Quote:
Originally Posted by acparker
Soot filter, or, alter the combustion mix to lower soot production.
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Carbon traps work fine for micro meter sized particles. GDI engines produce sub micro to nano meter sized particles. Standard traps would be largely ineffective.
Altering the combustion mix is not so much the issue as how and when the mix is injected. Also, how much EGR is being used. GDI engines usually inject well after all the valves have closed to provide maximum entrapment of air so no oxygen displacement occurs. But, this leaves little time for evaporation of the droplets and that leaves some small droplets in place when combustion starts resulting in fine carbon being produced. Also, side reactions become railroaded and thus you get hydrocarbons such as benzene slipping out of the tailpipe. Higher intake temperatures as well as an increase in mixture tumble and swirl help reduce carbon particles but they increase NOx.
Catalyst charged traps are in the works and this should just about eliminate the bulk of the black carbon soot. Also, increased fuel pressure and injector tip design will help reduce carbon formation much as has happened with diesels. At some point, lean NOx traps may make their way onto GDI engines to free up the design parameters.