2021 Engine thread

[roon]

Pourus structures are far more effective at heat transfer actually.

Such as?

[godlameroso]

Steel honeycomb, among other lattice based structures. There's certainly plenty to go around.

[63l8qrrfy6]

Pourus structures are far more effective at heat transfer actually.

Such as?

The puffy jackets you wear in the summer to cool you off.

[63l8qrrfy6]

Steel honeycomb, among other lattice based structures. There's certainly plenty to go around.

It can t be. Convection and radiation through air gaps is small compared to conduction in metal.

[godlameroso]

Steel honeycomb, among other lattice based structures. There's certainly plenty to go around.

It can t be. Convection and radiation through air gaps is small compared to conduction in metal.

Depends, with oil squirters under the pistons as is usually the case, there is less mass and more surface area for flowing oil to cool the underside of the piston.

[roon]

That's true, I thought you meant something like a closed cell structure.

[63l8qrrfy6]

Steel honeycomb, among other lattice based structures. There's certainly plenty to go around.

It can t be. Convection and radiation through air gaps is small compared to conduction in metal.

Depends, with oil squirters under the pistons as is usually the case, there is less mass and more surface area for flowing oil to cool the underside of the piston.

I thought of a close cell as roon too. But with an open lattice you run the risk of not circulating the oil properly if it gets stuck into crevices (or does not reach certain revices), plus all the mass that only serves to create extra surface area.

I still think that a fancy wavy gallery as close to the crown and grooves is the way to go.

[godlameroso]

Fair enough.

[wuzak]

Pourus structures are far more effective at heat transfer actually.

Such as?

The puffy jackets you wear in the summer to cool you off.

Generally they are worn in winter here, keeping people warm by reducing heat transfer to the environment.

Air gaps act like insulation - it is how double glazing works, for instance, and why the windows on the inside of airliners are not cold to touch.

[wuzak]

Forgive me for being daft, but isn't the point of having steel pistons to reduce heat transfer from the combustion chamber to the crankcase, via oil?

The reason for choosing steel is that it can cope with higher temperatures than aluminium.

Honeycomb structures beneath the crown could serve to reduced heat transfer, especially if they are enclosed.

The idea being that the more heat kept inside the combustion chamber the better. This would also be achieved with as high a coolant temperature as possible.

The more heat retained in the chamber the more power to drive the engine. Higher coolant temperatures increase transfer rates in radiators, reducing the size of those. Less heat transfer between combustion chamber and coolant also means smaller radiators.

Similarly, the less heat transfer through the piston the smaller the amount of cooling oil required. Which means a smaller oil cooler. And less power to drive the oil pump. Which means better aero and more power at the crank.

[roon]

Would it be possible/disadvantageous to cool an engine via the working fluid? As part of the cycle parameters, or to design a new cycle. Perhaps via:

-Over-expansion
-extra stroke/s
-fuel choice
-water injection a la 6-stroke concept

Negating the need for coolant, pumps, heat exchangers, etc. I wonder if the tradeoffs from cycle modification/diminished engine output could be outweighed by removal of cooling devices. All waste heat dumped out the exhaust along with and/or in-between the combustion products. Similar to a gas turbine.

[J.A.W.]

Would it be possible/disadvantageous to cool an engine via the working fluid? As part of the cycle parameters, or to design a new cycle. Perhaps via:

-Over-expansion
-extra stroke/s
-fuel choice
-water injection a la 6-stroke concept

Negating the need for coolant, pumps, heat exchangers, etc. I wonder if the tradeoffs from cycle modification/diminished engine output could be outweighed by removal of cooling devices. All waste heat dumped out the exhaust along with and/or in-between the combustion products. Similar to a gas turbine.

Well roon, as it happens...

Rotax/BRP do make an engine, an 850 twin 2T E-TEC for Ski Doo snowmobiles...

https://www.youtube.com/watch?v=pASvNm-YFwc

& although an efficient DI unit..
..when operating WFO, the engine injects extra fuel via its T-Bs, which both cools the engine internally..
& allows for the needed hard running fuel metering..
..it also features composite Al/Fe piston construction, to boot..

[wuzak]

Would it be possible/disadvantageous to cool an engine via the working fluid? As part of the cycle parameters, or to design a new cycle. Perhaps via:

-Over-expansion
-extra stroke/s
-fuel choice
-water injection a la 6-stroke concept

Negating the need for coolant, pumps, heat exchangers, etc. I wonder if the tradeoffs from cycle modification/diminished engine output could be outweighed by removal of cooling devices. All waste heat dumped out the exhaust along with and/or in-between the combustion products. Similar to a gas turbine.

Well roon, as it happens...

Rotax/BRP do make an engine, an 850 twin 2T E-TEC for Ski Doo snowmobiles...

https://www.youtube.com/watch?v=pASvNm-YFwc

& although an efficient DI unit..
..when operating WFO, the engine injects extra fuel via its T-Bs, which both cools the engine internally..
& allows for the needed hard running fuel metering..
..it also features composite Al/Fe piston construction, to boot..

It cools the induction charge, not the engine. There is still a cooling system.



http://www.snowmobile.com/manufacturer/ ... -850-e-tec

[J.A.W.]

I did not claim it was the sole cooling method/system..
..but actually, it does offer significant extra cooling*, internally.. via 'latent heat' effects..

..just as the BMW 801 engine which featured DI.. some decades ago..
also derived cooling benefit from extra fuel added similarly by aux' injection upstream ( to the air intake)..

..as needed.. ..to stave off 'heat-soak' induced power fade/melt-down - when running real hard..

This method is, of course, also specifically excluded from F1 by the current tech regs..

* If you have access to a (carb equipped) 2T powered road vehicle which has a temp gauge,
you can do an empirical test which demonstrates this..
..run it up to SOP temp, find a long downhill slope, & flick the ignition 'kill switch',& hold it WFO,
.. then by rolling it downhill, while still in gear, you can see the temp rapidly drop - in real time...

[Tommy Cookers]

extra fuel is said to alleviate running conditions that would otherwise distress an engine by reducing the flame temperature

whether this applies if the extra fuel still amounts to a leaner than stoichiometric mixture is a question