CNG car getting 80MPG

[Highmarker]

**Moderator Note--Thread moved from Gen 3 MPG poll thread.

Since I'm the one who selected 80+ MPG, I guess I better tell you how.

First off, this is my first post on Priuschat.com. Might I say, great site. You have a lot of members. This is great.

My equivalent gasoline miles per gallon right now is ~80 MPG. However, when gasoline was $4/gal last summer, I was averaging 170 equivalent miles per gallon. How did I do that you ask? Well, the answer lies in three letters...CNG or compressed natural gas. When gasoline was $4/gal last summer, I was paying $0.63/GGE (gasoline gallon equivalent). I get about 30 MPGGE (miles per gasoline gallon equivalent) but right now I am paying $0.97/GGE, so my gasoline equivalent MPG is ~80.

You hybrid (gasoline - electric) users are just like us CNG users. We all want to do our part in making the environment a better place. We all want to do our part in not giving our money to the oil producing terrorist countries. Compressed natural gas is pulled out of the ground right in the good ol' U.S. of A. If you would like to find out more about CNG and NGVs (natural gas vehicles) please visit cngchat.com. You'll find the forums there are set up just like they are here.

Did you know that Toyota is working on a Camry CNG-hybrid car? You can google it. It is pretty sweet looking.

[TonyPSchaefer]

Thanks for your post, HighMarker, and welcome to PriusChat!

We always like to hear about new ways to reduce our dependency on foreign oil and lower our consumption of fossil fuels. To that point, I have some questions about CNG that hopefully you can answer. (I know you said I could head over to CNGChat.com but for the sake of those who won't, let's bring some of the answers here. Feel free to provide links back to the forum if you want)

Isn't compressed natural gas a fossil fuel and doesn't this mean that it's also a non-renewable resource?

Second, I'm having a hard time with your math. It seems to me that you are not actually achieving 80 mpg but rather 80 miles for the cost of a gallon of gasoline. In my opinion, there's a difference. Here's a scenario I would like to propose: If I purchased gas when it was $2.00 per gallon and stored it in a drum, burning it in my 70mpg Prius when gas prices are $4.00 per gallon doesn't mean I'm now achieving 140mpg. It just means that I paid less for the fuel I'm consuming. In other words, if I pay less for a gallon of gas than the national average, my mileage doesn't go up.

As I say when I'm interviewing people at work to gather information, "explain it to me as though I'm a third grader."

[qbee42]

Tony, the OP can't do a real mpg calculation since CNG is a gas, not a liquid. A gallon of CNG could be almost any amount, depending on how much it is pressurized. Perhaps we could use a miles per unit mass metric.

Tom

[donee]

Hi Highmarker,

I think CNG is a not a great fuel to use in cars. Technically, its wonderful, but in its major usage (heating systems of buildings) its 70 plus percent efficienct, versus the 15 or so the average person would get in a car. Mass usage of CNG in cars with such lousy efficiency would quickly deplete CNG stocks. Do we really want to burn up CNG just to make car brake rotors hot ?

The best automotive use for CNG I think would be as back-up heating for Electric Vehicles in sub-freezing weather. You are still using getting a CNG conversion efficiency better than 70 percent, although its a little wastful, in that a car does not have the insulation of a building.

[Highmarker]

Originally Posted by TonyPSchaefer

Thanks for your post, HighMarker, and welcome to PriusChat!

We always like to hear about new ways to reduce our dependency on foreign oil and lower our consumption of fossil fuels. To that point, I have some questions about CNG that hopefully you can answer. (I know you said I could head over to CNGChat.com but for the sake of those who won't, let's bring some of the answers here. Feel free to provide links back to the forum if you want)

Tony,

Thank you for the welcome. I am definitely out of the league here at priuschat.com for I do not own a Prius nor do I own a gasoline-electric hybrid. My intent of coming on here and posting regarding NGVs is not, by any means, to raise up a firestorm between hybrids and NGVs, but rather to join the torches that each of us have been carrying individually. Hybrids and alternative fuel vehicles have the same goal. To answer you questions:

Originally Posted by TonyPSchaefer

Isn't compressed natural gas a fossil fuel and doesn't this mean that it's also a non-renewable resource?

Natural gas is a fossil fuel. It is finite just like gasoline. But the beauty of CNG is that it is a stepping stone to hydrogen which is a renewable resource. All the system components for CNG are similar if not the same for hydrogen. From storage tanks to fuel lines to regulators to mixers and injectors. The two main differences between CNG systems and hydrogen systems are storage tanks (3,600 psi for CNG and up to 10,000 psi for hydrogen) and gas flow controls (hydrogen is a smaller gas than natural gas).

