Flicks over to Gas in 15-20 secs in Summer

[CNGBiFuel]

This is hardly a complaint, more a query. My Necam factory fit flicks over to gas in 10-20 secs in summer and takes about 60-70 secs in February. I'm readign on here of conversions taking a mile or two to switch. Is that more normal and if so why? And whislt I'm on, why do we need liquid to start anyway? Surely the worst time to fire petrol into a perfectly decent engine is when it's cold.

So forgive me, but you've all got it wrong, you run petrol when the engine is hot and you can't find a gas supply. ie to get you home, not to get you 'there'.

My 60s Land-rover conversion with simpleton gas-ring type jobby nailed to a carb, fires up on LPG from cold all year round, [A lambda? Eh? What's that then??? ] so why do we need devil-juice when they fire-up without?

[John_C]

It's to remove any risk ofthe vaporiser freezing up, the engine coolant needs to be up to a certain temperature before switching to gas.

[capt jack]

The L in LPG stands for Liquid, which is the state in which LPG is held in the tank and through the fuel line. When it reaches the engine it needs to be vapourised to it's gaseous state - which requires heat. This heat is supplied by the car's cooling system - which needs the engine to be warmed up enough to let hot coolant through to the LPG vapouriser. To get the engine be warm enough to provide enough heat to vapourise the incoming LPG the engine has to run on petrol.

In the summer the engine will warm up faster (starting at an ambient of say 15 degrees) than it does in the winter, when the ambient is probably below freezing.

If the system isn't warm enough to get the LPG vapourised efficiently then the engine will be starved of fuel and will run like a three-legged donkey. Efficient vapourisation and fuel delivery is essential because the fuel is injected as a vapour into the inlet manifold where it is mixed with the inlet air.

Unlike a carburettor set-up, a fuel injected system needs to maintain a constant high fuel pressure to all injectors all the time, with the input of fuel into the manifold and thence to the combustion chamber being control by the opening and closing of the individual injectors. All this makes for a much more efficient fuel delivery, making fuel-injected cars more economical and reliable.

This is why the fuel pressure in a carbed engine is relatively low, whereas in a fuel injected engine the fuel line pressure can be 2 or 3 bar.

Your LPG'd car can be made to start on LPG but it wouldn't run very well until it had warmed up. With the system on my old V70 you pressed and held in the LPG changeover button as you turned the key, and the engine would start on gas. However, the LPG software would only allow you to do this 5 times before it would block the function, which would then have to be unlocked by a technician with the right software loaded into his computer!

Cheers

Jack

[CNGBiFuel]

Ah... thank you. I like to think I have brain, whereas in hindsight with this one, the answer was in the question. [Slaps hand on Forehead]

[Clifford Pope]

Mine's only a basic LPG mixer, but even so it is possible to ice up the vapouriser if I switch to gas too soon in cold weather.
I usually leave it until the moment that the temperature gauge needle just begins to move onto the scale. In warm weather that's after about 100 yards, in winter perhaps a mile.
The other advantge of choosing the moment is that there is always a momentary hesitation when it changes over. and I don't want it to do that just when pulling out into traffic