New: Defense of M.Sc. thesis:
The thesis defense by Mr. Farshid Masihizadeh, a M.Sc. candidate in aerospace engineering, entitled "Modeling of Evaporation and Thermal Decomposition of a Hydrogen Peroxide Droplet", will be held on 27-Jul-2026 at 14:00 (Tehran time) at the School of Mechanical Engineering of Iran 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 this research, a coupled numerical model has been developed to investigate the simultaneous process of single droplet evaporation and thermal decomposition of pure hydrogen peroxide (H₂O₂) vapor in a quiescent environment. A pure H₂O₂ droplet is considered in a hot, quiescent gaseous environment, and the conservation equations of mass, energy, and chemical species are solved in coupled form in the liquid and gas phases using a finite volume approach.
One of the main challenges of this research was determining appropriate kinetic coefficients for the single-step decomposition reaction of H₂O₂. For this purpose, the detailed decomposition kinetics of H₂O₂ were first solved using the Cantera library over a wide temperature range, and the resulting data were then converted to a single-step Arrhenius model through curve fitting. The pre-exponential factor A and activation energy E_a were extracted from this process and employed in the numerical model.
Given the lack of experimental data for H₂O₂ droplet evaporation and decomposition, model validation was carried out in two stages: first against evaporation and combustion data of normal heptane (n-C₇H₁₆) droplets as a reference hydrocarbon fuel, and then against ethanol (C₂H₅OH) droplet data due to the polar nature of this compound, which makes it closer to H₂O₂ in this regard.
The central question of this research was whether the thermal decomposition of H₂O₂ vapor can occur simultaneously with droplet evaporation and affect the evaporation rate and droplet lifetime. The results of this thesis show that this effect is real and direct: H₂O₂ vapors decompose within the boundary layer surrounding the droplet, and the released heat alters the temperature gradient around the droplet compared to the pure evaporation case. This change in the temperature gradient in turn affects the evaporation rate and droplet lifetime. Therefore, the mechanism by which decomposition influences evaporation is not merely delayed and mediated through an increase in ambient temperature, but rather through the direct modification of the temperature field in the droplet boundary layer simultaneously with evaporation.
A parametric analysis of the effect of ambient temperature and initial droplet diameter on the transient behavior of the system was conducted, and the results are presented in the relevant chapter. The findings of this research can be applied to the design and optimization of H₂O₂-based microthruster systems.

Keywords
Hydrogen peroxide, thermal decomposition, droplet evaporation, numerical modeling, droplet lifetime

 

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

 

New: Defense of M.Sc. thesis:
The thesis defense by Mr. Seyed Ahmad Reza Salehi, a M.Sc. student in aerospace, entitled "Modeling of Liquid Fuel Droplet Combustion under Near-Critical Conditions", will be held on 2025-06-11 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
The combustion of liquid fuel droplets represents one of the fundamental yet complex phenomena in the field of engineering, playing a pivotal role in the operation of thermal and propulsion systems, including combustion engines, turbines, reactors, and jet engines. In this context, the present study aims to numerically model the transient process of evaporation and combustion of a single-component fuel droplet under high-temperature conditions, atmospheric pressure, a quiescent environment, and zero gravity. To this end, the species, momentum, and energy conservation equations in the gas phase, as well as the energy conservation equation in the liquid phase, are numerically solved using a finite volume approach and a fully implicit method. Thermophysical properties are defined as temperature-dependent functions and vary with both time and space. Furthermore, the chemical reaction of the fuel is incorporated into the model using a global reaction mechanism. For validation purposes, the results obtained for heptane fuel are compared with experimental data in the temperature range of 470 to 740K for the pure evaporation process and with numerical data in the range of 1200 to 1600K for the combustion process. The effects of ambient temperature, initial droplet diameter, and the composition of the surrounding gas on the evaporation or combustion process have been examined. Consequently, variations in droplet diameter, average evaporation or burning rate, temperature, and flame position have been determined.
The results indicate that the impact of increasing temperature on the burning rate is approximately 3% greater than that of increasing the initial droplet diameter. On the other hand, increasing the initial surface temperature of the droplet leads to a reduction in droplet lifetime due to a shorter heating period, yet has no significant effect on flame temperature or location. Additionally, a threefold increase in oxygen concentration in the ambient air raises the flame temperature by over 1000K and causes the flame to form at radii very close to the droplet surface. In contrast, an increase in the initial carbon dioxide concentration exhibits an opposing effect to that of oxygen, weakening the flame formation.

Keywords: Evaporation, ignition, droplet combustion, liquid fuel, heptane, flame, modeling.

