Thursday, August 21, 2008

CNG - a month's view

Well, I'm home, I've got the truck, and it runs fine. Looks like eBay came through this time. I'm still a bit leary about making eBay purchases though. Now, what about this crazy CNG thing?

Let me start with the one shortcoming I've found. I was semi-aware of this from my research, but after actually living with it, I think it's a reasonable trade-off for the advantages.

The big thing is getting "enough" CNG. To explain this, you have to understand the fueling process. CNG tanks are high-pressure systems. The tank is pressurized to 3600 PSI (full). Natural Gas as its is transmitted to homes/etc is relatively low pressure (150 PSI I think). There-in lies the problem. You can't pressurize a 150 PSI feed directly to 3600 PSI (the pipe can't keep up), so you have to pre-fill a large storage tank at the fill station. Compressors take it off the pipeline and pressurize this big tank to 3600. The fueling pumps then fill your vehicle from this storage tank.

The problem is that when you have vehicle after vehicle filling up, the use the pressure in the tank faster than the compressors can replentish it. So the 3rd or 4th or 10th vehicles get progressively less pressure at fill-up. I've gotten fills as low as 1800 PSI. (3-4 gge). This leaves me sitting with around 1/2 a tank and the pump won't dispense more. More typical is to get around 2300-2500 PSI. The end result is that if I don't leave Tulsa with at least a 2300 PSI fill, I probably won't have enough CNG to get all the way back to the station. There have been a few mornings where about the time I get to Sand Springs, it cuts over to regular gasoline.

Still, I'm saving money. I've used 1 filled up with regular gas once since I've been home from the trip (a bit over a month), and am averaging about $5.50/day on CNG. I've still got 3/4 a tank of regular gas since that fillup. My estimation is that I'll use 1 tank of gasoline a month. Sure beats the heck out of 2 tanks a week!

My savings won't be quite what I expected if I'm forced to use regular gas, but the other benefits are worth consideration too. I'm not putting money in OPECs pocket at nearly the rate I was... my money is staying in Oklahoma. I've got a truck, which means I'm not dependent upon other people to haul stuff for me. I'm contributing to a cleaner environment as well.

Overall, I'm happy with the choice. If I had NG available at my land, I'd seriously look into one of those home filling systems, and would never burn a drop of regular gas unless I was going out of state.

Take a look at this site

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