Compressed Natural Gas (CNG) conversion to cars- any experience?

[QC]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

CNG octane is 130 [(R+M)/2]

Try this chart out. It shows 120+ (R+M)/2 for "CNG", and 104 for Propane.

One issue is that CNG can be made up of different ratios of Methane and other stuff. 99% pure methane is fairly common in the US, even in many pipelines. Buuuttt, you can also get below 90% with the rest being Ethane, Butane, Propane etc. Even inerts like Nitrogen. It's a problem. LPG, you have the same issue. Propane is not the only thing you find in LPG, and what we really buy most of the time is LPG, not literally "propane".

 

[halfmoa]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

One issue is that CNG can be made up of different ratios of Methane and other stuff.

Very good point and possibly one of concern...

 

[dolluper]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

Research octane. 112 funny how old is this.....nice table though

 

[QC]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

RON is still used Internationally . . .

 

[dolluper]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

Vehicle proprane in the states is 110 octane......supposed to contain butane

 

[Scott Danforth]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

The only reason CNG delivers lower power is that it displaces air in the cylinder. Propane too. Both have higher Octane. Natural Gas, primarily methane, is higher. 140 - 120 I think, but I'll look into that. If the engine is built around that, you can get very good performance, but of course with conversions they are built for gasoline. Propane is rarely, if ever, as low cost as Natural Gas and has bigger seasonal price swings. Propane is indeed easier to handle, store, and transport. One downside is it is heavier than air, while Methane is lighter than air. Methane spill? No such thing. Propane will not remain liquid at ambient temperatures and pressure, but in gaseous form will go down a drain . . .

The higher the octane rating, the higher the resistance to ignite.

Gaseous fuels generally have a lower power density than gasoline or diesel. here are a few charts
http://www.hrt.msu.edu/energy/pdf/heating value of common fuels.pdf
http://pointsandfigures.com/2011/04/27/natural-gas-vs-diesel/

two engines of exactly the same size in displacment, number of cylinder, etc. one diesel, one gaseous fueled. the Diesel will have nearly twice the power output. (I made my living designing gensets with both for many years)
Now, you can increase the boost pressure on the gaseous fueled engines and get a higher power density, however this comes at a cost of higher EGT's and higher cylinder head temperatures.

 

[QC]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

I pretty much agree Scott, but I was referring to the comments regarding gasoline conversions.

FWIW, what my company does is nat gas in compression ignition engines, we do not have higher EGTs of any significance.

 

[Fleetwin]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

All are correct that CNG and Propane are higher octane, generally, depending on which method is used to calculate.

It was also mentioned that todays conversions are just that. They are traditional gas engines that are converted. Base engine wise, all you need are hardened valve seats to deal with the "dry fuel".

You can get get higher performance out of a CNG engine with higher compression ratios. The added octane allows that. That's why a diesel engine conversion is possible.

Todays gas engine compression ratios are still climbing. Many are well over well over 10:1 and still climbing. With direct injection, they can go higher and still run well on our usual 87 octane (North America) fuel.

As compression ratios go up, CNG looks better and better.

It is also VERY TRUE that propane "puddles", meaning heavier than air. That can be a serious issue. Not so much with automotive but deadly in a marine application. CNG is lighter than surrounding air and dissapates much easier.

There are pros/cons on both sides. Just different. The applicatrion has to be looked at to make a determination as to the best alternative.

Very interesting alternatives becoming avialable.

 

[NoKlu]

Re: Compressed Natural Gas (CNG) conversion to cars- any experience?

They used to do lots of propane conversions up in Alberta but it's kinda gone the way of the Dodo bird. My Uncle was all excited to get a Suburban with propane, after spending a lot of money to get it working right it was no cheaper to do the same trip with a gas engine. It is cheaper than gas but you don't get the power or mileage so it was not worth the change. Also in the colder temps in winter they had constant problems.