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