Abstract
Research and/or Engineering Questions/Objective
For turbocharged gasoline direct injection (T-GDI) engines which require accurate air-fuel ratio control and ignition phasing, LP-EGR technology is challenging technology to apply due to the non-linear behavior of EGR flow and the phase delay from the long passage between the EGR gas inlet to the combustion chamber of LP-EGR system. The objective of this study is to realize the fuel efficiency benefit by developing proper LP-EGR hardware as well as control logic which can accurately model the EGR gas flow and required ignition phasing.
Methodology
LP-EGR hardware is added to the Hyundai’s new Theta 2.0ℓ T-GDI engine. The base engine is already equipped with high level of internal flow thanks to the variable port flap, 200bar direct injection system and high ignition energy coils which form a good basis for the application of LP-EGR. To generate the pressure differences for the LP-EGR system, a novel 3-way EGR valve is added which throttles the air flow towards the compressor inlet. This enables the possibility to supply the EGR gas in the low load region which is important to realize the fuel efficiency benefit. To develop the control logic, internal rapid prototyping is applied to the base engine management system hardware and software. The control logic for the LP-EGR is developed to account for the non-linearity of the EGR flow as well as the EGR flow phase delay. This allows the accurate control of ignition phasing which could maximize the fuel efficiency benefit.
Results
By applying the LP-EGR to the T-GDI engine using well-designed hardware and control logic, the EGR flow could be supplied in the regions just over BMEP 2bar, and 2~3% improvement in the fuel efficiency could be achieved in regions with BMEP lower than 7bar in the engine test bench. For higher loads above BMEP 7bar which is typical region for LP-EGR application, 4~5% improvement in the efficiency could be achieved. By applying the novel control logic developed, the EGR flow rate and phase delay could be effectively modeled that the combustion phasing remained in optimal region during the transient drive in the vehicle. With the developed control logic, the fuel efficiency benefit of engine test bench could be directly realized in the vehicle, and in FTP 75 combined city and highway mode, 2.5% fuel efficiency improvement could be realized with LP-EGR.
Limitations of this study
The control logic development is focused on the EGR flow rate and phase delay modeling. The control logics for the complete serial production are under development including the diagnostics of the system.
What does the paper offer that is new in the field including in comparison to other work by the authors?
By designing proper hardware and control logic, LP-EGR could be applied and controlled in low load regions just over BMEP 2bar in addition to the normal LP-EGR application region which is low-speed high load region.
Conclusions
By adequately designing the hardware and control logic, LP-EGR could be effectively used in gasoline turbocharged direct injection engines for fuel efficiency improvement. Especially, by modeling the EGR flow rate and delay phase accurately in low load region, significant fuel efficiency benefit could be realized in the vehicle.
Key Words : Low pressure EGR; Fuel Efficiency, EGR control logic, Ignition phasing