Effect of EGR Temperature on PFI Gasoline Engine Combustion and Emissions

Paper #:
  • 2017-01-2235

  • 2017-10-08
EGR is thought to be another technique to improve gasoline engine fuel economy and emissions. In order to investigate the impacts of recirculated exhaust gas temperature on gasoline engine combustion and emissions, experimental study was conducted on a turbocharged PFI gasoline engine. The engine was equipped with a high pressure water-cooled EGR system, in which different EGR temperature was realized by using different EGR coolant. One way is using the room temperature civil water named LT-EGR (Low temperature EGR), and another way is to use hot engine coolant named HT-EGR (High temperature EGR). Therefore, the recirculated exhaust gas temperature after EGR cooler of LT-EGR is generally lower than that of HT-EGR. The engine ran at 2000rpm and 3000rpm, and the BMEP varied from 0.2MPa to 1.0MPa. At each operating point, there were three conditions: without EGR, 10% LT-EGR, 10% HT-EGR. The results indicate that LT-EGR has a longer combustion duration and earlier ignition timing at 2000rpm. At high load, CA50 of LT-EGR could still keep steady and in appropriate range. However, CA50 of HT-EGR increases rapidly when BMEP is 1.0MPa. For engine emissions, increasing EGR temperature leads to higher HC emissions, slightly higher NOX emissions at high load and lower NOX at low load. As to CO emissions, the impact is not obvious. It is also found that LT-EGR could help to reduce fuel consumption by 1%~ 2%, and the fuel efficiency improvement is better at high load region. At high speed and high load working condition, the combustion and emissions characteristic difference between LT-EGR and HT-EGR was not evident. LT-EGR is thought to have a stronger inhibition effect on combustion, which can help suppress knock by controlling ignition timing and combustion phase. And lower exhaust gas temperature can reduce heat loss. These contribute to fuel consumption reduction.
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