Replacing Fuel Enrichment in a Turbo Charged SI Engine: Lean Burn or Cooled EGR 1999-01-3505
The objective of the research presented in this paper, is to examine the potential to suppress knock and to reduce the exhaust gas temperature by using either lean mixtures or mixtures diluted with cooled EGR, at high load conditions, in a turbo charged spark ignited engine. Engine tests were carried out with lean mixtures, rich mixtures and mixtures diluted by cooled EGR at various degrees of dilution and at various inlet temperatures. The effects on the combustion process was evaluated at constant brake mean effective pressure for various levels of dilution at two different engine speeds. Full load performance was compared with the standard fuel enriched case.
Both lean homogeneous operation and cooled EGR are possible replacements of fuel enrichment. Cooled EGR allows the use of a three-way catalytic converter at all operating conditions, resulting in substantially lower tailpipe emissions of CO and HC compared to rich operation. Lean homogeneous operation offers an even more substantial tail pipe reduction of CO and HC, but carries a penalty in NOx compared to cooled EGR.