F2008-06-152
Advanced Cooling Systems for Low Pressure Exhaust Gas Recirculation in a Turbocharged Diesel Passenger Car Engine
Turbocharged diesel engines have acquired a significant share of the European passenger car market and have the potential to develop their presence in other world markets. Nevertheless, an important factor in the success of diesel engines in the future is the ability to find cost effective, efficient solutions to meet increasingly stringent emission standards. In particular, the NOx emission limits for Euro 6 and Tier 2 Bin 5 are difficult or impossible to attain with conventional high pressure exhaust gas recirculation (EGR). One concept under investigation by numerous car makers is low pressure EGR, which enables higher EGR gas flow rates and therefore lower NOx emissions. Some of the challenges of this concept concern the cooling system: the high thermal load associated with cooling the increased EGR flow; the risk of fouling of the charge air cooler; and the occurrence of acidic condensation in the EGR cooler and the charge air cooler.
Engine tests were performed on a medium sized diesel passenger car engine in the Euro 4 series configuration with high pressure EGR and in a modified configuration with low pressure EGR. At operating points with the same air mass flow, the low pressure EGR allowed more EGR to be admitted to the engine and the cylinder to cylinder homogeneity of the air-gas mixture was greatly improved, strongly reducing NOx emissions without increasing smoke.
Once the benefit of the low pressure EGR system was confirmed, testing focussed on the influence of the cooling efficiency of the charge air cooler and EGR cooler on the emissions and fuel consumption. These same tests also evaluated the quantity and the composition of the condensates produced in the coolers. This investigation is important for defining the material requirements and validation tests for the heat exchangers in diesel low pressure EGR systems. Additionally, the management of the liquid condensates as well as other constraints related to the vehicle integration of the low pressure EGR system have important consequences for the heat exchanger technologies. Finally, an understanding of the impact of cooling strategies and operating parameters on the formation of condensation and on the engine performance allows an optimization of the overall system.
Poster presentation: Future powertrain solutions