Evaluation of a Variable Nozzle Turbine Turbocharger on a Diesel Engine under Steady and Transient Conditions

Abstract: The growing global call for reduced emissions and fuel consumption together with the market call for engines with higher power density and application-oriented torque curves can be met using turbochargers with variable geometry turbines (VGT). The second generation of VGT turbochargers is currently being developed and is starting to appear on the market. The most common solution is using of pivoted vanes forming a variable nozzle turbine (VNT). The adaptation of VGT turbochargers imposes new and different demands when it comes to the adaptation to the engine system as compared with conventional turbochargers.

A conventional turbocharger has a fixed operating point at every combination of speed and load. The operating line is then given by the system into which the turbocharger is incorporated. In the case of a VNT, the operating line can be determined within certain limits by different guide vane openings.

Using a VNT unit, it is possible to control the air to fuel ratio and turbocharger pressure conditions for a fixed operation point within certain limits. When integrated with the engine fuel control system, the new technology offers new opportunities to improve starting capabilities, steady state torque, transient response and change the soot/NOx relation over the load range. There is also a real potential to reduce the specific fuel consumption.

In this work a VNT system was tested under both steady state and transient conditions. The transient test includes load acceptance and acceleration in an engine test cell. The latter follows the propeller law and includes acceleration from idling and from low cruising load.

A test in a marine craft was performed as well. The aim of this test was to evaluate and improve the electronic control system for the turbocharger during transient operation.

The influence of vane clearance and the position of the vanes on turbine performance under different conditions are evaluated.

The main aim and purpose of the work is to provide a comprehensive study of the interaction between the engine and the improved charging system in order to visualise and summarise the benefits of the VNT system. Another aim is to gain a deeper understanding of VNT-engine interaction for the purpose of developing a control system.

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