Gasoline and Other Exotic Fuels.


With the price of gasoline going up I was considering how it relates to buying race gas and other non standard fuels that make an internal combustion engine go up and down and round and round. Just for goofs I wanted to look at the chemical composition of gasoline. Regarding the fact that 50% of it has cat pee in it, the rest is a mixture of hydrocarbons. Gasoline used to contain three basic ingredients; heptane, Iso Octane and tetraethyl lead. With these three ingredients the oil companies used to produce the best gasoline in the world. Iso octane is an octane booster. So is tetraethyl lead(TL). TL was banned a long time ago because it put out rather unhealthy lead by products which humans don’t utilize in a healthy way. So that left Iso Octane as the octane booster. There are some other products that were added but didn’t work as well as TL. I hear all the time when the subject of race gas comes up, how much more explosive and hotter it is than pump gas. This isn’t really true. High octane pump gas and race gas have burn rate controllers in them. These were chemicals like TL, iso octane etc. What they really do is slow down the flame front and promote more uniform flame propagation thru the combustion chamber. When fuel explodes all at once in the combustion chamber of your Japanese SUV, it is called detonation. It’s no different from watching a box of dynamite go boom. Same process. The gasoline rather than burning uniformly explodes all at once. This produces a shock wave that impinges on the piston crown, the valves, cylinder head. Not good for those in attendance! We want a controlled push on the top of the piston not a slug! Octane boosters  prevent detonation and promote the nice smooth push we are looking for. With the advent of computer controlled timing, compression ratios in cars has gone up, even thought the quality of US gasoline has gone the other direction. Higher compression and more spark lead (advance) aggravates detonation in low octane gasoline. So the car makers installed anti-knock sensors in the blocks and heads of the new motors that can “hear” detonation before it really starts happening big time. It sends this information back to the ECM (Electronic control module) which tells the ignition system to retard the timing bit by bit until the detonation goes away. It constantly keeps the timing ramped up close to detonation for the most power and economy. It works well  and allows for high-compression ratios. Higher compression adds power and torque by squeezing the air-fuel charge up tighter. This makes more power. It’s a mechanical power adder that can be designed into an engine without bolting anything on. Cool.

Okay lets take a look at other fuels. I’ll start with ethanol. We all know what this stuff is right? It’s the stuff the oil companies are fond of calling “oxygenators.” Yeah right. Ethanol is a grain alcohol. It’s chemical composition is C2H6OH. So we can call it a oxygenator because it has what’s called a hydroxyl group attached to it that makes it an alcohol. The (OH) part is the hydroxyl. One atom of oxygen and one atom of hydrogen. The rest of the formula contains two carbon atoms and six hydrogen. We have to be concerned with another 25 cent word called “stoichiometry.” This is a geeky name for air/fuel ratio. This ratio is the balance of fuel to air to achieve the best combustion. Gasoline’s best “stoich” is 14:7.1. It takes fourteen point seven parts of gasoline to 1 part air to burn best. Best power is less around 12:1. We also have to be concerned with the fuel’s latent heat energy. Another fancy way of saying how much heat-energy is in each fuel. This is measured in BTU’s. Gasoline is about 20,700 BTU’s per gallon! WOW! Ethanol is near half that at 12,800 BTU. So where are all these numbers going? To see how much energy is liberated we have to do some arithmetic with the numbers here. If you divide the fuels BTU content, in the case of gasoline, by its a/f ratio (14.7) you get 1408 BTU’s burned in one pound of air. Now lets look at what happens when you burn ethanol. More math. So ethanol’s BTU number is 12,800 divided by it’s “stoich” number or a/f ratio of 9 and we get 1422 BTU’s produced in the combustion of 1 pound of air and ethanol. Wow, an increase in thermal output! Not much of one granted but still better than gasoline. Ethanol has a couple of other things going for it besides better energy output, it has a pronounced cooling effect and a naturally high-octane number about 106 methinks. Well watering it down in our cat pee gasoline of today at the ratio of 10% also called “E10” at the pumps doesn’t really do anything for power. If you ran ethanol straight you would notice a slight improvement in power however, probably not very noticeable but I doubt your older car would ping on it either. Moving up the scale in fuels we come to methanol. This is a product of natural gas modification or wood distillations. Methanol is the dark cousin of ethanol. It’s very toxic and if you decide to take a swig of it will most likely kill you and cause you to go permanently blind all at the same time, so don’t get it inside you. It’s chemical composition is; CH3OH. Notice the hydroxyl group on the end? It has a BTU content of 9800. It’s even lower than ethanol, which is an advantage believe it or not. Methanol’s a/f ratio is 6.4:1. So if we divide 9800 by 6.4 we get whoa Nellie! 1531 BTU’s. Woo hoo! A considerable increase in heat energy per pound of air. This is the sole reason why alcohols produce better power in gasoline engines is their latent heat energy and the Air-fuel ratios. Not because they’re explosive, you can see by this that they aren’t even close , not because they’re alcohols and that’s what Robert Mitchum ran in his 50 Ford in the movie Thunder Road. The alcohols by their nature have a very cooling effect on engine components. They are so good at this that because of their air-fuel ratios, some car’s dont’ even bother with radiators! It’s true. Methanol fueled engines run very cool. Their inherent natural octane makes them a very good automotive racing fuel. Methanol for all it’s goodness has some dark sides to it as well. It is corrosive and hygroscopic to aluminum and some older non-nitrophyl seals. Higher compression ratios can be run in normally aspirated engines by a bunch without detonation at all. More spark lead can be and should be run. All of this makes mo powah!