 

New: Defense of Ph.D. thesis:

The thesis defense by Mr. Sajad Jabari Neek a Ph.D. candidate in mechanical engineering, entitled "Droplet Drying of Complex Fluids- Oleaster Extract", will be held on 2024-Dec-18 at 16:00 (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
The challenge of drying droplets of complex fluids often involves unique solutions due to the diverse issues associated with different fluids. Low-fiber oleaster extract is a colloidal pharmaceutical-nutritional substance, under investigation by pharmacists as a potential replacement for the currently available commercial oleaster powder, aiming to minimize the side effects of consuming the fibrous material of the fruit in the human body. The high water-to-solids ratio in this exract—resulting from the aqueous extraction method—leads to chemical spoilage, processing issues, and interest in spray drying. Given the lack of prior studies on this emerging extract, this thesis conducts various thermophysical investigations on this fluid under different temperature and concentration conditions, providing a detailed picture of its properties. The results indicate that due to the simultaneous presence of solid, liquid, and gas phases, this extract qualifies as a complex fluid.
Experimental analysis of the drying kinetics of single droplets of the extract under various drying chamber temperatures and initial droplet concentrations reveals that, after losing water during evaporation, the extract forms an impermeable shell upon reaching a critical concentration. The formation of this shell is attributed to the presence of insoluble hydrophilic compounds and the delayed crystallization of soluble materials on the droplet surface. This shell swells and deflates continuously as water vapor escapes, eventually leading to the formation of a particle with a dry and sticky shell, approximately the same size as the initial droplet, and in some cases, with a moist center. Increasing the drying chamber temperature to 200°C resolves the issue of a moist center, though the shell remains highly sticky.
Further investigations into vacuum drying revealed that the extract does not stabilize into a solid state under vacuum conditions. After dehydration in its most concentrated form, it retains a viscous fluid structure similar to honey. Based on these findings, it was concluded that oleaster extract is not suitable for spray drying. Differential scanning calorimetry (DSC) analysis showed that the low glass transition temperature of the extract (35°C) causes its stickiness. Consequently, maltodextrin (DE5), a permitted additive with a high glass transition temperature (approximately 200°C), was employed to improve the extract, and new formulations were created with more suitable glass transition temperatures. The results showed a significant reduction in the stickiness of the dried material, with no stickiness observed in the MS2 and MS3 formulations, and the particles were properly dried.
Considering the drying kinetics of low-fiber oleaster extract observed in the experiments, it seems feasible to model its behavior using a semi-empirical model based on evaporation theory and machine learning of the drying curve data. The proposed model can predict not only the effects of independent drying variables, such as chamber temperature, concentration, and initial droplet size, on the drying kinetics of the extract but also the conditions that lead to the formation of swollen particles—larger than the initial droplet size.

Keywords
Complex fluids, Low-fibrous extract, Oleaster extract, Single droplet drying, Drying kinetic
 

 

New: Defense of M.Sc. thesis:
The thesis defense by Mr. Erfan Dabbaghchian a M.Sc. student in aerospace, entitled "Simulation of flow leakage in impulse turbines' blade tip", will be held on 2024-September-03 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
A supersonic turbine is one of the main components of a turbopump, which serves as the power source for a liquid propulsion engine. When the flow rate is low, a high specific work is required for the turbine's operation. Due to the low flow rate, the blade height and consequently the aspect ratio will also be small. To reduce the losses associated with a low aspect ratio, partial admission turbines are used in turbopumps. In this approach, the gas flow only impacts a portion of the rotor blades. At the blade tips, a clearance is considered to prevent contact between the blade and the casing, which results in tip leakage flow. 
The focus of this study is to investigate the behavior of tip leakage flow in the space above the blades of a supersonic partial admission impulse turbine. This leakage flow is controlled by cavities specifically designed at the blade tips for this purpose. The study's approach involves numerical simulation and the use of artificial intelligence algorithms to predict the flow behavior within the turbine. To validate the numerical results, the performance of an existing partial admission turbine is simulated, and the obtained results are validated against its experimental data. Subsequently, the same turbine is simulated with modifications to the upper blade profile using several defined geometric parameters, including angle, setback, and cavity depth. 
Further steps in this research include analyzing the results of these modifications, creating a database to utilize artificial intelligence algorithms to replace simulations, and predict the turbine's performance. It is worth mentioning that in the end, the optimal blade tip cavity profile is provided by the artificial intelligence algorithm with a negligible error margin (less than 1%).
 
Keywords: Supersonic impulse turbine, blade tip leakage, neural network, simulation