进、排气壳对全流道大膨胀比涡轮性能影响研究

为了分析船用增压器涡轮机进、排气系统对涡轮级性能的影响,采用数值模拟方法对全流道大膨胀比跨声速涡轮与进、排气壳耦合计算,探索进、排气壳耦合对涡轮级性能参数的影响,结果表明:进气壳主要影响静叶10%和50%叶高前缘的来流气流角周向分布,静叶排会减弱进气壳带来的参数周向不均匀性,排气壳主要影响动叶尾缘0°与180°周向位置总压与静压分布,进、排气壳耦合涡轮级总静效率比均匀边界涡轮级下降0.25%。

Development of Turbocharger for Improving Diesel Engine Matching Performance

The two development ways of turbocharger technology to solve the problem of matching performance with diesel were presented. The ways of waste valve gate turbocharger and variable geometry turbocharger can solve the problem of engine’s low speed torque and achieve lower smoke level. Especially for variable geometry turbocharger, it covers all conditions of engine. It can not only improve the low engine’s speed torque and keep the power performance at high engine speed, but also cover wide engine speed performance that keeps lower fuel consumption and exhaust gas temperature in full load and part load matching. The results of theory analysis and experiment research showed that it’s the ideal solution to solve the matching problem of diesel engines.

Investigation of a Centrifugal Compressor and Study of the Area Ratio and TIP Clearance Effects on Performance

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and dif- fuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was stud- ied numerically. The impeller area ratio was changed by cutting the impeller exit axial width from an initial value of 4.1 mm to a final value of 5.1 mm, resulting in an area ratio from 0.792 to 0.965. For the rotor with exit axial width of 4.6 mm, performance was investigated for tip clearance of 0.0, 0.5 and 1.0 mm. Results of this simula- tion at design point showed that the compressor pressure ratio peaked at an area ratio of 0.792 while the effi- ciency peaked at a higher value of area ratio of 0.878. Also the increment of the tip clearance from 0 to 1 mm resulted in 20 percent efficiency decrease.

Experimental study on the effects of HP and LP EGR on thermal efficiency and emissions of a two-stage turbocharged diesel engine

An experimental study was performed to compare the effects of high-and low-pressure exhaust gas recirculation loops(HP and LP EGR loops)on thermal efficiency and emissions of a diesel engine.Tests were conducted on a 12-L six-cylinder turbocharged diesel engine under various operating conditions.We found that at a low speed of 1100 r/min,1 MPa BMEP,the LP EGR loop could achieve higher brake thermal efficiency and lower emissions than the HP EGR.This is because the lower enthalpy available at the turbine inlet of the HP EGR loop increased the fuel/oxygen equivalence ratio.For the HP EGR,the gross indicated thermal efficiency was reduced by 1%,but pumping losses were only reduced by 0.5%,compared to the LP EGR loop.At a higher speed of 1600 r/min,1 MPa BMEP,the HP EGR loop attained a higher brake thermal efficiency and lower emissions because of the relatively sufficient flow through the turbocharger.For the HP EGR loop,the gross indicated thermal efficiency was only reduced by 0.5%and pumping losses were reduced by 1.5%,compared to the LP EGR loop.Lower fuel consumption and a longer ignition delay made the distribution of fuel/oxygen equivalence ratio more homogeneous,leading to lower emissions.Our data also showed that at the high speed of 1600 r/min,0.55 MPa BMEP,the brake thermal efficiency of the HP EGR loop first increased,then decreased as the EGR rate increased.Therefore,under all conditions,a reasonable match of both EGR loops could achieve a good balance between fuel consumption and emissions of NOx and soot.

A novel experimental method to evaluate the impact of volute's asymmetry on the performance of a high pressure ratio turbocharger compressor

All components of a turbocharger compressor are axisymmetric except for the spiral-shaped,gas-collecting overhung volute.In this paper,a novel experimental method to evaluate the impact of the volute's asymmetry on centrifugal compressor performance is proposed and applied to a high pressure-ratio turbocharger compressor.This method can isolate the impact of the volute's asymmetry on the compressor performance for the first time.Experiments prove the considerable impact of the volute's asymmetry on the compressor performance,especially the stability and efficiency.The impact of the volute's asymmetry on compressor stability correlates with rotational speed and thus with the pressure ratio,constricting the stable flow range by up to 47 percent and decreasing the maximum efficiency by 4.8 percent at the design speed.The results provide evidence to exploit the potential of intrinsic non-axisymmetric flow induced by asymmetric volute to improve the performance of turbocharger compressor with a high pressure ratio.

Influence of volute distortion on the performance of turbocharger centrifugal compressor with vane diffuser

As the geometry of the volute of turbocharger compressor is non-axisymmetric,it causes a distortion at the outlet of the diffuser and influences the upstream components.A distortion model in which a pressure distortion was applied as outlet boundary condition was established to simulate the distortion induced by the volute.It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the outlet of the diffuser to replace the volute.Based on the distortion model which was verified,the influence of the amplitude of the distortion on the performance of centrifugal compressor was studied in detail.The results show that the distortion severely harms aerodynamic stability of the investigated compressor.The larger the amplitude of the distortion,the worse the performance of the compressor.The distortion induced by asymmetric volute propagates to upstream components and causes local flow separation at part of diffuser and impeller,and then causes the compressor surge.When the amplitude of the volute distortion is 10%,the stable flow range of the centrifugal compressor decreases to near zero.To authors’knowledge,the relationship between the compressor performance and distortion amplitude is first obtained quantitatively,which provides evidence to improve the performance of turbocharger compressor by decreasing the distortion induced by asymmetric volute.

Effect of a Curved Duct Upstream on Performance of Small Centrifugal Compressors for Automobile Turbochargers

Since the automobile turbochargers are installed in an engine compartment with limited space, the ducts upstream of the turbocharger compressor may be curved in a complex manner. In the present paper, the effect of a curved duct upstream on performance of small centrifugal compressors for automobile turbochargers is discussed. The computational fluid dynamics (CFD) analysis of a turbocharger compressor validated for the compressor model with the straight pipe applied to the compressor with the curved pipe are executed, and the deterioration of the performance for the curved pipe is confirmed. It is also found that the deterioration of compressor performance is caused by the interaction of the secondary flow and the impeller.

Effects of Reynolds number on the performance of a high pressure-ratio turbocharger compressor

The effects of Reynolds number on the performance of a high pressure-ratio turbocharger compressor were investigated by both experiments and numerical simulation. The experimental results show that the pressure ratio and the efficiency of the compressor respectively decrease by 7.9% and 6.9% when Reynolds number drops from 9.86×10 5 to 2.96×10 5 . The numerical simulation predicts a similar trend as the experimental results although it underestimates the deterioration of the performance under low Reynolds number conditions. According to simulation results, the boundary layer thickness increases at the inducer, which decreases the throat area and leads to smaller choke mass flow rate. The increments of the boundary thickness are relatively small at the rear part of the impeller. The boundary layer separation flow is severe. The interaction between boundary layer separation flows and leakage flows causes the high loss region at the rear part of the impeller passage under low Reynolds number condition.