Different hardware approaches implementing low-pressure exhaust gas recirculation during the dynamic operation of turbocharged gasoline engines

Abstract

External exhaust gas recirculation (EGR) provides an opportunity to increase the efficiency of turbocharged gasoline engines. Among the competing technologies and configurations, low-pressure EGR sets the biggest challenge regarding its dynamic behavior. As a result, only some of its feasible stationary potential can be used during dynamic engine operation. This limitation is mainly caused by two circumstances. On the one hand, both, the optimized EGR rate and the EGR tolerance, exhibit inhomogeneous distribution over the engine load, with low values at low loads and vice versa. On the other hand, the volume between the EGR valve and inlet valves is large for the configuration with the exhaust gas supply before the compressor, as it is the case for LP-EGR. Consequently, the time span between the EGR valve adjustment and the change of the EGR rate at the inlet valves is long in relation to the engine’s fast load dynamics. This causes a difference between the set point and actual value of the EGR rate in the case of a negative load step, which can result in low efficiency or even in an unstable engine operation point. The focus of this paper is on hardware variations designed to minimize the disadvantage of low-pressure EGR, while optimizing its efficiency during dynamic operation and preferably attaining its stationary potential. The system portfolio investigated includes different concepts known from the literature as well as self-developed solutions. The analysis of all chosen system configurations is executed theoretically at first, using 1D-CFD simulation. One selected system configuration is investigated in detail with the help of engine test bench measurements. In the end, these results are evaluated with regard to a possible series application.