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question on internal combustion engine mounting variation


hoola
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While the efficiency loss due to the reciprocation of the pistons in an typical automobile  engine are well known, what if the engine were mounted horizontally, and laid flat with it's pistons arranged to move fore and aft and in alignment to the direction of the vehicle?  Would the inertial mass of the pistons/rocker arms moving backwards, and now in alignment with the vehicle motion, cause a slight gain in overall velocity to the vehicle due to simple momentum transfer? While the return piston travel would cancel out any forward velocity gain, would that not essentially remove the reciprocation losses as  found in a normally mounted engine, with the piston travels not in alignment with vehicular motion? in this case the engine would have to be an inline, as in a simple in line four cylinder, with no modifications other than the mounting change.

Edited by hoola
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  • hoola changed the title to question on internal combustion engine mounting variation
Posted (edited)

the mass of the piston/rocker arm assembly shuttles back and forth, absorbing energy from the system each time the direction of travel changes that otherwise would be available for rotational kinetic energy for the drive train. This is the main reason the wankel engine or turbines are tried to reduce this loss.

Edited by hoola
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35 minutes ago, hoola said:

absorbing energy from the system

But how does that absorb energy? I've never heard that. The Wankel engine might be able to rev higher, and thus give a higher power output per unit weight, but I havn't heard that it's more efficient. From memory, they were pretty thirsty.

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with each stroke of a piston, the direction of travel changes 180'.   The piston stops and has to be re accelerated twice each time the crankshaft completes a single turn. The wankel design is flawed in that the seals are difficult to keep working and the main inefficiencies deal with things other than reciprocation losses, which is complicated by the poor emmisions a wankel inherently has.  There are youtube videos that describe the extent of these reciprocation losses should you wish to find a more detailed explanation.

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3 hours ago, hoola said:

with each stroke of a piston, the direction of travel changes 180'.   The piston stops and has to be re accelerated twice each time the crankshaft completes a single turn. The wankel design is flawed in that the seals are difficult to keep working and the main inefficiencies deal with things other than reciprocation losses, which is complicated by the poor emmisions a wankel inherently has.  There are youtube videos that describe the extent of these reciprocation losses should you wish to find a more detailed explanation.

There may be a misunderstanding here. There is nothing energy-absorbing about the change of direction of the piston.  Its momentum changes, but then so does the momentum of another piston on the crankshaft to compensate.  The kinetic energy of the piston is transferred by the crankshaft to the flywheel  - and/or to other pistons - and then back to the piston again as it accelerates in the opposite direction. Don't rely on YouTube videos for explanations: many of them are made by idiots or people that can't explain things properly. The main losses in a reciprocating engine, apart from thermodynamic ones, are pumping losses (obviously and inevitably) and friction losses. Both can be considerable.  There are many sliding surfaces, e.g. piston rings sliding on the cylinder liner, plain bearings, cam followers against cams, and so forth. 

On your original question, it makes no difference how the engine is mounted in the vehicle. The momentum transfer takes place internally in a well-designed engine. Any momentum transfer that is not internally compensated will merely make the engine and vehicle vibrate at the frequency of the piston's motion. There is either way no net momentum transfer to the vehicle - unless the engine blows up and throws a piston of course. 😊  

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1 hour ago, exchemist said:

There may be a misunderstanding here.  Etc

+1 for a detailed explanation.

 

I would like to add the following.

Momentum will be accompanied by moment of momentum and momentum changes by (unwanted) torques.

That is why, in the many arrangements that have been used including the one you proposed, the pistons are aranged to reciprocate about the driveshaft axis.

Auto engines configurations and mountings have included the upright inline and transverse, the angled (between horizontal and vertical) inline and transverse,  and the horizontally mounted 'flat' engines.
Transverse mounting adds the requirements of changing the drive direction.

Older aero piston engines went the whole hog with radially mounted multicylinder engines.

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Posted (edited)

while I can see how placing the engine's piston travel inline with the vehicle motion (almost certainly) does not add any additional velocity to vehicle motion, I am surprised to see the issue of the reciprocation motion of each individual piston as not an inherent loss to a conventional style auto engine.

