Influence of a low pressure EGR loop on a gasoline turbocharged direct injection engine

This paper presents an experimental study of a low pressure EGR loop on a spark ignition (SI) Gasoline Turbocharged Direct Injection (GTDI) engine that will improve the understanding on the advantages and disadvantages of this strategy. Two steady engine operating conditions were investigated, 10 bar and 17 bar at 2000 rpm. At partial load conditions a combustion, performance, air management and exhaust gas emissions study was performed in order to analyses the EGR effect on the GTDI engine. The main advantages found were the reduction in fuel consumption due to the better combustion phasing, and the reduction in pumping losses and heat losses through the cylinder walls. A reduction on NOx, CO and soot was also observed when introducing EGR at these operating conditions. The main disadvantage found was the water condensation after the intercooler. At high load conditions similar analysis and conclusions to the partial load conditions are obtained. The EGR also allowed the combustion to be phased in a more efficient angle by reducing the risk of knocking, which helped reduce the exhaust gas temperature, despite the elimination of the fuel enrichment strategy. A reduction on CO and soot raw emissions was also observed when introducing EGR, as observed at partial load conditions, but a high reduction in NOx, CO, HC and soot emissions was observed after the catalyst since the fuel enrichment strategy is eliminated when cooled EGR is introduced. The main disadvantage found was the turbocharger limitation since higher compression ratio is required in order to keep the same air mass flow as the reference conditions without EGR. The original turbocharger is not designed to provide this higher compression ratio at low engine speed and high load. Results confirm how introducing EGR is a suitable strategy to control knocking and reduce simultaneously exhaust gas temperature and fuel consumption, but the disadvantages found in this investigation must be solved to assure its feasibility as a powerful technology to be implemented in future SI engines.