Compressed Natural Gas...I'll try to answer your questions

Discussion in 'Performance & Fuel' started by Highmarker, Jun 14, 2011.

  1. Highmarker

    Highmarker Rockstar

    Several members have asked that I "spill my beans" on compressed natural gas (CNG) vehicles or natural gas vehicles (NGV).

    First off, I will tell you a little about myself. I am a design engineer working a company that does research and development on composite overwrapped pressure vessels (COPVs) - like paintball cylinders, self-contained breathing cylinders (SCBA) for firefighters, compressed natural gas cylinders, high pressure hydrogen cylinders, the list goes on. I have designed and tested my fair share of high pressure (3,000 psi +) tanks.

    Now onto the world of CNG. NGVs have been around for a long time, the first NGV was invented back in the 1920's. NGVs have slowly gained some ground and now there are approx. 150,000 NGVs in the US today. There are two main reasons why NGVs have not taken over the automotive industry like in other countries:

    1. Chicken and egg issue - What do you have first, cars that run on natural gas or fueling stations to fill the cars that run on natural gas? The automakers don't want to mass produce NGVs because there is not a lot of fueling stations. The fueling station manufacturers don't want to make fueling stations if there are no NGVs to fill up.

    2. Three letters - E.P.A. - This is a heated topic. There are good arguments on both sides. The EPA is concerned because it is possible to convert a vehicle to run on both gasoline and CNG and have the CNG burn DIRTIER than gasoline. Yes, CNG can burn dirtier than gasoline. If the guy doing the conversion does not know his stuff, then you can burn up a cat in no time and also either the hydrocarbons, CO, or NOx will go through the roof. The EPA has a mandate out that it is illegal to tamper with the OBD emissions system of the original manufacturer unless you have an exemption from the EPA to do so. This is only valid for a vehicle which is within its "useful life". This has created a "bottle neck" for aftermarket conversion shops to convert vehicles to CNG. The EPA has recently relaxed their rules a little bit but still require that the converted vehicle be tested to prove that it runs cleaner on CNG than on gasoline.

    With NGVs, safety is the main concern. All CNG converted vehicles should comply with NFPA 52 installation code. High pressure gas is a serious thing and should not be underestimated. Now, don't be scared, CNG is actually safer than gasoline. When you get into an accident, and your gasoline tank is punctured, the gasoline just pools on the ground and if there is a fire - bye bye. With CNG, when there is an accident most likely the tank will not rupture (it is designed to withstand serious loads). If there is a fire, the natural gas will not ignite. Natural gas can only ignite if the air-fuel ratio is between 5% and 15%. In other words, not enough air - natural gas will not ignite, too much air - natural gas will not ignite. If your tank vents the gas due to a fire, then the gas will float away. Natural gas is lighter than air.

    The key here is finding someone who "knows their stuff" on performing a good solid conversion. I have seen my fair share of shady conversions that even scare the crap out of me. Don't sacrifice safety for money.

    Now on to your questions....
  2. Caddiac

    Caddiac Epic Member 5+ Years 1000 Posts

    So what kind of range can you expect out of CNG compared to gasoline on a per unit basis? Where do you buy it?

    I have heard of companies in California that sell home CNG units but they are not available outside of California. The home unit basically fills you tank from the natural gas line running to you home. That would be a viable option for me since I do not know of any place near my home where it is available.

    What kind of cost to convert a typical v8 to run on CNG?
  3. aloxdaddy99

    aloxdaddy99 Epic Member 5+ Years 1000 Posts

    I know that in Norfolk VA one of the utility companies use CNG to power their fleet of cars. I don't think they use it in their utility trucks but they do use it in the cars the meter readers drive and cars like that. I was told (never looked into the truth of it) that if a company had CNG that they also had to make it available to the public. Most likely at a higher price. When I lived in the Tidewater area I worked at a compressor company that manufactured service pumps to fill CNG cylinders. I think they got in on it early hoping for the big CNG boom.
  4. ChromeSilver02

    ChromeSilver02 Epic Member 5+ Years 500 Posts

    This is some great information Jared, I am also an engineer so I am familiar with E.P.A strict guidelines. LOL. But from your experience what is the usually the pay back period for a CNG vehicle?
  5. Highmarker

    Highmarker Rockstar

    First off, CNG is measured in Gasoline Gallon Equivalents (GGEs) see

    There are three types of NGVs:
    1. Dedicated - these vehicles run exclusively on CNG. The engines in these vehicles are specifically tailored to CNG. The miles per gge are comparable to their gasoline sisters. Example: Honda Civic GX and Honda Civic LX get approx. the same miles per gge or miles per gallon.

    2. Bi-fuel - these vehicles can run on either gasoline or CNG. The engines in these vehicles are tailored to run on gasoline. So when running on CNG, they are not optimized for fuel economy nor power. Typically at highway speeds there will be little if any notice in miles/gee versus miles/gallon. City driving is different. On CNG, the miles/gge is lower than miles/gallon on gasoline.

    3. Dual-fuel - These vehicles are diesel/CNG vehicles that run about 70% CNG and 30% diesel at the same time. I don't have much experience with these vehicles, but from what I've heard they have increased horsepower.

    BRC Fuelmaker makes a vehicle refueling appliance or VRA. Yes you can use the natural gas in your home to fill your CNG vehicle. They are available almost anywhere natural gas is used in the home (even outside of California). The most common unit is the Phill, but BRC Fuelmaker makes other models as well.

    The cost on converting a typical V8 is about $8,000 - $12,000. The most expensive component is the CNG tank. Tanks vary in price by size. A brand new 20 GGE tank is about $3,500. Depending on the type of system that is installed the price may go up or down. The most inexpensive system is what is known as a fumigation or aspiration system. This system dumps the natural gas into the air intake. The most common system now days is the injection system. In a bi-fuel vehicle, a CNG injection system is totally separate from the gasoline injection system. On my truck I have two injectors per cylinder. So I 8 gasoline injectors and 8 CNG injectors.

    ---------- Post added at 06:40 PM ---------- Previous post was at 06:28 PM ----------

    Payback period depends on two things:

    1. Tax incentives - Each state is different on how much you will recieve as a tax credit for converting or purchasing a NGV. You need to check with your state and see if there are incentives for NGVs. For example, in Utah there is up to a $2500 tax credit for converting or purchasing a NGV.

    2. How much you drive versus how much CNG is at the pump - Again this varies from station to station and state to state. See and see how much CNG at the pump is near you. On that note, most of the stations in California, New York, Arizona, Nevada, and Colorado are owned by Clean Energy. They buy the natural gas from the utility company and compress it and sell it at the fueling station. Clean Energy's CNG is typically 50 to 80 cents cheaper than gasoline in that area. Utah and Oklahoma are different. In those states, the fueling stations are ran by the local gas utilities and their prices are set by the state's public service committee (PSC). It literally takes an act of Congress to raise or lower the price of CNG in those states.

    Here is my example on payback:

    In 2007 I bought a 2001 Chevy Cavalier (bi-fuel) for $5300. I got a $2500 Utah tax credit and I was saving 6 to 7 cents a mile when running CNG. So, in just over 43,000 miles the car had paid for itself ((5300-2500)/.065=43077) and then any miles driven after that is pure savings.

    If you would like to do some digging about CNG yourself see there is a wealth of information there.
    Last edited: Jun 14, 2011
    1 person likes this.
  6. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    That was good reading Jared. Thanks for the info.:great:
  7. Highmarker

    Highmarker Rockstar

    You're welcome. I have been involved with NGVs for about 5 years now. Hope you win the ROTM voting. (I voted you for you) Sweet ride.
  8. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    Thank you for your vote.:great:
  9. stephan

    stephan Rockstar 4 Years 5000 Posts

    That's some good info Jared, Thanks:great:
  10. Highmarker

    Highmarker Rockstar

    The biggest difference between gasoline and CNG vehicles is obviously the high pressure natural gas. Typically the CNG system is has a max pressure of 3,600 psi with some systems designed for 3,000 psi. At a typical fueling station there are dispensors for both 3,600 psi systems and 3,000 psi systems. The tank is not like your gasoline tank. In fact, CNG tanks have expiration dates. Most tanks have a 15 year service life from the date of manufacture. That means that once the expiration date has passed, the tank must be removed from the vehicle and destroyed. This is regardless of the condition of the tank. The tank must also be inspected by a certified inspector for any damage or deteriation.

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