Thread: Intercooler and fuel efficiency

Fuel economy is made/lost at cruising speeds. For that you don't need an intercooler.
But as soon as you're pushing higher speed or towing the boost climbs and it'll help a lot. Efficiency gains around 5% at high load.

Originally Posted by Dougal

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But as soon as you're pushing higher speed or towing the boost climbs and it'll help a lot. Efficiency gains around 5% at high load.

An intercooler in itself cannot, as far as I can see, affect fuel consumption. All it does is allows the intake of a greater mass of air (at a small cost of pumping loss). The only advantage of this increased mass of air is that it allows more fuel to be burnt at any particular specified rpm and boost, giving more power in proportion to the fuel burnt. The only effect I can see is to increase the available power throughout the range - if you use this increased power, the result will not be increased fuel economy!

John

Originally Posted by JDNSW

An intercooler in itself cannot, as far as I can see, affect fuel consumption. All it does is allows the intake of a greater mass of air (at a small cost of pumping loss). The only advantage of this increased mass of air is that it allows more fuel to be burnt at any particular specified rpm and boost, giving more power in proportion to the fuel burnt. The only effect I can see is to increase the available power throughout the range - if you use this increased power, the result will not be increased fuel economy!

John

Carnot efficiency John. Lower intake temps = higher efficiency.
Then you've got reduced turbocharger boost required for the same air consumption.

Feel free to look up industrial diesel engine specs. You'll find close to identical engines sold in non turbo, turbocharged and then turbo intercooled. The fuel consumption curves improve from non turbo to turbo and then again from turbo to turbo intercooled.

Originally Posted by Dougal

Carnot efficiency John. Lower intake temps = higher efficiency.
Then you've got reduced turbocharger boost required for the same air consumption.

Feel free to look up industrial diesel engine specs. You'll find close to identical engines sold in non turbo, turbocharged and then turbo intercooled. The fuel consumption curves improve from non turbo to turbo and then again from turbo to turbo intercooled.

I believe you - but I just have difficulty believing that the effect will make any difference in a vehicle application (as opposed to the generally fixed load on an industrial engine), and especially in a conversion such as is proposed, where it is unlikely the boost will be changed or, indeed the fuelling (except to change the maximum, perhaps).

In any case, I suspect that as usual, the fuel saving, if any, will be masked by the almost inevitable effect of any boost in power - the vehicle is no longer driven at the same speeds and rates of acceleration as before the power boost, so more extra fuel is used than is saved. In other words "I've now got more power, so I'll use it".

John

Originally Posted by JDNSW

I believe you - but I just have difficulty believing that the effect will make any difference in a vehicle application (as opposed to the generally fixed load on an industrial engine), and especially in a conversion such as is proposed, where it is unlikely the boost will be changed or, indeed the fuelling (except to change the maximum, perhaps).

In any case, I suspect that as usual, the fuel saving, if any, will be masked by the almost inevitable effect of any boost in power - the vehicle is no longer driven at the same speeds and rates of acceleration as before the power boost, so more extra fuel is used than is saved. In other words "I've now got more power, so I'll use it".

John

The nature of the load doesn't matter, a more efficient engine uses less fuel to do the same work.
The boost is changed via exhaust temp which is changed via intake temp. Basically the intercooler drops intake temp which drops exhaust temp and naturally drops boost at part load.
Dropping boost drops drive pressure which is a pumping loss.

When I found and fixed the problem with my injection pump about 7 years ago my travel times dropped as I was able to pull higher speeds up hills, pass more often etc.
Yet my overall fuel consumption didn't change. Because the vast majority of driving was still at the same speed limit.
Driving faster up hills in higher gears wasn't costing me any more fuel either. This does sound counter-intuitive, but the digital readout on my newer tdi car shows exactly that.
More torque allowing you to pull higher gears can save fuel.

Thank you both for the replies.
I was thinking that an intercooler would not help once off boost and possibly even hurt fuel economy (slightly) due to pumping loss. But it makes sense what Dougal said about holding a higher gear as the intercooler would have more effect because boost would rise as fuel increases.
This is just my thinking based on my limited knowledge and zero experience with turbos.

I think I'll go with no intercooler for now as I'm on a budget and have already worked out my plumbing to go under the air filter which may possibly lend itself to a water to air later.

Thanks again.
:-)

Just be warned, that once its up and running you'll likely never intercool it
I've even got a WTA sitting on the shelf, but its just so reliable and trouble free I can't bring myself to start pulling it apart and messing around with it.

I've been meaning to throw a thermocouple in the inlet to see how hot the air is from the turbo, but haven't got around to it.
If yours has a working wastegate it will be interesting to compare EGT's etc as mine has the w/g wired shut - I didn't have a suitable actuator at the time I fitted it, and its never made it far enough up the priority list since!

Next build will be a better turbo and an intercooler, but thats a wee way off yet. The T25G still does a pretty reasonable job.

PS: I need to do some work to improve inlet restriction as my setup easily trips the filter indicator even with a brand new filter. Try and keep everything as big and smooth as possible on the inlet side of the compressor (air filter, snorkel, ducting etc) and stay away from corrugated hose to connect your snorkel up with.

Steve

Originally Posted by steveG

Just be warned, that once its up and running you'll likely never intercool it I've even got a WTA sitting on the shelf, but its just so reliable and trouble free I can't bring myself to start pulling it apart and messing around with it. I've been meaning to throw a thermocouple in the inlet to see how hot the air is from the turbo, but haven't got around to it. If yours has a working wastegate it will be interesting to compare EGT's etc as mine has the w/g wired shut - I didn't have a suitable actuator at the time I fitted it, and its never made it far enough up the priority list since! Next build will be a better turbo and an intercooler, but thats a wee way off yet. The T25G still does a pretty reasonable job. PS: I need to do some work to improve inlet restriction as my setup easily trips the filter indicator even with a brand new filter. Try and keep everything as big and smooth as possible on the inlet side of the compressor (air filter, snorkel, ducting etc) and stay away from corrugated hose to connect your snorkel up with. Steve

I've fitted 3" pipe across the curve of the barrel to maximise air flow. The filter indicator tripped when I added corrugated hose.