Quote:
Originally Posted by 2000mc
Lean ratios burn slower, and expose the engine to combustion temperatures for longer durations.
Does anyone know how the ignition timing differs in cars w/ lean burn at a given rpm and map?
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When my Gen1 enters LB the ignition timing advances .. thus tiny bit more time .. I have not logged the exact map of it .. but yes .. at the same 2,000 RPMs LB or non-LB .. the LB has slightly advanced ignition timing for each combustion event portion.
Ignition timing is retarded when my Gen1 enter rich AFR... thus slightly less time.
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Caution however in this line of thinking .. the combustion event might be a fraction of a second longer in LB and shorter in Rich... but the total time of that power stroke per ICE cycle (for the same RPM) is not changed.
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I find it also useful to think of more 'complete' combustion .. closer to stoich and in Rich there are enough unburned hydrocarbons (un-used fuel energy) in the exhaust ... to be used as fuel energy for the NOx Cat .. in LB there are not enough unburned hydrocarbons (unused fuel energy) in the exhaust to be used as fuel energy for the NOx Cat.
2nd thing I find useful .. is ICE efficiency .. the Gen1 Insight ICE was tested and shown that the LB operation improved the BSFC (efficiency) by ~20% .. soo more of the fuel energy was being efficiently converted to shaft work by the ICE while in LB.