Running engine (diesel) with the ignition turned off

[convey]

You're trying to wind back and dumb down the conversion.

I asked you what determines VC?

What nonsense.... Next time you ask for a pint of beer you expect to get a pint of beer , not just a space.

Next time you order a beer, ask for it to be poured without a glass and let us know how you get on.

Volume isn't the stuff, it's just a measurement of the physical dimensions.

So, have you changed your mind 180° now and are confirming that the shape (dimensions) of the combustion chamber is relevant, because that's what it looks like to me.

 

[Stemar]

Blimey, are you lot still fighting?

A bunch of trolls squabbling over a bridge

 

[convey]

It's about getting them to think beyond the "what is", to the "how or why 'what is'".

And pointing out how stupid the original statement 'that piston and combustion chamber shapes don't affect compression ratio" was.

Once we get to the point of admitting that, in fact, piston and combustion chamber shapes determine the compression ration, we will be able to go back even further and consider the debate over whether, in general, a hemi-head and a bowled-piston is likely to create sufficient compression to run a diesel engine with.

Again, for convey's information, the huge hump has nothing to do with the CR of the Levis engine.

I apologise for not having an encyclopediac knownledge of every internal combustion engine ever produced. Can you show me a photo of a Levis 2 stroke cylinder head and piston and I might be able to respond. As far as the high compression KTM engine, like I said, you're talking about a tiny proportion of high performance engines equivalent to humans that can run sub-10 second 100m. Yes, it can be done but, no, only a tiny minority will ever be able to do it, and one has to wonder why they bother (no answer necessary, it's a competition sports bike, right?).

I'm going to apply an "exceptions dont prove a rule" maxim here.

 

[VicS]

deleted

 

[VicS]

[QUOTE="convey, post: 7293606, member: 179769"

Next time you order a beer, ask for it to be poured without a glass and let us know how you get on.
[/QUOTE]

Another good example of how the volume is not determined by the shape.... It does not make any difference to the volume if the glass is a tankard or a straight sided glass. A pint glass will hold a pint of beer whatever its shape.

Now answer the question:

What is your definition of compression ratio ?

 

[scottie]

Could somebody find and operate the off switch for this pointless ongoing farce

Please?

 

[convey]

I am happy to end it with something that is just as likely to get me banned if that is what is required?

Another good example of how the volume is not determined by the shape.... It does not make any difference to the volume if the glass is a tankard or a straight sided glass. A pint glass will hold a pint of beer whatever its shape.

Shape = dimensions.

As I wrote above, for some bizarre purpose, you're changing the argument from shape (dimensions) to kind of shape.

So, if you're incapable of following an analogy, what determines the various shapes of beer glass, and hence their volume?

(FWIW, I'd prefer sticking to cylinder heads and VC rather than explaining the analogy to you).

It's hysterical ... you just won't admit what determines the VC at any cost despite it making you look like a dick. You're digging your heels in like a 5 year old.

So, try it just once, what determines the VC?​

You can't use an equation, unless you understand what the components of the equation means.

 

[rogerthebodger]

I am happy to end it with something that is just as likely to get me banned if that is what is required?


Shape = dimensions.

Shape does not equal dimensions.

You can have the same shape with different dimensions. Both linear an volumetric .

As Vic demonstrated with a cone, a cube and a sphere. They are different shapes and different linear dimensions but the same volume.

You can have pistons with a different shape crown but displace the same volume.

The pistons yo posted pics in fact have a very similar shape by different volumes and its this different volumes that affect the CR not the shape.

I think you are confusing shape with size (volume)

 

[JumbleDuck]

Shape = dimensions.

I have been resisting, but it's time for lapse.

"Shape" is not the same as "dimensions". In fact, "shape" is what is left when you ignore dimensions. A sphere is a shape. A cube is a shape. A stellated dodecahedron is a shape. The piston of my 49cc moped is the same shape - across the top, anyway - as a piston from my 2247cc car.

Similarly, "dimensions" often ignore shape. Just think of how many different "10 metre" yacht designs there are. Same dimension, different shapes.

The combination of "shape" and "dimension" is "geometry". Compression ratio depends on clearance volume which in turn depends - amongst other things - on the geometry of cylinder crown and of the cylinder head.

 

[Beneteau381]

I think that it was actually Convey that Rotrax was addressing?

Richard

I know, I was being a smarty pants as well because I know what the strange shaped hump in the low compression two stroke is for

 

[Beneteau381]

I should not think so!

Again, for convey's information, the huge hump has nothing to do with the CR of the Levis engine.

Hee hee

 

[Beneteau381]

I think that it was actually Convey that Rotrax was addressing?

Richard

PS Why is the deflector provided on the top of the piston head in two-stroke IC engine? - Quora

 

[rotrax]

It's about getting them to think beyond the "what is", to the "how or why 'what is'".

And pointing out how stupid the original statement 'that piston and combustion chamber shapes don't affect compression ratio" was.