Originally Posted by TonyPSchaefer

Second, I'm having a hard time with your math. It seems to me that you are not actually achieving 80 mpg but rather 80 miles for the cost of a gallon of gasoline. In my opinion, there's a difference. Here's a scenario I would like to propose: If I purchased gas when it was $2.00 per gallon and stored it in a drum, burning it in my 70mpg Prius when gas prices are $4.00 per gallon doesn't mean I'm now achieving 140mpg. It just means that I paid less for the fuel I'm consuming. In other words, if I pay less for a gallon of gas than the national average, my mileage doesn't go up.

Your assessment of my miles/gallon is correct. I am not really achieving 80 mpg only that I am paying less for a gallon of CNG than for a gallon of gasoline. So my wallet feels like I'm getting 80 mpg.

But isn't it, at the end of the day, what we're all looking for: Have a cleaner environment and make it easier on our wallets. Hybrids and alternative fuel vehicles do both.

[Highmarker]

Originally Posted by qbee42

Tony, the OP can't do a real mpg calculation since CNG is a gas, not a liquid. A gallon of CNG could be almost any amount, depending on how much it is pressurized. Perhaps we could use a miles per unit mass metric.

Tom

Tom,

What you say is partially correct. It is difficult to get a real mpg calculation from CNG because you can't always fill it up to the exact level every time. This is due to the compressibility factors of natural gas such as air temperature and compressor pressure at the pump just to name a few.

CNG is measured in GGEs (gasoline gallon equivalent). This is essentially the amount of CNG it takes to equal the energy that you get from a gallon of gasoline. You can check out wikipedia and search for GGE.

The best way to estimate your mpg on CNG is to calculate your mpg over several fill ups and not just one.

[Highmarker]

Originally Posted by donee

Hi Highmarker,

I think CNG is a not a great fuel to use in cars. Technically, its wonderful, but in its major usage (heating systems of buildings) its 70 plus percent efficienct, versus the 15 or so the average person would get in a car.

Donee,

Please state your source of this statistic?

CNG, which is more than 85% methane, has an octane rating of 130. The optimum compression ratio for CNG is 13-14:1. This is much higher than gasoline which is 8-9:1. If you are running a bi-fuel car (gasoline/CNG), then I can understand having an inefficient CNG system because the compression ratio is lower than optimum. But not as low as only 15% efficient.

If the United States has one of the biggest (if not the biggest) natural gas reserves in the world, why would you want to not use it. Why would you want to give your money to countries ruled by terrorists? And I don't understand the comment: "Let's not use natural gas a vehicular fuel, becuase it will make our rates for heating our homes go through the roof!" So, you're okay to have gasoline rates (keep in mind where the money is going) go through the roof, to keep your heating rates low?

[qbee42]

Originally Posted by Highmarker

Tom,

What you say is partially correct. It is difficult to get a real mpg calculation from CNG because you can't always fill it up to the exact level every time. This is due to the compressibility factors of natural gas such as air temperature and compressor pressure at the pump just to name a few.
<snip>

No, what I said is completely correct. Miles Per Gallon is a meaningless measurement when you are dealing with gaseous fuel. Because CNG is a gas, you need to provide more information to quantify the amount of fuel. Volumetric measurements will work if you also supply temperature and pressure. Mass would be simpler, as in X miles per kilogram.

Tom

[Matt Herring]

If you want a standard CNG to gasoline converter you might want to use this X-Prize link that is widely accepted as the parallel measurement for several different types of "fuel" as it converts usage to the "MPGe" universal measurement. This might settle some disputes on usage in this thread as it puts CNG usage into mpg terms.

[Highmarker]

Originally Posted by qbee42

No, what I said is completely correct. Miles Per Gallon is a meaningless measurement when you are dealing with gaseous fuel. Because CNG is a gas, you need to provide more information to quantify the amount of fuel. Volumetric measurements will work if you also supply temperature and pressure. Mass would be simpler, as in X miles per kilogram.

Tom

Tom,

You and I are talking the same thing here. The National Institute of Standards and Technology (NIST) has defined that 5.66 pounds of natural gas is equal to one gasoline gallon equivalent. This means that the energy you get from 5.66 pounds of CNG (regardless of volume, temperature, pressure, etc.) produces the same energy as a gallon of gasoline. When CNG is dispensed at the pump for vehicles, it is sold as a GGE (gasoline gallon equivalent) which is based off of the NIST definition. Now, where it gets confusing is that natural gas has different Btu ratings depending on the quality of the gas. Typically it is between 890 - 950 Btu/cu. ft. This makes the volume of gas necessary to get 1 GGE between 120 cu. ft. and 127 cu. ft.

I agree with you that measuring your fuel economy in a NGV on a "miles per gallon" basis is not the best way to do it, but what else do we got? Unless you want to weigh your vehicle before and after you fill up. That's why I just average my fuel economy over several fill ups and not just one.