A first exhaust gas turbocharger of the first set is operated alone when the need for charge air is minimal, and {HEAD ~ a second exhaust gas turbocharger} of {TAIL ~ the first set} is switched on when the need for charge air increases 
of
A first exhaust gas turbocharger of the first set is operated alone when the need for charge air is minimal , and { HEAD ~ a second exhaust gas turbocharger } of { TAIL ~ the first set } is switched on when the need for charge air increases
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH