New: Defense of Ph.D. thesis:

The thesis defense by Mr. Mohammad Younesi, a Ph.D. candidate in mechanical engineering, entitled "Gas Dynamic Heating Usage for Starting Combustion", will be held on 30-Sept-2025 at 14:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.

Abstract
In the Hartmann-Sprenger tube, the interaction of an under-expanded jet flow with a closed-end tube generates a strong sound in the environment, accompanied by an increase in gas temperature at the end of the tube. In this thesis, the process of temperature increase due to this phenomenon is studied to measure its potential for initiating combustion. Therefore, two experimental approaches and numerical simulation were adopted. In the experimental approach, 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-up. Although measurement limitations prevented rapid temperature recording, a maximum temperature of 740 degrees Celsius was recorded. Other experimental indications indicate a 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 approach, so the numerical approach 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 was investigated in detail by numerical simulation. In this way, 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 continuous passage of compression waves and expansion fans 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 waves, 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 type of gas 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 monatomic gases with larger specific heat ratios give the highest temperature increase. It was also shown that if a combination of these two parameters is multiplied by the transient time of the phenomenon, the behavior of all gases is more or less the same.
In another section, the autoignition of a premixed stoichiometric mixture of hydrogen and oxygen in a Hartmann-Sprenger tube was investigated numerically. For this purpose, a skeletal chemical mechanism capable of covering the initiation and extinction processes, 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.

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