نشریه مهندسی مکانیک مدرس
سال بیستم شماره 6 (خرداد 1399)

Ceramic Matrix Composites (CMCs) are designed to overcome the main drawbacks of monolithic ceramics, especially their brittleness, in high-performance and safety-critical applications. Owing to the inherent properties of CMCs, especially heterogeneous structure, anisotropic thermal and mechanical behavior, and the hard nature of fibers or matrix, the machining process becomes extremely challenging as the generated surface suffers from undesirable quality. Taking the high hardness of ceramic matrix into account, grinding with diamond abrasives is the only efficient way for machining of CMC materials. The aim of this paper was to study the influence of grinding parameters (cutting speed, feed speed, and depth of cut) and different cooling-lubrication conditions (i.e. dry, fluid, and minimum quantity lubrication) on surface roughness, process efficiency, and tool wear. The results indicated that MQL leads to the best results in terms of surface quality and process performance. Furthermore, increasing of cutting speed and feed speed decreased and increased surface roughness, respectively, while depth of cut had an insignificant effect on the roughness value. Regarding the experimental results, four machining strategies considering quality, productivity, and efficiency criteria were developed. Eventually, the material removal mechanism was evaluated using SEM photos, indicating that brittle fracture is the dominant removal behavior of CMC materials.

Fuel system is one of the most important parts of the micro gas turbine. Due to the variation of environmental conditions such as temperature, relative humidity of air and height in different geographical locations, the operational features of the fuel system change. In this study, the fuel system of the GTCP85-180 gas turbine is modelled by applying PID mechanical controller. The governing equations of the controller is coupled with classical thermodynamic equations of the gas turbine and the effects of different environmental conditions on start-up and norminal operation of the motor are investigated. The range of variations of the environmental conditions is choosed by considering the geographical locations of Iran. The results of the numerical simulation were verified by comparing the numerical results obtained with written code in Matlab software with experimental measurements. The results showed that the environmental temperature has the strongest effect on the operational features of the fuel control system and causes 16.3% variation of exhaust gas temperature, 3.7% variation of fuel discharge, 14.7% variation of start-up time of the motor and 4.7% variation of fuel pressure in injectors. Also, the start-up operation of the motor showed more sensitivity to environmental conditions compared to normal operation of micro gas turbine.

The goal of this paper is to design an online control interface for knee prosthesis based on the electromyography (EMG) signals of active thigh muscles. According to the time dependent nature of electromyography signals, translating such signals into precise commands in practical applications is a challenge for scientists. First stage for designing an online control interface is to design and implement a test setup for examining the proposed online control interface. To serve this purpose, active knee prosthesis is designed and manufactured using an elastic actuator mechanism. In order to measure the EMG signals, active muscles were detected based on the fundamental of muscles anatomy. In the second stage, filtering and data segmentation were utilized for electromyography signals smoothing, decreasing noises and reducing signal dimensions. Furthermore, time-delay neural network was used in order to map time domain features of EMG signals onto kinematic variables of knee joint. The angle and angular velocity of knee joint were estimated with accuracy of 0.85 (R2) for two locomotion modes including non-weight bearing and ground level walking. To implement online estimation of angular position, time domain features and neural network with 50 hidden layer’s neurons and 2 seconds time delay were used. Finally, online angular position estimation of knee joint was implemented on the designed test setup and results confirm proper tracking of online control interface.

In this study, the effect of using of aluminum oxide and silicon oxide nanoparticles simultaneously into dielectric has been investigated in the process of electrical discharge machining of titanium alloy Ti-6Al-4V. After analyzing the parameters affecting the process of the electrical discharge machining using nanoparticles, intensity of the current, concentration, pulse on time, and particle composition were considered as input parameters. The effect of each parameters has been investigated on three levels; the material removal rate (MRR), the tool wear rate (TWR) and the surface roughness (SR) of the work piece. With respect to the development of the industry in the use of environmentally friendly dielectrics, deionized water was used as the dielectric fluid. Also, Design Expert software has been employed for the design of the experiments, analysis of the results and optimization of the parameters. The results showed that the best surface morphology is obtained by machining with the addition of nanoparticles in the relative composition of 50%. In this percentage of the composition, the surface roughness has the least value of the crack and the recast layer. In addition, the maximum value of the MRR and minimum value of TWR can be achieved in 12A of current intensity, 100µs of pulse on time and 75% of relative composition.

