Effects of LP and HP cooled EGR on performance and emissions in turbocharged GDI engine

Abstract

An experimental investigation was performed with a view to comparing low and high pressure exhaust gas recirculation fixed on a turbocharged GDI engine, focusing on analyzing their impacts on fuel consumption, combustion process and pollutant emissions. Following reference condition (EGR=0), the main engine and turbocharger parameters were measured and comparative analysis of four load operating conditions with LP and HP EGR was investigated. A mean pressure balance, which referred to engine heat balance theory, was introduced to facilitate analyzing engine energy conversion processes. The optimal combustion phase, caused by ignition advance due to the EGR dilution effect, became vital factor for reducing BSFC. At high load, PMEP didn’t contribute to the decrease of BSFC with both LP and HP EGR; at partial load, however, PMEP played an important and positive role in the decrease of BSFC. And their different operating principles, caused by LP and HP EGR, were analyzed. In exhaust emission, NOx and CO emissions were reduced because of the lower combustion temperature and the extended combustion duration. The high speed and high load condition with HP EGR allowed the engine to operate nearer to stoichiometric condition, the result of which lead to the decrease of unburned THC, THC emissions increased with the other operating conditions.