Well, I had an idea. It would involve extensive modification, but I think it would work.
The idea would be to efficiently burn ethanol. It has an octane around 110 IIRC.
To fully utilize this, you would want an engine with a compression ratio around 13 to 1, and a small camshaft. This would build a lot of compression, and would be a very efficient engine on ethanol. You might as well forget about burning gasoline in it though (can you say ping?)
I dont see another alternative fuel becoming available for spark ignition engines any time soon. As far as I see it, ethanol is the best one, in the form of E85. And to truely utilize its potential, you need higher compression.
well with this ideal you say small camshaft do you mean smaller lobe seperation? I heard once about 'moonshine" used to be ran in cars? question on this would it still be legal to build a stihl.. and burn this... and where would you get a forumal my granpa's dead so I don't know any older folks that may had made it...
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Oh there's plans you can get to build the still. I spent $30 and got some plans on the internet, when I get some time I'll dig up the place. I have yet to build it though. It is legal, but you have to put something in it to make it un-drinkable, as well as get a permit. I have a project engine out in the garage (FE 352) that I was going to build up like this for alcohol, but funds ran out, so it's on the back burner.
On the cam:
What I mean is a quicker IVC (intake valve closing) event. This will allow the motor to build more compression. The more compression is built, the more efficiently the fuel mixture burns. Since alcohol has less BTU's than gasoline, you need the extra efficiency. Fortunately, alcohol has a very high resistance to pinging and detonation, so you can get away with dynamic compression ratios that would be rediculously high with gasoline. So theoretically, with ethyl alcohol, you end up with the same or better power and mileage than gasoline, when the fuel is used to it's full potential. The reason people complain about alcohol in their fuel making them get worse gas mileage, is that their motor was not built to fully take advantage of it.
On compression ratios:
There are two forms of compression ratios. The first is the static compression ratio. This is the one that everyone talks about. It is simply the swept volume over the combustion volume. But there's more to it.
The next is the dynamic compression ratio. The engine only starts building compression when the intake valve closes. Before that happens, the compression is bled off back into the intake. So when you figure compression from the time the intake valve closes, you get the dynamic compression ratio. THIS is what you really need to concern yourself with when building an engine, but most people dont. They hold to old rules about "you use this cam with this compression ratio" and so on. In general, these recommendations will put you in the ballpark, but dynamic compression ratio is the reason behind it. Smaller duration cams generally close the intake valve earlier than longer duration cams. Keep that in mind.
How this has to do with alcohol:
Alcohol has a very high resistance to detonation and ping. Detonation and ping is caused primarily by too much compression. Note, you can have a 10:1 engine that doesn't ping on 87 octane with a long duration cam, where the same engine would ping like crazy with a small duration cam, due to dynamic compression.
With alcohol, you've just changed the rules. Now, you can build an engine with a nice high static compression ratio (like 12:1 for example) AND a short duration cam that will get you good mileage. This is since the dynamic compression ratio will be very high. Even though the alcohol has fewer BTU's than the gasoline, you've just built an engine that will make it work to it's full potential. Power will be good, drivability should be good, and mileage will be good.
Torque1st, Can't agree with you on the tank size thing.....that calculator thing you posted is kinda interesting, but it doesn't give the whole story. Yes, ethanol contains about 2/3rds the btus of normal gasoline. But gasoline can only tolerate something like 9 to 1 compression, and thus burns at about 25% thermal efficiency. Ethanol, with a better octane value (R+M/2 is something like 115 ) and much higher latent heat of vapourization ( 3X gasoline ) can tolerate 12 to 1 with ease. This all gives an ethanol engine much better thermal efficiency, like 35-40 %. So if the gasser is taking in 120K btus and making usefull work out of 30K, and we compare that to the alky burner taking in 90k btus and getting 30-35K of work from it, alcohol can win in liquid miles per gallon, IF, and this is critical, the compression is high enough. An ethanol engine is also harder to start in cold weather, so where you live could play a part. Supposing one were to convert to alcohol and not raise the compression adequately, then, yeah, you would need more of it. The problem is that an 8 to 1 engine can be made to run either, but the 12 to 1 engine can't. DF, @ his Dad's house
Hmm, he makes an interesting point there but again, the same can be said for propane, though the price is going up on that as well. an LPG engine at 12.5:1 is pretty efficient, and if setup right can make an insane pulling engine. Thats the whole reason I bought my truck, it is on propane, its a bigblock, and I know it will run on even 13.5:1 CR, you just really have to watch the temp.
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