Quote:
Originally Posted by mja1
The main reason we have EFI is to tune exactly to spark. The point where carbs become more efficient is above 26-27:1 AFR.
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Not just for the spark... EFI at it's core is about precise control of the Fuel ... it is commonly used in spark ignition engines ... but that is for other reasons... not for any need of a spark for a EFI system.
I can give you
sources of a OEM EFI engine being tested to run at up to a peak of 25.8 : 1 ... do you have any examples to share of an carb based OEM ICE test showing the 26+ you claim here? ... or any non-OEM modded system?
AFRs more than a certain point are not even readily combustible ... it is the combination of a swirling effect with the tuning of the spark just right that can allow for the effective combustion of a very lean AFR... the swirling EFI can create intentionally uneven AFR points inside the combustion chamber , in controlled ways and controlled timing ... and for effective LB high AFRs this is beneficial... in a general AFR that is not otherwise effectively combustible the controlled swirling effect and timing of a EFI system can achieve combustion where it could not be achieved otherwise...
In theory a modern EFI system like this can be used to run even non-spark / compression ignition engines at higher AFRs than they would be able to achieve otherwise ... I don't see a Carb based system being able to do this.
Even modern diesel engines without an hypothetical EFI system take advantage of a noneven AFR mix in the combustion chamber in order to achieve combustion of AFRs leaner than would be possible at a even AFR mix.
Carb based systems have inherently less control of the fuel in the combustion chamber than a EFI based system does... the carb based system concept is dependent on the concept of a preAFR mix ... this concept does not allow for the same level of precision fuel control in the combustion chamber that a EFI allows.... a premix or an even mix is not always the best mix in the combustion chamber itself.
Although at high enough AFRs it is reducing , not improving ICE net operating efficiency ... and without higher net operating efficiencies you aren't increasing MPG or FE any more.
Quote:
Originally Posted by mja1
I guess I wasn't clear that the idea couldn't be achieved on any old stock carb. Or any old engine for that matter. It'd be a very tricky process
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Which would exclude the entire market for the '200' MPG carburetor.
Are you thinking of an experimental ICE design from the ground up?
Quote:
Originally Posted by mja1
Most FI systems run at least 30psi (most stock ones 45-65), where carb can run less than 5psi. Much easier to 'preheat' a lower pressure fuel.
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I don't see any reason why the pressure of the fuel has any significant effect on how 'easy' it is to preheat ... the amount of energy needed to raise a given amount of fuel any arbitrary temperature is purely a function of the specific heat of the fuel and the total mass of fuel being heated.
I also don't see a low fuel pressure being a significant advantage ... if anything I see it has been well proven as a significant disadvantage in many ways.
I also don't see a net efficiency benefit of spending fuel energy to preheat the fuel above the amount of preheating one can get from the ICE's operating waste heat... and 450+ is significantly above that point.
Also , Preheating the fuel is a very different topic from the 200 mpg carburetor ... it works for and on different principles.