Automotive Science and Engineering

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In this study, a numerical simulation using the CFD software, FLUENT, has been conducted to examine the effect of various shapes of the venturi component sections in order to find the optimum venturi specifications to increase the EGR rate with minimum pressure loss at the part load operation range. The CFD results reveal that the venturi should be precisely optimized to introduce the required amount of EGR to the engine manifold. Then, the optimum venturi was manufactured, and it was installed on the engine intake system. By using the optimum Venturi EGR system instead of original system the 26% increase in EGR flow rate to the engine manifold is observed. In the second part of the paper, an experimental investigation was carried out on a “Lister 8-1” dual fuel (diesel – natural gas) engine to examine the simultaneous effect of inlet air pre-heating and EGR on performance and emission characteristics of a dual fuel engine. The use of EGR at high levels seems to be unable to improve the engine performance at part loads, however, it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency, resulting in reduced levels of both UHC and NOx emissions. CO and HC emissions were reduced by 24% and 31%, respectively. The NOx emissions were decreased by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.

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A newly developed heavy duty diesel engine in dual fuel mode of operation has been studied in detail. The main fuel would be natural gas and diesel oil as pilot injection. The importance and effects of mixture preparation and formation through ports, valves and in cylinder flow field with different swirl ratio and tumble on diesel combustion phenomena is an accepted feature which has been studied using a developed CFD model together with a KIVA3-V2 code. This analysis is capable to investigate engine geometry, valves lift, and valves timing turbo charging, and its effects on dynamic flow field with variable dual fuel ratio on power and emission levels output. This complete open cycle study of a dual fuel engine has been carried out originally and for the first time and by considering complete grid consisted of four moving valves, two intake ports, two exhaust ports, and the port runners. It is found that important complex flow structures are developed during the intake stroke. While many of these structures decay during the compression stroke, swirl and tumble can survive. The effect of increased swirl ratio at the end of the compression stroke for the D87 engine with a piston bowl is clearly observed in this study. This is important for aiding in good fuel spray atomization. The formation, development, and break-up of tumble flow are seen, contributing to an increase in turbulent kinetic energy at the end of the compression stroke. The complete engine flow field, i.e. the inlet jet, and formation of swirl in the intake ports, is also clearly shown in the study. Results of these simulations assist in the improved understanding of the intake process and its influence on mixture formation and flow field in a dual fuel engine.

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Temperature is one of the effective parameters in erosion of spark plug electrodes. In this research, temperature of spark plug was measured in engine's different operation conditions with two types of fuels: compressed natural gas and gasoline. Test results showed that, temperature of center electrode is lower than ground electrode and maximum difference between them is 110ºC that occurs at 2500 rpm and full load conditions. Maximum temperature of spark plug occurs with CNG under full load conditions and 6380 rpm. In these conditions, ground electrode’s temperature reaches to 960ºC which is very prone to pre-ignition. On the other hand, center electrode’s temperature is 195ºC higher than the same condition with gasoline as a fuel which cause more electrode erosion rate. This temperature rise lead to cold type spark plug selection because of its better heat transfer. Spark plug erosion was studied after endurance tests with CNG as a fuel. Electrodes have non uniform wear patterns and consequently gap growth is not uniform. The average gap growth for two sets of spark plugs after two similar 200 hr endurance tests is 49.6%

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Global air pollution is a serious threat caused by excessive use of fossil fuels for transportation. Despite the fact that diesel fuel is a big environmental pollutant as it contains different hydrocarbons, sulphur and crude oil residues, it is yet regarded as a highly critical fuel due to its wide applications. Nowadays, biodiesel as a renewable additive is blended with diesel fuel to achieve numerous advantages such as lowering CO2, and CO emissions as well as higher lubricity. However, a few key drawbacks including higher production cost, deteriorated performance and likelihood to increase nitrogen oxide emissions have also been attributed to the application of diesel-biodiesel blends. Expanded polystyrene (EPS), known as a polymer for packaging and insulation, is an ideal material for energy recovery as it holds high energy value (1 kg of EPS is equivalent to 1.3 liters of liquid fuel). In this study, biodiesel was applied as a solvent of expanded polystyrene (EPS) during a special chemical and physical treatment. Various percentages of EPS in biodiesel blended diesel were tested to evaluate the fuel properties, emissions and performance of CI engine. The results of the variance analysis revealed that the addition of the additive improved diesel fuel properties by increasing the flash point as well as the reduction of density and viscosity. Despite a 3.6% reduction in brake power, a significant decrease in brake specific fuel consumption (7.26%) and an increase in brake thermal efficiency (7.83%) were observed at the full load and maximum speed of the engine. Additionally, considerable reductions of CO, CO2, NOx and smoke were achieved.

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In the present paper, a complete literatures review of thermal barrier coating applications in diesel engines is performed to select a proper type and to find coating effects. The coating system has effects on the fuel consumption, the power and the combustion efficiency, pollution contents and the fatigue lifetime of engine components. Usually there are several beneficial influences by applying ceramic layers on the combustion chamber, including the piston, the cylinder head, the cylinder block, intake and exhaust valves by using a plasma thermal spray method. Several disadvantages such as producing nitrogen oxides also exist when a coating system is used. In this article, all effects, advantages and disadvantages of thermal barrier coatings are investigated based on presented articles.

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Running the industrial components at a proper temperature is always a big challenge for engineers. Internal combustion engines are among these components in which temperature plays a big role in their performance and emissions. With the development of new technology in the fields of ‘nano-materials’ and ‘nano-fluids’, it seems very promising to use this technology as a coolant in the internal combustion engines. In this study, a nano-fluid (Al2O3-Water/Ethylene Glycol (EG)) is used as an engine coolant along with an optimized heat exchanger to reduce the warm-up timing. The effect of nano-fluid concentration is considered here by using their corresponding governing equations, such as momentum and energy. The engine coolant thermal behavior calculation is carried out based on the lumped method. The obtained results indicated that using different percentage of nano-fluid mixtures (by volume), such as Al2O3- Water/EG as engine coolant enhances the heat transfer coefficient and reduces the warm-up timing which, in turn, results in reduced emissions and fuel consumption.

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Air pollution is one of the major issues about the diesel engines in todays' world. It is a special concern in those areas that have difficulty meeting health-based outdoor air quality standards. Natural gas has low emission and resource abundance and also conventional compression ignition engine can be easily converted to a dual fuel mode to use natural gas as main fuel and diesel as pilot injection. The main object of this work is to investigate the effect of number of injector nozzle hole on the combustion and exhaust emission in a gas engine ignited with diesel fuel. We use one and three-dimensional simulation in parallel way in order to analyze the performance and combustion process of a dual fuel engine. The experimental results have also reported and compared with the simulated data.

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Cooled exhaust gas recirculation is emerging as a promising technology to address the increasing demand for fuel economy without compromising performance in turbocharged spark injection engines. The objectives of this study are to quantify the increase in knock resistance and to decrease the enrichment and emission at high load. For this purpose four stroke turbo charged Spark Ignition engine (EF7-TC) including its different systems such as inlet and exhaust manifold, exhaust pipe and engine geometry are modeled using GT Power Software. As predicted, using cooled EGR at high load enabled operation at lambda near to one with the same serial engine performances, which offers substantial advantages Such As BSFC reduction (up to 14%), and emission reduction (CO, NOx).

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In spark ignition (SI) engines, the accurate control of air fuel ratio (AFR) in the stoichiometric value is required to reduce emission and fuel consumption. The wide operating range, the inherent nonlinearities and the modeling uncertainties of the engine system are the main difficulties arising in the design of AFR controller. In this paper, an optimization-based nonlinear control law is analytically developed for the injected fuel mass flow using the prediction of air fuel ratio response from a mean value engine model. The controller accuracy is more increased without chattering by appending the integral feedback technique to the design method. The simulation studies are carried out by applying severe changes in the throttle body angle to evaluate the performance of the proposed controller with and without integral feedback. The results show that the proposed controller is more effective than the conventional sliding mode controller in regulating the AFR without chattering.

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In this paper, a numerical study is performed to provide the combustion and emission characteristics resulting from fuel-reactivity controlled compression ignition (RCCI) combustion mode in a heavy-duty, single-cylinder diesel engine with gasoline and diesel fuels. In RCCI strategy in-cylinder fuel blending is used to develop fuel reactivity gradients in the combustion chamber that result in a broad combustion event and reduced pressure rise rates (PRR). RCCI has been demonstrated to yield low NOx and soot with high thermal efficiency in light and heavy-duty engines. KIVA-CHEMKIN code with a reduced primary reference fuel (PRF) mechanism are implemented to study injection timings of high reactivity fuel (i.e., diesel) and low reactivity fuel percentages (i.e., gasoline) at a constant engine speed of 1300 rpm and medium load of 9 bar indicated mean effective pressure (IMEP). Significant reduction in nitrogen oxide (NOx), while 49% gross indicated efficiency (GIE) were achieved successfully through the RCCI combustion mode. The parametric study of the RCCI combustion mode revealed that the peak cylinder pressure rise rate (PPRR) of the RCCI combustion mode could be controlled by several physical parameters – PRF number, and start of injection (SOI) timing of directly injected fuel.

