sub zero and very hot temperatures and intercoolers
Discussion
Was out nipping to the shops last night. In my ibiza cupra in minus temperatures and as predictable the engine pulled very strongly. The engine was just warming up and so i imagine that the charge pressure was higher and the mixture would of been quite strong (lots of dense air as less heat soak and lots of fuel). But it got me thinking clearly an intercooler will have more effectiveness when the ambient temperature is very low and so the engine will be more powerful so is this why aircraft tend to use force fed engines when flying at high altitude due to the temperature and thinner air overall? And conversely at what ambient temperature will an intercooler not be able to do much at all, what kind of temperatures does charge pressure reach?
I should add to this when you look a rally car the exhaust gasses are glowing orange (well actually the metal must be) with the heat and i know the two halves of the turbo are usually shielded but surely even the intake side of the turbo when under hard load must be getting into a couple of hundred degrees? correct me if I'm wrong. So how can an intercooler expect to shed so much heat and consequently what sort of temperatures does the engine block then actually inhale so to speak.
I should add to this when you look a rally car the exhaust gasses are glowing orange (well actually the metal must be) with the heat and i know the two halves of the turbo are usually shielded but surely even the intake side of the turbo when under hard load must be getting into a couple of hundred degrees? correct me if I'm wrong. So how can an intercooler expect to shed so much heat and consequently what sort of temperatures does the engine block then actually inhale so to speak.
Edited by Andy ap on Tuesday 12th March 11:43
Edited by Andy ap on Tuesday 12th March 12:00
I think the primary reason aero engines were forced fed was to enable them to climb higher into the thinner atmosphere as you said.
As for the other stuff, I've always found any petrol engine pulls better from cold before the lambda kicks in. As you say, cold air, more fuel etc.
I think you're heading in the direction of getting intercoolers to operate at below ambient on a summer's day? It's possible with an air-water intercooler (such as used on the Mercedes and Jaguar V8 Supercharged engines) that has a large resevoir that you can put ice into. Eaton superchargers generate a lot of heat (hence being known as 'Heatons') and turbos certainly warm up the charge air considerably at high boost. 80-100 deg C compressor outlet temps aren't uncommon.
During 6 or 7 years of turboing, I found this kind of intercooler to be more effective overall, but it does carry with it a lot of extra baggage, so air-air intercoolers are much simpler and lighter in this respect.
As for the other stuff, I've always found any petrol engine pulls better from cold before the lambda kicks in. As you say, cold air, more fuel etc.
I think you're heading in the direction of getting intercoolers to operate at below ambient on a summer's day? It's possible with an air-water intercooler (such as used on the Mercedes and Jaguar V8 Supercharged engines) that has a large resevoir that you can put ice into. Eaton superchargers generate a lot of heat (hence being known as 'Heatons') and turbos certainly warm up the charge air considerably at high boost. 80-100 deg C compressor outlet temps aren't uncommon.
During 6 or 7 years of turboing, I found this kind of intercooler to be more effective overall, but it does carry with it a lot of extra baggage, so air-air intercoolers are much simpler and lighter in this respect.
BTW, with an extra "artificial" heat sink, any intercooling system can operate at over 100% effectiveness (for example, chilled water (below ambient temp) for an air-water-air system or dry ice packed into rad for air-air system etc. The air-air system is ultimately more effective that the air-water-air system because it only has one system boundary to cross rather than two.
You can also get lower than ambient air charge temperatures using over expansion techniques (intercool at a higher entropy (pressure) and then expand the gas further)
Planes use forced induction to increase intake air density at altitude, where the falling ambient pressure would otherwise limit maximum performance dramatically.
Upheat from the turbine to compressor by conduction is minimal in practise when compared to the upheat from the compression proccess itself. Most systems will have approx 40-50 degC as a general target for manifold air charge temperature during full load operation in a 25degC ambient.
As specific outputs increase, boost pressures also climb. Typical modern turbo diesels are now running 3barg at peak torque, and approaching 180degC compressor outlet temperature.
