نشریه سوخت و احتراق
سال یازدهم شماره 3 (پیاپی 24، پاییز 1397)

Oil-based lubricants are a stable source for lubricating moving parts in mechanical systems. Low oxidative stability and high pour point are the major problems of vegetable oils that prevent their extensive use as a lubricant. In this study, two-stage transestrification method was used to improve the disadvantages of non-edible rapeseed oil. In the first step, methyl ester of non-edible rapeseed oil was produced by transestrification method using an ultrasound power. In the second step, using ultrasound power the reverse transesterification reaction of methyl ester with tri-methyl propanol was examined. In order to increase the reaction rate of biolubricant production, the ultrasound system was used, which is a new way to production of biolubricant. The ultrasound power by creating the phenomenon of cavitation causes proper mixing and improving the mass transfer and increasing the biolubricant production rate. The effects of independent variables such as pulse, amplitude, and time on the efficiency and energy consumption was investigated using RSM method. It should be noted that the variables such as temperature, the molar ratio of methyl ester to tri-methyl propanol, catalyst concentration, and vacuum pressure were considered constant. The biolubricant yield and energy consumption were 82.2% and 116.726 kJ under the optimized conditions, i.e., a pulse of 40%, an amplitude of 82.01%, and a reaction time of 60 min. The biolubricant was confirmed using nuclear-hydrogen magnetic resonance spectra (H-NMR). The physical and chemical properties of the synthesized biolubricant have been evaluated by measuring standards. The biolubricant prepared (using ultrasonic method) from non-edible rapeseed oil complies with the criteria dictated by ASTM D6751 standards. The physical and chemical properties of the synthesized biolubricant conform to the reference lubricant (ISO VG 10). Regarding the results, it was found that using ultrasonic system the biolubricant can be produced in much less time than the traditional method. The bioubricant production with ultrasonic system can be introduced as a new method to the world.

water electrolysis is one of the best methods for high purity Hydrogen (and Oxygen) production. Using nonprecious and durable electrocatalysts with low overpotential and high activity instead of noble metals as cathode is one of the most investigated subjects. In this project, Nickel nanoparticles have been grown on the reduced graphene oxide support and deposited on Nickel foam substrate to employ as HER catalyst. The structures of this catalyst were investigated by various techniques such as FT-IR, XRD, and SEM. These techniques showed that applied method for synthesis of a porous and homogeneous elctrocatalayst was successful. To evaluate the electrochemical behavior of this nanocatalyst, cyclic voltammetry and linear sweep voltammetry were applied. The electrocatalytic activity of Ni/rGO was improved after 500 CV cycles. The observed overpotential of Ni/rGO would be -281 mV at the current density of 10 mA cm-2 and Tafel slope of -126 mV dec-1. Whereas, these parameters for Ni/rGo after 5 CV cycles are -303 mV and -149 mV dec-1, respectively. Finally to study the performance of these nanoparticles in a real condition, an alkaline electrolysis cell was used. Ni/rGO exhibited the cell voltage of 1.9 V at the current density of 200 mA cm-2.

In this study, the effective parameters on the amount of biodiesel production from date seed oil via three heating methods of conventional, microwave, and ultrasonic were assessed. In order to carry out the biodiesel production process, the esterification reaction using sulfuric acid as catalyst was firstly performed to reduce the free fatty acid content of date seed oil to the standard amount for transesterification reaction. The results showed that 1 wt.% of catalyst and 8-9 molar ratios of methanol to oil were the optimum amount for all of biodiesel production methods. In other words, utilized method has no effect on the amount of catalyst and methanol in the reaction. The temperature of 56 °C was selected as an optimum temperature in the conventional heating method and the power of around 300 W provided the highest yield in both microwave and ultrasonic methods. However, the major different was in the reduction of reaction time. It decreased from 90 min for conventional method to equilibrium point 7.5 and 3 min for ultrasonic and microwave methods, respectively. According to energy consumption, microwave method was known more suitable than ultrasonic method. The results of modeling presented that suggested models were in good agreement with the experimental values. Methanol/oil molar ratio and reaction temperature in the conventional method, amount of catalyst and methanol in the microwave method and power of ultrasonic waves in the ultrasonic method had the highest influence on the conversion of date seed oil to biodiesel.

