Running engine (diesel) with the ignition turned off

[NotBirdseye]

I think convey right there has pointed out his own misunderstanding of the concept of the Engine compression ratio...

 

[convey]

However many times you repeat it, it's simply not true. The conversation is just going above your and his head, probably because in his entire career, he's not had to consider it. I accepted pages ago that I'm only deal with a fitter and gave up trying to enlighten him.

You don't even realise how dumb the counter arguments are, culminating in the one below.

So here is two people who have to have the last word, trying to out last word the other.

Nah, it's just a whole load of handflapping because small clique can't admit their engine god said a really stupid thing.

The shape of the piston crown or cylinder head does not affect the compression ratio.

And they still can't answer, or admit what determines the volume.

It's pathetic.

Now they're saying, "Oh, but he only meant if it was a square or spherical piston instead".​

Really? I don't think so ...

Look, the piston could have Mickey Mouse ears and it would not matter ... as long as the combustion chamber had holes for them to fit on. The same 3/4 phsyical things would still determine the CR, not the equation. The ratio only descibes their relationship.

(cue: someone going off to Google to see if there was ever a square or spherical piston to make it look l ike I am wrong)

 

[rogerthebodger]

Any one who knows metrology will know several ways to measure volume without knowing the linear dimensions.

When I reprofiled cylinder combustion chambers and balanced the volume of combustion chambers I could not just take the linear dimensions I would measure the volume with a burette.

An external volume like the volume of a domed piston you would use a measuring jug or graduated bowl like SWMBO uses in the kitchen.

 

[RichardS]

I accepted pages ago that I'm only deal with a fitter and gave up trying to enlighten him.

You can't get quicker that a Kwik Fit fitter, we're the boys to trust.

Richard

 

[penberth3]

Now, how about that #348 edit?

Richard

Are you keeping notes?

 

[NotBirdseye]

He's keeping score. I had deducted a point... but on reflection he deserved a point back for the underlying principle...

 

[RichardS]

He's keeping score. I had deducted a point... but on reflection he deserved a point back for the underlying principle...

Richard

 

[VicS]

A shape is described by its dimensions. The two are inseparable.
You're moving the goal posts here to introduce ridiculousness, a sort of reductio ad absurdum (reduction to absurdity) of spheroidal, pyramidal pistons. Show me any.
And let's be clear, I've always argued it was the match of the piston crown and cylinder head not the shape of one, as Paul introduced.
You're basis your conculsion on a fallacy. "the only dimension you can measure is the volume".
Really?
So if I take a ruler and do a π r² I can't measure the top piston? I can't measure the deck height, I can't measure the pin height, I can't measure the depth of a hemi-spherical chamber, and divide by 2 the spherical dimensions?
Why not just use the manufacturing drawings used for the design, either for the casting or the CNC?
But how do you know the volume in the first place is something was not measured?

I have here four objects
One is a cube with a side length of 4.64 cm
The second is a cuboid measuring 10 cm x 5 cm x 2 cm
The third is ball with a diameter of 5.76 cm
The fourth is a cone with a height of 10 cm and base diameter of 4.37 cm

If you determine the volume of these, no matter if you use Shaw's jug method, Archimedes' bath-tub method or Covey's measuring stick method, you will find they all have a volume of 100 cm³
All four are different shapes but have the same volume, proving that varying shape does not determine volume

I also have two other balls one has a diameter of 4.57 cm, the other a diameter of 7.26 cm.
You will find that these are 50 cm³ and 200 cm³ respectively

Combined with the ball in the first series of objects you can now see that I have three objects with the same shape but with different volumes, proving that varying volume does not determine shape.

Compression ratio of an internal combustion engine is defined as the ratio of the volume enclosed in the cylinder at outer dead centre to the volume enclosed at the end of the compression stroke, or expressed differently the ratio of the swept volume plus clearance volume to the clearance volume where the clearance volume is the volume enclosed by the piston at top dead centre.