Aluminum-silicon alloys have vast applications in-vehicle components, such as the piston. Usually, such parts are under thermal and mechanical cyclic loadings, and therefore, they should have enough fatigue strength. For strengthening methods, the heat treatment and the addition of nanoparticles could be mentioned. In this research, the effect of the simultaneous use from SiO2 nanoparticles and the heat treatment was investigated on the high-cycle fatigue lifetime of the piston alloy, which is the novelty of this study. The stir-casting method was used for adding nanoparticles into the aluminum matrix, and the T6 heat treatment was done on samples. The microstructure was examined by the optical microscopy and also the field-emission scanning electron microscopy (FESEM), and high-cycle bending fatigue tests were performed, under fully-reversed loading conditions. Based on FESEM images, no agglomeration of nanoparticles was observed in the matrix. In addition, it was found that using SiO2 nanoparticles, heat treatment, and the combination of two approaches, caused to the improvement of the fatigue lifetime, for 304, 411 and 237%, respectively. According to high-cycle bending fatigue data, the fatigue strength coefficient of the piston alloy increased by the heat treatment, and the addition of nanoparticles.

Using vapor chambers is a useful way to control the temperature of electronic components. In this study, two vapor chambers with identical dimensions have been tested. The condensation part of one of them is hydrophobic, the second is simple and there is no hydrophobic operation. In this study, the effect of lateral surface insulation on both vapor chambers, the effect of other parameters, including vapor chamber angle with the horizon, different heat loads produced by the heat source (printed circuit board), geometric deformation of the heat source in a fixed area, and also, change the location of the heat source installation on the evaporator floor, on the thermal performance of the vapor chamber, due to the hydrophobicity of the condensation part of the vapor chamber, has been studied as experimental work and compared with the simple vapor chamber. Also, the impact of installing the heat source on the entire floor of the evaporation section, by increasing the area of it, in both vapor chambers have been investigated. Experimental results show that hydrophobicity and increase of heat, in total and in most cases, decrease the thermal resistance of the vapor chamber. The thermal performance of the vapor chamber has also been improved by installing the printed circuit board across the evaporator floor and it depends on other parameters investigated in this study. Also, insulating the side surfaces, increases the thermal resistance in the simple vapor chamber and reduces thermal resistance in the vapor chamber with the hydrophobic condensation section.

Recent energy-saving policies in Iran led to more insulation implementation in buildings. Therefore, the occurrence of anti-insulation increases in the building industry. The anti-insulation phenomenon is the reverse function of insulation that causes cooling energy increment rather than energy saving. This phenomenon is an important and effective factor in energy consumption and the resident’s comfort. However, it has not been considered in thermal insulation studies worthily. Therefore, in this study, the anti-insulation occurrence temperature set-point is detected under eight climates of Iran by simulation in the EnergyPlus software. Four thickness of polystyrene insulation is evaluated under three insulating methods including external, mid and internal insulation. Results indicate that the anti-insulation occurs in six climates of Iran. Furthermore, cold and marine climates are more likely to anti-insulation occurrence than hot climates. The anti-insulation happens at a lower temperature by increasing the insulation thickness. In external insulation, due to usage of the wall’s thermal mass, anti-insulation occurs in high temperatures compared with mid and internal insulation methods.

