RL7
09-21-2010, 02:31 PM
I just saw someone here talking about cng. I posted this in Advanced Technical at 3si, thought it was interesting:
I was looking for a cng fuel pump thinking it may be a well-made high-flowing pump being cng injectors are 1600cc or so. Of course, once I came out of this temporary stupor, I realized compressed gas does not need a fuel pump. At that point I got a little curious about cng and figured I'd look into it.
The biggest issue with running cng is the size and weight of the tanks. The gas is compressed to something like 3600psi. Because of this and the fact that it is in a vehicle, the tanks need to be very robust. CNG is sold in units called Gas Gallon Equivalents (GGE)- this is the amount of fuel that has the same energy content as one gallon of gasoline. For cng this is 126.7 cubic feet (at 1 atm). I found some stats for tanks and a 9.4 gge tank has a volume of 105 L or 27.7 gallons. A 9.6 gge composite tank weighs about 120lb and steel tanks are much heavier. So to have the same capacity we have with gasoline, we would need a storage vessel larger than 50 gallons and it would probably weigh over 200 lbs. That would probably not really be a choice for a car as small as ours, so we would more likely have to sacrifice capacity and carry around 10 GGEs. These tanks are very expensive and are supposed to be inspected every 3 years or after any accident. It would be nice to find one at a junkyard. That isn't completely out of the question since some cars and trucks in the US have been using CNG for a pretty long time. CNG is suprisingly safe.
I think the fuel system has to be completely reworked. As I mentioned earlier, there is no fuel pump, but a regulator instead. The low pressure side is still 100+ psi. You would need giant injectors to make any sort of power.
Now the good part- CNG is rated at something like 130 octane. It can run at much higher compression and/or timing advance and/or boost. This is what initially caught my attention. The other good thing about it is that it does not contaminate the engine oil at all and I believe it runs much cooler. The general consensus seems to be that it is much easier on an engine than gasoline. Recently people are companies starting to attempt to make performance oriented cng vehicles. Volkswagen has two Scirocco GT24 cng powered race cars that have already done well in endurance events. They are supposed to make 330hp or so. Then there's a streamliner by Lessman Racing that is shooting for 400 mph on the salt.
Links:
http://www.volkswagen-motorsport.com/web/news/index.php?&flash=no&lg=e&st=483&id=3834
http://lessmanracing.com/?page=streamliner
CNG is usually a little cheaper than gasoline, but obviously much harder too find. We do produce a good amount of cng domestically though. It would definitely be an interesting thing to try. I'm wondering if you could run cng with high boost and high compression to make a lot of power.
I was looking for a cng fuel pump thinking it may be a well-made high-flowing pump being cng injectors are 1600cc or so. Of course, once I came out of this temporary stupor, I realized compressed gas does not need a fuel pump. At that point I got a little curious about cng and figured I'd look into it.
The biggest issue with running cng is the size and weight of the tanks. The gas is compressed to something like 3600psi. Because of this and the fact that it is in a vehicle, the tanks need to be very robust. CNG is sold in units called Gas Gallon Equivalents (GGE)- this is the amount of fuel that has the same energy content as one gallon of gasoline. For cng this is 126.7 cubic feet (at 1 atm). I found some stats for tanks and a 9.4 gge tank has a volume of 105 L or 27.7 gallons. A 9.6 gge composite tank weighs about 120lb and steel tanks are much heavier. So to have the same capacity we have with gasoline, we would need a storage vessel larger than 50 gallons and it would probably weigh over 200 lbs. That would probably not really be a choice for a car as small as ours, so we would more likely have to sacrifice capacity and carry around 10 GGEs. These tanks are very expensive and are supposed to be inspected every 3 years or after any accident. It would be nice to find one at a junkyard. That isn't completely out of the question since some cars and trucks in the US have been using CNG for a pretty long time. CNG is suprisingly safe.
I think the fuel system has to be completely reworked. As I mentioned earlier, there is no fuel pump, but a regulator instead. The low pressure side is still 100+ psi. You would need giant injectors to make any sort of power.
Now the good part- CNG is rated at something like 130 octane. It can run at much higher compression and/or timing advance and/or boost. This is what initially caught my attention. The other good thing about it is that it does not contaminate the engine oil at all and I believe it runs much cooler. The general consensus seems to be that it is much easier on an engine than gasoline. Recently people are companies starting to attempt to make performance oriented cng vehicles. Volkswagen has two Scirocco GT24 cng powered race cars that have already done well in endurance events. They are supposed to make 330hp or so. Then there's a streamliner by Lessman Racing that is shooting for 400 mph on the salt.
Links:
http://www.volkswagen-motorsport.com/web/news/index.php?&flash=no&lg=e&st=483&id=3834
http://lessmanracing.com/?page=streamliner
CNG is usually a little cheaper than gasoline, but obviously much harder too find. We do produce a good amount of cng domestically though. It would definitely be an interesting thing to try. I'm wondering if you could run cng with high boost and high compression to make a lot of power.