Predictive GT-Power Simulation for VNT Matching on a 1.6 L Turbocharged GDI Engine

The thermal efficiency benefits of low-pressure (LP) exhaust gas recirculation (EGR) in spark-ignition engine combustion are well known. One of the greatest barriers facing adoption of LP-EGR for high power-density applications is the challenge of boosting. Variable nozzle turbines (VNTs) have recently been developed for gasoline applications operating at high exhaust gas temperatures (EGTs). The use of a single VNT as a boost device may provide a lower-cost option compared to two-stage boosting systems or 48 V electronic boost devices for some LP-EGR applications. A predictive model was created based on engine testing results from a 1.6 L turbocharged gasoline direct injection (GDI) engine [1]. The model was tuned so that it predicted burn-rates and end-gas knock over an engine operating map with varying speeds, loads, EGR rates and fuel types. Using the model, an assessment of VNT performance was performed using compressor and turbine maps made available from Honeywell Transportation Systems. Results show that the single VNT device supports LP-EGR across the operating map while maintaining realistic full-load performance and maintaining or improving upon thermal efficiency compared to a twin-scroll turbocharger. This work was done as part of the Environmental Protection Agency’s continuing assessment of advanced light-duty automotive technologies to support setting appropriate national greenhouse gas standards.