Today, piezoelectric actuators are widely used in micro-positioning applications due to unique features such as high precision, fast response and high natural frequency. Despite the aforementioned characteristics, nonlinear characteristics such as hysteresis deteriorate the precision of piezoelectric actuators. In order to reduce the effect of hysteresis in control applications, external sensors are used for feedback control schemes. But, high costs and space limitations are prohibitive factors which limit the application of external sensors. Hence, an alternative is using self-sensing methods that is based on electromechanical characteristics of piezoelectric materials which eventually eliminate external sensors. In this research, self-sensing method is applied for position estimation in piezoelectric actuators. The most conventional method is based on the linear relation of electrical charge and actuator position which the position can be estimated by measuring the actuator charge. But this method is faced with serious challenges due to charge drift, especially at low frequencies. For this purpose, a method for modeling and compensating of charge drift is proposed. Then, by linearization of the electric charge-position relation, the self-sensing method is implemented based on the compensated electric charge measurement. Experiments have confirmed that this method can effectively estimate the actuator position with 1.5% estimation error in the presence of charge leakage.

In this study, techno-economic comparison of monocrystalline and concentrating photovoltaic power plants for the selected cities of Kerman province was carried out. After modeling the implied photovoltaic systems and validating the modeling results of the monocrystslline photovoltaic system with the measured data of an installed 5kW monocrystalline photovoltaic power plant at the Graduate University of Advanced Technology, daily and yearly electrical energies production analysis for both plants was presented. Then, the electrical efficiency and the performance factors, including capacity factor, final yield, reference yield and the performance ratio were determined. The economic analysis results showed that the northern cities of Kerman province had more favorable economic indicators, so internal rate of return, balanced cost of electricity, net present value, and benefit-cost ratio for the monocrystal photovoltaic plant were 21-22.1%, 13.3-13.9 dollars per kilowatt, 2-4.2 thousand dollars, and 1.04-1.09, respectively and for the concentrating photovoltaic plant were 24.9-28.6%, 8.8-10.2 dollars per kilowatt, 17.1-30.5 thousand dollars, and 1.24-1.43, respectively. Finally, a comprehensive comparison was made between the conventional PV systems and the CPV system for two scenarios: the same capital investment cost and the same nominal installed power. Results showed that at both scenarios, the concentrating photovoltaic is superior to the monocrystalline PV plant, in a way that Kerman and Jiroft cities, as the best cities, had the net present value of 30.5 thousand dollars and 21 thousand dollars, respectively.

In this study, a portable parabolic solar cooker is designed and fabricated, and the daily performance of the solar cooker is investigated from the energy and exergy viewpoints. One of the important challenges of the parabolic solar cookers is the reduction of their performance in the windy conditions. In order to evaluate this issue, the effect of 0.2, 2, 4 and 6m/s wind speeds on the energy and exergy efficiencies of the solar cooker is studied. Based on the results, the energy efficiency of the parabolic solar cooker is 34.52-46.19% and the exergy efficiency is 2.11-5.60% during the experiment. The experimental results indicate that water can boil in the windy conditions using the fabricated solar cooker although the time required to boil water increases by rising the wind speed. According to the results, in the wind speed of 6m/s, the time taken to boil 2 liters of water is about 40min. Furthermore, the energy and exergy efficiencies of the parabolic solar cooker in the wind speed of 6m/s are 20.08% and 1.99%, respectively, lower than those in the wind speed of 0.2m/s.

In recent years, industrial applications of composite sheets have been increasingly expanded due to their extremely different properties such as high strength, low density, and good corrosion resistance compared to single layer sheets. For this reason, in the current study, it is investigated the flanging of composite metal sheets. Also, the behavior of an aluminum-copper sheet, cladded using explosive welding, during incremental forming of a circular collar have been experimentally and numerically studied. In addition, the experimental results are used to validate the numerical simulation of the forming process. At first, in order to understand collar forming of the perforated sheet, the effect of hole diameter, forming direction or layer arrangement on dimensional accuracy, thickness distribution and forming force were investigated and then, the effect of hole flanging and collar forming were compared using two strategies. The results show that by decreasing the initial hole diameter of sheet, the average vertical maximum force increases by 9%, the minimum thickness decreases and its location shifts toward the center of sheet. Aluminum-copper arrangement also experiences a 7% reduction in average force and a 4% increase in minimum thickness due to the protective property of copper layer in tensile state compares to copper-aluminum. Besides, the multi-step method leads to a 6% minimum thickness increase due to better material flow compared to single-step method.

