Quote:
Originally Posted by drmiller100
Quote:
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Originally Posted by t vago
For straight gasoline, maximum fuel economy is seen at an AFR of 17:1.
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The above statement is probably true under certain conditions, but many more examples abound where it is untrue. |
Just my 2 bits
Honda's Lean Burn in the Gen-1 Insight does go significantly above this ... been independently
tested to go as lean as 25.8:1 ... I suspect Honda ICE engineers have a firm grasp on ICE engineering ... ie they wouldn't have gone that lean 25.8:1 as a peak or as lean as the 22:1 they have published for this engine as a more general case lean burn AFR ... if it was going to hurt net ICE operating efficiency.
While that by itself might lead someone to think that Honda's leaner lean burn is automatically evidence of leaner is better efficiency ... I would caution against that kind of direct leap... this specific ICE could very well be an exception to a more general ICE rule of thumb ... and there might have been other engineering motivations to design this than for higher peak efficiencies.
There are a variety of reasons they might have done that to improve the net operating vehicle efficiency ... some of them are for better conversion efficiency ... but better under specific conditions might not be the peak efficiency point for a given ICE .... or from another perspective ... it might be used as a method to mitigate other potential sources of low efficiency.
Raising the efficiency of a low efficiency point in the operating range for a ICE might still not be the peak efficiency point for that ICE ... thus the peak efficiency might not be increased ... even if the efficiency at a specific low efficiency point is increased ... or even if it allows for the net operating efficiency is increased.
Just because it allows for the net operating efficiency to be increased ... does not mean these leaner AFRs being run all the time would also increase the net operating efficiency over the entire ICE operating window.
In the Honda Gen-1 Insight case ... the ICE was designed for it ... AFR changes , the timing changes, V-Tech on/off, etc ... they didn't pick one thing for the whole ICE operating band ... they made a very dynamic system that can change the operating characteristics of the whole engine significantly ... and a lot of those dynamic changes they are making are happening fairly quickly ( by human standards ) and automatically in the background.
So while 17:1 AFR may or may not be the peak ICE AFR for highest net operating efficiency always for all contexts and conditions and for all straight gasoline engines ... unless you want to get a lot more complicated in a custom designed and built ICE with a more dynamic system ... it might be a good enough rule of thumb for a significant majority of most cases... which in this context of aftermarket mod of a OEM ICE , might not be a bad place to start.