You can also get lower than ambient air charge temperatures using over expansion techniques (intercool at a higher entropy (pressure) and then expand the gas further)
Planes use forced induction to increase intake air density at altitude, where the falling ambient pressure would otherwise limit maximum performance dramatically.
Upheat from the turbine to compressor by conduction is minimal in practise when compared to the upheat from the compression proccess itself. Most systems will have approx 40-50 degC as a general target for manifold air charge temperature during full load operation in a 25degC ambient.
As specific outputs increase, boost pressures also climb. Typical modern turbo diesels are now running 3barg at peak torque, and approaching 180degC compressor outlet temperature.
Max_Torque said:
...
Upheat from the turbine to compressor by conduction is minimal in practise when compared to the upheat from the compression proccess itself. Most systems will have approx 40-50 degC as a general target for manifold air charge temperature during full load operation in a 25degC ambient.
As specific outputs increase, boost pressures also climb. Typical modern turbo diesels are now running 3barg at peak torque, and approaching 180degC compressor outlet temperature.
Interesting stuff (especially the "target"). I had digital thermometer wired to the intercooler today on the way into work (ambient 1c on the dash) and the temp typically was just below the teens during slow driving that hardly saw any boost. However a 40-70mph sprint out of town on the dual carriage way quickly saw around 24c which then dropped a couple of degrees on cruising.Upheat from the turbine to compressor by conduction is minimal in practise when compared to the upheat from the compression proccess itself. Most systems will have approx 40-50 degC as a general target for manifold air charge temperature during full load operation in a 25degC ambient.
As specific outputs increase, boost pressures also climb. Typical modern turbo diesels are now running 3barg at peak torque, and approaching 180degC compressor outlet temperature.
I'm trying to work out of the oem unit is up to the job of having "the turbo turned up a bit" so to speak
Max_Torque said:
Upheat from the turbine to compressor by conduction is minimal in practise when compared to the upheat from the compression proccess itself. Most systems will have approx 40-50 degC as a general target for manifold air charge temperature during full load operation in a 25degC ambient.
I saw exactly that on my old [standard] Polo GTI (1.8T) in the VCDS measuring blocks. The IAT sensor just before the throttle on that engine. It had a tiny little side mount air-air cooler and only just coped with the standard 8psi boost. Many folk go for R3vo type serial port remaps, double the boost and then run into inconsisent performance issues beacuse the ECU is seeing excessive IATs.I remember a mate's Golf 1.8T that he'd fitted a bigger turbo to and ran at 20psi. He also fitted an 'uprated' side mount cooler (all ally instead of plastic end cans) and during a road test, the IAT went from ambient (20 on the day) to 70 deg C by the time it hit 3rd gear at WOT.
On a turbo engine I built myself using a Spearco air-water core inside flow corrected end cans, 3 gallon water tank in the boot (with 40% VAG G12 coolant), Meziere pump and a large heat exchanger, I was averaging 10-12 above ambient in the summer / autumn and 4 - 8 above over winter. The IAT (open bead type) on that engine was directly in the intake manifold. That was chilling 15psi from a GT3582R.
I was pleased with the results of that but as mentioned previously, 'chargecoolers' necessitate a lot of additional baggage.
Max_Torque said:
You can also get lower than ambient air charge temperatures using over expansion techniques (intercool at a higher entropy (pressure) and then expand the gas further)
I Can see how that works what with expanding gasses being colder and compressed gasses being hotter So if your intercooler is large does that mean the actual charge pressure drops to below atmospheric pressure and so consequently you get a cooler charge (obviously with the airflow and convection in mind) but then it has to be compressed again by the incoming boost as it leaves the intercooler so is it in merit to have the intercooler as close to the inlet manifold as possible? Also if the car was stationary or say had a very low airflow over the intercooler would it have to be very big for the pressure in the intercooler to drop in temperature sufficiently enough for it to be cooler than atmospheric temperature and for it to heat up again as it leaves en route to the engine. Now obviously an intercooler spreads the charge pressure out over a large area for more efficient convection and to try and elimnate hot spots, but due to this pressure drop Is there such a thing as too big an intercooler? i.e. can you end up getting a pulse effect?
