نشریه سوخت و احتراق
سال دوازدهم شماره 3 (پیاپی 28، پاییز 1398)

In this research, zeolite Y was synthesized using extracted silica from rice husk ash as a silica source. Hydrothermal and hydrothermal assisted ultrasound methods were used for zeolite synthesis. Effect of ultrasound on physico-chemical properties of the synthesized sample has been investigated. The properties of the synthesized zeolites were determined using XRD, FESEM, FTIR and BET analysis and their performance were investigated in the catalytic cracking of liquid hydrocarbons in a fixed bed reactor. The gaseous and liquid products properties were determined using GC and SIMDIS analysis. Also density, viscosity and refractive index of the liquid products were ascertained. The results showed that the synthesized zeolite by ultrasound pretreatment prior hydrothermal method had approximately better catalytic performance because of the effect of ultrasound irradiations on the zeolite crystallinity and particles surface grooving. According to XRD results, the crystallinity of the synthesized zeolite by ultrasound pretreatment prior hydrothermal method was 21% greater than prepared sample using conventional hydrothermal method. By using the FTIR analysis after reaction test, it was shown that the structure of zeolite Y remained after reaction.

In this paper design and implementation of a MILD combustion system in a 100 kW boiler was investigated from technical and economic viewpoints. The main objective of this study is determination of the factors affecting the stability of the combustion regimes in a typical domestic utility boiler, leading in simultaneous thermal efficiency enhancement and emission reduction. In particular, the so-called MILD combustion was established in a conventional boiler equipped with an ordinary premixed burner without requiring to replace with expensive modern burners. In the experiments, the qualitative and quantitative features of MILD regime such as uniform temperature distribution in the combustion chamber, volumetric and weakened flame, increased efficiency and decreased NOx emissions were achieved. The results showed a 10% fuel saving as well as 13% reduction in NOx. In addition, the economic evaluation of presented method to establish MILD combustion was performed using the net present value and payback period measures. The analysis results suggest that investment in the MILD system retrofitting plan is cost-effective and economically attractive in similar cases.

In the current paper, the optimum conditions for bioethanol production from sugars were surveyed. Then the operational condition effect on some physical characteristics of bioethanol fuel was investigated. 27 types of bioethanol samples from sugarcane molasses, sugar beet molasses and sugar cane juice were produced at anaerobic fermentation condition in three different temperature levels of 25 ˚C, 30˚c and 35 ˚C and in three different time levels of 24h, 48 h and 72 h. Then the values of density, kinematic viscosity and flash point were calculated in triplets. The results showed that with increasing the temperature and time processing, the viscosity, density and flashpoint would be decreased. The sugar type had a significant effect on these parameters. The closest value of viscosity to its standard amount was related to sugarcane molasses, producing at 25 ˚C and after 72 h fermentation, which was 1.5174 cSt. The nearest amount of density to its standard value was reported 0.9560 which was attributed to sugarcane juice producing at 35˚C and after 72 hours and for flashpoint it was 24.5 ˚C which belonged to sugarcane juice at 30 ˚C and 72 hours. The most bioethanol concentration was 74 gr.L-1 which was produced from sugarcane juice at 35 c◦ and after 72h.

In this study, oxy-combustion is numerically investigated under MILD conditions. This novel combination is ‎simulated in a laboratory-scale furnace with parallel fuel and oxidant jets and a recirculating flow. With nitrogen ‎removal from the oxidant stream, zero NOx emission for gaseous fuel systems is expected. Combustion field is ‎modelled using a well-stirred reactor and computational fluid dynamics. In the CFD modelling, RANS equations ‎are solved using RNG k-ε and EDC model is employed to model the turbulence-chemistry interaction. The effect ‎of oxidizer preheating and CO2 dilution on the combustion field as well as flue gas composition is investigated. ‎The results indicate that the flame maximum temperature does not experience a significant increase when the ‎preheat temperature rises, positively affecting the temperature distribution at the cost of CO emission which is a ‎direct consequence of higher recirculation and mixing rate. Also, a kinetic study on the chemical effect of CO2 ‎presence reveals that CO production path through CH3O radical is more strengthened compared to the main path ‎through formaldehyde when increasing the dilution level. When diluting the oxidant, methylene’s role become ‎more influential in CO formation than when pure oxygen is used, contributing to higher CO emission. CO2 defeats ‎CH4 and O2 to absorb the free H radicals, causing higher levels of CO production.‎

An experimental investigation has been done on the effective parameters on biogas extraction from the combination of food waste (FW) and cow manure and organic. Samples of FW were collected from the university restaurant and they mixed with the manure with different ratios of 1: 1, 1: 2, 1: 3, 3: 1 in a 1 liter polymeric bottles. These bottles embedded in a hot water bath at a thermophilic temperature of 55-60 ° C in a period of 15 days. The volume of biogas produced was measured. The results of gas production showed that the ratio of 1: 1 obtained the highest volume of cumulative gas ( 5 liters). Ten grams of chemical additive of silica gel and organic additives like rosemary plant, walnut shells, banana and tomato skin were added to the optimum selected ratio of digester. The produced cumulative biogas was increased 24.4%, 7.2%, 2.3%, 1.9%, 6.6% by volume respectively in compare with that of optimum based mixture. During the digestion period, PH changes showed that the highest volume of biogas was generated in neutral pH. And the use of walnut shells resulted in PH stabilization in the process. Measuring thermophysicsl properties (Total solids, volatile matter, moisture content, ash content), for the mixture of food waste and manure were shown the high capacity of food waste to convert to biogas (43%) Based on the laboratory experiments, energy analysis was performed for portable biogas reactor.

In this paper, methane pool fire and fire plumes with two heat release rates of 14 and 45 kW are simulated using Large-Eddy Simulation (LES) method. In order to investigate the accuracy of various combustion models, two combustion models of Eddy Dissipation Model (EDM) and Infinity Fast Chemistry (IFC) have been evaluated with a one-equation sub-grid scale model. The simulated results are in a good agreement with experimental measurements, and show the scaling relations of mean temperature and velocity in each pool fire region including stable flame, intermittent and plume. Results indicate that, EDM combustion model have a better prediction of mean velocity and temperature while it have more computational time. In addition, by incorporating Fast Fourier Transform (FFT) analysis on the transient results of temperature and velocity, the prevailing frequency for the temperature and velocity is equal which is 2.75 Hz for the current case. Moreover, energy cascade of eddies shows the accuracy of the LES in predicting pool fire dynamic.

In the present work, the noise of a turbulent non-premixed free flame is calculated. A Hybrid method with Lighthill analogy along with a CFD simulation is used to evaluate combustion noise. In this way, the reactive flow equations are solved by the Large Eddy Simulation and Partially Stirred Reactor model to simulate the interaction of turbulence and reaction. Then the combustion noise source terms including heat release fluctuation and non-isomolar combustion are extracted and used as the sources of Lighthill analogy. The assumption of compact flame is applied to the Lighthill equation and the Green function is used to calculate far field pressure fluctuations. It was shown that in low and medium frequency sound pressure level is in a good agreement with experimental data. By the way at the high frequencies the pressure level does not follow the experimental data. This discrepancy can be related to the compact flame assumption used in analytical solution. The results show that this analytical method can produce acceptable results with a low computational cost. Also, the noise emitted by the non-isomolar fluctuations is negligible against that of heat release fluctuations and can be ignored.