Any point in warming up diesel fuel?

[kingsway]

I've read a lot about CAI and WAI - and understand cold air is best for a diesel - but I can't recall reading anything about any benefit from warming the fuel itself...

My VAG diesel does have a temperature controlled valve in the fuel return that can dump warm fuel from the injector-pump back into the top of the fuel filter to help prevent waxing/blockage of the filter in cold weather.

But I noticed while tinkering today that after I P&G'd on a 14 mile round trip the injector pump hardly warmed up at all...

So I was wondering if there might be any efficiency benefit if I was to run a longer fuel supply pipe around my top radiator hose to warm it up a bit?

I know it is essential to warm up fuel in order to run vegetable oil (to reduce viscosity) - but would it make any difference at all with straight diesel fuel??

TIA

[jtbo]

My car has heated fuel filter, coolant heats the box where fuel filters sits, that is to help it cope with cold weather, don't know if it is helping or harming fuel economy though. However as such is factory installation, it might not harm at least much.

[ConnClark]

It can help a little with fuel economy. This 1936 research paper shows an increase in thermal efficiency once a 300 degree F threshold was reached. http://aerade.cranfield.ac.uk/ara/1936/naca-tn-565.pdf

Note initially results showed a decline in efficiency until the 300 degree F thresh hold was reached. This may have been due to the low compression ratio engine used (13.5 to 1). With a higher compression ratio engine the threshold would be at a lower temp. Also note that the fuels compressibility changes with temperature and this can have an effect on injection timing.

[Ryland]

From what I remember, warmer fuel creates smaller droplets in the combustion chamber and that the larger the drops of fuel the more soot is produced, so if I understand correctly, warmer fuel would create less soot and thus would burn cleaner.

[oil pan 4]

Find a way to get the engine warmed up faster.
The fuel at your injector tip is going to be pretty close to the temperature of the block.
Use grill block, electric fans, EGR during warm up and so on.

Heating the fuel isn't going to do much good once the engine is warmed up.
If you have a rotary injector pump you don't want to send it hot diesel fuel.

[slowmover]

In big trucks it's sort of taken for granted that performance drops off as the fuel in the tanks heats over the course of a normal (not cold) day. More a driver sensitivity thing.

But I've wondered the same thing. Controlled intake air temps and controlled fuel temps seem to be complementary.

.

[Piwoslaw]

In a commonrail system (like PSA's HDi) the second fuel pump builds up crazy high pressure, warming the fuel. The part of the fuel which didn't make it to the injectors returns to the fuel tank, and there is a small radiator along the way to make sure that the fuel isn't too hot. I read in technical manual that something like 60-65°C is the optimal temperature.

I wonder if it wouldn't be a hazard to run too hot fuel through the high pressure pump?

[Diesel_Dave]

I don't think there would be much of an effect. Like oilpan said, I don't thing any "pre-warming" is going to affect the temperature at injection hardly at all. I guess slightly hotter fuel might possibly help FE by decreasing the ignition delay--but my guess is that effect would be almost nothing. This is especially true to common rail systems, where the high pressure pump will have pressurized the fuel up to 10-25,000 psi. Ignition delays are very, very short with common rail systems anyway.

On an older mechanical-style fuel injection system, I'm not sure what the effect would be. Changing the fuel temp will change both the fuel density and bulk modulus. Both these factors determine how quickly the fuel pulses travel down the fuel lines, thus it could affect the injection timing. Of course if you wanted to achieve that effect you could just change the injection timing without warming the fuel.

[AXMonster]

Originally Posted by Piwoslaw

I wonder if it wouldn't be a hazard to run too hot fuel through the high pressure pump?

Yes, fuel pump failure will occurr in the long term. The fuel temperature into the pump has a maximum and thats why fuel coolers are fitted.... IIRC its about 90°C for the Bosch VP44 pump. Possibly due to lubricity?

[oil pan 4]

You can also change the fuels ignition properties by adding something like diesel clean power service. It raises the certane number and is proven to increase fuel economy.
I believe the active chemical that makes the changes are organic peroixdes, these are very unstable chemicals, they don't handle rapid temperature and pressure changes very well.