We have demonstrated that volume is not determined by shape therefore we can say that compression ratio, because it is defined solely by volumes, is not determined by the shapes of the defining volumes

QED

 

[black mercury]

Convey, could you please tell us if you are discussing the static compression ratio or are you talking about the dynamic compression ratio. The two are very different. Static compression ratio is purely academic, the important one is the dynamic compression ratio when the engine is running, which will vary with engine speed and load. The design of the combustion chamber, piston crown, fitting of swirl flaps, if turbo or supercharged, etc etc, will all go towards determining the dynamic compression ratio.
So, which is it?

 

[convey]

Static, but I don't think any of those will affect dynamic the way the cams will. It's all about intake cam timing.

We have demonstrated that volume is not determined by shape therefore we can say that compression ratio, because it is defined solely by volumes, is not determined by the shapes of the defining volume

No, you have not.

All you're attempting to do is a 'peanut under the shell' game, to re-define the meaning of the word "shape", and what the conversation was about; and further displayed a lack of techincal understanding by fudging your statement with your use of the words determined and defining.

What you've written is, " volume is defined solely by volume", so same the question remains,

What "defines" the volume at TDC?​

A volume is defined not defining. That's like saying a vacuum makes its container.
--

I live in the real world. Never at one moment did I ever consider Mickey Mouse pistons matching Donald Duck combustion chambers.


This entire discussion started because I pointed out the engine as animated was unlikely to work because matching dished pistons with a hemispherical combustion chamber was unlikely to produce a sufficient CR.


I was then told this was nonsense, that the shape of the piston and the shape of the combustion chamber had no effect defining CR, only the equation did. A ridiculously stupid statement, because the shape of the piston and the shape of the combustion chamber determines the CR (equations only describe it).

I mean, if you want to talk about "shapes", why not let's discuss penis shaped pistons and vagina shaped combustion chambers, just to make it even sillier? I hope the motor has good lubrication because a lot of heat is going to be generated by them, but the same principles would apply. The bell end would also interfere with the flame front and therefore combustion, however, it might assist in scavenging on the down stroke.

--

So, the big lesson to take from all this is equations don't determine anything. Piston and combustion shapes (dimensions) do. Equations only describe what's going on.

 

[NotBirdseye]

?‍

 

[rogerthebodger]

Static, but I don't think any of those will affect dynamic the way the cams will. It's all about intake cam timing.



No, you have not.

All you're attempting to do is a 'peanut under the shell' game, to re-define the meaning of the word "shape", and what the conversation was about; and further displayed a lack of techincal understanding by fudging your statement with your use of the words determined and defining.

What you've written is, " volume is defined solely by volume", so same the question remains,

What "defines" the volume at TDC?​

A volume is defined not defining. That's like saying a vacuum makes its container.
--

I live in the real world. Never at one moment did I ever consider Mickey Mouse pistons matching Donald Duck combustion chambers.


This entire discussion started because I pointed out the engine as animated was unlikely to work because matching dished pistons with a hemispherical combustion chamber was unlikely to produce a sufficient CR.


I was then told this was nonsense, that the shape of the piston and the shape of the combustion chamber had no effect defining CR, only the equation did. A ridiculously stupid statement, because the shape of the piston and the shape of the combustion chamber determines the CR (equations only describe it).

I mean, if you want to talk about "shapes", why not let's discuss penis shaped pistons and vagina shaped combustion chambers, just to make it even sillier? I hope the motor has good lubrication because a lot of heat is going to be generated by them, but the same principles would apply. The bell end would also interfere with the flame front and therefore combustion, however, it might assist in scavenging on the down stroke.

--

So, the big lesson to take from all this is equations don't determine anything. Piston and combustion shapes (dimensions) do. Equations only describe what's going on.

Clearly we cannot understand what you are attempting to get at why don't you tell us so we can just move on.

 

[NotBirdseye]

No no, he's trying... in effect... to deny that Area x Height = Volume. Because it's an equation and merely describes what is going on and doesn't define anything....

 

[rogerthebodger]

No no, he's trying... in effect... to deny that Area x Height = Volume. Because it's an equation and merely describes what is going on and doesn't define anything....

You are correct. He if fixated on shape or something defines the CR where as its the 2 volumes as we already stated countless times.

 

[convey]

No no, he's trying... in effect... to deny that Area x Height = Volume. Because it's an equation and merely describes what is going on and doesn't define anything....