Edited by hoola
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5 minutes ago, hoola said:

while I can see how placing the engine's piston travel inline with the vehicle motion does not add any additional energy to vehicle motion, I am surprised to see the issue of the reciprocation motion of each individual piston as not an inherent loss to a conventional style auto engine.

But reciprocating in itself incurs no automatic energy loss. Imagine a spring in a vacuum holding a weight. Pull it down and release it, you have a simple reciprocating motion. But it's not losing energy because of the reciprocation. The only energy loss is due to heat produced in the metal of the spring, so it will finally stop going up and down. But the reciprocation itself doesn't consume energy. The loss of kinetic energy, as the weight stops, is transferred to the spring, or back to gravitational potential. 

In the engine, it's being transferred back to the flywheel, or the other pistons, as one piston stops. As stated above, the energy losses are in friction and gaseous drag. 

If the pistons and con rods were consuming energy as you suggest, they would overheat in no time.

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3 minutes ago, mistermack said:

But reciprocating in itself incurs no automatic energy loss. Imagine a spring in a vacuum holding a weight. Pull it down and release it, you have a simple reciprocating motion. But it's not losing energy because of the reciprocation. The only energy loss is due to heat produced in the metal of the spring, so it will finally stop going up and down. But the reciprocation itself doesn't consume energy. The loss of kinetic energy, as the weight stops, is transferred to the spring, or back to gravitational potential. 

In the engine, it's being transferred back to the flywheel, or the other pistons, as one piston stops. As stated above, the energy losses are in friction and gaseous drag. 

+1

17 minutes ago, hoola said:

while I can see how placing the engine's piston travel inline with the vehicle motion (almost certainly) does not add any additional velocity to vehicle motion, I am surprised to see the issue of the reciprocation motion of each individual piston as not an inherent loss to a conventional style auto engine.

Where do you think this supposedly lost energy goes when the piston crown stops and then changes direction.

Hint in order to stop it there must be a force and therefore there must be an equal and opposite reaction force on something else.

Edited by studiot
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studiot, you ask where does the energy go when the piston crown stops and then changes direction....it goes into the piston, as drawn from the spinning crankshaft....you have to put energy into a mass to start it moving or to change it's  direction of motion. Is this not a simple newtonian rule?

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3 hours ago, hoola said:

studiot, you ask where does the energy go when the piston crown stops and then changes direction....it goes into the piston, as drawn from the spinning crankshaft....you have to put energy into a mass to start it moving or to change it's  direction of motion. Is this not a simple newtonian rule?

If you read my post about this you will see I say the (kinetic) energy of the piston goes into the flywheel (and in some cases other pistons) and then comes back to the piston on its return stroke. Just as in @mistermack's  sprung mass example, the kinetic energy goes into potential energy in compressing or stretching the spring and then comes back to kinetic energy again.  But the total energy of the system stays constant, if there is no friction or other source of loss. That's what the crank does: transforms linear kinetic energy into rotational energy and back again.  

Think of a single cylinder engine. Every power stroke, the piston gives a kick to the flywheel, which is then able to move the piston back on the exhaust, induction and compression strokes, slowing down all the while, until it is given another kick by the next power stroke. The flywheel is the kinetic energy store and its speed changes  throughout the cycle as it gains energy from, and loses energy to, the piston.

When the piston decelerates, it does work on the crankshaft and flywheel, and then the crankshaft and flywheel do work on it to accelerate it again. No net energy loss need  occur.

Edited by exchemist
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it does seem I was incorrect in my assessment of the reciprocal loss, as the pistons slow down at the end of travel, returning the start up energy. The fact that the engine is a closed system was the key....my idea that energy must be used to slow down the mass is from an open system, say a space craft in space needing to exert energy to slow down. Thank you studiot and exchemist.

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1 hour ago, hoola said:

it does seem I was incorrect in my assessment of the reciprocal loss, as the pistons slow down at the end of travel, returning the start up energy. The fact that the engine is a closed system was the key....my idea that energy must be used to slow down the mass is from an open system, say a space craft in space needing to exert energy to slow down. Thank you studiot and exchemist.

Yes, that's it exactly. For an isolated mass, you would need to do work on it from outside in some way, to accelerate it.  But for the piston in an engine, it just exchanges kinetic energy with the flywheel and crank, twice per revolution of the engine.  

