CNG pump compressor DIY home refueling

[vlad]

Let's share info and experience about how to fuel up your car/truck at your home with CNG. After searching the web for a while I decided to start this new thread. Here is what we have:

1. Only few commercial pumps are available for home use. They are all super expensive to buy(5k-7k) and every few thousand hours you have to pay 2k to rebuild it.

2. What kind of equipment is used to pump CNG? In most cases it is 3-4 stage reciprocating piston compressor. The same technology is used for high pressure compressing air, nitrogen and other gases.

3. I found some info about one pump that uses hydraulics to compress CNG. Very good idea but.... It costs 6.5k and I can't find even one real review from somebody who used it....

4. I found some info :

http://www.youtube.com/watch?v=kzSiL3h2pUU

He used Bauer high pressure air compressor modified to pump CNG. I have no details but it seems to me he vented crank case to intake and vented safety pressure relief valves (they are after each stage to protect from over-pressure)

5. I found some info about using low pressure CNG and active carbon (adsorption method): http://web.anl.gov/PCS/acsfuel/prepr...03-96_0246.pdf
This is very cool but I don't have enough equipment to test it.... Also Carbon will add extra weight to already heavy tanks and it is not cheap

[vlad]

My own project is like this:

1.I have a diesel truck and I want to add CNG to get better fuel economy and extra power...

2. I only need 2 GGE for my daily driving. 50% CNG 50% diesel will give me 60-70 mile range. If I need more I can just use diesel...

3. As a DIY project I will try to keep pressure as low as possible/practical. My tanks are 3 ft3. To get 2 GGE@ 3 ft3 I need to pressure CNG to 1200-1300 Psi.

4. I don't like 3-4 stage air compressors because they are noisy, expensive, run very hot, expensive to fix/rebuild....

5. I am thinking about "hybrid" system:

1 stage is going to be AC compressor (York 210 style). It will boost pressure from 2 Psi to 200 Psi. This compressor is a real beast and can run 200 Psi all day long. Cost is low ($50 used-$150 new) parts are cheap. Easy to fix. Compressor will be turned by hydraulic motor.

2 stage is going to be hydraulic cylinder pushed/pulled by another hydraulic cylinder

I decided to use hydraulic power unit to run compressor (via hydraulic motor) and hydraulic cylinder (hydraulic side). In this case I can put power pack isolated from gas compression unit and I don't need to worry about arks and sparks....

Now let't talk about CNG....

[P-hack]

the costs of compressing it are not trivial when compared to electric vehicles.

per: Wise Gas Home Refueling

it looks like it takes about 2kwh per gallon equivalent to refuel w/CNG. A nissan leaf takes about 22kwh to recharge, and the cng still has a major efficiency hit when it gets converted into power in the ICE, so say 22kwh is ~2 gallons worth of cng. The cost of compression is very roughly 1/6 the available power of the cng.

[vlad]

The problem is it only takes 5 Nissan Leaf to move my boat or a trailer....

Bicycle is even better you need nothing no gas no electricity, no even licence, but we are all drive our cars and trucks.....

Here in Canada 1 liter diesel = $1.4

Last month I used 270 Liters diesel equivalent CNG for heating cooking etc my home. I paid total $100 for it. 100/270=37 cents/Liter 1KW electricity cost 10 cents, so even if it adds 5 cents per liter equivalent 37+5=42 cents is still a sweet deal compare to $1.40....

I know that CNG burns cleaner, it is better than diesel for environment, it is good for diesel engine you can extend your oil changes etc, but question is how to get it in my tank???

Let's talk about pumps......

[P-hack]

Do you drag your boat 70 miles/day?

[vlad]

The cost of extra vehicle and it's insurance and extra maintenance doesn't make sense to me.

[P-hack]

Is a diesel CNG conversion like $5000? plus $6000 for cng@home? how many years/decades till you break even (assuming NG & electric stay low cost)?

I could see something low-tec/low pressure, i.e. propane liquifies fairly easily, so separate it out from the NG for your vehicle and use the rest for heating? But compared to a $2k 5 speed beater with basic liability insurance, you are looking at a large money hole IMHO.

[euromodder]

If you're into the global warming greenhouse thing : don't vent methane into the atmosphere.

This kind of DIY set-up running @ 3600 psi gives me the creeps.

[P-hack]

yah, don't vent methane. Just looked it up, the propane is like %5 of NG anyway, you would need to heat a school year round to keep up with the excess methane. Even at 3600 psi NG is ~1/3 the energy density of gasoline.

I don't think you can simultaneously "go green", drive your diesel truck everywhere, AND save money. Not without a fair bit of sweat equity anyway.

[t vago]

If you're looking to improve the efficiency of your Diesel truck, why not do something like add a CAI, or add water injection, or put in a freer-flowing exhaust or induction system? Diesel engine efficiency is related to how well it can pass stuff within it (freer-flowing exhaust and induction), as well as how much stuff it can pass (colder air or water).