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As an effective means of improving engine output, turbocharging has been widely used in engines. However, due to the inherent mismatch of a turbocharger to a reciprocating machine, a turbocharged machine does have some drawbacks,such as the reduction in transient performance, low torque backup, low torque and etc. One solution to these problems is to dynamically vary the size of the turbine stage, reducing the swallowing capacity of the turbine at lower gasflows and increasing the swallowing capacity at high gasflows. A turbocharger fitted with such a turbine is called “Variable Geometry” turbocharger. In general, there are two types of variable nozzle turbocharger. One is the traditional gas turbine approach of using a set of individually pivotable nozzle guide vanes (1) (2), and the other is with axial movable nozzle vanes (3) (4) (5).

An axially movable vane turbocharger has been modified based on the basic aerodynamic design principles, and good performance is obtained. The details of design and engine bench testing results of several vane variations are presented, and the most suitable assembly nozzle with two separate vanes is then developed. These have produced a simple design with a minimum number of the moving parts. Experimental data also show that the new turbocharger efficiently expands the effective torque band and get the low fuel consumption at a wide engine speed range.

This report describes with the performance test of a diesel engine using a new variable scroll type turbocharger (VS turbocharger). The experimental variable scroll is relatively a simple structure in which several scroll pieces are jointed by pins, located inside of exhaust turbine inlet flow passage. The scroll is varied by the control rod according to exhaust flow volume, and as a result, the A/R ratio that effects to the performance of turbocharger is varied. To compare the performances of variable scroll type turbocharger with a conventional turbocharger with waste gate, a test of diesel engine equipped with each was performed. The experimental results show that VS turbocharger increases more than the conventional turbocharger in boost pressure at lower engine speed, and the wide torque range is ensured. Also, the experimental scroll pieces did not showed signs of trouble from heat wear during experimentation ensuring reliability.

A new variable scroll type turbocharger has been developed, which is a kind of variable geometry turbocharger. This paper describes a method for determining the shape of a scroll chamber of a turbine housing of the turbocharger. The basic idea is to vary the flow area using the scroll according to exhaust gas flow. The scroll consists of several scroll pieces joined to form a linked variable structure. The shape of the scroll pieces is decided on the basis of an Archimedes’ curve. The device developed is relatively simple.