So I know absolutely nothing about chemistry, so can someone explain to me why lead was added to gasoline in the first place? Disregarding its toxicity, what benefit does lead buy you?
> It is a fuel additive, first being mixed with gasoline beginning in the 1920s as a patented octane rating booster that allowed engine compression to be raised substantially. This in turn increased vehicle performance and fuel economy.
"The Man Who Accidentally Killed The Most People In History"
These things are possible without lead as well, it just costs more money to do so.
You can dump as much fuel in the cylinder as you want (in fact, most airplane operating handbooks call for a very rich mixture on takeoff because of the cooling effect).
People have been looking for alternatives for a long time, but it's difficult because leaded aviation gasoline is not a very large market, and there are substantial regulatory obstacles.
But adding high-octane gas to a normal engine doesn't make it go any more boom, in fact, it goes less boom because it doesn't burn as much when it booms.
Modern engines can be designed to advance or retard timing based on knock, so they can run on different octanes and provide different power curves.
And that's exactly where i was wrong :-)
On many modern cars, high octane gas gives you more boom. They are designed for high octane gas, but the engine management computer is able to detect low octane gas and prevent damage from predetonation-- giving up some power.
>They are designed for high octane gas The vast majority of modern engines are designed for 87 octane, and not downrated to 87 octane, because that would give you poorer performance than a clean sheet 87 octane design, and single digit percentages matter here.
There's a whole lot of cars that say "Use premium fuel only" with compression ratios of >10.5:1, but rely upon anti-knock sensors to retard timing (and adjust mixture) to avoid detonation with 87 octane fuel.
I was a professional mechanic around that time, and I had coworkers that thought that not only would high-octane gas give more power, would also swear it increased fuel mileage. Neither is true. High-octane fuel has less energy per gallon than lower octane fuel, it can’t give better mileage. (Now, “mechanic” != “engineer”, but c’mon, guys.)
[0] Yes, Captain Pedantic, I’m aware of knock sensors and computerized ignition timing. It was a quarter century ago.
This stuff started to show up in the late 1970's-- the 1981 280ZX Turbo my dad had was equipped with a knock sensor and would retard timing and add fuel.
By the mid-90's this was relatively common.
More or less, if you want to build a light weight/high power engine you want a higher compression ratio. As the piston travels upward on the compression stroke higher pressures are achieved and this allows designers to take advantage of different crank/cylinder characteristics to make more power in a smaller, lighter package.
We used lead in car gas because engine timing technology and fuel delivery technology were analog/mechanical and really very limited in terms of tuning potential. The cheap hack was just to use a fuel that was more resistant to burning in the first place. Just add a hotter spark/ignition system and it was good to go design wise. Given the old tech running in most GA planes, this was a natural thing to do at the time and the problem was well understood. To point here, modern non-lead additives have been around for a long time and the problem can be adequately solved with a non-lead substitute.
If you wanna get deep with this, take your old normally aspirated car and bolt a turbo on it!
(In comparison, it was well-known at the time that ethanol can also increase octane, and it wasn't protected by patents.)