Incremental forming of metal sheets is one of the new methods of metal forming with high flexibility in batch production of complex geometries. Due to the absence of a matrix and the gradual applying of forming forces, the forming limit in this process is increased compared to conventional ones. In this research, formability, forming, and finally fracture of aluminum/copper bilayer sheets produced by explosive welding method in the single point incremental forming process are studied. In the numerical prediction of growth and onset of fracture of sheets in this process, the Xue-Wierzbicki damage criterion was used as the VUMAT subroutine in Abaqus software. Using the numerical model, variations of the stress triaxiality and equivalent plastic strain as the variables affecting the damage growth in the incremental forming process were analyzed and explained, and the effect of cyclic and nonlinear loading in this process was shown. Experimental results show a different failure height of various geometries due to different loading conditions. Also, using the verified numerical model, in addition to predicting crack growth location, the fracture height in the formed geometries was predicted by 4.06% difference with respect to the experimental results.

High corrosion resistance, proper mechanical properties, and biocompatibility of Ti-6Al-4V alloy make it suitable for medical (dentistry and orthopedic implants), military and electronic industries. The greatest disadvantages of this alloy are poor wear resistance, low fatigue strength and poor tribological properties. The aim of this study was to apply an adhesive coating to improve both corrosion and wear properties of the Ti-6Al-4V alloy. Surface modification of alloy was done by nitrogen plasma nitriding in both electrolyte plasma and atmosphere plasma environment. Finally, the TiN layer was coated on the modified samples, using cathodic arc evaporation technique. The microstructural investigation, surface morphology, and coating thickness were studied by field emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy. The grazing incidence X-ray diffraction (GIXRD) was applied to study the phases in the coatings. The corrosion resistance was studied with potentiodynamic polarization and electrochemical impedance spectroscopy. The wear resistance and the coating coefficient of friction were tested with pin-on-disc machine. The corrosion resistance of the samples was improved by applying the coatings and the plasma-nitride/TiN double-layer coating showed the best corrosion resistance with current density of 1.46×10-7A/cm2 and corrosion potential of -0.3V. On the other hand, the lowest thickness reduction in wear test was observed in double-layer coatings, so that the thickness reduction for both double-layer coatings, was less than 4μm, after 300m sliding.

In this study, multipurpose testing equipment with a sub-scale model of a specific tandem rotor helicopter constructed to conduct a number of experiments to accurate understanding from the tandem rotor's outwash in ground effect. The experiments conducted as measuring rakes were positioned at two distances equal to 1.5 R and 3R from the rotor(s). Unlike the experiments that have been performed in wind tunnels or in special hover chambers, these experiments were performed in an open environment with fewer side walls effects. The results show that when the single rotor operates in a fixed altitude, and the blades tip velocity of 0.2M, the outwash velocities reduces as the flow moving away and vice versa, but for tandem rotors, increasing the rack distance from the model does not have a noticeable effect on the average values of the flow velocity. A comparison of the results of these measurements with the CH-47D helicopter outwash patterns confirms the accuracy of the obtained patterns and showed that the overlap between the rotors increases the velocity values and causes to the occurrence of maximum outwash velocity at lower altitudes. No overlap between the tandem rotors makes the outwash flow pattern of each of them similar to a single rotor. Increase in ground effect as the height of the rotor(s) decreases to 1R, changes the flow pattern in the forward and aft of the model helicopter. In this altitude, unlike their operation in altitude of 2R, the outwash flow increases when moving away from the rotor(s).

