Exhaust resonance effect on the 2-stroke engine aspiration is investigated via one-dimensional simulation on GT-Power.Result shows that exhaust resonance is established when the number of oscillation periods per engin...Exhaust resonance effect on the 2-stroke engine aspiration is investigated via one-dimensional simulation on GT-Power.Result shows that exhaust resonance is established when the number of oscillation periods per engine cycle derived from the engine speed and exhaust length is an integer.Exhaust resonance may raise or lower the trapping ratio,and the specific effect depends on the value of the number of oscillation periods per engine cycle.There is a liner regression relationship between the trapping ratio and average after back pressure.The primary way to improve the trapping ratio with the exhaust resonance is to increase the average after back pressure.The optimum exhaust resonance state is the one that suits the port timings so that the peak of exhaust pressure lies within the after charging period,raising the average after back pressure.For the case where the exhaust duration is 184°CA and the scavenge duration is 111°CA,the optimum number of oscillation periods per engine cycle is 3.展开更多
Swirl-Loop Scavenging(SLS) improves the performance of 2-stroke aircraft diesel engine because the involved swirl may not only benefit the scavenging process, but also facilitate the fuel atomization and combustion. T...Swirl-Loop Scavenging(SLS) improves the performance of 2-stroke aircraft diesel engine because the involved swirl may not only benefit the scavenging process, but also facilitate the fuel atomization and combustion. The arrangement of scavenge port angles greatly influences incylinder flow distribution and swirl intensity, as well as the performance of the SLS engine. However, the mechanism of the effect and visualization experiment are rarely mentioned in the literature. To further investigate the SLS, Particle Image Velocimetry(PIV) experiment and Computational Fluid Dynamics(CFD) simulation are adopted to obtain its swirl distribution characteristics, and the effect of port angles on scavenging performance is discussed based on engine fired cycle simulation. The results illustrate that Reynolds Stress Turbulence model is accurate enough for in-cylinder flow simulation. Tangential and axial velocity distribution of the flow, as well as the scavenging performance, are mainly determined by geometric scavenge port angles ageom and βgeom . For reinforcement of scavenging on cross-sections and meridian planes, ageomvalue of27° and βgeom value of 60° are preferred, under which the scavenging efficiency reaches as high as 73.7%. Excessive swirl intensity has a negative effect on SLS performance, which should be controlled to a proper extent.展开更多
In the present study, the performance of a 4-stroke diesel engine was experimentally evaluated upon adding Al2O3 or SiO2 nanoparticles to the engine oil （SAEISW40）. The viscosity and density of the resulting nanolub...In the present study, the performance of a 4-stroke diesel engine was experimentally evaluated upon adding Al2O3 or SiO2 nanoparticles to the engine oil （SAEISW40）. The viscosity and density of the resulting nanolubricants were determined while varying both the nanoparticle volume fraction and the temperature. Field emission scanning electron microscopy （FE-SEM） showed that the nanoparticles had a spherical morphology and dynamic light scattering analysis determined some aggregation of the nanoparticles in the engine oil. A pin-on-disc test apparatus was used for friction and wear analysis in the presence of the nanolubricants. Examination of wear scars by FE-SEM and energy dispersive spectroscopy found evidence of ball bearing and surface polishing effects, which were responsible for improvements in the tribological properties of the oil. The performance of these nanolubricants in a 4- stroke diesel engine test rig was assessed, and the greatest improvements in the tribological behavior and engine performance were observed when employing 0.3 vol% Al2O3.展开更多
文摘Exhaust resonance effect on the 2-stroke engine aspiration is investigated via one-dimensional simulation on GT-Power.Result shows that exhaust resonance is established when the number of oscillation periods per engine cycle derived from the engine speed and exhaust length is an integer.Exhaust resonance may raise or lower the trapping ratio,and the specific effect depends on the value of the number of oscillation periods per engine cycle.There is a liner regression relationship between the trapping ratio and average after back pressure.The primary way to improve the trapping ratio with the exhaust resonance is to increase the average after back pressure.The optimum exhaust resonance state is the one that suits the port timings so that the peak of exhaust pressure lies within the after charging period,raising the average after back pressure.For the case where the exhaust duration is 184°CA and the scavenge duration is 111°CA,the optimum number of oscillation periods per engine cycle is 3.
基金supported by the Basic Research Program of the National Natural Science Foundation of China (Nos. 51775025 and 51205015)China Key Research and Development Plan (No.2018YFB0104100)。
文摘Swirl-Loop Scavenging(SLS) improves the performance of 2-stroke aircraft diesel engine because the involved swirl may not only benefit the scavenging process, but also facilitate the fuel atomization and combustion. The arrangement of scavenge port angles greatly influences incylinder flow distribution and swirl intensity, as well as the performance of the SLS engine. However, the mechanism of the effect and visualization experiment are rarely mentioned in the literature. To further investigate the SLS, Particle Image Velocimetry(PIV) experiment and Computational Fluid Dynamics(CFD) simulation are adopted to obtain its swirl distribution characteristics, and the effect of port angles on scavenging performance is discussed based on engine fired cycle simulation. The results illustrate that Reynolds Stress Turbulence model is accurate enough for in-cylinder flow simulation. Tangential and axial velocity distribution of the flow, as well as the scavenging performance, are mainly determined by geometric scavenge port angles ageom and βgeom . For reinforcement of scavenging on cross-sections and meridian planes, ageomvalue of27° and βgeom value of 60° are preferred, under which the scavenging efficiency reaches as high as 73.7%. Excessive swirl intensity has a negative effect on SLS performance, which should be controlled to a proper extent.
文摘In the present study, the performance of a 4-stroke diesel engine was experimentally evaluated upon adding Al2O3 or SiO2 nanoparticles to the engine oil （SAEISW40）. The viscosity and density of the resulting nanolubricants were determined while varying both the nanoparticle volume fraction and the temperature. Field emission scanning electron microscopy （FE-SEM） showed that the nanoparticles had a spherical morphology and dynamic light scattering analysis determined some aggregation of the nanoparticles in the engine oil. A pin-on-disc test apparatus was used for friction and wear analysis in the presence of the nanolubricants. Examination of wear scars by FE-SEM and energy dispersive spectroscopy found evidence of ball bearing and surface polishing effects, which were responsible for improvements in the tribological properties of the oil. The performance of these nanolubricants in a 4- stroke diesel engine test rig was assessed, and the greatest improvements in the tribological behavior and engine performance were observed when employing 0.3 vol% Al2O3.
