نشریه سوخت و احتراق
سال چهاردهم شماره 1 (پیاپی 34، بهار 1400)

The dynamics of transcritical shear flames of GH2-LOX and GCH4-LOX has been investigated numerically. Present results have been compared with available experimental data that show reasonable agreement. The standard k-ε model is applied to simulate flow field. For the combustion and turbulence interaction a steady laminar flamelet model (SLFM) with real gas table has been adapted. Real gas flamelet tables obtained from the Cantera open source code. Initially, it is observed that in the physical space, the difference between real gas condition and ideal gas is significant in terms of the position and dimensions of the flame for the transcritical state. In the mixture fraction space, there is no significant difference between the real gas solution and the ideal gas. However, in near extinction point there is considerable difference. On the other hand it is shown that in the transcritical shear flames the mass flux ratio of fuel and oxidizer is most important parameter from view-point of flame shape and dimension. With increase of the mass flux ratio, the turbulent viscosity and heat transfer in the shear layer increases drastically. Accordingly, the pseudo-boiling phenomenon causes the flame shape and dimension changed remarkably. In the GCH4-LOX flame due to higher density of methane, at the lower mass flux ratio (about 5), a strong recirculation appeared in the front of the flame, while in the GH2-LOX flame this vortex formed around mass flux ratio of 25.

The two-dimensional numerical simulation of the spray flame formed in a laminar counterflow configuration has been performed to investigate flame regimes and its effect on changes in important species and radicals. Ethanol is used as a liquid spray fuel and the skeletal mechanism of ethanol/air with 40 species and 180 preliminary reactions is used for combustion reactions. The Sauter mean diameter of fuel droplets and randomly injected into the air inlet are considered using a UDF code, and the motion of the droplets is calculated using the Lagrangian approach. The results show that the predominant flame regime is Non-Premixed in the high equivalences ratio, high strain rates and large droplet diameters. Also, the combustion reactions are suppressed in the center areas of the flame, due to the reduction of the oxidant fraction and the OH mass fraction, and the flame index is zero, which indicates the internal group of droplets in this area.

In this study, a six-lump kinetic model is proposed for describing the catalytic cracking of gas oil over Y zeolite. The feedstock and products were classified into six discrete lumps, including feed, kerosene, gasoline, liquefied petroleum gas, dry gas, and coke. A time-on-stream exponential function was used to describe the deactivation mechanism. Experimental data for 5 temperatures between 500-600 °C and residence time of 60-120 s were applied for the estimation of kinetic parameters. The estimated activation energies were in the range of 40–85 kJ.mol−1, the preliminary reactions exhibited lower apparent activation energies than secondary reactions. By increasing the reaction temperature from 500 ° C to 650 ° C at the reaction time of 240 min, the progress of the secondary reactions of coke production increases, and the deactivation function decreases from 0.955 to 0.735, After 300 min it reached 0.892 and 0.466, respectively. This means that at higher temperatures, the catalyst deactivation occurred faster. Analyzing the results for the distribution of products under different operating conditions showed that a temperature of 550 ° C and a residence time of 60 to 80 s are optimal for the production of gasoline and kerosene.

The objective of this study was to investigate the pyrolysis of Arundo donax in a fixed bed reactor under CO2 atmosphere. Pyrolysis experimental include the effect of temperature (540, 650 and 750 °C) on the yield of pyrolysis products. After pyrolysis, the proximate and ultimate analysis of bio-oil properties was investigated. The results showed that the maximum yield of bio-oil (33.7%) was obtained at a temperature of 650 °C. By increasing the temperature from 540 to 650 °C, the yield of bio-oil increases and the amount of bio-char decreases. Regarding the effect of temperature increase on the amount of gas, the results show that from 540 to 650 °C, the amount of gas increases and then decreases. The results of gas chromatography – mass spectrometry (GC-MS) showed that the obtained acidic liquid is dark in color with a combination of chemical compounds including acids, alcohols, aldehydes, furfurals, furans, phenols and some aromatic substances. The presence of these compounds indicates that the bio-oil obtained could potentially be used as fuel. Also, the experimental formula of bio-oil obtained was CH1.44O0.54N0.003 with a calorific value of 27.64 MJ/kg.

Due to the higher efficiency of the detonation wave compared to the deflagration wave, in recent years, attention has been attracted to the use of detonation waves in engines. For this purpose, various engines such as pulse detonation engines and rotating detonation engines are proposed. Because of the better performance of rotating detonation engines, the purpose of this work is investigation of detonation propagation wave inside the rotating detonation engine (RDE) chamber numerically and with a three-dimensional approach. The purpose of the present work is investigation of the propagation of the detonation wave inside the rotating detonation engine (RDE) which has been done numerically by considering three-dimensional approach. For this purpose, Navier-Stokes equations is solved with taking into account energy and species conservation equation for the reacting flow. Because of high computational cost, a one-step global chemical reaction is used. The results of the present study are compared with the results of the Chapman-Jouguet detonation wave. The results show that there is a good agreement between the temperature and wave velocity. Also, according to the simulation results, the structure of the detonation wave was well extracted. After creating the initial condition, the detonation wave is created and starts moving at a certain speed. In the following, the performance parameters of the present chamber are examined in order to be used in turbine engines, which shows the remarkable performance of this type of chambers.

In this study, the evaporation of liquid oxidizer inside a combustion chamber during engine start-up in a low-pressure environment is numerically investigated. In thruster starting stage, first, a portion of oxidizer which has been evaporated inside the injector capillaries fills the void inside the combustion chamber and causes a pressure rise (up to 0.2 bars). This makes the injection of oxidizer as fluid possible and now the evaporation rate can be investigated. In the investigated thruster the mass flow of injected liquid is 3 grams per second and the type of injector is pressure-swirl. Numerical simulation in this study is based on an Eulerian- Lagrangian method known as Discrete Phase Method (DPM), which investigates the interaction of two phases using Navier-Stokes Equations. A verification is done to support the results of the method used in order to obtain quantitative variables essential to this study. The tendency of fluids to reach a stable state after an abrupt process of flashing is visible in the results of this study. After a small period of time around 20 milliseconds a stable temperature around 264 kelvins is reached which causes a stable pressure of 7 kPa in the combustion chamber.

This numerical research conducted using CONVERGE Computational Fluid Dynamic (CFD) code and devoted to assessing the simultaneous and separate impacts of Diesel Direct Injection Timing (DDIT) (16 to 6 Crank Angle (CA) Before Top Dead Center (BTDC) with 2 CA steps), combustion chamber geometry (re-entrant (baseline), cylindrical, and wide-shallow chamber), and applying syngas (20 and 40% of total energy per cycle) in a heavy-duty off-road RCCI engine. In the case of combustion simulation, the SAGE combustion model was used coupled with a detailed chemical kinetic mechanism consist of 72 species and 360 reactions. Results showed that under baseline operating conditions (DDIT of 10 CA BTDC and using re-entrant piston bowl) increasing the syngas to diesel ratio up to 40% caused a 3.4% rise in heat transfer loss and simultaneous reduction in Nitrogen Oxides (NOx) about 12%, Particulate Matter (PM) up to 88%, and Hydro-Carbons (HCs) nearly 82% compared to Pure Diesel Combustion (PDC) conditions. Besides, utilizing the wide-shallow combustion chamber along with diesel injection at 16 CA BTDC at diesel- 40% syngas combustion operating conditions led to the increment of heat transfer loss (7%), combustion loss (2.5%), and also, simultaneous reduction of NOx (3%), PM (37%), HC (62%), and gross indicated efficiency (4.7%) compared to baseline PDC case.