نشریه سوخت و احتراق
سال پانزدهم شماره 1 (پیاپی 38، بهار 1401)

The search for alternative ways to produce important fuels such as gasoline is crucial. One of these technologies is the process of converting methanol to gasoline, which will have a high economic position in the future. A common catalyst for the MTG process is the ZSM-5 zeolite, which, despite its many benefits, is rapidly deactivated. Therefore, the production of a suitable catalyst with high stability and resistance to coke deposition, is of great interest in the industry. In this study, the efficiency of a composite catalyst consisting of ZSM-5 and Beta zeolites in improving coke stability and distribution of liquid products has been studied. To reduce the costs, the two zeolites were synthesized using a template free method and using a cheap natural source like rice husk. The results showed that with the introduction of Beta zeolite, the acidity of the composite catalyst decreased, which in addition to improving the structural properties of the catalyst by creating mesopores, improved the performance in the MTG process so that on this catalyst, deactivation time increased by 60%. Moreover, the study of process kinetics using Crambeck model, which included 3 lumps of methanol / dimethyl ether, light olefins and gasoline, showed that the results of the model were in good agreement with the results of the laboratory datas.

In this paper, the dynamic modeling of a D-type boiler was performed during a step increase in loading. The D-type boilers are used in industry to produce process saturated steam. In these types of boilers, heat absorption occurs in two sections of the furnace and the convection section. The pipes of the convection section are indirectly exposed to heat, causes the flow direction to change from the upper drum to lower drum and vice versa. One of the special features of this boiler is that the drum circulation loop is natural and as a result, the hydraulic balance equations of the system must be considered. In the present modeling, the equations of water-side were considered in one-dimensional and the equations of flue gas-side were considered in three-dimensional space using the zonal method. The transient continuity and energy equations of the water-side form a system of nonlinear ordinary differential equations which were solved using the Runge–Kutta method. To solve the water and gas-side equations in two-way coupling method, a Fortran computer program has been developed. Investigation of the boiler operating parameters during start-up can help to improve the existing control system. The comparison of the present results with the test data of the desired boiler showed that maximum modelling errors are equal to 4.8, 1, and 6.8 percent for steam pressure, drum water temperature, and outlet steam of boiler during start-up, respectively. Also, the boiler response to a step increase in consumer steam demand is less than 20 seconds.
.

V94.2 gas turbine is one of the most widely used gas turbines for power generation in Iran. In this study, a brief literature review of damage analysis and life estimation of V94.2 combustor is presented accompanied with aerothermal and thermomechanical analyses in the real operation condition. Since creep failure is one of the limiting factors in the life time of combustion chambers, creep life prediction is insvestigated in this paper. Creep time rupture prediction is one of the most important steps of the creep life calculation. Therefore, first, aerothermal and structural analyses are performed considering the effect of the creep failure on the combustion chamber. Next, creep time rupture is calculated using two well-known methods Larson-Miller and Sherby-Dorn parameters. These parameters for IN617 are extracted as a function of stress based on creep experimental data. The accumulated creep damages of 40’000 hours of full-load operation in the combustion chamber are reported for both above methods. Critical nodes limiting the component life are diagnosed from the detected critical creep damage region. According to the results, the creep rupture time prediction technique plays a vital role in the specification of critical creep damage region, temporal damage variation and consequently, creep life estimation. Therefore, the calculated damage from one technique can be three times greater than the results from the other technique.

Fuel system and proper fuel-air mixing are important challenges in spark ignition engines. Due to time consuming fuel atomization process, determining the best start position for fuel injection is vital in engine performance. In the present work, a single-cylinder research engine equipped with a fuel injection system for gasoline and natural gas, with the ability to adjust spark timing and start of injection positions was used at 1800 RPM and a compression ratio of 11. At a fixed fuel ratio of dual mode, the result showed 9o crank-angle difference between optimum spark advanced of full-load and half-load. At half-load fuel injection period, fuel mass fractions and engine speed were fixed and crank-angle position of start of injection (SOI) was varied along a cycle by a 45o crank-angle step. For each adjusted fuel SOI position, in-cylinder pressure of 400 successive cycles and related HC and CO emissions were collected. The obtained results showed that the emissions were changed by varying SOI position of each fuel fixing fuel injection periods. The emitted gas changes were significant for gasoline SOI variation in compared with those of natural gas. Also, from changes of standard deviation and coefficient of variation of indicated mean effective pressure, it was observed that their highest values occur when gasoline SOI is 15o crank-angle after induction top center.

In many atomizers, the breakup of the annular liquid sheet exiting from the atomizer is responsible for the formation of the spray and the determination of the spray characteristics. This paper studies the instability of the annular liquid sheet exiting from the effervescent atomizer at high gas to liquid mass flow ratios, in order to better understand the primary breakup process in this type of atomizer. Therefore, the dispersion equation obtained from the 3D linear stability analysis has been solved for the flow conditions of the annular liquid sheet exiting from the effervescent atomizer at 0.38 L/min liquid flow rate and high aeration ratios of 1.24% and 1.84%. The results showed that in the aerated ratios studied, the axisymmetric para-sinusoidal perturbation modes are the predominant in the breakup of the annular liquid sheet. In addition, it was observed that with increasing aeration ratio, the liquid sheet will breakup at shorter wave lengths. Also, the results of the study of the effect of viscosity on the instability of the annular liquid sheet showed that the viscosity of the liquid has some stabilizing effects and non-viscose assumption of the liquid at high aeration ratios can cause errors in calculations of the stability of the annular sheet breakup and the breakup length.

Mathematical modeling is used as a tool to predict the combustion behavior of fuels. The use of detailed chemical kinetics mechanisms in combustion models increases computational time. Metaheuristic optimization algorithms are one of the methods used to reduce the detailed mechanisms. The purpose of this paper is to investigate the possibility of using continuous metaheuristic algorithms in binary space to reduce the combustion mechanism of dimethyl ether fuel. For this purpose, particle swarm optimization and differential evolution algorithms have been used in a combination with angular modulation to map the continuous space to binary one and reduce the dimensions of problem from 351 to 6. Finally, a detailed mechanism with 79 species and 351 reactions is reduced to 17 species and 43 reactions. It has been showed that the reduced mechanism predicts the results of detailed mechanism in constant pressure and laminar premixed flame reactors very well with maximum error less than % 0.95.
 
.

The hybrid microwave-combustion synthesis method is a facile and rapid pathway for fabrication of nanocatalysts. In this study, the effect of combustion atmosphere on physicochemical and catalytical properties of CuO/ZnO/Al2O3 nanocatalysts as the catalysts of the steam methanol reforming process was investigated. For this aim, three types of nanocatalysts under different oxygen concentration atmosphere were prepared. The characteristic properties of synthesized nanocatalysts were studied by XRD, FESEM, EDX, BET, and FTIR analyses. It was understood that the crystallinity of copper species is lower than the other samples which led to higher dispersion of copper sites as the main core for steam methanol reforming reaction. Moreover, higher surface area and better surface morphology of CZA-O60N40 resulted in higher methanol conversion. Nevertheless, its higher dispersion of Zn(100) crystallite facet led to more CO production as the undesired product.