 The last bad boy we come to is Nitromethane. This is the product from the nitrification of propane. It goes thru some other processes too. We don’t want to run nitro in our SUV. Huh uh! Nitro has a terrible octane number of like 50 or 60! It’s air fuel ratio is 1.60:1. It has no hydroxyl group on it because it’s not an alcohol. It’s chemical composition is: CH3NO2. Notice it has two extra oxygen atoms attached to it? Nitro’s BTU content is really in the crapper at 4500 BTU. So more math and we come up with 2813 BTU for each pound of air and nitromethane burned. Holy Cow Bat Man! Big big difference! This fact alone makes Nitromethane a great race fuel. It used to be combined with some very strange and dangerous chemicals to make it get along inside a top fuel motor. I used to see fuel recipes in the old hot rod magazines of the fastest fuel cars of the day. IT’d go something like 10%methanol, 5% hydrazine, 5% benzene, 75% nitro. All the other chemicals were used as “ignition modifiers.” Lighting a 1.60:1 fuel air mixture in the 1950’s and 60s, was pretty good trick because we didnt’ have the great electronic ignitions of today. So they had to jiggle the cans a bit to get it working. Adding hydrazine to nitromethane was a really bad idea. After it set around in the can it would turn into a high explosive all by itself! I’ve heard old horror stories about old nitro cans blowing up at the drag strip when the crews would “toss them over the fence”! Some top fuel teams would really push the envelope and add more nitro than was the norm. This was called “tipping the can.” Yeah nitro used to come in steel five gallon cans. Not plastic carbouys like today. At one time I was about to race a top fuel Harley Davidson. Yep I had some serious brain fade at that period in my life. I had a Boris Murray chassis that Boris hisself built. Boris had a top fuel Triumph motorcycle dragster that featured two 750 Triumph Twins mounted in tandem on the bike. He ran it on fuel. Would smoke the back tire the entire quarter-mile. I got to be pretty good friends with Boris, he is a nice guy. Looked like he walked in off of a Hollywood movie set. Tall, over six feet, thin, dark hair, side burns, and a great smile. Boris told me that most of the Harley racers at the time were not using hydrazine in Nitromethane any longer but instead something almost as bad Propylene Oxide. I never had to worry about mixing up my own fuel and I eventually sold the frame and so ended my career as a top fuel Harley pilot. Guess God had other plans for me A? Well I know this is aimed at a select few but I hope some folks got something out of this? That’s all I want.

Dave .

One thought on “Gasoline and Other Exotic Fuels.

  1. Dave I love the article, You are a generation ahead of me so this is good knowledge! Could you do old eyes a favor and change the color of font?
    I have Olds questions and will contact you soon!
    Best regards
    Doc

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