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Many studies have been done on hybrid vehicles in the past few years. The full hybrid vehicles need a large number of batteries creating up to 300 (V) to meet the required voltage of electric motor. The size and weight of the batteries cause some problems. This research investigates the mild hybrid vehicle. This vehicle includes a small electric motor and a high power internal combustion engine. In most cases the car’s driving force is created by an internal combustion part. A small electric motor, which can operate as engine starter, generator and traction motor, is located between the engine and an automatically shifted multi-gear transmission (gearbox). The clutch is used to disconnect the gearbox from the engine when needed such as during gear shifting and low vehicle speed. The power rating of the electric motor may be in the range of about 15% of the IC engine power rating. The electric motor can be smoothly controlled to operate at any speed and torque, thus, isolation between the electric motor and transmission is not necessary. The present study evaluates the properties of the mild hybrid vehicle, its structure and performance and proposes an energy control model for its optimum operation.

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Among human activities, motor vehicles play the most important role in air pollution. Air pollution has negative impacts on people and on the environment. In this paper the effect of oxygen-enriched air (20.8%, 21.8%, 22.8%, 23.8% and 24.8%) and different bioethanol-gasoline blends (zero, 5%, 10%, 15%, 20% and 25%) in different engine speeds (1000 rpm, 2000 rpm and 3000 rpm) on the amount of pollutants, particles, and fuel consumption were studied. To do so, a four-cylinder, four-stroke gasoline engine with Siemens fueling system was used. The results showed that when oxygen percentage in the inlet increased from 20.8% to 24.8%, the average amount of UHC, CO, fuel consumption and the number of fine and coarse particles decreased 126.75%, 11.25%, 17.02%, 77.37% and 243.25%, respectively, while the amount of CO2 and NOX increased 5.36% and 113.27%, respectively. Also the results showed that when bioethanol percentage in the mixture increased from zero to 25%, the average amount of UHC, CO2, CO and the number of fine and coarse particles decreased 104.53%, 3.45%, 34.57%, 41.42% and 96.09%, respectively, while the amount of NOX and fuel consumption increased 163.41% and 15.75%, respectively.

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Proton exchange membrane (PEM) fuel cells being employed in fuel cell vehicles (FCVs) are promising power generators producing electric power from fuel stream via porous electrodes. Structure of carbon paper gas diffusion layers (GDLs) applying in the porous electrodes can have a great influence on the PEM fuel cell performance and distribution of temperature, especially at the cathode side where the electrochemical reaction is more sluggish. To discover the role of carbon paper GDL structure, different cathode electrodes with dissimilar anisotropy parameter are simulated via lattice Boltzmann method (LBM). The distributions of temperature through the GDL as well as the distribution of temperature on the catalyst layer are presented and analyzed. The results indicate that when the carbon fibres are more likely oriented normal to the catalyst layer the distribution of temperature becomes more uniform. Besides, the maximum temperature occurs in this case.

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To improve the engine performance and reduce emissions, factors such as changing ignition and injection timing along with converting of port injection system to direct injection in SI(spark-ignited) engines and hydrogen enrichment to CNG fuel at WOT conditions have a great importance. In this work, which was investigated experimentally (for CNG engine) and theoretically (for combustion Eddy Break-Up model and turbulence model is used) in a single- cylinder four-stroke SI engine at various engine speeds (2000-6000 rpm in 1000 rpm intervals), injection timing (130-210 crank angle(CA) in 50 CA intervals), ignition timing (19-28 CA in 2 degree intervals), 20 bar injection pressure and five hydrogen volume fraction 0% to 50% in the blend of HCNG. The results showed that fuel conversion efficiency, torque and power output were increased, while duration of heat release rate was shortened and found to be advanced. NOx emission was increased with the increase of hydrogen addition in the blend and the lowest NOx was obtained at the lowest speed and retarded ignition timing, hence 19° before top dead center. 