Fine grain materials exhibit excellent mechanical properties and are widely used in various industries. One way to produce fine grain bar is by using the severe plastic deformation techniques. Cyclic extrusion and expansion of the sample is used as one of the methods of severe plastic deformation for production of fine-grained bars. As the length of piece increases, the friction force increases, so that the required force for shaping operation is increased to such an extent that the process cannot be performed. For solving this problem, the "Cyclic Extrusion and Expansion under Hydrostatic Pressure" is proposed as a new method of severe plastic deformation for production of long-length fine-grained bars. In this method, the forming operation was done by using a pressure oil, so the hydrostatic compressive stresses are applying to the material and improve the mechanical properties. Also, the results of simulation of finite elements of this method show the effect of friction coefficient on the forming force and independence of the forming force from the bar length due to the hydrostatic process. Therefor the process is capable of producing rods of long length and fine structure. Results of pure copper rebar underwent this process showing that the yield strength and final strength increased by 200% and 33%, respectively. Also, the sample hardness increased substantially by 120%, and the distribution of relatively homogeneous hardness in rebar diameter was obtained. The microstructure results showed a fine-grain after the process, with the grain size reduced to 8μm in center and 5μm in outer diameter.

Due to their excellent mechanical, electrical and thermal properties and ease of production, metallic bipolar plates are a suitable replacement for graphite and composite plates. Stamping is one of the most applicable processes to produce theses plates from a manufacturing cost point of view. Due to its excellent corrosion resistance and low density, titanium rises as a potential option for the manufacturing of the bipolar plates. In this paper, the formability of titanium bipolar plates having a thickness of 0.1mm with a parallel flow field has been experimentally investigated. The formability of the sheet was evaluated at warm temperatures using different forming speed and lubricants. After the experimental implementation of the designed tests based on the Taguchi method, the fracture depth of the microchannel of stamped samples was extracted. The results showed that the most elongation of the sheet will be achieved at 100℃. Likewise, the forming speed and temperature are the most effective parameters on the forming depth, respectively. On the other hand, the effect of the lubricant is not tangible compared to the other mentioned parameters. The maximum forming depth equal to 0.494mm was obtained using an experiment with a forming temperature of 100℃, speed of 4.8mm/min, and lubrication with MoS2.

Deep drawing process is one of the most important processes of sheet forming, which is widely used in the deformation of metal sheets in order to produce parts with complex geometry. Several studies have been carried out on some steels with good formability such as low-carbon and austenitic stainless steels. Among different types of plain carbon steels, high carbon eutectiod steels are capable to withstand cold and warm working without formation of any defect, due to their fully pearlitic microstructure without the presence of proeutectoid phases and nano-sized cementite lamella. However, no comprehensive research has been conducted on the deep drawing process of eutectoid steel. In the present research, the formability of CK75 steel sheets was experimentally evaluated using warm deep drawing process. Warm deep drawing process of the CK75 steel was studied in the temperature range near and below the eutectoid transformation temperature. The results show that deformation at 700°C (near to the eutectoid temperature) lead to the uniform distribution of thickness and less instability. On the other hand, maximum instability (e.g. thinning) was obtained by warm deformation at 550°C. At the temperature above the eutectoid transformation temperature, due to the formation of multi-phase structure and non-uniform distribution of cementite particle, the workability was reduced and led to the occurrence of rupture during deep drawing.

