محمد يونسي

In the Hartmann-Sprenger tube, the encounter of a sub-expan‎ded jet flow with a closed-end tube causes a strong sound in the environment along with an increase in the gas temperature at the end of the tube. In this thesis, the process of temperature increase due to this phenomenon is studied in order to measure its potential for starting combustion. Therefore, two experimental methods an‎d numerical simulation were adopted. In the experimental method, the effect of factors affecting the problem, such as geometric conditions an‎d operational conditions, on the gas temperature at the end of the tube was investigated in a laboratory set. Although measurement limitations prevented rapid temperature recording, a maximum temperature of 740 degrees Celsius was recorded. Other experimental indications confirm the rapid temperature increase in a fraction of a second. It was shown by numerous experimental tests that the resulting temperature can ignite gaseous an‎d solid fuels. Due to hardware limitations, some of the operational conditions could not be examined in the experimental method, so numerical simulation was used. In the numerical simulation section, the averaged Reynolds-Navier-Stokes equations were solved for different geometries an‎d operating conditions. First, the existence of a volume of gas trapped at the end of the tube an‎d its details were investigated by numerical simulation. By using two different gases, it was shown that a part of the gas is always trapped at the end of the tube, separately from the inlet jet flow. The compression an‎d expansion of the trapped volume an‎d the passage of compression waves an‎d expansion fans continuously inside it lead to an increase in the temperature of the trapped gas. It was confirmed that over time, the penetration of the inlet gas into the end of the tube an‎d the exit of part of the gases from this area, along with the expansion wave, cause the maximum expected temperature not to be achieved. It was also shown that the effect of the shape of the tube, especially the shape of its closed end, is related to the volume of trapped gas, an‎d the smaller the volume of trapped gas, the greater the temperature increase. Next, the effect of the gas type on the heating generated was investigated using numerical simulation an‎d it was confirmed that the ratio of specific heats an‎d the molecular mass of the gas play a role in heating; so that monoatomic gases with larger specific heat ratios give the highest temperature increase an‎d if the combination of these two parameters is multiplied by the transient time of the phenomenon, the behavior of all gases is almost synchronous. In another part, the autoignition of a premixed stoichiometric mixture of hydrogen an‎d oxygen was investigated using numerical simulation. For this purpose, a skeletal chemical mechanism capable of covering the processes of its initiation an‎d extinction, consisting of 14 reactions an‎d 8 species, was used. The delay time in its initiation for different conditions was investigated, an‎d in this way, the best conditions for its initiation were determined. It was shown that the geometry used only at a single inlet pressure value has the lowest ignition delay.

گرمايش ديناميك گازي , هارتمن اسپرنگر , لوله تشديد , اشتعال تشديدي , گيرانه تشديدي

Gas dynamic heating , Hartmann-Sprenger , Resonance tube , Resonance ignition , Acoustic igniter

Mohammad Younesi

Hojat Ghassemi