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NVSmith · 05-01-2012, 06:37 PM

Fellas,

-I’m neither a chemist not a physicist nor do I play one on TV but something doesn’t pass the common sense test.

-Given: a gallon of gas produces 114,000 BTU, or thereabouts, under ideal conditions.
-Given: a gallon of +/- 180-190 proof ethanol produces about 76,000 BTU also under ideal conditions.

-Then 10% of a gallon of alcohol will IDEALLY produce 7,600 BTU and 90% of a gallon of gasoline will IDEALLY produce 102,600 BTU, the combined BTU rating is 110,210 BTU, about 97% of the rating of a gallon of gas. Since the alcohol will be burning under less than ideal conditions one may infer that the actual total BTU produced will be lower at a given stoich mixture.

-On the other hand, as Christ properly points out, there are other variables to consider. According to what limited research I was capable of understanding, the addition of alcohol will actually LOWER the stoich ratio, but the electronics in the ECU automatically compensate for this. Alcohol, as noted before, also has other effects on engines such as lowering the cylinder temperature thus, perhaps, aiding in more efficient combustion. As Old Mech pointed out the mixture can have adverse effects on emissions. One assumes that there must be some positive effects as well or the government wouldn’t be pushing 10-15% alcohol mixtures.

-Christ, RE: post # 11, can we infer that alcohol has a higher explosive reaction (“rate of detonation” is the term used in my explosives class). Is there a way to confirm this? I also wonder if lower initial residual temperature will, over time, be a true effect. It’s a poor analogy, but a coal stove isn’t very warm during the first minutes of burning, but does finally heat up. Hence the cooling systems built into any internal combustion engine.

-Mech, as an old soldier, your #12, to me, leaves a few things out. Norma lists about 47 gr of 203-B for a 150 gr round nose FMJ. If you were to put 47 gr of #200, their fastest powder, the cartridge might well detonate and demolish the rifle. On the other hand, if you loaded 47 gr of MRP, which is designed for large case capacity in relation to bore size, you might have something close to a squib load. At the very least the velocity of the 150 gr bullet would be very low. Yes, 20mm powder is fairly slow burning. It is also possible that the primer your brother used just wasn’t powerful enough to get the powder going. It sounds as if he had a “progressive burn” where more powder was actually burning the further down the barrel the round went. Friction probably also played a part due to low initial velocity from the chamber. I worked with a black powder riflesmith who taught me how to calculate the length of barrel needed for a given bullet/powder combination. He would start with a known over length barrel and then cut it back an inch at a time until unburned powder particles showed on the snow (or sheet). That signified that the proper sized “combustion chamber” had been achieved. Personally, I’d only use 20mm powder to: a) reload 20mm or b) fertilize my garden. Gunpowder (not black powder) makes great fertilizer. Just don’t smoke while applying it.

-To (finally) wrap up, I’d love to know what a proper alcohol internal combustion engine would look like: cylinder head and piston dome shape; number/size of valves; bore vs. stroke, etc.

-Thanks, guys. This is fascinating!

05-01-2012, 06:37 PM	#16 (permalink)
NVSmith NVSmith Join Date: Apr 2012 Location: MacDill AFB, FL Posts: 10 Thanks: 3 Thanked 3 Times in 2 Posts	Just a few items Fellas, -I’m neither a chemist not a physicist nor do I play one on TV but something doesn’t pass the common sense test. -Given: a gallon of gas produces 114,000 BTU, or thereabouts, under ideal conditions. -Given: a gallon of +/- 180-190 proof ethanol produces about 76,000 BTU also under ideal conditions. -Then 10% of a gallon of alcohol will IDEALLY produce 7,600 BTU and 90% of a gallon of gasoline will IDEALLY produce 102,600 BTU, the combined BTU rating is 110,210 BTU, about 97% of the rating of a gallon of gas. Since the alcohol will be burning under less than ideal conditions one may infer that the actual total BTU produced will be lower at a given stoich mixture. -On the other hand, as Christ properly points out, there are other variables to consider. According to what limited research I was capable of understanding, the addition of alcohol will actually LOWER the stoich ratio, but the electronics in the ECU automatically compensate for this. Alcohol, as noted before, also has other effects on engines such as lowering the cylinder temperature thus, perhaps, aiding in more efficient combustion. As Old Mech pointed out the mixture can have adverse effects on emissions. One assumes that there must be some positive effects as well or the government wouldn’t be pushing 10-15% alcohol mixtures. -Christ, RE: post # 11, can we infer that alcohol has a higher explosive reaction (“rate of detonation” is the term used in my explosives class). Is there a way to confirm this? I also wonder if lower initial residual temperature will, over time, be a true effect. It’s a poor analogy, but a coal stove isn’t very warm during the first minutes of burning, but does finally heat up. Hence the cooling systems built into any internal combustion engine. -Mech, as an old soldier, your #12, to me, leaves a few things out. Norma lists about 47 gr of 203-B for a 150 gr round nose FMJ. If you were to put 47 gr of #200, their fastest powder, the cartridge might well detonate and demolish the rifle. On the other hand, if you loaded 47 gr of MRP, which is designed for large case capacity in relation to bore size, you might have something close to a squib load. At the very least the velocity of the 150 gr bullet would be very low. Yes, 20mm powder is fairly slow burning. It is also possible that the primer your brother used just wasn’t powerful enough to get the powder going. It sounds as if he had a “progressive burn” where more powder was actually burning the further down the barrel the round went. Friction probably also played a part due to low initial velocity from the chamber. I worked with a black powder riflesmith who taught me how to calculate the length of barrel needed for a given bullet/powder combination. He would start with a known over length barrel and then cut it back an inch at a time until unburned powder particles showed on the snow (or sheet). That signified that the proper sized “combustion chamber” had been achieved. Personally, I’d only use 20mm powder to: a) reload 20mm or b) fertilize my garden. Gunpowder (not black powder) makes great fertilizer. Just don’t smoke while applying it. -To (finally) wrap up, I’d love to know what a proper alcohol internal combustion engine would look like: cylinder head and piston dome shape; number/size of valves; bore vs. stroke, etc. -Thanks, guys. This is fascinating!