A first exhaust gas turbocharger of {TAIL ~ the first set} is operated alone when {HEAD ~ the need} for 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 { TAIL ~ the first set } is operated alone when { HEAD ~ the need } for 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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH