ESE's works engine tuner

[Larry Wiechman]

Maybe the next step would be two separate liquid cooling systems. One configured to cool the incoming charge. The other to deal with the heat from combustion.

[Vannik]

Is that really a good idea?

Water is about 50c degree hot or more.
Surrounding air is about 20-30c hot when aiming air at them.

Make some flat surfaces instead and mount copperfins, aim air at them with some ducts and hoses from high pressure area in front of vehicle.
The inner radius is ofcourse better to run water inside because it´s hard to point surrounding air into them, but with some engineering it would be possible to lead air into some channels, but with quite low effiancy.

https://physics.stackexchange.com/qu...ption-capacity

[Frits Overmars]

Frits - Perhaps I'm not understanding correctly, but on the FOS port shape image it lists the center top radius should be 75% of bore. In the attached Aprilia image the top radius appears to be 95mm on a 53mm bore (179% of bore). Much larger then the 75% listed.

Max, the bore dimension on that drawing is "Ø 53,1 (Prelavorato)" which, as Google Translator will tell you, means raw, unfinished. The same goes for other dimensions in that drawing, like the exhaust port height and its center and corner radii. Besides, that drawing is quite an oldie; it doesn't show the RSA cylinder.

Is that really a good idea?
Water is about 50c degree hot or more. Surrounding air is about 20-30c hot when aiming air at them.
Make some flat surfaces instead and mount copperfins, aim air at them with some ducts and hoses from high pressure area in front of vehicle. The inner radius is ofcourse better to run water inside because it´s hard to point surrounding air into them, but with some engineering it would be possible to lead air into some channels, but with quite low effiancy.

Patrick, the water temp in an Aprilia RSA125 is about 40°C (in the RSA250 it was about 50°C because otherwise the radiator size would have to be huge) but I'll admit that the cooling water is hotter than the surrounding air.
Following your reasoning, I should switch from watercooling to aircooling. Something tells me there has to be a catch. For example that a liquid will absorb heat a thousand times better than a gas, more than compensating for the smaller temperature difference between coolant and the object being cooled.

[SwePatrick]

Max, the bore dimension on that drawing is "Ø 53,1 (Prelavorato)" which, as Google Translator will tell you, means raw, unfinished. The same goes for other dimensions in that drawing, like the exhaust port height and its center and corner radii. Besides, that drawing is quite an oldie; it doesn't show the RSA cylinder.

Patrick, the water temp in an Aprilia RSA125 is about 40°C (in the RSA250 it was about 50°C because otherwise the radiator size would have to be huge) but I'll admit that the cooling water is hotter than the surrounding air.
Following your reasoning, I should switch from watercooling to aircooling. Something tells me there has to be a catch. For example that a liquid will absorb heat a thousand times better than a gas, more than compensating for the smaller temperature difference between coolant and the object being cooled.

Yes i know water transports heat a lot better, but i would almost guess it actually heats up the transfers instead of cooling them, inside the cylinder and more upwards there´s a whole other problem, due to combustionheat very close to the piston,liner etc etc.(i was also guesstimating the coolingtemp)
The outside of the transfers are quite far away from the heat, especially when having water upwards in cooling jacket as a 'barrier'.
But if having a separate system with about 25-30degree water it would cool them, a lot!
It would in my world be far better if isolating the heat transfer from the gearbox(as some already do) and coolingfins under the crankhousing(as some already have, and aim air to them from the fairings high pressure zone)

The small amount of powerincrease one might gain from cooling the transfers outside would probably be eaten up by needing bigger waterpump, etc etc.

One can also coat the whole crankcase together with the transfers with some heat barrier, this to get 'free' energy that doesn't cost energy at some other place.

And if having possibilities, run methanol fuel and get 'too cold' problems instead

[andreas]

Regarding cooling:
1. Separate ex duct cooling system
2. no PV to shade the upper duct face, use a retarded atac or other means
3. Those aux ex ducts i.e the bridges must be particulary bad for heating the return charge- and they dont do much to aid the wave intesity in the first place? Maybe they can be omitted from the main exhaust circuit and just waste into the atmosohere?

[Frits Overmars]

The outside of the transfers are quite far away from the heat, especially when having water upwards in cooling jacket as a 'barrier'. But if having a separate system with about 25-30degree water it would cool them, a lot!

With ambient temperatures of 25° to 30° you would need an infinitely large radiator with infinitely low efficiency and infinitely high air resistance.
If there is room for a larger radiator, it is much more efficient to use it to cool the really hot water.

It would in my world be far better if isolating the heat transfer from the gearbox (as some already do) and coolingfins under the crankhousing.... One can also coat the whole crankcase together with the transfers with some heat barrier...

Isolating the gearbox heat is effective; cooling fins under the crankcase can work as well, but they may be counterproductive if the exhaust pipe is right below them.
That is why the Aprilia RSA125 had a carbon fiber heat shield between the cases and the pipe.


My favorite is barrier-coating all surfaces that are hotter than the gas passing over them (that excludes the exhaust duct because of the even hotter exhaust gases).

[ken seeber]

The thought behind doing this was driven loosely on KZs, but it is equally applicable to any engine (virtually all) with the exposed transfer passages.

With a piston crown around 250 deg, the intake charge has no chance to do anything but heat up on its journey into the transfer passages. Say a KZ was running at 39 kW and it obeyed the rule of thumb that 30% of fuel energy went to power, 30% to coolant and 30% to exhaust, then we could make a guess that the piston received 40% of the coolant energy = (39/3)*0.4 = 5.2 kW.

Air flow rate into a KZ, making some assumptions = 0.125 * a delivery ratio of 2.5 = 0.312 lit/rev @ 12500 rpm = 3750 lit/min = 62.5 lit/sec = 0.0625 met^3/sec @ 1.2 kg/met^3 = 0.075 kg/sec.

Using Q (kilowatt) = M (kg/sec) * Cp (kJ/kg) * ∆t (deg)

5.200 = 0.075 * 1.005 * ∆t

Therefore ∆t = 66 deg

So, if air-in temp was 25 deg, then after heating via the crankcase, it would then rise to 91 deg. So I could be wrong in my assumptions, the units or the maths but, if not, one can see that the air is already hot without any blowback from the exhaust when not at max power revs being added to the picture.

With a coolant temp of say 40 deg from the radiator, then this can only be of help in reducing the charge temp, hence increasing density and power and reducing the tendency for detonation.

Unfortunately this would not be an allowable addition or modification to a rule abiding KZ engine, but only something that could be introduced by the manufacturer for a subsequent 3 year homologation period.

Apologies if any of the above calcs are wrong.

[SwePatrick]

Ken, to think about:
Heat transfer from cylinder into airstream isn´t 100% effective.
The fresh gasses are traveling very fast and only the boundary layer is touching the transferwalls.
Thereby there´s a very little transfer of heat into the main bulk flow, it is some yes, but it´s very very hard to calculate.


Not quoting Ken:
I would say a barrier between gearbox and crankcase would be best if having a channel that is flowed with air from the fairing and away from engine somewhere suitable just to flush away the heated air in the channel.
I´m assuming this as i did a quite similar modifications in AMG mercedes, i put a flexible hose to pressurized duct in front of car(only 40mm diam), then lead it to flow cold air underneeth the intake manifold(v8 engine) this made a really noticable performancegain, if driving slow it did almost nothing, as expected, but if runing at 100km/h the inlet air temp sank about 13 degrees.
And if braking fast and rapidly take off again, i gained almost 0.2s 0-100km/h, this is almost free power to be had =)

[Vannik]

Ken,

Your calculations is spot on but conservative. A typical crankcase gas temperature for a watercooled but not crankcase cooled racing 2T 125cc making around 45hp is measured around 110degC to 120degC. Anyone that had to emergency strip one of these engines after a race will tell you the crank webs are above boiling point.

The flow through the transfers is highly turbulent and highly unsteady so no boundary layer worth anything has time to form. I find it strange that engine builders like to quote fully developed steady flow boundary layers derived for steady tube flow as being similar to what happens in an engine's ports. They are totally non similar.

[Muhr]

https://farnam-custom.com/resources/calculators

[jbiplane]

A bit offtopic question dont related to cooling. But my question can be very simple for local Gurus.
Does anyone have an idea where to source good quality easy to get helical gears to use in light engenes one stage reducers?
Yes it is possible to produce, but using of shelf components says of moto could cut the cost.
For this power range helical gears with module 1.5mm (1.75 or 2 if 1.5mm problematic) will work fine.
Big gear can have 56...60 teeth and small 17...20

[Condyn]

Does laminar flow even occur in two strokes?

I have a question for whoever has experience testing, in regards to cooling air cooled engines. ( I think TZ covered this some 2000 pages ago )
The copper “ gaskets “ that extend out from between the clamping surfaces and transform into cooling fins. I know copper conducts heat better than aluminum. I have been tossing the idea around of making a 4mm cylinder spacer out of copper that extends outwards to dissipate heat. Good idea? Bad idea? What other tricks have proven worthy of assisting in cooling an air cooled?

[wobbly]

The whole idea of cooling the transfer duct outer faces , was started by Jans sucess ( as is usual ) in cooling the opposite face , near the bore.
The kart engines have the carb and airbox directly in front of the crankcase - finning in this area does nothing , as there is no airflow.

I fitted a clamped on under plug temp sensor to the TM , with a tapped hole on the transfer duct face about 1/2 way up between the gasket split line and the water jascket.
The water exiting the head , on track , was at 42* , the cylinder outer wall temp I data logged at almost twice that - even with 142Km/Hr air passing over it at 22*

And the case behind the ignition ie the transfer entry area , maybe even hotter - im still unsure as to the temp of the oil in the clutch side cover on the other side.
But my idea to cool the transfer duct entry area in the case , with water flowing over the main bearings , would cool the trapped air behind the ignition , as well as the side cover oil.

In my opinion the idea of having a cylinder air shield facing the oncoming high speed air would have no discerable effect.
The whole upper cylinder liner is surrounded by water , any cooling of the cylinder outer water jacket would have virtually nill effect on the shape of the bore due to any temp delta across the alloy.

[SwePatrick]

Does laminar flow even occur in two strokes?

I would say never in any engine, just more or less turbulent.

As far as i know, there is a boundary layer even if the airmass is turbulent, just different 'size/thickness'.

And i´m with Einstein, there isn´t any free power if 'mechanicly' power the system that allows for a power increase.
Perpeteum mobile you know..

So if wasting energy in the pit/garage with a heatbarrier you gain the energy back on the track= win!
Wasting energy on the track to get energy on the track = fail!

[TZ350]