Abstract
Market trends for increased specific engine power and more electrical energy on the powergrid indicated that 3kW+ is not unrealistic, and, along with customer demands for fuel consumption improvements and emissions reduction, are driving requirements for the electrification of components, including turbochargers. The objective of the study was to understand how much energy could be recovered from an existing GTDI (Gasoline Turbocharged Direct Injection) engine for such a device.
GTDI engines waste significant exhaust enthalpy, since even at moderate loads the WG (wastegate) starts to open. This effect is required to reduce EBP (Exhaust Back Pressure). Another factor is catalyst overheating protection and lambda enrichment is used to perform this. Normally the catalyst is placed downstream of the turbine. However, the turbine has a temperature drop across it when used for energy recovery. Since catalyst performance is critical for emissions, the only reasonable package location for an additional device is downstream of it. This is a challenge for any additional energy recovery, but a smaller LPT (Low Pressure Turbine) is a design requirement, optimised to operate at lower turbine pressure ratios.
A WAVE model of the GTDI engine was adapted to include a TG (Turbogenerator) and bypass throttle (WG) with the TG in mechanical turbocompounding configuration, and calibrated with steady state dynamometer data in order to estimate drive cycle benefit using a KP (Key Point) analysis. This includes power and fuel consumption. A further sensitivity analysis on a higher engine speed indicates that significant energy recovery can be achieved.
KEYWORDS – Turbogenerator, Electric Turbocompounding, Energy Recovery, Engine Downsizing, Low Pressure Turbine, 1-D Simulation