Study on Low-Temperature Traction Behavior of a Space Lubricating Oil No.4116

The traction behavior of space lubricating oil No. 4116 was measured and analyzed at various oil inlet temperatures below 0 ℃ and various rolling speeds under normal loads by a test rig simulating the operating conditions of space bearings. A traction coefficient calculation model was presented. The rheological property and rheological parameters of the lubricant at a low oil inlet temperature were analyzed based on the Tevaarwerk-Johnson model. The results showed that the lubricating oil No. 4116 was sensitive to the rolling speed and had lower sensitivity to the normal load. This lubricating oil is more suitable for applications under high speed when it is used below 0 ℃. It behaves as an elastic-plastic fluid operating below 0 ℃. Both the average limiting shear stress and the average elastic shear modulus have a negative correlation with the rolling speed and oil inlet temperature and have a positive correlation with the normal load.

Effects of Ambient Conditions and Nozzle Design on the Velocity of Clustered Diesel Jets

The measurement of droplet velocities in Diesel sprays close to the nozzle is important because of the complexity of in-nozzle flow, spray break-up and evaporation. However, the measurement of droplet velocities in the dense region of Diesel sprays is very difficult or impossible by means of widely used laser diagnostic techniques, in particular under engine-like high-pressure and high-temperature conditions. The limitations of phase Doppler anemometry （PDA） and particle image velocimetry （PIV） prevent the application to the ultra-dense region of the spray. It was demonstrated that these problems can be greatly reduced by the laser flow tagging （LFT） technique. It was also demonstrated recently that LFT measurements can be conducted in clustered Diesel jets with improved spatial resolution and increased number of simultaneous measurements in the near-nozzle region. In the present work, the nozzle design, the temperature and pressure of the ambient air, and the fuel rail pressure are varied, in order to investigate the influence on the near-nozzle jet velocity and the underlying physical mechanisms.

Performance Characteristics of Single Cylinder Diesel Engine under Different Operating Conditions

Recently, it is predicted that the fossil fuels will be sufficient for a few decades at the present extraction rates. So, the performance studies of the internal combustion engines play an important role to achieve the best operating point at different weather temperatures. In the present study, the effects of the inlet air temperatures on the engine performance characteristics were studied at different cooling loads. Several experiments were carried out on a single cylinder diesel engine （SCDI）. The performance characteristics of SCDI included： brake power, specific fuel consumption, brake thermal efficiency and exhaust emissions （carbon dioxide, CO2, carbon monoxide CO, and hydrocarbon HC）. The findings show that the inlet air temperature and cooling conditions have appreciable effect on the performance characteristics of the SCDI especially at low cooling rate. It can be concluded that the high cooling rate leads to the enhancement in the brake thermal efficiency, the b.s.f.c, and the emitted COz, CO, and HC. On the other hand the high cooling rate leads to the decrease in the volumetric efficiency. So, a compromising between the inlet air temperature and the cooling rate should be recommended for the engine best performance.

Supersonic Cavity Based Combustion with Kerosene/Hydrogen Fuel

A comparative study with kerosene and hydrogen fuel in a model scramjet combustor has been carried out nu- merically. The effect of fuel-air equivalence ratio on the flow field properties in a cavity based mixing mechanism at a freestream Math number of 2.08 has been probed. The investigation has been carried out in a two dimension- al numerical model where a cavity of length to depth ratio of 2 is mounted on one of the walls of the flow channel The flow field shock structure is observed to change with the change in fuel-air equivalence ratio. Total pressure loss is observed to depend both on fuel air equivalence ratio and the fuel type. The spread of fuel in the test sec- tion shows marked variation with the equivalence ratio. Performance of injector location on the fuel-air mixing is also probed during the course of the investigation.

Liquid phase 3D printing for quickly manufacturing conductive metal objects with low melting point alloy ink

Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks.From an alternative way,here we proposed the method of liquid phase 3D printing for quickly making conductive metal objects.Through introducing metal alloys whose melting point is slightly above room temperature as printing inks,several representative structures spanning from one,two and three dimension to more complex patterns were demonstrated to be quickly fabricated.Compared with the air-cooling in a conventional 3D printing,the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly improves the speed in fabricating the target metal objects.This unique strategy also efficiently prevents the liquid metal inks from air oxidation,which is hard to avoid otherwise in an ordinary 3D printing.The key physical factors(such as properties of the cooling fluid,air pressure within the syringe barrel and needle diameter,types and properties of the printing ink)and several interesting intermediate fluids interaction phenomena between liquid metal and conventional cooling fluids such as water or ethanol,which evidently affecting the printing quality,were disclosed.In addition,a basic route to make future liquid phase 3D printer incorporated with both syringe pump and needle arrays was also suggested.The liquid phase 3D printing,which owns potential values not available in a conventional method,opens an efficient way for quickly making conductive metal objects in the coming time.