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2 hours ago, hoola said:

it does seem I was incorrect in my assessment of the reciprocal loss, as the pistons slow down at the end of travel, returning the start up energy. The fact that the engine is a closed system was the key....my idea that energy must be used to slow down the mass is from an open system, say a space craft in space needing to exert energy to slow down. Thank you studiot and exchemist.

 

17 hours ago, hoola said:

studiot, you ask where does the energy go when the piston crown stops and then changes direction....it goes into the piston, as drawn from the spinning crankshaft....you have to put energy into a mass to start it moving or to change it's  direction of motion. Is this not a simple newtonian rule?

You are mixing up thermodynamics and mechanics.

No you do not need to put energy into a mass to start it moving.

Stand under my window where the flower pots are and let me push one off the ledge.
When it hits your head tell me how much energy I put into it.

No the engine is not a closed system.
Mass in the form of air/fuel mixture enters and echaust exists.
It is known as a constant flow system or pseudo-closed since the same amount of mass exits as enters.
But that entering mass brings (chemical) energy with it.
So it is not an isolated system.The rising piston does work compressing the gas.
The expanding gas then does work on the piston.

Although work and energy have the same units and are different aspects of the same phenomen, there are subtle differences I suggest you look up.

https://www.google.co.uk/search?q=difference+between+work+and+energy&source=hp&ei=3YPVYdboC43KgQbT-6qYCw&iflsig=ALs-wAMAAAAAYdWR7R2QBD6hUnxptAl9631h-LuTuAZn&ved=0ahUKEwiWy9faw5r1AhUNZcAKHdO9CrMQ4dUDCAg&uact=5&oq=difference+between+work+and+energy&gs_lcp=Cgdnd3Mtd2l6EAMyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEOgsIABCABBCxAxCDAToOCC4QgAQQsQMQxwEQowI6CAgAEIAEELEDOg4ILhCABBCxAxDHARDRAzoFCC4QgAQ6CAguELEDEIMBOgUIABCxAzoICC4QgAQQsQNQAFj8LmCSMmgAcAB4AYAB2ASIAdI6kgELNi45LjguMy41LjGYAQCgAQE&sclient=gws-wiz

But +1 for accepting that you were not exactly correct before.

 

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1 hour ago, studiot said:

 

You are mixing up thermodynamics and mechanics.

No you do not need to put energy into a mass to start it moving.

Stand under my window where the flower pots are and let me push one off the ledge.
When it hits your head tell me how much energy I put into it.

No the engine is not a closed system.
Mass in the form of air/fuel mixture enters and echaust exists.
It is known as a constant flow system or pseudo-closed since the same amount of mass exits as enters.
But that entering mass brings (chemical) energy with it.
So it is not an isolated system.The rising piston does work compressing the gas.
The expanding gas then does work on the piston.

Although work and energy have the same units and are different aspects of the same phenomen, there are subtle differences I suggest you look up.

https://www.google.co.uk/search?q=difference+between+work+and+energy&source=hp&ei=3YPVYdboC43KgQbT-6qYCw&iflsig=ALs-wAMAAAAAYdWR7R2QBD6hUnxptAl9631h-LuTuAZn&ved=0ahUKEwiWy9faw5r1AhUNZcAKHdO9CrMQ4dUDCAg&uact=5&oq=difference+between+work+and+energy&gs_lcp=Cgdnd3Mtd2l6EAMyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEOgsIABCABBCxAxCDAToOCC4QgAQQsQMQxwEQowI6CAgAEIAEELEDOg4ILhCABBCxAxDHARDRAzoFCC4QgAQ6CAguELEDEIMBOgUIABCxAzoICC4QgAQQsQNQAFj8LmCSMmgAcAB4AYAB2ASIAdI6kgELNi45LjguMy41LjGYAQCgAQE&sclient=gws-wiz

But +1 for accepting that you were not exactly correct before.

 

You can treat an "ideal" flywheel, crank and piston assembly as a closed system, for the purpose of understanding why there are no intrinsic energy losses in the motion. 

All the other stuff, while obviously true of real engines, is extraneous to the problem. 

