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In this paper, mass flow rate and location of leakage in natural gas pipeline has been estimated simultaneously using inverse analysis. For doing so, at first natural gas transient flow in pipeline has been simulated numerically; this simulation is named direct problem. In the direct problem, it is assumed that the mass flow rate and location of leakage is definite and the governing equations are inhomogeneous well-known Euler equations. In these equations, the leakage effect has been considered as a source term. Steger–Warming flux splitting method has been used for numerical analysis of these equations. Then the location and mass flow rate of gas leakage of pipeline have been estimated simultaneously using Levenberg-Marquardt method for parameter estimation. This method is an iterative algorithm and based on minimizing the sum of the squares of the errors which are difference between pressures computed by the direct problem and pressures measured by pressure gauges. The results of the direct problem have good agreement with Mac–Cormack method and characteristics method of specified time intervals. The results of the inverse analysis demonstrate that Levenberg-Marquardt algorithm is stable and efficient enough to estimate simultaneously the mass flow rate and location of leakage in natural gas pipeline.

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The structural integrity of welded joints in natural gas transportation through large diameter steel pipes requires the experimental determination of material mechanical properties in seam weld via destructive and non-destructive testes. In this paper, the metallurgical and mechanical characteristics of multi-pass girth weld in seam weld, heat affected zone (HAZ), and base metal of a pipe with 56 inch outside diameter, 0.780 inch wall thickness is determined. To do this, chemical analysis, standard metallography, tensile and impact tests and hardness experiments were conducted. The metallographic results demonstrated that different sub-zones in welded joint had different microstructure. The existence of different chemical contents in different weld passes and the presence of hard phases (such as martensite due to uncontrolled heat cycles) had direct effects on mechanical properties of the seam weld and HAZ. From the hardness test result, it was found that HAZ and centerline of the seam weld had the minimum and maximum hardness levels, respectively. Furthermore, the minimum Charpy impact energy was found in the seam weld centerline.

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At a Compressed Natural Gas (CNG) filling station, natural gas is stored in the high pressure reservoirs. The pressures within these reservoirs have huge effects on fast filling process of a natural gas vehicle’s (NGV) cylinder and the difficulties associated with the filling process. The accurate modeling of the fast-fill process is a complex procedure which should be thoroughly studied to optimize the filling process. Here, a theoretical analysis has been developed to study the effects of various parameters on the CNG filling process and the conditions. The analysis is based on the first and second laws of thermodynamics, conservation of mass and the AGA8 equation of state. The required properties of natural gas mixtures have been calculated making use of the AGA8 equation of state (EOS) and thermodynamics relationships. It is found that, the composition of natural gas is very effective on the CNG filling process and final in-cylinder values. For various Iranian natural gas compositions, the optimized filling stations' reservoirs pressure has been found.

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Steel pipes with different cracks may be unsafe if the geometry of crack is larger than a specific size. The failure assessment diagrams are widely used to investigate the safety of such cracked pipes. These diagrams include three levels, in each of which the area under the failure assessment curve is the safe area, where as the outer are is unsafe. In this study, the API X65 gas transmission pipe with 48 inches outside diameter (commonly used in Iran's energy transmission lines) is investigated under constant internal pressure of 7 MPa for the first time in Iran. In order to analyze the critical crack length, a pipe with fixed crack depth of 8 millimeter and crack lengths of 100, 130, 160, 190, 220 and 250 millimeter is considered. Similarly, for analyzing the critical crack depth, a pipe with fixed crack length of 150 millimeter and crack depths of 3, 5, 7, 8, 9 and 10 millimeter is assumed. Using ABAQUS modeling and standard BS7910 equations, the location of loading points is investigated in failure assessment diagram. The results indicated that, in the case of fixed crack depth (8 millimeter), the critical crack length was 220 millimeter. For the case of fixed crack length (220 milimeter), a critical crack depth of 9 millimeter was obtained.

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Using natural gas as a clean fuel is raising. In many industrial combustion systems, like industrial furnace and boilers, a large portion of heat transfer is done by radiation and using natural gas in these industrial systems leads to decrease in radiation heat transfer that faces the Manufacturers with many problems. The addition of solid reactant particles into the flame is one of the attractive methods that are considered by many researchers to increase the radiation heat transfer in non-luminous flame such as hydrogen and natural gas flame. In this study, the effect of coal particles injection into the natural gas diffusion flame on flame structure, radiation heat transfer, temperature profile, and thermal efficiency has been considered. The results show that the injection of coal particles into the natural gas by increasing the solid soot particles in the flame structure, increases the reaction surface and flame luminosity and with increasing the radiation emissivity coefficient, increases the radiation heat transfer and thermal efficiency 43% and 21% respectively. Whereas change in flame temperature is very low and is 47˚C in its extreme limit.

