| As the measure of improving the performance of diesel on low working condition, variable nozzle rings have been applied more and more widely. Although there are more and more variable geometry turbochargers on vehicle diesels, this technique is not applied on ships' engines. Because ships' engines are mostly two-stroke diesels, it is worth to be concerned about the feasibility and other problems with variable nozzle rings.This thesis researches axial-flow constant pressure turbochargers of ships' two-stroke engines applying variable nozzle ring.Firstly, this thesis introduces the performance and transient characteristic of supercharged diesel engine on low working condition, and expatiates the significance of applying variable nozzle rings on constant pressure turbochargers.Secondly, it expatiates the basic performances of air compressor and turbine, and makes a model for the matching between turbocharger and diesel, points out the problems when ship's two-stroke diesels match variable geometry turbochargers. Then, comparing the Ainley-Dunham measure of estimating axial turbine aero performance for calculating the common turbocharger's energy losing and giving an example, it analyzes the work changing of turbo when changing the section of nozzle ring, points out the effect of energy losing after using variable nozzle ring.Finally, the thesis refers the mathematical model of matching between VGT and vehicle engine, offers the instruction for ships' two-stroke engines applying variable nozzle ring by the results of vanes' angles changing as the changing of diesel's load characteristic and speed characteristic. Then it discusses the changing range of the vanes of variable nozzle ring angle, and qualitatively explains how to change the flow area of nozzle ring according to the conditions.The conclusions redound to the developing and extending of axial-flow constant press turbocharger with variable nozzle ring, and lay a foundation for later work.
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