Characteristics of Turbocharger with TiAl Turbine Wheel in a Downsizing GDI Engine 2013-01-2499
Steady and transient tests in a downsizing Gasoline Direct Injection (GDI) in-line 4 cylinders 2.0 liter engine were carried out to investigate characteristics of turbocharger with Titanium aluminide (TiAl) turbine wheel. The density of TiAl material is lower than Inconel 718 (Inconel) which is raw material for conventional turbine wheel. The objective of this study was to investigate the effect of light rotational inertia of turbine wheel on engine performance. Performance of TiAl turbine wheel turbocharger itself was also compared to that of Inconel turbine wheel turbocharger. Except for the turbine wheels, all experimental conditions were matched to be the same load and engine speed conditions. The compressor total-to-total pressure ratio of TiAl turbocharger was higher under part load condition due to higher turbocharger speed of TiAl turbocharger, which was led by lower rotational inertia of TiAl turbine wheel, while the engine performance was not much improved. In addition, brake specific fuel consumption (BSFC) was little deteriorated due to lower swallowing capacity of TiAl turbine. Under wide open throttle (WOT) conditions, the engine torque was slightly lower compared to Inconel turbocharger case. This was due to the same reason, which was lower swallowing capacity. However, difference of BSFC between both turbochargers was not big because of other affecting factors such as ignition timing and over fueling. In the transient test, the time for boost pressure build-up of TiAl turbocharger was shorter by up to 13.04 % than that of Inconel turbocharger. Turbocharger speed of TiAl turbocharger was also higher at the same time after onset of acceleration. In addition, the time for the reaching peak engine torque was shorter by at most 10.24% in case of TiAl turbocharger compared to that of Inconel turbocharger.