نشریه تحقیقات موتور
پیاپی 69 (Winter 2023)

In gasoline engines, pre-chamber spark ignition systems are used to achieve high efficiency and low NOx emissions when operating under lean conditions. While a cold pre-chamber spark plug can lead to misfiring and flame quenching under cold start or part load operation, a hot pre-chamber can result in uncontrolled pre-ignition phenomena under full load operation. This paper presents an approach to adjust the heat range of a pre-chamber spark plug and thus, the temperature of the mixture in the pre-chamber, according to the operating condition. Furthermore, higher mixture temperatures in the pre-chamber are intended to enhance the inflammation under lean conditions and to extend the lean limit. For this purpose, a glow plug is integrated into the pre-chamber, whose temperature can be controlled as a function of the operating point. A real-time closed-loop control strategy was applied by using the correlation between the glow plug tip temperature and its electrical resistance. The developed ignition element is called Hot Surface Assisted Spark Ignition (HSASI). In addition to a functional test, a variation of the engine temperature was performed on a single-cylinder, gasoline fueled research engine at the Karlsruhe University of Applied Sciences. In the first step, the influence of the glow plug assistance on the flame development angle and the combustion stability was determined. Subsequently, the air-fuel equivalence ratio λ was varied and the lean limit of unassisted and glow plug assisted spark ignition were determined. Experimental investigations for a constant air-fuel equivalence ratio and a constant ignition timing show that a higher glow plug resistance and thus a higher glow plug temperature shortens the flame development angle and shifts the center of combustion to earlier crank angles. Furthermore, the positive influence of the active glow plug on the flame development angle and the combustion stability increases with retarded ignition timing. With λ = 1.5 and a constant center of combustion (8 °CA after top dead center firing), the ignition timing can be retarded by 4.5 °CA. When operating with lower coolant temperature, an active glow plug increases combustion stability and extends the lean limit by Δλ = 0.1.

In current research we studied different powertrain options for a given B-class sedan vehicle in terms of fuel consumption target. The considered options include two engines and a base manual gearbox assuming the gear numbers and ratios can be changed. We concentrated on 5 and 6 speed gearboxes and used two parallel techniques to optimize gear ratios of the manual gearbox due to in-cycle fuel consumption which leaded to approximately the same results. To predict the fuel consumption in NEDC cycle, a longitudinal dynamic model of the vehicle was developed in GT-Suite environment. Two approaches by which we optimized the gear ratios were a direct optimizer based on genetic algorithm and a set of DOE analysis tools provided by GT-Suite software. The best result we got among all configurations was the combination of a 1500 cc turbocharged engine with a 5-speed manual gear box with optimized gear ratios based on DOE analysis technique. In this case we reached to 13.5% reduction in in-cycle fuel consumption.

Air Pollution is one of the significant problems in Tehran. Understanding the role of different sources can result in better decision-making. Some pollutions are not emitted directly from sources and are present in the atmosphere due to chemical reactions. Therefore, using air quality modeling can be beneficial to our understanding of these phenomena. An air quality modeling system was used first to model the base case of ambient pollutions. Then, the emissions of passenger cars and taxies were omitted separately to determine the role of their contribution to air pollution. The modeling results showed an acceptable performance with the index of agreement of 0.84 and 0.61 for ozone and particle matter (PM), respectively. The accumulated contribution of passenger cars and taxies to PM AQI was 14 units. However, their role in ozone formation was complex.

The direct injection of gaseous fuels involves the presence of under-expanded jets due to the high pressure-ratios and the strong gas compressibility. Understanding the physical development of such processes is essential for developing Direct Injection (DI) devices suitable for application in internal combustion engines fueled by methane or hydrogen. In this work a coupled experimental-numerical characterization of a spray, issued by a multi-hole injector, was performed. The experimental characterization of the jet evolution was recorded by means of schlieren imaging technique and then a numerical simulation procedure was assessed using the measurements for validating. A density-based solver, capable of simulating highly compressible jets and developed within OpenFOAM environment, was used to study the effects of thermodynamic conditions on the development of the injection process. The obtained results shed more light on the characteristics of the gaseous spray demonstrating how these features really affects the development of the injection process and the quality of the air/fuel mixture.

Better performance and the regulatory requirements concerning combustion emissions have caused downsized GDI engines and consideration of strategies for improving in-cylinder mixture preparation. The sprays characteristics of the fuel injectors of GDI engines have been widely investigated by researchers. The interest in studying the characteristics of the spray is due to a strong relationship with the subsequent combustion reaction and thus with the engine's thermal efficiency. This paper analyzes the mixture formation of the spray employing an experimental laser apparatus that was used to measure the spray penetration in a constant volume chamber (CVC) and simulations performed by the fast response CFD CONVERGE software. The fuel injector used in the tests was a six-hole direct injection injector with iso-octane fuel. The measurements were taken 100 mm downstream from the injector tip along the axis with 20 MPa injection pressure. During experiments, it was observed that spray development is not symmetrical with the vertical axis, and with decreasing chamber pressure, it develops faster. Moreover, the average spray development velocities in simulations are in good agreement with experimental results.

In recent years, the automotive industry has expanded its usage of magnesium alloys because to their favorable metallurgical properties. It is, however, vital to coat the magnesium components like piston in the car engines because of their harsh working environment. In this study, beyond the introduction of novel plasma electrolytic oxidation coating for AZ31 Mg alloy, the metallurgical characteristics of coating generated in silicate and aluminate electrolytes are also examined. Phase studies revealed that along with the presence of MgF2 and MgO in both coating, Mg2SiO4 and MgAl2O4 were discovered in coatings created in silicate and aluminate electrolytes, respectively. The application of PEO resulted in a considerable drop in corrosion rate, such that the corrosion rate of the coating formed in silicate electrolyte is 2.24×10-6 A.cm-2 and that of the coating created in aluminate electrolyte is 9.5×10-7 A.cm-2, which are 30 and 68 times lower than the rate of uncoated samples, respectively. Additionally, as compared to the uncoated sample, the coating enhances the surface electrical resistance by 72 and 94 times. The microscopic analysis showed that the average diameter of porosities in PEO coating made by silicate electrolyte is higher than that of coating made by aluminate electrolyte