Edited by Andy ap on Tuesday 12th March 15:23
Cooler air temp changes the rate at which fuel burns, which then allows you to change timing a bit.
So a nice cold engine will in theory get colder air inside it than when it's at operating temp, which means, iirc, the fuel burns slower, which means you inject earlier (more advance).
But since cars without these fancy additions (sensors/corrections) also feel sharper in the cold, then you'd assume that the timing change makes it feel better (though it might not be for other reasons)... so cold air advances the ignition = more power?
Does the engine in question here (1.8T) have a charge air temp sensor, or do they correct for injection based on look up tables around vehicle speed, ambient temp, coolant temp, IAT etc?
Dave
So a nice cold engine will in theory get colder air inside it than when it's at operating temp, which means, iirc, the fuel burns slower, which means you inject earlier (more advance).
But since cars without these fancy additions (sensors/corrections) also feel sharper in the cold, then you'd assume that the timing change makes it feel better (though it might not be for other reasons)... so cold air advances the ignition = more power?
Does the engine in question here (1.8T) have a charge air temp sensor, or do they correct for injection based on look up tables around vehicle speed, ambient temp, coolant temp, IAT etc?
Dave
Andy ap said:
...at what ambient temperature will an intercooler not be able to do much at all...
IIRC, that depends on the efficiency of the intercooler at a given charge pressure amongst other things.an intercooler is only efficient when the design allows it to be...if it's designed for 15psi max pressure and you put 20 psi through it it will be less efficient, obviously
when the charge temperature soaks into the intercooler and the intercooler itself reaches or goes higher than ambient it's no longer efficient (to an extent). it still works but nowhere near as well, this is usually a design flaw if it does it on a standard car.
Rover T16 intercoolers for instance. standard boost is 12psi and at that pressure they work well, however, up the boost to 15 and that's the limit, go over 15 psi and your gonna get alot of heat soak.
The catalyst matrix is indeed in the back box of a factory spec WRC car. It prevents it melting completely when the antilag system is used, but although it starts as an genuine active catalyst, pretty much the first time the car is driven in anger, the unburnt fuel contaminates the catalysts and it no longer functions as a catalyst.................
So if a charge cooler is used instead for example, aside from the extra complexity, weight and as has allready been said the extra barriers to pass. I assume its then down to cost and ease of manufacture and also ease of maintenance to stick with an intercooler rather than air-water-air system?
Road cars work well with charge coolers, because the water in the system acts as a temporary heat sink (due to the high specific heat capacity of water). As road cars tend to be loaded transiently (i.e. full load accel for say 15 sec, then off load, often for minutes at a time) you can "get away" with a less efficient LTR (Low Temperature Radiator) that cannot actually reject the full heat requirement. In this case, the water in the system is heated up during the high load operation, but then is cooled back down to around ambient over the next "rest" period. What a lot of people don't realise is than in the average road car chargecooler system, it is the engines intake air that actually removes a lot of the heat from the system (as at part load off boost, the intake air temp is now lower than the water temp in the charge cooler system, and so heat is pulled into the air charge at part load (which is good for economy).
For a competition car, the sustained requirement for power output tends to make a conventional air-air system a better bet (higher efficiency (when cooled by a decent ambient airflow path), simpler, & lighter)
For a competition car, the sustained requirement for power output tends to make a conventional air-air system a better bet (higher efficiency (when cooled by a decent ambient airflow path), simpler, & lighter)
Max_Torque said:
Stuff
To yourself & Stevie and I hope this isn't a daft question.For an air-air intercooler, how important is the intercooler being directly exposed to moving air?
My shopping car has a front mounted unit which sits to the side of the radiator and is also covered by the bumper, so only around 1/3 of the thing is directly exposed to air as the car moves along.
A friend has mentioned pressure, i.e. if there is lower pressure at the rear of an intercooler then it shouldn't matter if there it isn't directly exposed to air as air would be sucked through.
However everything I've read points to intercoolers being exposed to maximum direct air.
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