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5 hours ago, exchemist said:

All the other stuff, while obviously true of real engines, is extraneous to the problem. 

I don't quite agree.

Things are slightly more complicated than this.

An ideal flywheel, crank and piston assembly by itself is a closed system. Yes.

So it will continue its state of motion or rest indefinitely.

But if you want to supply shaft work you require to input that energy somehow.

And since some of the shaft work output of an IC engine goes to run absolutely necessary auxiliary devices, continuous energy input is required.
 

:)

Edited by studiot
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14 minutes ago, studiot said:

I don't quite agree.

Things are slightly more complicated than this.

An ideal flywheel, crank and piston assembly by itself is a closed system. Yes.

So it will continue its state of motion or rest indefinitely.

But if you want to supply shaft work you require to input that energy somehow.

And since some of the shaft work output of an IC engine goes to run absolutely necessary auxiliary devices, continuous energy input is required.
 

:)

Getting an engine to do work is extraneous to the problem in mechanics that the OP was trying to resolve. But never mind, it's solved now anyway.   

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7 minutes ago, exchemist said:

Getting an engine to do work is extraneous to the problem in mechanics that the OP was trying to resolve. But never mind, it's solved now anyway.   

No, an engine will not run without it.

An assembly as described without friction or any load will need at least an initial input of work (energy) to start.
Thereafter it will continue in its state of motion as you describe.

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Posted (edited)

as far as my original concept of laying the engine flat,  that could  advantage a lower vehicle center of gravity, but it's orientation to vehicle motion  is no doubt irrelevant.

Edited by hoola
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7 hours ago, hoola said:

as far as my original concept of laying the engine flat,  that could  advantage a lower vehicle center of gravity, but it's orientation to vehicle motion  is no doubt irrelevant.

As in the VW beetle (originally Hitler's "Strength Through Joy" car), the Porsche series derived from it and the VW camper van, all of which use flat 4 or flat 6 "boxer" engines. As the cylinders are more exposed, these can also make air cooling practical, simplifying the design.

Which reminds me of a story from my time in the Lubricants division of Shell UK, at the end of the 70s. Some fellow lodged a quality complaint that the Shell engine oil he had bought had gone solid in the sump and ruined his engine. We analysed a sample of the strange jellylike material from his engine and found traces of what seemed to be the oxidation products of ethylene glycol.  Further enquires revealed that as winter was coming on, he had decided it was time to put antifreeze in the engine. He had opened the only filler cap he could see and poured it in........ 

We also, at that time, made a special product for British Rail, called Rotella HST, for the Paxman Valenta engines in the High Seed Train. These were prone to leak traces of coolant into the oil system. From memory this product had some sort of boosted antioxidancy, to resist the autocatalytic effect of glycol oxidation products in the oil. But I digress. 

 

Edited by exchemist
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14 hours ago, hoola said:

as far as my original concept of laying the engine flat,  that could  advantage a lower vehicle center of gravity, but it's orientation to vehicle motion  is no doubt irrelevant.

The angle of the 'v' on opposed cylinder engines contributes to the 'smoothness' of the engine.
Flat 4 or flat 6 configurations are popular, as is 90o for V8s and 60o for V6s.
This has to do with the equal distribution of firing pulses in the 720o cycle.

Lately manufacturers have been using balance shafts to smooth out engine vibrations, and coming up with all sorts of weird angles, in order to make the engine more compact.

"Since 1991, Volkswagen has produced narrow angle VR6 engines with V-angles of 10.5 and 15 degrees. These engines use a single cylinder head shared by both banks of cylinders, in a design similar to the 1922-1976 Lancia V4 engine. The VR6 engines were used in transverse engine front-wheel drive cars which were originally designed for inline-four engines. Due to the minimal extra length and width of the VR6 engine, it could be fitted to the engine compartments relatively easily, in order to provide a displacement increase of 50 percent."

From

V6 engine - Wikipedia

Edited by MigL
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Posted (edited)

interesting on the narrow angled engine...and the putting antifreeze in the oil seems like an mcast thing to do. I talked to a guy in the 70's who had a vw hippievan and he added an oil cooler aftermarket device that he said helped in summer, though sometime he stuck pot down the oil filler.....

Edited by hoola
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