Yes, equations only describe what's going on, not define what's going on.

But, no, the equation of the volume would be far more complex than V=πr2h (area of piston top times length of the stroke), because of the additional volume of the combustion chamber.

What defines what is going on is the shape (dimensions) of the piston and combustion chamber. The opposite of what was said where we started.

Why, because they define the volume at TDC, that then defines the ratio.

 

[rogerthebodger]

Yes, equations only describe what's going on, not define what's going on.

But, no, the equation of the volume would be far more complex than V=πr2h (area of piston top times length of the stroke), because of the additional volume of the combustion chamber.

What defines what is going on is the shape (dimensions) of the piston and combustion chamber. The opposite of what was said where we started.

Why, because they define the volume at TDC, that then defines the ratio.

As has been demonstrated before its the volumes that important. The same volume can be made up by ib different shapes as demonstrated by VicS.Vic also demonstrated then you can have the same shape with different volumes.

You are confusing the two.

You an calculate the volume of any shape by breaking the shape in to sections that become a shape that can be calculated and all all the resolution volumes together to get the overall volume.

This is done with areas when calculation the 3rd or 4th moment of area for beam stress analysis.

The more complex the shape the more elements you need to break the volume or area into so the overall calculation become more complex.

What I think you are trying to get at is that if you change a piston in an engine with a piston that had a bigger or smaller shape in the piston crown you will change the CR providing and other shapes than make up the combustion chamber does not change.

In this setup of cause the CR will change because the volume of the combustion chamber will change. A change to any of the volume in the cylinder will change the volumes hence the CR.

We just don't understand what you are trying to prove.

 

[VicS]

No, you have not.

Demonstrating that volume is not determined by shape is exactly what I have done. I have shown that either shape or volume can vary independently of the other.

All you're attempting to do is a 'peanut under the shell' game, to re-define the meaning of the word "shape", and what the conversation was about; and further displayed a lack of techincal understanding by fudging your statement with your use of the words determined and defining.

The words "determined" and "defining " were chosen for the difference in their meanings.

What you've written is, " volume is defined solely by volume", so same the question remains,

What "defines" the volume at TDC?​

​

What I actually wrote was, "We have demonstrated that volume is not determined by shape therefore we can say that compression ratio, because it is defined solely by volumes, is not determined by the shapes of the defining volumes"​

The sentence as a whole, as written and punctuated, makes sense, You are just quoting random words from it.​

​

The volume at TDC is the volume enclosed by the piston and the adjacent part of the cylinder when the crank is at top dead centre.​

A volume is defined not defining. That's like saying a vacuum makes its container.

The defining volumes are those volumes used in the definition of compression ratio.
--

I live in the real world. Never at one moment did I ever consider Mickey Mouse pistons matching Donald Duck combustion chambers.


This entire discussion started because I pointed out the engine as animated was unlikely to work because matching dished pistons with a hemispherical combustion chamber was unlikely to produce a sufficient CR.


I was then told this was nonsense, that the shape of the piston and the shape of the combustion chamber had no effect defining CR, only the equation did. A ridiculously stupid statement, because the shape of the piston and the shape of the combustion chamber determines the CR (equations only describe it).

None of this rambling nonsense has anything to do with my post.

I mean, if you want to talk about "shapes", why not let's discuss penis shaped pistons and vagina shaped combustion chambers, just to make it even sillier? I hope the motor has good lubrication because a lot of heat is going to be generated by them, but the same principles would apply. The bell end would also interfere with the flame front and therefore combustion, however, it might assist in scavenging on the down stroke.

Having demonstrated a lack of understanding of mathematics and engineering and poor literacy you now descend to vulgarity. Perhaps it is time for the the forum admin team to award you a period of shore leave so that yo can find some courses in these subjects

--

So, the big lesson to take from all this is equations don't determine anything. Piston and combustion shapes (dimensions) do. Equations only describe what's going on.

Equations do not describe what is going on . They are algebraic expressions of the principles and definitions involved

 

[penberth3]

……..I live in the real world...…

Comments, anybody?

 

[Beneteau381]

Comments, anybody?

Woop woop!

 

[jbweston]

Comments, anybody?

Let's hope the protagonists are running out of steam.