Mike Croley wrote:David Redszus wrote:Oxygenated race gas like Renegade K-16 , will always make more power in a normally aspirated engine than non - oxygenated gasoline .
Sorry, that is not even close to being correct. There are several reasons.
The presence of oxygen (which has NO BTU value) must displace hydrocarbons (which do have BTU value), and so more fuel is needed just to get back to the same starting point.
If two fuels were identical in every respect except for oxygen content, some conclusions could be drawn with adequate testing and optimized tuning. But that is not the case. Oxygenated fuels are completely different in the composition, evaporation characteristics, BTU potential, ignitability, completeness of burn, etc, etc, etc.
The real trick to fuel evaluation (besides what the engine likes or does not like) is to know the distillation curve and the stoich value. Or a good fuel chemist.
That's an interesting hypothesis David , not correct , but interesting . As to larger jetting when using oxygenated fuels , i doubt that would come as much of a surprise to anyone . In fact , most oxygenated race fuels have that very suggestion in their spec sheets . In your final observation , you're right . The real trick to fuel evaluation isn't a trick at all . It's the lessons handed down from long hours on the dyno over decades by hundreds of thousands of engine builders learning what engines do or do not like .
Sorry Mike, but it is absolutely correct.
Just because a fuel contains an oxygenate, does not mean it must be run richer or with larger jets (or re-mapped). What matters is not oxgenate content but rather fuel stoichiometic value. And that comes as a big surprise to some folks who sell fuels.
Experience with a specific engine is indeed valuable and the engine is the final determinant in fuel selection. But builders might not have any experience with newer fuel blends or blends with altered characteristics. Now you can either spend thousands of dollars and hundreds of hours, through a trial and error process, trying to find the right fuel blend for that engine.
Or you can enlist the assistance of someone who knows fuel blends, and when coupled with in-cylinder combustion pressure measurement, will find the correct solution very, very quickly. Without the destruction of engines that normally accompanies trial and error tuning.
I don't know how this "logic" can be valid or not but none of the fuels will be burning at the correct, best stoichometric ratio because the "compromised" AFR. The alcohol will be burned with too much air to make best power (lean burn) and the gas will be burned with too little air to best power (rich burn).
The alcohol and gasoline do not burn separately. The required fuel ratio is a function of the weighted mass average of the stoich value of each fuel component. Gasolines typically have many components, (50 for race fuels, 450 for pump gas), each with different characteristics. Alcohols typically only have two components, alcohol and water.
As the blend components of a fuel are changed, so are ALL the aforementioned characteristics that affect optimum evaporation, ignition and combustion.
One might ask, why do Formula One teams have very close working relationships with oil company fuel chemists?
Maybe they know something.