The Design and Development of Small Radial-Flow Turbo-Chargers

Abstract

Turbo-chargers are already well established for Diesel engines of moderate and high outputs, and there is no reason why this should not also apply to Diesel engines of 100 h.p. and upwards. In the former case, axial-flow turbines are used, but these suffer from serious disadvantages in the smaller sizes, so that radial-flow turbo-chargers are more likely to be adopted.

The range of applications on the smaller Diesel engine is very extensive compared with its larger counterpart, and in particular, automotive engines will have a serious influence on the design and development of the small turbo-charger. Owing to the rapidly and widely varying load conditions, the component efficiency must be high, and the rotating assembly as light as possible to give rapid response times. This involves intensive development of turbine and compressor, and the use of shaft speeds of 40,000–50,000 r.p.m., which until recently would have been regarded as impracticable for service conditions where a life of several thousand hours must be accepted.

The automotive field is also highly competitive, and production quantities are large. Consequently, the design of the turbo-charger must be such that it can be made economically and in large numbers, and at the same time be as efficient as possible over a wide range of operational conditions. Although economic conditions may fix the minimum size of the turbo-charger, the limit does not yet appear to have been reached on an aerodynamic basis, and reasonably high component efficiencies are readily attainable with rotors of 4 inches diameter or less.

The onset of exhaust smoke in some automotive service applications will not only dictate the matching conditions for the turbo-charger, but may also necessitate some further development to prevent it being a limitation on the power output from a given installation.