Turbochargers

Abstract

Various types of exhaust-driven turbochargers have been designed for supercharging reciprocating internal combustion engines. A turbocharger consists basically of a compressor and a turbine coupled on a common shaft. The exhaust gases from the engine are directed by the turbine inlet casing on to the blades of the turbine and subsequently discharged to atmosphere through a turbine outlet casing. The exhaust gases are utilised in the turbine to drive the compressor, which compresses the air and directs it to the engine induction manifold, to supply the engine cylinders with air of higher density than is available to a naturally aspirated engine. There exist a number of different types of compressors and turbines (or expanders), but few of these are ideally suitable to form the basis of an exhaust-gas driven supercharging system. The combination of a single-stage centrifugal compressor and a single-stage axial flow or radial flow turbine is almost universally used in turbochargers. The former type with the axial flow turbine is used for most of the medium and large size engines suitable for rail traction, industrial and marine purposes and the latter type with the radial flow turbine for small engines of the automotive (truck and automobile) type. A detailed analysis of centrifugal compressors, axial and radial flow turbines has been deferred to chapters 3, 4 and 5. This chapter is concerned with the specific requirement placed on a compressor-turbine for turbocharger use; the methods of comparing types and performance; and description and comments on typical turbochargers.