Electric Car Charger

[stillp]

Yes, but LPG is heavier than air. Hydrogen isn't.

 

[ban-all-sheds]

Indeed it is, which is why they don't let you take LPG cars through the Channel Tunnel.

I would imagine that what you say about tanks containing liquified gas may be true, provided that there is not a source of ignition around at the moment of rupture and liquid-gas-transition.

Heat from friction experienced by the escaping gas can be enough to ignite it, but maybe not with the quantities you'd have in a passenger car.

 

[stillp]

Indeed it is, which is why they don't let you take LPG cars through the Channel Tunnel.

The stupid thing about that is that you can take a caravan with an unsecured LPG cylinder connected by a push-fit, perished rubber hose, but not a factory-converted LPG car.

 

[ericmark]

Interesting so lets put another spanner in the works. Do you need to use duty paid petrol. It is not running the car it only charges the battery so a TVO conversion would mean you could run on 28 sec gas oil without really breaking the law. Or could you?

So if I have an electric can and put a diesel generator in a trailer can that generator run on gas oil? or would it need DERV (Diesel Engine Road Vehicle) always got me that narrow boats were allowed to mix "Red" and "White" diesel and the white diesel was still called DERV even though not used in a road vehicle.

 

[ban-all-sheds]

The stupid thing about that is that you can take a caravan with an unsecured LPG cylinder connected by a push-fit, perished rubber hose, but not a factory-converted LPG car.

Why am I not surprised.

 

[SimonH2]

A hydrogen BLEVE might be spectacular.

Except that you won't get one. The hydrogen is compressed gas - it has to be cooled to "f**k that's cold" levels before it can be liquified. One of the things they don't mention with hydrogen is the amount of energy that needs to go into it to get it to either a "very high pressure" gas, or a very cold and high pressure liquid. AFAIK road vehicles only use gas, it's not practical to keep it cold enough to store it as liquid.

I forget the figures now, but from a talk a while ago, I think it was something like 35kg of steel to make a tank holding 7kg of fuel. Yeah, very practical

LPG would worry me more than hydrogen.

It shouldn't worry you - at least no more than petrol or diesel. It has risks, and they are different to petrol and diesel, but overall I don't think the risks are higher - just different.

LPG wouldalso immediately turn to gas, wouldn't it?

Very quickly, but it would leave things "pretty nippy". At atmospheric pressure it boils off at -40˚ - spill a largish quantity and it'll initially flash boil but will soon cool off and it's boiling rate will be constrained by how quickly it can get heat in. In cold weather I've seen droplets fizzing around inside the gun after refuelling, and done maintenance (replacing a valve) where you draw off what you can, but the pressure is too low to keep pumping it. You take the valve out, and sat in the bottom of the tank is some liquid propane just simmering away at -40˚.

I would imagine that what you say about tanks containing liquified gas may be true, provided that there is not a source of ignition around at the moment of rupture and liquid-gas-transition.

That's an important factor. If there's a spillage, I'd rather it be propane than petrol. The flammable mixture range for petrol is significantly wider than for propane - so if you have a propane spillage there will be a significant period when the mixture is too rich to burn - and it'll disperse quite quickly in any breeze. Spill petrol, and it evaporates much more slowly, and together with it's higher flammability range, you'll have more flammable mixture for longer - and for good measure, the ignition temperature is lower so it can be ignited by things that are too cool to ignite propane.

If you consider a vehicle fire, then the situation is interesting.
Assuming the petrol tank doesn't have a leak, then pressure will build as it heats up. Sooner or later you'll get to a temperature and pressure where the tank (usually plastic these days) ruptures and you get the BLEVE event BAS mentions. So suddenly you get a big fireball of boiling petrol sprayed around the vicinity.
The LPG tank has a pressure relief valve (at least if it meets standards in any country I know about). When it gets hot enough, the relief valve will lift (typically at about 25 bar) and vent gas. This tends to look dramatic in videos and is sometimes described as the "tank failing". Many valve sets also have a fusible link so that when it gets hot enough, the link melts and the remaining contents are released (depressurising the tank). This is even more dramatic, and is often described as the tank "exploding" when it's done no such thing - it's just a very big bunsen burner.
What can get interesting is if the tank vents into the vehicle. That "shouldn't happen", but I can see it being possible if things get hot enough to melt the valve box and ducting before having made the windows break (admitting air to the vehicle interior). In that situation you can get a buildup of gas, which then erupts in a flash when air is admitted - but again, this is not an explosion. Getting a flammable mixutre build up, during a fire, would (I think) be incredibly difficult.

EDIT: For standard compliance, the LPG tank valve set has to be capable of completely venting the contents of the tank it's designed to fit, before the steel gets to a temperature where the integrity of the tank is compromised. So sit a full tank on a bonfire, and it'll be empty before there's a risk of the tank bursting.

 

[stillp]

LPG would worry me more than hydrogen.

It shouldn't worry you - at least no more than petrol or diesel. It has risks, and they are different to petrol and diesel, but overall I don't think the risks are higher - just different.

In at least one respect, LPG is safer than petrol or diesel, in that the system can detect leaks, and has a shut-off valve on the tank that operates if excess flow is detected. WIth a petrol engine, if a fuel line is ruptured in a crash the pump will continue to operate until the tank is empty or the power to the pump fails.

 

[ban-all-sheds]

Bear in mind that I said LPG would worry me more than hydrogen, not more than petrol.

 

[stillp]

Ah yes, you did that.