Comparative Analysis of Pre- and Post-Catalyst Exhaust Gas Recirculation Systems for Turbocharged Spark-Ignition Engines

Abstract Low-pressure exhaust gas recirculation (LP-EGR) systems are widely used in current spark-ignition engines due to benefits in knock control, heat transfer losses, and pumping work. Usually, the gases are extracted downstream of the aftertreatment system (ATS). Consequently, an intake throttle valve or an exhaust backpressure valve is required to ensure recirculation at low speeds and loads, increasing the pumping losses. The current work explores the potential of an alternative architecture where the exhaust gases are extracted before the aftertreatment system to reduce such losses and increase fuel efficiency. For this purpose, a fully instrumented 1.3 L turbocharged direct-injection spark-ignition engine with variable valve timing (VVT) and a Euro 6d aftertreatment module is employed. Both pre- and post-aftertreatment extraction architectures are implemented, using the same LP-EGR cooler and overall length to minimize the variations induced by the pressure drop of the LP-EGR line itself. The results show that at low and intermediate speeds and loads, the exhaust gas extraction before the aftertreatment does provide around 2% lower fuel consumption for most of the operating conditions, thanks to the expected benefits in pumping work. However, as the speed and load increase, combined deteriorations in the compressor inlet temperature and the combustion performance for the precatalyst layout shorten the fuel consumption benefit, making both layouts equivalent.