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In this study, modeling of a fuel jet which has been injected by high pressure into a low-pressure tank are investigated. Due to the initial conditions and the geometry of this case and similar cases (like CNG injectors in internal combustion engines (ICE)), the barrel shocks and Mach disk are observed. Hence a turbulence and transient flow will be expected with lots of shocks and waves. According to the increasing usage of this type of injectors in ICE, more studies should be conducted to find the most accurate and beneficial models for modeling this phenomenon.

In order to find an accurate and beneficial turbulence model ,in this study, three Reynolds-averaged Navier–Stokes (RANS) turbulence models (SST k-ω, RNG and standard k ) and large eddy simulation (LES) turbulence model were compared by the fuel jet characteristics in three regions (outlet of the nozzle, at Mach disk and at the downstream of the flow). Although the LES model needs more time for each test, the results are more reliable and accurate. On the other hand, RANS turbulence models have lots of errors (more than 10 percent) especially for predicting the characteristics of fuel jet at Mach disk.

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In this paper an idea for hybridization of conventional vehicles has proposed. The case study performed on one of the common vehicles on country roads i.e. Samand. This vehicle has high production volume but low fuel performance therefore hybridization of it could be attractive for its manufacture. This paper aims that the hybridization idea and its structure to need minimum mechanical modifications. In consequence attractiveness of this idea for industry could be high. A cost optimization has been performed for sizing of additional components such as electric motors and battery modules and the simulation results has been adopted to verify the proposed idea for case study with hybrid simulation of GT-Suit and MATLAB softwares.      

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Changing various parts of different types of engines in the maintenance phase was always a remarkable question. Purpose of the present study is identifying the performance and emissions of a diesel-fueled engine (OM457) before and after replacing connecting rod and crankshaft with another engine (OM444) in the same engine family.

At the first step, a solid model was made then some CFD analyses were done and, results were compared with previous studies for validation after that in the CFD modeling the impact of these parts replacement were observed, and the performance and emissions of this engine were compared with data before replacements.

As the result of these replacements, compression ratio and performance were decreased. HC and CO were increased due to lower air-fuel ratio, and NO_X was decreased because of the lower temperature of in cylinder. Lowering the CR of a diesel engine will reduce the NOx emission numerously but the increase in other emissions will be slight. So for the environment issues lowering the CR will be a practical and low cost method.

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In this research, the separate and simultaneous effects of pilot-main injection dwell time, pilot fuel quantity, and hydrogen gas addition on combustion characteristics, emissions formation, and performance in a heavy-duty diesel engine were investigated. To conduct the numerical study, valid and reliable models such as KH-RT for the break-up, K-Zeta-F for turbulence, and also ECFM-3Z for combustion were used. The effects of thirty-one different strategies based on two variables such as pilot-main injection dwell time (20, 25, 30, 35, and 40 CA) and pilot fuel quantity (5, 10, and 15% of total fuel per cycle) on NDC and DHC were investigated. The obtained results showed that by decreasing pilot-main injection dwell time due to shorter combustion duration and higher MCP, MCT, and HRRPP, amounts of CO and soot emissions decreased at the expense of high NOx formation. Also, increasing pilot fuel quantity due to higher combustion temperature and less oxygen concentration for the main fuel injection event led to an increase of NOx and soot emissions simultaneously. The addition of H2 due to significant heating value has increased IP and improved ISFC at the expense of NOx emissions but considerably decreased CO and soot emissions simultaneously.

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This study uses real driving cycles of a city bus and a standard driving cycle “WLTP” to implement a full comparison for energy demand and fuel consumption for different propulsion systems (i.e., Diesel ICE, Fuel cell and Electric engines). To better understand the comparison, a life cycle assessment is conducted using “GREET” and “GHGenius” software, which represents a clear demonstration of side effects and emissions of each engine on the environment. The results show that for “WLTP” cycle the bus needs 2423kJ energy for traveling each kilometer while the averaged amount of energy for traveling one kilometer of real driving cycle reaches to 1708kJ. By computing total energy use of  an electric bus we conclude, electric buses use almost 58% of electric energy for driving and the rest is lost. Then fuel cell and internal combustion engine buses have energy efficiency of 36% and 24% respectively. Concerning LCA analysis, it becomes apparent that unlike efficiency, electric buses are not environmentally benign as fuel cell buses. LCA analysis showed that fuel cell buses that use steam reforming hydrogen production process are a cleaner option than electric buses. Finally, since diesel buses produce the most emission, especially CO2, and consume the most energy in the total life cycle, they have no advantage for public transportation fleet.