Gasoline Engine Load Control Using Variable Geometry Turbine Turbochargers

The Variable Geometry Turbine (VGT) turbocharger, which has been proven on Diesel engines, has ability to improve both low end torque and fuel consumption. Because the engine load is directly related to the intake manifold pressure on conventional gasoline engines, the flexibility of varying the turbocharger operating condition efficiently by using a VGT turbocharger can be used to control the engine load.
A VGT turbocharger has been tested on a 2.0L production gasoline engine, which was originally equipped with a Fixed Geometry Turbine (FGT) turbocharger with a waste-gate. Experimental work has been carried out at wide-open-throttle (WOT) conditions at 2000 rpm. The maximum torque with the VGT turbocharger was 41Nm (15.4%) higher, and the minimum torque that can be achieved at WOT was lowered by 52Nm because of the flexibility of fully opening the VGT at low boost pressure conditions. By varying the VGT actuator position, the operating range that can be controlled was between 184Nm and 308Nm, 93Nm larger than that can be controlled using the waste-gate on the FGT turbocharger.
The VGT turbocharger experimental data was compared with simulation data collected from a calibrated 1-D engine model with FGT turbocharger. At 2000rpm 229Nm, compared with the FGT turbocharger, the lower pumping work resulted in 1.5% BSFC reduction and the extended spark timing window resulted in another 1.4% fuel consumption improvement.