نشریه تحقیقات موتور
پیاپی 16 (پاییز 1388)

In this study a polymer electrolyte fuel cell (PEFC) model is analyzed for automotive application and the parameters that are affecting its performance such as relative humidity, mass flow rate, temperature and pressure of inlet gases also, heat and water management are major issues in these cells are investigated. Here, the equation of continuity, momentum, conservation of spices, energy, charges together with electrochemical kinetic for all regions within the cell is developed as a single-domain and solved numerically. The voltage and power density profiles are derived in terms of current density for different operating conditions. The result indicates that increasing temperature and pressure for all output voltages would improve cell performance. Forhigh voltages where there is no phase changes in the cell, increasing the percentage of humidity and reducing mass flow rate would have a positive effect on cell performance, but at low output voltage by increasing relative humidity and reducing mass flow rate would hamper cell performance. Also increasing inlet pressure, humidity and mass flow rate results in partial power loss of fuel cell.

In this study the effect of varying the behavior of 457-LA diesel engine cooling system has been conducted using research facilities installed on a test bed with W400 eddy current dynamometer. Insufficient information on the engine thermal regime has resulted in the wrong belief that the engine performance and life can be extended by reducing the temperature of the circulating cooling water. Theoretical studies and the experimentalresults of the present study show that for an engine under loading condition, any variation in the cooling system, particularly, reducing the cooling water temperature, increases the mechanical stresses due to change in allowable tolerances. Other consequences, such as increased fuel consumption and pollution, result in after burning and thermal stresses and corrosion in the exhaust system. At the same time, meaningful reduction in measured power and torque has been observed for the case of reduced cooling water temperature. In contrast, increase in the cooling water temperature limit, using standard and optimized diesel fuel, can result in superior characteristics for power, torque, fuel consumption and pollution.

Since adding MTBE to gasoline leads to destructive biological effects such as untreatable diseases, it has been couple of years that this material is omitted from gasoline in developed countries. The main objective of this research paper is substituting ethanol for additive substance MTBE as well as studying the effect of ethanol as a fuel on the performance, pollutant production and fuel consumption of a spark ignition motor and finally achieving an optimal ethanol-gas composition. The Experiments were carried out regarding to cases of Full and Part load. The full load Experiment was performed in terms of varies speeds of motor and the part load one utilize speed ranging from 2000 to 3000 rpm. The ignition time (duration) was optimized in the entire Experiment. The achieved outcomes demonstrate that when ethanol rate is changed in a composition, the volumetric efficiency, power and torque of the motor is boosted. Besides, specific fuel consumption in low-speed is cut and it is increased in accelerations. On the other hand, ethanol in the composition has led to a considerable decrease in the amount of HC pollutant. CO pollutant is lessened to some extent while NOx rate shows a nominal accession. XU7JP/L3 motor is studied in this research paper.

In this study, performance parameters of a diesel engine were investigated using biodiesel fuel. Maximum cylinder pressure and exhaust gas temperatures increased with increasing biodiesel percentage in diesel-biodiesel fuel blends up to 40% (B0-B40), but with increasing of biodiesel fuel percentage beyond B40 (B40-B100), the maximum cylinder pressure decreased. Brake power was constant for all blend ratio at the constant engineload; this is due to this fact that engine speed was adjusted at constant value (730 rpm). Fuel consumption and brake specific fuel consumption decreased with increasing of biodiesel percentage in diesel-biodiesel fuel blends up to 40% (B0-B40), but with increasing biodiesel fuel percentage higher than B40 (B40-B100), these variables were increased. So, it was concluded that fuel blends with 40% biodiesel is an optimum fuel regime and it has been recommended for stationary diesel engines. Results indicated that with increasing engine load, fuel consumption increases. B40 (40% biodiesel, 60% diesel fuel) resulted in the minimum brake specific fuel consumption. Air consumption for all levels of engine load and fuel blends was constant and little deviations were due to changing in laboratory ambient temperature. Air to fuel ratio (A/F) increased from B0 to B40 and it decreased from B40 to B100. Maximum magnitude of A/F ratio for different diesel- biodiesel fuel blends was observed at B40.

In this study, Cetane number of different blends of Biodiesel fuel produced from restaurant waste cooking oil (WCO) and Diesel fuel was measured using a standard CFR engine. The effect of Biodiesel fuel blends on ignition delay of a indirect injection diesel engine (M8/1 Lister) was investigated. Cylinder pressure versus crank angle by Kistler-6123 Piezoelectric transducer is measured. All the blends of fuel were tested under afixed speed of 750 rpm and full load condition and the start of fuel injection at 21 degree of TDC. Ignition delay was obtained from the cylinder pressure curve and its derivatives method. Experimental results showed that with increasing biodiesel percentage in biodiesel/diesel blended fuel, cetane number increases from 57 for net Biodiesel up to 63 for net Diesel and ignition delay increases from 13.8 oCA to 8.83 oCA respectively. Cetanenumber was effectual in physical ignition delay; however density and viscosity were effective in chemical ignition delay. For prediction of ignition delay, an experimental model on the basis of Cetane number, density and viscosity was used. A non-linear regression model by using SPSS 14 software was found between ignition delay cetane number, density and viscosity with R2=0.998 and the error less than 0.5 oCA

It is well-established that control of fuel injection which is consisted of injection configuration and injection timing has an important role in engine performance, especially in pollutants’ formation. However, there are a few studies about the effect of the injection configuration on the performance of a diesel engine. In the present study, a FIRE computational fluid dynamic (CFD) code has been used in order to simulate the injection processes as well as the combustion of a direct injection diesel engine in five different injection configurations. The present results show that the minimum amount of NO is achieved using a triangular injection configuration resulting a significant decrease in the engine power. Furthermore, the smoke formation decreases sensibly using pre-injection and post –injection. The results also indicate that the minimum amount of unburned hydrocarbons in the exhaust is achievable using post-injection in the engine.

In the history of automotive industry, many extensive efforts have been done to design systems that make it possible to reduce emission and increase the efficiency of the vehicles. Since the emission of pollutants is directly proportional with the fuel consumption, therefore any effort to achieve the optimum fuel consumption leads to reduced pollutants. One of the most effective systems available for reduction of fuel consumption is continuously variable transmission system (CVT) which has been developed considerably during the last decade. Presently, an important issue that the automotive manufacturers in Iran and all over the world face with it is the feasibility of replacing the traditional manual transmission with CVT systems from the viewpoint of the fuel consumption. Here, the fuel consumption of a vehicle with a manual transmission iscompared with the same one equipped with a chain drive CVT system. By using the Genetic Algorithm, the fuel consumption of the vehicle with the mentioned CVT system, which is controlled automatically by ECU, is optimized. The results concerning the comparison between the two mentioned systems indicate that even if a skilled driver shifts the gears of the vehicle with the traditional transmission manually in a way that theoptimum fuel consumption is reached, the fuel consumption in the vehicle equipped with CVT transmission will be considerably less than that with manual gearbox transmission