A work in progress.

[euromodder]

Originally Posted by 320touring

you starting a thread for the car?

I know, I know I should ...

I for one would be intrigued to see what the CNG setup looks like compared to LPG

• CNG is stored as a gas despite the 200 bar / 2900 psi tank pressure - LPG is stored as a liquid.
• 2-stage pressure reduction system, the 2nd stage using variable output pressure based on the engine's demand and is heated by the engine coolant.
• large, voluminous cylindrical tanks for CNG rather than space-saving donut type tanks for LPG.
• VW have increased the compression and fitted hardened valves + seats, so no messing about with valve lube etc. like with LPG
  (valve lubing is often needed on retrofitted CNG cars though)
• Monovalent car, so the driver can't select which fuel to use (which you can in LPG or CNG-retrofitted cars) - it runs on CNG until the tanks are empty.

[320touring]

Originally Posted by euromodder

I know, I know I should ...

Consider thyself admonished!

[*]CNG is stored as a gas despite the 200 bar / 2900 psi tank pressure - LPG is stored as a liquid.

Hmm- thats some pressure-similar to a modern common rail diesel- guess it explains the tanks!

[*]2-stage pressure reduction system, the 2nd stage using variable output pressure based on the engine's demand and is heated by the engine coolant.

Similar to a vapourisor on an LPG setup? except with pressure control as well. sounds good- inso far as it is load reactive

[*]large, voluminous cylindrical tanks for CNG rather than space-saving donut type tanks for LPG.

How does that impact on the available space in the Up!? does it reside in the location usually reserved for the petrol tank?

[*]VW have increased the compression and fitted hardened valves + seats, so no messing about with valve lube etc. like with LPG
(valve lubing is often needed on retrofitted CNG cars though)

so similar to LPG in that its a drier fuel than petrol, and some cars can suffer valve seat recession due to using it? Jaguars need valve lube for LPG, but the BMWs I have are happy without it

Interesting re the compression! does CNG have a higher RON rating, but lower calorific value?

[*]Monovalent car, so the driver can't select which fuel to use (which you can in LPG or CNG-retrofitted cars) - it runs on CNG until the tanks are empty.

ah, so no handy "range extender" option then? I did like that about LPg


Cheers for the insight (ecomod punFTW!)

[euromodder]

Originally Posted by 320touring

Consider thyself admonished!

Similar to a vapourisor on an LPG setup?

Yes.

How does that impact on the available space in the Up!? does it reside in the location usually reserved for the petrol tank?

The 2 gas tanks are underneath the car, one on either side of the rear axle.
The fuel tank is reduced to 10 liter / 2.6 US gal .
There's no well for a spare wheel - which I haven't been carrying for the last 3 years anyway. You do get a compressor and some fix-a-flat gooey ...
The trunk floor is mounted a few cm higher - and lacking the well.
The whole CNG system adds about 100kg - most of that is the weight of the tanks.

so similar to LPG in that its a drier fuel than petrol, and some cars can suffer valve seat recession due to using it?

Yeah. CNG doesn't lube at all.

Interesting re the compression! does CNG have a higher RON rating, but lower calorific value?

It's 130 RON.
Caloric value of the gas I use most often is low, below 10.

ah, so no handy "range extender" option then? I did like that about LPg

After the gas is gone, there's only the 10 L petrol tank.
I chickened out at 9.5L recently.
Effectively giving a 528km combined range.

10L should be OK for some 200km, but as the car briefly uses petrol after tanking CNG (100 yards or so) you never really know how many km it has done on petrol.


VW wants you to replace the petrol every 6 months to keep it from going stale.
So the first 2 years, that's what I'll do