Nowadays, a considerable part of the energy is the result of the combustion of hydrocarbon fuels in combustion systems. Therefore, efforts to improve and modify combustion processes and reduce the undesirable byproducts are of great concern. Among all the efforts made to improve the performance of combustion systems including reduction of pollutants, reduction of soot emissions has received special attention. This is due to the fact that soot emission is one of the major pollutants that have irreparable effects on human health, and affects the quality of life. Since the first step to reduce the soot pollution is to provide a comprehensive overview of its structure, mechanisms and also the effective parameters of its production, in this study, the phenomenon of soot formation and oxidation are investigated using one of the multi-step models presented for the formation and oxidation of soot to identify the behavior and parameters affecting soot formation. Numerical modeling of this phenomenon is carried out using KIVA-3V code. The results of the simulation are validated using the experimental data of pressure and the amount of soot formed in the combustion chamber of a two-stroke diesel engine with a direct injection system. Soot characteristics i.e., mass, volume and volume fraction of soot, species concentration, soot concentration, particle number density, average particle diameter, and the time and place of soot content in the combustion chamber are discussed as outputs of the model. The results show good agreement with the experimental data.

Low temperature combustion (LTC) engines such as homogeneous charge compression ignition engine (HCCI) have lower nitrogen oxide (NOx) and particle matter (PM) with higher efficiency. In this paper, one single cylinder, air cooled, direct injection Yanmar diesel engine is converted to HCCI engine fuelled with ethanol. Variation of combustion parameters, emissions and combustion noise level were studied by using 30 steady state HCCI operating points at 1350 RPM for four levels of equivalence ration at different intake air temperature (Tin). The results indicate that due to with lower amount of adiabatic flame temperature for HCCI engine, exhaust temperature (Texh) is lower than typical catalyst light-off temperatures (260°C) so, with using catalyst converter for this kind of engine the efficiency of catalyst converter may decrease. With increasing the Tin for all equivalence ratios the combustion noise level (CNL) increase and reach to the higher amounts near 90 dB (ringing region). With retarding the combustion timing, the adiabatic flame temperature decreases so higher amount of air pollution (unburned hydrocarbon (uHC)) is produced and engine operates near misfire region.

In this work, new method for removal of sulfur dioxide from combustion gases was studied. Al2O3, Cu-Al2O3, and Mo-Al2O3 were examined as the catalysts for reduction of sulfur dioxide to elemental sulfur with methane and their performances were compared in terms of SO2 conversion and selectivity. The effects of temperature, SO2/CH4 molar ratio, and reaction time on SO2 reduction were studied. The operating temperature range was 550–800 °C and it was observed that the reaction is strongly temperature dependent. Performance of the catalyst extremely enhanced when molybdenum and copper were added as promoters, and the Al2O3-Cu (10%) catalyst showed the best performance between of all the catalysts in terms of SO2 conversion and selectivity. For the Al2O3-Co(10%) as the best catalyst, the conversion of 99.5% and selectivity more than 99.5% were achieved at 750 °C. Effect of molar feed ratio of SO2/CH4= 3-1 was studied and stoichiometric feed ratio showed the best performance. Also, investigation of reaction time for catalysts showed a good long-term stability for SO2 reduction with methane in 5 hours.

Using GDI technology has a lot of challenges for automotive manufacturers such as a combustion development so PFI engines have been produced and even, in some markets, their production is increasing. Regarding to the strict emission legislations, PFI engines need improvement and using novel technologies. One of these technologies is APFI concept. This concept could approximately achieve the main advantages of GDI technology by less cost and challenges. In this study, the effect of APFI on the wall wetting, fuel distribution in combustion chamber and output power are investigated. It shows that using this concept could decrease fuel film mass on intake system about 75 percent. In the other hand, fuel distribution in combustion chamber (around spark plug) becomes homogenous which causes improvement in combustion progress and increases in-cylinder peak pressure. Investigations show that the APFI engines are sensitive to the injection timing so the optimum time for start of injection is investigated.