Experimental investigation and energy-exergy analysis of hydrogen direct-injection engine equipped with different turbochargers

Owing to its superior combustion performance, abundant reserves and clean combustion products, hydrogen has been regarded as a promising alternative fuel for internal combustion engines (ICEs). The direct injection hydrogen internal combustion engines can offer larger power without the risk of backfires, compared to port fuel injection. To avoid the NOx emission and improve the power output, lean boosting is adopted to reduce the pressure-increase rate and combustion temperature. As well as the low exhaust temperature of hydrogen engine, which pose significant challenges for the turbocharger system. Against this background, an experimental study was carried out on an 8.2 L DI hydrogen engine. Three types of turbochargers were compared: wastegate turbocharger (WG), variable geometry turbocharger (VGT), and two-stage turbocharger (TS). All tests were performed under operating conditions constrained by pre-ignition and super-knock, aiming to maximize thermal efficiency. The brake thermal efficiency (BTE) varied from 31.1% to 34.4% across the tested engine speeds. The TS turbocharger yielded the maximum BTE of 34.4% at 1300 rpm. This work further investigated the effects of different turbochargers on the energy and exergy distributions of the engine. Energy analysis results reveal that the two-stage turbocharge exhibits the lowest exhaust energy loss, the variable geometry turbocharger demonstrates the lowest coolant energy loss, and the wastegate turbocharger achieves the lowest intercooler loss. Exergy analysis results indicated that the TS system achieved the maximum total available exergy efficiency of 67.9% at 1600 rpm, accompanied by the minimum exergy destruction.