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This is a study of the effect of synchronous combustion of gas-gasoil, achieved through the injection of gasoil droplets into natural gas flame, on the flame luminosity and radiative heat transfer. Droplets were injected by a single-hole micro-nozzle with a hole diameter of 100 μm and injection pressure of 9 bars. A photovoltaic cell was used to determine the luminous radiation and the total radiation of flame was measured by a thermopile. Also, the combination of chemiluminescence and IR photography of flame were employed to determine the qualitative distribution of soot particles in flame. The results show that the synchronous combustion of gas-gasoil raises the soot content of flame, leading to an increase of the luminosity and volume reaction of flame 38 and 2.5 times in comparison to the non-injection mode. Also, for the synchronous combustion of gasoil and gas with a mass fraction of 10%, the flame temperature changed only 95˚C, whereas the flame radiation rose as much as 52%. The improvement of flame radiation in synchronous combustion of gas-gasoil is due to the enhancement of flame emissivity coefficient in the IR region of electromagnetic wavelengths. Meanwhile, the injection of gasoil droplets increased the CO and NO pollutants by 4 ppm and 35 ppm in comparison to the non-injection mode; Due to the low mass flow rate of injection, however, the increase does not exceed the allowable limit for outlet pollution.

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The increasing global realization of natural gas as a relatively abundant energy is evident from available data on increasing share of natural gas in meeting world energy requirements. India is one of the countries whose dependence on imported gas are constantly increasing. With large population and growing economy, this country is a main natural gas importer. In this paper, game theory is used to model how to enter Iran, Russia and Qatar into the natural gas market in India. Due to information available for all players, each player guesses his rival strategy, and does not wait for his action. Thus, this game is assumed to be of static nature with perfect information. Nash equilibrium solution was applied to the game among the three countries. Each player has two strategies: (1) to maintain the current market strategy and (2) the market development strategy (to enter Indian natural gas market). Due to rational behavior of three players, the equilibrium is obtained through the market development strategy. In equilibrium, players do not get the best outcome (Nash equilibrium is a balanced equilibrium, which is not established necessarily in a situation where the players have the greatest outcomes.

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Exchange rate in Iran has been facing fluctuations for many years, and has been affected the economic structure. Therefore, studying the changes in Exchange rate is of great importance. In this regard, the present paper studies the effects of exchange rate shocks on investment and employment within a systematic multi-regional computable model using GTAP.8 in 2007. To assess the impact of these changes, two scenarios of a 10% increase and reduction in the exchange rate are considered. The results confirm the same movements of price and exchange rate. Increase in the exchange rate in agriculture, industry and mining sectors has caused a reduction in production and employment, but has caused an increase in both variables in the service, oil and gas sectors. The decline in the exchange rate has resulted in fall of production and consequently and employment in the service, oil and gas, sectors, but it has caused an increase in both variables in agriculture, industry and mining sectors. The total investment in all areas examined is in line with exchange rate changes. Therefore, positive exchange rate shocks can increase overall employment rate. The issue is important because the share of employment in the service, oil and gas sectors is more than its share in agriculture, industry and mining ones. In addition, the positive exchange rate shock results in an increase in investment, regarding the structure of exports and imports.  

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Air staging is defined as the supply of inadequate air from the primary stage to the reaction zone, and the completion of the air supply through the next stage or stages. This study is concerned with the optimization of the air staging system of a burner with two air inlets and one fuel (natural gas) inlet with the help of numerical modeling. The equivalence ratio of the primary air (with the assumption of a fixed total air mass flow rate), and the distance between the two air inlets constitute the design variables of the problem. In the previous research works, the air staging technology has been mainly employed as a method to reduce the emission of NO. However, in the current study, in addition to the emission of NO, the emissions of CO and soot, and radiative heat transfer from the flame are considered as the objective functions. The results show that increasing the level of air staging (or the equivalence ratio of the primary air) has contradictory effects on the objective functions so that, as positive influences, it increases the radiative heat transfer from the flame and decreases the emission of NO, and as negative effects, it increases the emission of both CO and soot. The results also indicate that when all the previously mentioned objectives are considered simultaneously, the optimal case, which is selected based on the Pareto front concept, is the case in which the primary air is about 20% of the theoretical air.

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In this study, the double stage mixed refrigerant LNG system is investigated, which is known for having the highest efficiency among the liquefaction cycles. The main purpose is to evaluate the performance double stage mixed refrigerant LNG system of point of view effect of variations the environmental and operating conditions of feed that has not been previously discussed. Such as variable environmental conditions during liquefaction processes, temperature, pressure and feed gas composition are. To view the response of the DMR liquefaction system to these changes, system which has been designed and implemented, was selected as the base case.The Results show that with decreasing temperature and increasing pressure feed natural gas, as an advantage, specific shaft work decreases and since in this case, minimum approach temperature in heat exchangers only slightly reduced than the allowed amount 3°C therefore with accepting a safety factor less (to insignificant amount) than the optimal case, can be used of this available advantage. Also, with increasing temperature and decreasing pressure of feed natural gas, while increasing the specific shaft work as well as temperature cross occurs in heat exchangers and means to from entering of the feed natural gas in the area prevented with special controls. Also, any changes in mole fraction of natural gas components make temperature cross in heat exchangers. And due to the change of the natural gas components mole percent, during the life of the well, should over time, the refrigerant composition in the cycle is optimized regarding to new conditions.

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Structuralintegrity assessments of pipelines play a key role in the design and safe operation of pipeline systems. Gas pipelines currently experience internal transmission pressures up to 15 MPa in low ambient temperatures. Combination of high strength and good toughness is essential for the steels and welded joints used in pipelines. In this study, the KIC toughness has been determined for base metal and seam weld of a pipe of grade API X65, following the ASTM E1820 standard. The API X65 steel is the most commonly used pipe material in Iran highpressure gas transportation pipelines. The fracture toughness tests employed sidegrooved and fatigue precracked compact tension specimens, extracted from the original pipe, to determine the crack growth resistance curves based upon the unloading compliance method using the single specimen technique. From these, KIC values of 302 MPam1/2 and 262 MPam1/2 were obtained for base metal and seam weld, respectively. These results produce toughness data which serve to evaluate and compare crack growth resistance of base metal and seam weld metal and to determine the critical sizes of acceptable cracks in pipelines.

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With growing environmental pollution and concerns about fossil fuel depletion worldwide, there is an urgent need to find a solution for this problem. Using alternative fuels, such as natural gas, which can burn much cleaner than petrol or gasoline and as an advantage, it’s much cheaper than other conventional fuels and is much more widely available than oil in our planet. The most effective way we can utilize this alternative fuel in the common internal combustion engine, is by means of direct injection technology. Before natural gas can be utilized in common automotive engines, it’s necessary to conduct simulations and thus optimize these engines to maximize output power prior being built. Optimizing engines can only be achieved through simulation. KIVA-3V is a well-accepted engine simulation tool, recognized by industrial users and researchers. KIVA-3V lacks the ability to simulate gaseous fuel injections as it’s only designed to deal with liquid fuels. In this research, researched the governing equations on gas injections and used them to develop a numerical code for KIVA-3V to enable simulation of gaseous injections. We validated our modified version of KIVA-3V with two different sets of experimental data which we previously had. We showed our modified KIVA-3V code can effectively simulate gaseous injections producing very exact results. The gaseous fuel considered in this research is pure methane.

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Natural gas characteristics make it an attractive choice for replacing with oil fuels which causes climatic problems and environmental pollutions in the world. Generally, using natural gas in an internal combustion engine leads to lower volumetric efficiency of the engine, but gas direct injection technology would improve volumetric efficiency. Furthermore, more research is essential for improving the effectiveness of direct injection engines. A partially stratified charge is an appropriate idea for combustion efficiency improvement in direct injection engines. In the present study, a port injection engine is converted to direct injection engine and feasibility and condition of partially stratified mixture formation are investigated. Also, its effects on combustion and efficiency of the engine, with regards to location and injection timing of injector are noticed. Numerically simulation of current study shows that the formation of partially stratified charge, because of using air-guided method and located injector between air intake valves, is so hard and inaccessible. The high momentum of CNG jet makes a rapid motion of injected gas fuel and is not able to perform an appropriate mixture of air and fuel. Accordingly, an increase in air and fuel ratio is locally seen in the combustion chamber as this causes a drop in combustion efficiency. Although the increase in flame propagation and heat release can be expressed as results of this study, however, the benefits of rapid burning of CNG combustion due to the problems that are mentioned are not so impressive.

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Welding residual stresses decrease designing stress in natural gas transmission pipes with large diameter under high internal pressure. The outside diameter and wall thickness of API X70 steel in this research are 1423 and 19.8 millimeter. Hole drilling is the most common technique in order to measure residual stresses. Because of large diameter of this pipe, its transportation to conduct hole drilling test is a big problem so cutting a finite sample is desired. In this study standard dimension of this sample plate is analyzed and simulation of welding process is done from which and residual stresses in different directions are obtained. Residual stresses in the thickness direction is presented for the first time. The results showed separating a finite sample with the size of 320×440 millimeter is appropriate to do hole drilling test. The location and amount of the maximum residual stress is evaluated and compared for both simulation and experimental samples. Variation in hoop and longitudinal residual stresses on both internal and external surfaces of pipe samples are investigated. Also validation of simulation results with the experimental results of the same pipe is perfomed. Maximum residual stress (460MPa) is measured on inner surface of the pipe (96 percent of yield stress) which is reduced to 200MPa (42 percent of yield stress) after hydrostatic test. Because residual stress after hydrostatic test is lower than half of yield stress, hole drilling technique is validated after hydrostatic test.

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Concerns for climate change, reduction of greenhouse gas emission and environmental pollution, besides economically dependency on fossil fuels and political aspect motivate governments and policy makers to take into account replacing usual vehicle with alternative fuel vehicles (AFVs) such as Compressed Natural Gas Vehicles (CNGV) and Gasoline-Electric Hybrid Vehicles (GEHV). The air pollution in Tehran is a serious concern that based on this problem, CNGV has been introduced to Iranian market from 10 years ago. On the other hand, with the approval and notification of the removal of the electric vehicle importation’s tariff law, GEHV has been entered into the market of Iran as a new entrant. The purposes of this paper is to identify the effective factors to choose AFVs for drivers in Tehran and the assessment of effects of the incentive policies that increase AFV shares and computing their willingness to pay (WTP) for AFV under different incentives. This study designed a questionnaire which includes 3 parts: current vehicle features, dominant travel characteristics, socio-economic properties and the prioritization of effective factors on new vehicle purchase, and the tendency of AFVs choice with different scenarios representing different features. A random sample of 365 respondents was interviewed in a face-to-face survey in February 2016 in the technical inspection centers and in compressed natural gas stations. Finally, for the determination of effective factors on current and new vehicle purchase with revealed preference information and the assessment of AFVs usage tendency with stated preference information, the Multinomial Logit models have been used and WTPs are calculated. The incentive policy in Tehran, like previous studied countries, was the most influential factor in motivating consumers to buy AFVs in comparison to improvement of AFV specifications. The results show that drivers’ WTP is 5 MT for free access to even-odd area for CNGV and 12 MT for GEHV, also WTP for free access to pricing area in Tehran central business district is equal to 10 MT for CNGV; i.e. people tend to pay this extra cost for AFVs to access to pricing areas. These values are comparable with similar studies in cities located in developed countries. However, the results of this study show that WTP for fuel cost in Iran is considerably less than WTP of people driving in developed countries. The fuel cost and access time to gas stations are influential variables on CNGV choice. The vehicle acceleration and driving range are influential variables on GEHV choice.

 

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In this paper, a model based on GMDH Type Neural Network, is used to predict gas price in the spot market while using oil spot market price, gas spot market price, gas future market price, oil future market price and average temperature of the weather. The results suggest that GMDH Neural Network model, according to the Root Mean Squared Error (RMSE) and Direction statistics (Dstat) statistics are more effective than OLS method. Also, first lag of gas price in the future market is the most efficient variable in predicting gas price in spot market.

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One of the major problems in the world is the supply of energy. Biodiesel is one of the alternative fuels and renewable energy sources. The use of B₅ biodiesel in diesel fuel mixtures is common and most countries have planned to use B₂₀ biodiesel. The use of natural gas in diesel engines and the study of the possibility of using it in high quantities is another new solution, which can reduce dependence on diesel fuel. In this study, biodiesel was produced from waste oil by transesterification process and used in two levels of 5 and 20% in diesel composition. Then natural gas was used in three levels of 60, 70, and 80% (% G / T) in the diesel engine. Engine tests were performed at full-load at 1500 rpm. In general, the test results showed that in conditions where biodiesel B₂₀ was used in the composition of diesel fuel and gaseous fuel was used in the amount of 80% in a diesel engine, suitable conditions in terms of reducing emissions, increasing energy efficiency, and reducing economic costs were obtained; Under these conditions, compared to a conventional diesel engine, brake power, and energy efficiency increased by 8.86 and 29.06%, respectively. Also, brake specific fuel consumption, CO and CO₂ were reduced by 26.5, 57.58, and 4.54%, respectively. Although the amount of NOx increased slightly, but, decreased the economic cost compared to diesel 26.47% $/kwh, so the results were valuable.