I decided to get all my pesky questions out today. This one is general:
I understand about a lean fuel to air ratio making the engine run hot and increasing the NOx output. What I have never understood is why decreasing the amount of fuel/air/combustion cycle makes an engine hot. It seems like less fuel would make smaller explosions > less heat > cooler running engine.
Well my memory didn't serve me farther then remembering the book to look the facts up in.
From:
Motorcycle Tuning for Performance, by Carl Shipman Copyright 1973
"The reason power is reduced" (my note: And therefore temperature) "is a complexity. The chemical reaction between gasoline and air requires some elevated temperature to start it, after which it should generate enough heat to maintain the burning process.
Combustion moves outward from the point of origin (the spark plug) just like a grass fire spreads from the burning match that started it. Each part of the periphery of the flame front raises the temperature of the adjacent fuel to the combustion temperature. If the grass is green, wet or not present, it won't burn.
Similarly, if there are an overabundance of fuel (gasoline) molecules in the combustion space, they tend to insulate one set of burning fuel-air molecules from the next set and prevent the transfer of heat outwards to unburned mixture. This leads to unburned" (My note: un-used) "pockets of the air and possibly pockets of mixture that never burn at all.
There are other factors. The vaporization of excess droplets of fuel tends to cool down the entire combustion volume, reducing the effective pressure. The fuel vapor exerts part of the total pressure in the cylinder, during induction, reducing the pressure which the air can attain, and thus the weight of air in the cylinder." (My note: reduces the overall amount of fuel air charge, read heat potential)
"The net effect is that power" (My note: and therefore heat potential) "is reduced when the mixture is made rich..."
"Major internal cooling results from evaporation of the fuel droplets..."
I appreciate you looking it up for me, and relaying this complex process.
In the explanation you sight it seems to me that the key is the line: "Major internal cooling results from evaporation of the fuel droplets..."
Paragraph #3 uses the word “overabundance” and paragraph #4 uses the word “excess” so to me they seem to be describing why an overly rich mixture would not produce as much power (heat) as a properly balanced mixture.
Hmm, that sounds fishy to me. To my knowledge, a slightly rich mixture generates more power than an "ideal" mixture, so long as it's not gone overboard.
You are correct Foxpaw. There is an ideal ratio for maximum power around 12:1, different from the chemically correct ratio of 14.7:1. And to mix it all up the Insight by virtue of its stratified charge runs as lean as 24:1 without the detrimental effects that a normal internal combustion engine would suffer.
And all gasoline internal combustion engines require different ratios depending engine temperature, load, & speed. One reflection as to why the lean burn window feels so small.
As so often in life, I was looking for a simple answer to a complex problem. Now that I have learned a little more I see:
-The error of my ways
-The path to greater enlightenment (the library)
-The inappropriateness of using a lot of space here in pursuit of an answer only peripherally related to Insights.
I will restrain myself from inquiring upon the reaction sequence of a fast breeder reactor
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Lean and hot
