Clean EGR for Gasoline Engines - Innovative Approach to Efficiency Improvements and Emissions Reductions Simultaneously

Paper #:
  • 2017-01-0683

Published:
  • 2017-03-28
Abstract:
External EGR has been used on diesel engines for decades. It has also been used on gasoline engine in the past. It was recently reintroduced on gasoline engines to improve fuel economy at mid and high engine load conditions, where EGR can reduce fuel enrichment. Fuel enrichment causes fuel penalty and high soot particulate numbers, which will be limited by Europe RDE legislation from 2017 onwards. Under stoichiometric conditions, gasoline engines can be operated at high EGR rate (> 20%), but compared to diesel engines, it needs extreme cooling (~50°C) to gain the maximum fuel economy improvement. However, external EGR and its problems at low temperatures (fouling, corrosion & condensation) are well known . To avoid this, Tenneco introduced a coated Gasoline Particulate Filter in the EGR loop to clean the EGR gas by removing particulates, HC, NOx and CO. Only CO2, N2 and H2O will remain in the cleaned EGR. After cooling of cleaned EGR water condensation appears clearly with neutral pH-values and almost no particulates. This characteristics allows cleaned EGR to cool down with less risk. Using cooled clean EGR, gasoline combustion temperature is reduced significantly, which reduces engine knocking, engine-out soot particulates, engine heat losses and fuel consumption at the same time. Engine testing with cooled clean EGR at high loads confirmed that fuel consumption can be reduced by more than 10% and particulate numbers by more than 75%. Engine knocking was suppressed and exhaust temperature was reduced noticeably. This allows a significant increase of engine compression ratio improving fuel economy in the entire engine map further. To ensure this benefits an effective EGR cooling system will be required. The technology for cooled clean EGR is available and will be a strong enabler for significant fuel economy improvement of gasoline engines in the near future.
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