Bottom line up front: I found this interesting, but this wouldn't be considered highly practical information.
This is a study done by two engineering students in Thailand in 2019.
VW-Aero Engine Cylinder a Head Cooling Efficiency Investigation
https://www.mdpi.com/2504-3900/39/1/4/pdf
From the paper:
" The aim of this paper is to investigate cooling efficiency of Volkswagen automotive conversion engine in experimental aircraft by using CFD simulation of cylinder head and barrel model including
internal baffle plates with boundary condition of airspeed between 50–100 kt (58–115 mph)."
They start by discussing some US homebuilt aircraft designs that use VW-based engines. Then, they made a CFD model of the externals of a Type 1 cylinder head and (2) cylinder set along with an air shroud, and tried to see how well it would cool at various airspeeds (air density and temperature at 6000 MSL standard day).
They assumed the aircraft was operating at 75% power and that the "Heat Generation Rate" was 44 kW. Note: It's not clear to me what this "heat generation rate" represents. 44 KW= 59 HP, so that corresponds well to the mechanical out of a 2180cc engine at 75% power. But, maybe that's also what the authors assumed would end up needing to be shed by the cylinders and cylinder heads (the remainder of the waste heat going out of the exhaust, through the oil cooler, etc), The authors don't make this clear. Anyway, the amount energy shed by the heads and cylinders is probably close to the mechanical output of the engine, I've seen this approximation elsewhere.
Here's the model of the head, cylinders, and the shroud they designed to enclose everything (intake at the top front, exhaust at the lower rear):
Predicted Flow and air temperatures inside the shroud:
Predicted temperatures at various airspeeds from a starting temp of 180C (356F):
(Above) 200C is about 400F, so according to this graph we'd need to be forcing air into the shroud at an airspeed of about 80 kts if we want to keep the temps down to about 350F. Again, this is for a 2180CC engine at (presumably) approx 60 HP output.
(Below) Here's the graph for an assumed starting temperature of 240F (465F)
I gotta say I don't understand this. I don't know why they chose to do a run at two different starting temps (180C and 240C), and why the stabilized temps of the cylinders and head would be different because of the starting temps. Regardless of the starting temps, the stabilized temps of the various parts of the shroud should depend only on the heat input to the metal and the rate at which it was removed (which varies by airspeed, given a fixed head, cylinder, and shroud geometry). IMO, it would have been better to show us the stabilized temperatures VS airspeed at two different heat input levels (corresponding to different HP levels).
For the record, I doubt that they engaged in the detailed flow analysis of the cooling passages of the cylinder head needed to really know how much heat would be shed by the cylinder head. They didn't include the topmost part of the head, the exhaust flange, etc. And, I don't know if that particular shroud design was something they thought was optimum, something they'd seen elsewhere, etc.
Still, it's kinda interesting that a couple of students from halfway around the world would picked this topic for their study.
There are more illustrations in their paper (at the link above).
This is a study done by two engineering students in Thailand in 2019.
VW-Aero Engine Cylinder a Head Cooling Efficiency Investigation
https://www.mdpi.com/2504-3900/39/1/4/pdf
From the paper:
" The aim of this paper is to investigate cooling efficiency of Volkswagen automotive conversion engine in experimental aircraft by using CFD simulation of cylinder head and barrel model including
internal baffle plates with boundary condition of airspeed between 50–100 kt (58–115 mph)."
They start by discussing some US homebuilt aircraft designs that use VW-based engines. Then, they made a CFD model of the externals of a Type 1 cylinder head and (2) cylinder set along with an air shroud, and tried to see how well it would cool at various airspeeds (air density and temperature at 6000 MSL standard day).
They assumed the aircraft was operating at 75% power and that the "Heat Generation Rate" was 44 kW. Note: It's not clear to me what this "heat generation rate" represents. 44 KW= 59 HP, so that corresponds well to the mechanical out of a 2180cc engine at 75% power. But, maybe that's also what the authors assumed would end up needing to be shed by the cylinders and cylinder heads (the remainder of the waste heat going out of the exhaust, through the oil cooler, etc), The authors don't make this clear. Anyway, the amount energy shed by the heads and cylinders is probably close to the mechanical output of the engine, I've seen this approximation elsewhere.
Here's the model of the head, cylinders, and the shroud they designed to enclose everything (intake at the top front, exhaust at the lower rear):
Predicted Flow and air temperatures inside the shroud:
Predicted temperatures at various airspeeds from a starting temp of 180C (356F):
(Above) 200C is about 400F, so according to this graph we'd need to be forcing air into the shroud at an airspeed of about 80 kts if we want to keep the temps down to about 350F. Again, this is for a 2180CC engine at (presumably) approx 60 HP output.
(Below) Here's the graph for an assumed starting temperature of 240F (465F)
I gotta say I don't understand this. I don't know why they chose to do a run at two different starting temps (180C and 240C), and why the stabilized temps of the cylinders and head would be different because of the starting temps. Regardless of the starting temps, the stabilized temps of the various parts of the shroud should depend only on the heat input to the metal and the rate at which it was removed (which varies by airspeed, given a fixed head, cylinder, and shroud geometry). IMO, it would have been better to show us the stabilized temperatures VS airspeed at two different heat input levels (corresponding to different HP levels).
For the record, I doubt that they engaged in the detailed flow analysis of the cooling passages of the cylinder head needed to really know how much heat would be shed by the cylinder head. They didn't include the topmost part of the head, the exhaust flange, etc. And, I don't know if that particular shroud design was something they thought was optimum, something they'd seen elsewhere, etc.
Still, it's kinda interesting that a couple of students from halfway around the world would picked this topic for their study.
There are more illustrations in their paper (at the link above).
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