Current Issue : July - September Volume : 2019 Issue Number : 3 Articles : 5 Articles
The present study provides a feasible strategy for minimizing automotive CO2 emissions\nby coupling the principle of the Atkinson cycle with the use of bioethanol fuel. Motor cycles and\nscooters have a stroke to bore ratio of less than unity, which allows higher speeds. The expansion\nto compression ratio (ECR) of these engines can be altered by tuning the opening time of the intake\nand exhaust valves. The effect of ECR on fuel consumption and the feasibility of ethanol fuels are\nstill not clear, especially for short stroke engines. Hence, in this study, the valve timing of a short\nstroke engine was tuned in order to explore potential bioethanol applications. The effect of valve\ntiming on engine performance was theoretically and experimentally investigated. In addition, the\napplication of ethanol/gasoline blended fuels, E3, E20, E50, and E85, were examined. The results\nshow that consumption, as well as engine performance of short stroke motorcycle engines, can be\nimproved by correctly setting the valve controls. In addition, ethanol/gasoline blended fuel can\nbe used up to a composition of 20% without engine modification. The ignition time needs to be\nadjusted in fuel with higher compositions of blended ethanol. The fuel economy of a short stroke\nengine cannot be sharply improved using an Atkinson cycle, but CO2 emissions can be reduced using\nethanol/gasoline blended fuel. The present study demonstrates the effect of ECR on the performance\nof short stroke engines, and explores the feasibility of applying ethanol/gasoline blended fuel to it....
The aim of this paper is to investigate the design in similarity of a centrifugal\ncompressor for micro gas turbine and the related scaling effects on performance\nusing CFD investigations. This work is part of a research project carried\nout by the Department DIME of the University of Genova, with the purpose\nof investigating the performance of a micro gas turbine in the change\nfrom 100 kW electrical output to 250 kW, while maintaining the compressor\npressure ratio and geometry in similarity. The first part of the work focuses\non the comparison between the original and the scaled machine, while the\nsecond part of the study deeply investigates the tip gap effect in the new configuration.\nThe aim is to provide information about the performance of the\ncompressor designed in geometrical similarity and to evaluate the tip gap\nheight impact. From the efficiency point of view, the scaled-up machine has\nhigher efficiency (up to 1.4% increment in design conditions) keeping the\nsame technological limit for impeller manufacturing. However, the variation\nof tip gap height in the range 0 ÷ 1 mm strongly affects this parameter, leading\nto 10% alteration in design conditions between the ideal and worst case.\nThe results, both in terms of overall performance and flow fields, are widely\ndiscussed in order to obtain simple yet reliable correlation for preliminary\ndesign....
Thanks to the adoption of high pressure, direct injection and jet ignition, plus electrically\nassisted turbo-compounding, the fuel conversion efficiency of Fédération Internationale de\nl'Automobile (FIA) F1 engines has been spectacularly improved up to values above 46% peak\npower, and 50% peak efficiency, by running lean of stoichiometry stratified in a high boost, high\ncompression ratio environment. Opposite, Federation Internationale de Motocyclisme (FIM) Moto-GP\nengines are still naturally aspirated, port injected, spark ignited, working with homogeneous\nmixtures. This old fashioned but highly optimized design is responsible for relatively low fuel\nconversion efficiencies, and yet delivers an outstanding specific power density of 200 kW/liter. The\npotential to improve the fuel conversion efficiency of Moto-GP engines through the adoption of\ndirect injection and jet ignition, prevented by the current rules, is herein discussed based on\nsimulations. As two-stroke engines may benefit from direct injection and jet ignition more than fourstroke\nengines, the opportunity of a return of two-stroke engines is also argued, similarly based on\nsimulations. About the same power, but at a better fuel efficiency, of todayâ??s 1000 cm3 four stroke\nengines, may be obtained with lean stratified direct injection jet ignition engines, four-stroke of 1450\ncm3, or two-stroke of 1050 cm3. About the same power and fuel efficiency may also be delivered\nwith stoichiometric engines direct injection jet ignition two-stroke of 750 cm3....
This work focuses on the influence of the rotational and travel speed on the strength of AA 2024 T3 friction stir welded lap joints.\nTensile tests were carried out on minispecimens extracted from different welding zones. A central composite design was applied to\nidentify the relative importance of the variable factorsâ?? effects and their interaction on yield/ultimate strength and elongation for\nboth the heat affected-zone (HAZ) and nugget zone. Surface methods and gradient algorithms were used to optimize the yield\nstrength of the joints. Shear and microhardness tests were executed to achieve a more complete mechanical characterization....
According to the actual size parameters, the finite element model (FEM) of friction stir\nwelding (FSW) was established, and the FEM was updated by experiments. The FSW of the 2A14-\nT6 high-strength aluminum alloy was simulated under a reasonable welding process parameter\nrange, and the welding process parameters with good simulation effect were determined. The test\nwas carried out under the same parameters, and the axial force of the FSW tool and temperature of\nthe workpiece measuring point were collected. The comparison between the simulated data and the\nexperimental data is reasonable, indicating the correctness of the FEM. The microstructure analysis\nof the welded joint shows that the grain size in the upper part of the weld nugget was smaller than\nthat in the middle and lower parts, and there are obvious boundaries of grain size in each region of\nthe joint. The hardness of the joint in the upper layer is higher than that in the middle and lower\nlayers, and the minimum Vickers hardness value of the joint appears near the interface between the\nthermo-mechanically affected zone and the heat-affected zone on both sides of the weld. Tensile\ntesting shows that the strength coefficient of the joint reaches 82.5% under this process parameter,\nand the sample breaks at the intersection of the material flow during stretching. After analyzing the\nfinal mechanical properties of the joint, we found that a degree of aerospace application can be\nachieved. Under this parameter, the welding test was carried out on the top cover of the rocket fuel\ntank. Firstly, melon valve welding, which is relatively difficult in welding conditions, was carried\nout, and a high-quality joint with good surface and no defects was obtained....
Loading....