In this research, the behavior of conical and hemispherical shells, made of steel and aluminum, respectively, subject to impact loading has been investigated using experimental and numerical methods. The energy absorption capacity of these adsorbers has been calculated and the effect of foam injection on the collapse behavior and energy absorption capacity of aluminum hemispherical shells has been determined. The effect of geometrical parameters on the collapse behavior and adsorption capacity of steel conical adsorbers has also been investigated. Numerical simulations have been performed using the Abaqus finite element software and the results have been compared with the results of the experiments. In Numerical analysis, three damage models, Johnson-Cook, GTN, and modified Rousselier have been used. The Johnson-Cook damage model is available in Abaqus software but the GTN and the modified Rousselier damage models have been created through programming in Abaqus software. The results show that the modified Rousselier damage model is more accurate than the other damage models. Also, in this research, the effect of thickness of conical shells on their efficiency has been investigated and it becomes clear that increasing the thickness of absorber increases efficiency. In addition, foam injection does not a positive effect on the hemispherical absorber performance.

Piezoelectric actuators are the most common choice for position control with ultra-high precision. Despite the significant advantages, the linear and nonlinear dynamics of these actuators, such as hysteresis, could decrease the precision of the control system. In this research, a controller based on the sliding mode method is proposed for position control of piezoelectric actuator. Sliding mode control is a model-based and useful method in nanopositioning systems. In this research, Bouc-Wen model is used for description of the actuator’s behavior. In this model, the linear dynamic is modeled with mass, stiffness and damping terms, and the hysteresis is modeled by its nonlinear dynamics. Usually, there are mismatch and uncertainty between the physical system and mathematical model. For stability analysis of the prevalent sliding mode control, the upper bound of uncertainty must be known. But, in practical systems, this is not possible, simply. On the other hand, selecting the large values for this bound, increases the controller gain and distances it from the optimum value. The proposed adaptive robust control eliminates the dependency to the upper bound of uncertainty. This is done by introducing an online adaptive law for estimating this bound. Proposing this law, asymptotic stability of the closed-loop control system is proven. Implementing the presented method on the laboratory setup and simulator software, its effectiveness is shown by simulation and experimental results.

Incremental tube forming process is capable of manufacturing tubes with different cross sections and dimensions using simple and inexpensive forming tools. In the current study, seven different ductile failure criteria are used in finite element simulations in order to obtain the forming limit diagram (FLD) of Al6063 aluminium tubes at high temperatures. The predicted FLD using these criteria are compared with experimental data to select the optimum criterion. Standard universal tensile tests in different temperatures and strain rates along with Zener-holloman parameter are performed to calibrate the failure criteria. The effects of process parameters including temperature, forming depth and forming feed are considered. The results showed that failure criteria can predict the time and location of rupture in incremental tube forming process with a good accuracy. In high temperatures, Cockroft-Latham and normalized Cockroft-Latham criteria which consider the effect of the largest tensile stress had the best prediction. Investigation of temperature and strain rate showed that by increasing temperature, the forming limit goes higher but increasing strain rate causes to decrease it.

The internal combustion engine’s warm-up period is one of the most important sources of emissions, especially unburned hydrocarbons (UHC). Due to the low temperature of combustion chamber wall during the warm-up period, the flame is quenched rapidly near the walls and piston surface and the air-fuel mixture in the vicinity of the wall does not burn and leave the combustion chamber unburned which increases UHC emissions of internal combustion engines during the warm-up period. In the current study, using MATLAB R2018b software and numerical solution methods, a code is developed based on XU7 engine data to determine the effect of wall temperature on the flame quenching distance. The results showed that by increasing the cylinder wall temperature, flame quenching distance during the engine warm-up period, for two cases of constant and pressure based Peclet number, was decreased by 46 and 22%, respectively. The results also indicated that the flame quenching distance had a downward logarithmic behavior over time, which is the opposite of the thermal behavior of the combustion chamber walls during the engine warm-up period, which is an upward logarithmic behavior.

