Liu, T., Zhang, F., Chao, Y., Hu, Z. et al., "Effect of EGR Temperature on PFI Gasoline Engine Combustion and Emissions," SAE Technical Paper 2017-01-2235, 2017.
In order to investigate the impacts of recirculated exhaust gas temperature on gasoline engine combustion and emissions, an experimental study has been conducted on a turbocharged PFI gasoline engine. The engine was equipped with a high pressure cooled EGR system, in which different EGR temperatures were realized by using different EGR coolants. The engine ran at 2000 r/min and 3000 r/min, and the BMEP varied from 0.2MPa to 1.0MPa with the step of 0.2MPa. At each case, there were three conditions: 0% EGR, 10% LT-EGR, 10% HT-EGR. The results indicated that LT-EGR had a longer combustion duration compared with HT-EGR. When BMEP was 1.0 MPa, CA50 of HT-EGR advanced about 5oCA. However, CA50 of LT-EGR could still keep steady and in appropriate range, which guaranteed good combustion efficiency. Besides, LT-EGR had lower exhaust gas temperature, which could help to suppress knock. And its lower exhaust gas temperature could reduce heat loss. These contributed to fuel consumption reduction. For HT-EGR and LT-EGR, IMEP was similar at every operating point, but LT-EGR had lower pumping loss than HT-EGR, which also helped to reduce fuel consumption. Based on the above-mentioned factors, it was found that LT-EGR could help to reduce fuel consumption by 1%~ 2%, and the fuel efficiency improvement was better at high loads. Engine emissions were also discussed.