How much fuel does a car use for ignition?

How much fuel is burnt for ignition? All of it is burnt for ignition, that how an internal combustion engine works! (very nearly all of it anyway).

The actual amount of fuel used for each ignition event depends totally on the displacement of the engine and how wide the throttle is open. The engine needs around one part of fuel to 14.7 parts of air (by weight) under cruise conditions, so work out from there :D

Brake specific fuel consumption is possibly what you are asking for? e.g. at 256 g/(kW·h) a 100bhp engine running at maximum power would consume just over 19kg of fuel in an hour, or about 26 litres/5.7 gallons at normal temperatures.
 
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I was wondering this too, but more specifically - does it use more fuel to start your car and leave it for say 5-10 mins when starting it from cold, before driving it off, or would it not make that much of a difference to fuel consumption to just start it from cold in the morning and drive off?

I generally warm mine for 5-10 mins before I leave the house, as I like to have it warm inside and the windows demisted.
 
panthro said:
I was wondering this too, but more specifically - does it use more fuel to start your car and leave it for say 5-10 mins when starting it from cold, before driving it off, or would it not make that much of a difference to fuel consumption to just start it from cold in the morning and drive off?

I generally warm mine for 5-10 mins before I leave the house, as I like to have it warm inside and the windows demisted.
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Don't leave a cold engine sitting there idling for that long. Leave it 30 seconds to get the oil pressure up and then drive off. Everything will warm up quicker than just idling which ultimately does "less" damage to the engine.

Also idling doesn't warm the gearbox up whereas driving does. So using your method when you do come to drive off you will have a warm engine and a cold gearbox.
 
Dogbreath said:
How much fuel is burnt for ignition? All of it is burnt for ignition, that how an internal combustion engine works! (very nearly all of it anyway).

The actual amount of fuel used for each ignition event depends totally on the displacement of the engine and how wide the throttle is open. The engine needs around one part of fuel to 14.7 parts of air (by weight) under cruise conditions, so work out from there.
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I think you were taking the question a bit too literally there ;) He is asking how much the fuel tank level drops when you start the engine. He wasn't asking about combustion mixture ratios and the like :D
 
NathanE said:
I think you were taking the question a bit too literally there ;) He is asking how much the fuel tank level drops when you start the engine. He wasn't asking about combustion mixture ratios and the like :D
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Was just about to say why complicate things :p, I just want to know the typical amount burnt on ignition.
 
Don't know if this is relevant to what the OP is asking, but what about the drain of starting on the battery and the subsequent fuel used to charge it up again...
 
thefullcollapse said:
i heard its the equivilent of idling for 5 minutes
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May depend on the car, and presumably better for newer cars.

Both my TT and BMW both say in the manual to turn off the engine if stationary for more than 30 seconds as this uses less fuel.

Ed: Of course this is from warm, not sure if we are talking about from cold wouldn't make much difference except for the choke?
 
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NathanE said:
Don't leave a cold engine sitting there idling for that long. Leave it 30 seconds to get the oil pressure up and then drive off. Everything will warm up quicker than just idling which ultimately does "less" damage to the engine.

Also idling doesn't warm the gearbox up whereas driving does. So using your method when you do come to drive off you will have a warm engine and a cold gearbox.
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Why would leaving an idling engine damage it?
 
Wear happens on cold engines, the longer it is running when cold, the more wear.

Hence it is best to drive off as soon as you have started it as it allows the engine to warm up faster.
 
My brother (who is a qualified mechanic) reckons it is about the equivalent of 3 miles worth of driving for an average (i.e.1.6 or so) car.
 
Simon said:
Wear happens on cold engines, the longer it is running when cold, the more wear.

Hence it is best to drive off as soon as you have started it as it allows the engine to warm up faster.
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Not convinced myself. IMHO an idling engine @ 1k revs is going to warm up at close to the same rate as one at 2k revs - however at 2k revs there would be more potential for damage.
 
therealnerd2 said:
Not convinced myself. IMHO an idling engine @ 1k revs is going to warm up at close to the same rate as one at 2k revs - however at 2k revs there would be more potential for damage.
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Why will there?

Cam loadings are higher, and there is less oil flow through the oil pump. Also an engine at 2k rpm will warm up much much faster.
 
at 4c... 10.6ms
at 16c.. 11.0ms
at 27c.. 8.8ms
at 38c.. 4.0ms
at 54c.. 3.4ms
at 71c.. 2.5ms

that's 4 injectors, opening time of 1ms, running at 3bar, flowing 140cc(x4)

at idle the car uses a PW of around 1.9ms, and around 3500rpm it is approx 4.1ms.
 
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