Quote:
Originally Posted by Hersbird
Right, so lets start a thread on lean burn, that is where the most potential benefits are to be had here, not with vapor carbs. You can do it with custom tuning on standard FI systems. I would bet though just like with manufactures having to ditch lean burn, it doesn't meet modern ultra low emissions requirements. I have long wondered what kind of economy we are giving up at the expense of ultra clean emissions.
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The problem, as you pointed out, is emissions. However, it is not as one would think. NOx drops drastically after about 18:1 mass AFR as the combustion temperatures fall. The problem becomes the erratic nature of lean combustion. When the coefficient of variability (COV) of the pressure trace exceeds 5% of scale, the combustion is defined as erratic. HC and CO spike as unburned or partially burned fuel is found in pockets of low temperature fuel mixes. Early Honda lean burn engines as well as other designs utilized EGR to add heat to the fuel mixture. They ran at 22:1 AFR. However, the slight traces of HC and CO could not be dealt with as well as what little NOx was produced since the traditional three way catalyst could not be used to deal with emissions products in a non-stoichiometric mix. However, if you could strengthen the lean combustion and all but eliminate the hydrocarbon portion of the pollutants you could then deal with the NOx as diesels currently do with NOx traps and a reducing compound.