Once we get to the point of admitting that, in fact, piston and combustion chamber shapes determine the compression ration, we will be able to go back even further and consider the debate over whether, in general, a hemi-head and a bowled-piston is likely to create sufficient compression to run a diesel engine with.



I apologise for not having an encyclopediac knownledge of every internal combustion engine ever produced. Can you show me a photo of a Levis 2 stroke cylinder head and piston and I might be able to respond. As far as the high compression KTM engine, like I said, you're talking about a tiny proportion of high performance engines equivalent to humans that can run sub-10 second 100m. Yes, it can be done but, no, only a tiny minority will ever be able to do it, and one has to wonder why they bother (no answer necessary, it's a competition sports bike, right?).

I'm going to apply an "exceptions dont prove a rule" maxim here.

More total twaddle convey.

Hundreds of thousands of motorcycle competition only and street engines use very high compression ratio's, close to the KTM Moto 3 ratio. Coming in with cars now too as emmision control and fuel efficiency are becoming more desirable.

I was selling Husquvarna's sixteen years ago with electric starting and 12:1 CR.

Regarding a hemi head and a bowled piston, are you trying to get a spherical combustion chamber?

To achieve what you suggest is eminently possible but the hemisphere would be very small.

For example, a 2 litre diesel engine would require a combustion space in each cylinde of 25cc's to give 20:1 compression. Hard to fit the valves and injector in that spherical space

No designer would compromise in that way. A space a little smaller than a golf ball has been used with indirect injection diesels to achieve something like you suggest.

Indirect injection diesels less common now for manufacturing reasons.

Same results with direct injection and a simpler cylinder head.

You are moving the goalposts. Your origonal statement on another thread was that the piston alone controlled compression ratio.

I pointed out that in my 50 year experience of preparing high performance engines, balancing the combustion chamber volumes was important. I - and many others - have found that a BMC A Series Cooper 'S' engine, fitted with four identical pistons can, and usually did, have four different combustion chamber volumes, measured by burette. Hence four different compression ratio's.

A piston is easy, by comparison to a cylinder head, to make. They must be, as I have made two, both of which are still working.

So if we assume the specifications were adhered to with the pistons, the extra space, or reduced space, in the combustion chambers comes down to manufacturing of the cylinder head. The Weslake Patent heart shaped combustion chambers of the BMC A Series were never, in my experience, the same volume.

So an engine of this type, 4 pistons of the same OE spec or parts supply part number, woul have up to four different compression ratios, by as much as .75 of a ratio.



From which we can see clearly that the piston, of course, has an effect on the Compression ratio, but is only one part of the requirement.

 

[rotrax]

PS Why is the deflector provided on the top of the piston head in two-stroke IC engine? - Quora

Only pre Schnurle loop scavenge types. The deflector stopped about half of the fresh charge swanning off down the exhaust port before it did any work.

Many American outboards used deflector pistons.

I'm done here.

To get back to the OP, who's question has been answered many times, unless the battery is disconnected from the alternator, in my experience there is no problem. Disconnect the battery from the alternatoe, diodes go pop in the regulator/rectifier.

Engine keeps going.

 

[VicS]

I am happy to end it with something that is just as likely to get me banned if that is what is required?

that's the only sensible thing you've suggested in the entire thread.

Shape = dimensions.

Shape ≠ dimensions

So, try it just once, what determines the VC?

V_c is the volume enclosed by the piston at tdc. It includes the volume of any bowl in the piston crown, the volume of combustion space in the cylinder head and the volume determined by the deck height ( where deck height is what you were measuring with your bridge gauge) and the cylinder bore diameter​

Now answer the question. ................. What is your definition of compression ratio?

 

[black mercury]

I am happy to end it with something that is just as likely to get me banned if that is what is required?

Go for it!

 

[convey]

Shape ≠ dimensions

What shape cannot be described by its dimensions?
What has dimensions but is not a shape?

This is starting to sounds like some Aristotelean riddle.

 

[rogerthebodger]

What shape cannot be described by its dimensions?
What has dimensions but is not a shape?

This is starting to sounds like some Aristotelean riddle.

dimensions are defined as length ,width and height.

What do we mean by Dimension?
A measurement of length in one direction. Examples: width, depth and height are dimensions. ... a square has two dimensions (2D), and a cube has three dimensions (3D). In Physics it can also mean any physical measurement such as length, time, mass, etc.

Time is also considered in astrophysics and a dimension. and in mathematics you can have many dimensions in multidimensional arrays.

But in the physical world we only have 3

An irregular shape shape cannot be defined by its dimensions.

Some examples of regular and irregular shapes.

It not an Aristotelian riddle it your lack of understanding.

 

[VicS]

What shape cannot be described by its dimensions?
What has dimensions but is not a shape?

This is starting to sounds like some Aristotelean riddle.

Dimensions do not describe shape

Now answer the question.......... What is your definition of compression ratio ?

 

[convey]

dupe