Abstract
The basic development objectives for turbocharged commercial diesel engines are in most cases similar:
Increase the engine's rated power and torque at low engine speeds, improve the transient response, and, simultaneously, reduce fuel consumption and emissions.
An increased air mass flow for the rated power point basically requires a larger turbocharger. The wish for overproportionately more air, i.e. boost pressure, at low engine speeds means however, that the engine should be matched to a relatively small turbine and compressor. The ideal solution would be a combination of both.
The regulated two-stage turbocharging system corresponds to such an ideal case. In this system, two differently sized turbochargers are positioned in series, with a regulated bypass control and optional intercooling.