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Thread: CNG (Compressed Natural Gas)

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    CNG (Compressed Natural Gas)

    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...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.

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    The Boss Feedback Score 0 arthur92710's Avatar
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    I am also Interested in running dual fuel. The low cost, decreased engine wear and high octane defeat the slight loss in power. I saw a CNG kit on ebay, 6 cylinder, around $450. It came without a tank. LPG might be better as you can use the same tank/gas from your propane grill. Many forklifts run on LPG and its easy to find. Anyone know of a reasonable LPG kit. Are there any legal requirements to run it?

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    I think LNG would be the way to go. A lot more work to get the system working but in liquid form much more capacity and range in the tank. Also you are carring your own coolant for the intercooler. Using LNG to cool the intercooler way below ambient temps would build a lot more power.

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    The Boss Feedback Score 0 arthur92710's Avatar
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    Yeah, it would be cool and high octane. Will there be flames coming out of the exhaust, (Awesome!)?

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    Rice Patrol verified Feedback Score 0 Mean Green's Avatar
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    There was a guy in TN that had an RB20DET in a 240sx that was powered from the same gas used in forklifts...not sure the exact type but he had the tank mounted in the trunk and everything. IIRC it made a decent amount of power.

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    Forum User Feedback Score 0 reallyxxxxxxloud's Avatar
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    CNG was used in my home country of New Zealand for many years but it was a fail. And it is not that safe. There have been deaths from it exploding, hence why the short life testing of the tanks!!! It is if used as a duel fuel it is gutless as hell. Due to the different tuning of the two fuels there's a compromise. In Australia there's a company called "Gas Research", they specialise on LPG and there are some under 11 second drag cars. I used to have a GM Holden HQ GTS that had a red 202 ci 6cl with triple SU carbs and I got sick of having to balance tune them all the time so I went independent LPG with a Gas Research injector plate which replaces the "factory carb setup" (they had direct injection manifolds as well). I noticed about a third power increase. Says a lot in itself. But then again in both fuels if your wanting big big power forget it, the LPG/CNG fuel quality just isn't there and you'll end up chasing your tail...
    Last edited by reallyxxxxxxloud; 10-20-2010 at 01:53 AM.
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