirals themselves are the same: they are wound from steel wire with a diameter of 6.7 mm; the spiral length is 940 mm; the outer diameter of the spiral is 49 mm; and the pitch of the turns is 24 mm.…”

Specific Aspects of Modeling Gas Mixture Explosions in the Atmosphere

“…Figure 23 provides photos of the explosion during Experiment 4 (every 3rd frame). The time interval between the photos is 12.5 ms. Let us take a look at and analyze the data acquired during an explosion of an acetylene-air mixture without the use of turbulizers (accelerators of the explosive combustion process) [30][31][32][33][34] and with the ignition source located 0.7 m above the floor (Experiment 4). The explosion was filmed at the frame rate of 240 frames per second.…”