The aim of this paper is to compare the electric power output of the photovoltaic Module (PV) and photovoltaic-thermal water collector (PV/T). The electrical efficiency of photovoltaic Modules is greatly reduced by increasing their surface temperature. The hybrid photovoltaic-thermal collector consists of a PV Module with a thermal collector attached behind it. The circulating fluid in the collector removes heat from the module and increases its electrical efficiency. In the first part of this paper, a theoretical analysis of a liquid PV/T collector is made based on thermal modeling using the first law of thermodynamics. An unglazed hybrid photovoltaic-thermal collector with serpentine tubes has been designed and manufactured to validate the theoretical results. Then the collector has been tested for three days and results have been compared with a sample photovoltaic module. The theoretical calculations were performed using Matlab software and its results showed good agreement with experimental results. Our finding shows a maximum increase of 6% in the electrical efficiency of PV/T in comparison to the PV module. At the same time, the water temperature has increased by 5°C.

In the current study, an infrared-solar dryer powered by a photovoltaic-thermal system was designed, manufactured and tested in the Shahid Bahonar University of Kerman. The drying time, temperature, and the amount of electrical energy consumed during the drying process were investigated for potato slices with thicknesses of 3 and 7mm in the dryer. The amount of airflow rate in the photovoltaic-thermal system, which was supplied by a fan, was controlled during the experiments. The power of this fan was supplied directly from photovoltaic panels and the remaining amount of electrical energy produced by the panels was transferred to an infrared radiation source for drying the product. The results showed that the best drying condition is at 0.004kg/s with the radiation source. The significant advantage of this system compared to systems that use only the radiating source or hot air, as well as systems that part of their electricity or total electricity is provided by the city's electricity, is a significant reduction in time of drying process and energy consumption, along with is that the total energy for the drying process is provided by solar energy. The system was also designed to transfer the heat of the photovoltaic panels to the inlet air of photovoltaic-thermal collector to increase the temperature of the air and decrease the photovoltaic temperature and therefore to improve the thermal and electrical energy efficiency.

Considering the disadvantages of gasoline and natural gas as mono-fuel in SI engines has made the researchers improve the performance and reduce the pollutant as the advantages of the application of dual-fuel engines. On the other hand, lean-burn in the engine may lead to reduced pollutants. In the present study various mixtures of gasoline and natural gas with the gasoline as the dominant fuel, including 100, 87.5, 75 and 62.5% in weight-base gasoline and the rest natural gas (respectively named as G100, G87.5, G75, G62.5) in lean-burn condition with 0.9 as the equivalence ratio are investigated. At 1800rpm and 10 compression ratio, cylinder pressure variations of 350 successive cycles of each mixture were recorded using a single-cylinder research engine. First of all, the raw data were processed and the optimized knock-free advance for each individual mixture was determined. Later on, the performance of all four mixtures in the corresponding optimized advance was explored. The results revealed that by increasing the amount of natural gas in the mixture, the CO pollutant reduced however the amount of HC initially increased which was followed by a decreasing trend. The amount of NOx had a direct relation with the appearance of the natural gas. In the lean-burn condition, a better performance was observed for G75 in comparison with G100 and the other mixtures.

Reducing energy consumption in production is an urgent need. In manufacturing processes, especially machining, more than 90% of the environmental impacts are due to energy consumption in machine tools. The purpose of the present study is to estimate and compare the energy consumption of AISI 316 steel milling process in conventional (wet) and minimum quantity lubrication (MQL) modes as well as the experimental measurement of energy consumption in each of these two modes. Studies have suggested different types of energy consumption modeling in machining but few studies have been conducted on the use of these modeling techniques and the minimum quantity lubrication method has been rarely compared with the wet state in terms of energy consumption. Empirical experiments were used to confirm the modeling performed to predict energy consumption in the milling process. The results show that the proposed method is efficient and practical for predicting energy consumption with 5% error. After confirming the modeling, using two levels for feed rate and spindle speed and applying full factorial design of experiments, energy and power consumption in MQL and wet cutting modes using the power meter connected to the input 3-phase power cable of the milling machine were experimentally measured. Energy consumption in the minimum quantity lubrication method was decreased by 16% compared to the wet state. The average power consumption in MQL milling is 33% lower than in wet milling.