Running engine (diesel) with the ignition turned off

[NotBirdseye]

The thread actually began with this, then moved on to other things:

O.O THE HOLY GRAIL... IT HATH BEEN FOUND
Praise be to penberth.

 

[convey]

Since you tried to sell us some nonsense about compression ratio being dependent on the shape of the piston

I've pulled you up how many times for misrepresenting me, however, I uploaded two photos of pistons; one 8.5:1 compression ratio, the other 10:1 compression ratio. If the shape did not matter, why would they affect the compression ratio?

(What I wrote many times was that it was a combination of all the physical factors including shape of piston and chamber)

The volume at the end of the compression stroke, or clearance volume, is the volume enclosed by the piston and the adjacent end of the cylinder when the crank is at top dead centre.

Well, the "end of the cylinder", as you call it, is called the deck height and the height of the first piston ring.

But you're missing out the shape of the combustion chamber.

For no other reason that it's fun and pretty ... ICE engines are basically air pumps, the purpose of the fuel being to heat the air up to cause it to expand.

Did you know Rudolph Diesel's earliest engines were powered by coal dust? Rolls Royce even used to run in their big aircraft engines with it, and GM demonstrated an engine running on coal again back in the 1980s.

 

[Beneteau381]

Someone already snitched to them, but they won't say who.

Can the adults get back to discussing the finer details of the old Suck Squeeze Bang Blow cycle now?

I don't even remember Earlybird taking part in the discussion, did they appear at the climax specifically to be offended by it?

Who told you someone snitched? That would be a breach of the info rules?

 

[RichardS]

Who told you someone snitched? That would be a breach of the info rules?

The Mods will tell you that a post of yours has been subject to a report if you are warned or sanctioned but they won't tell you who reported it.

Richard

 

[Beneteau381]

The Mods will tell you that a post of yours has been subject to a report if you are warned or sanctioned but they won't tell you who reported it.

Richard

Ah, hasnt happened to me yet.

 

[rotrax]

I've pulled you up how many times for misrepresenting me, however, I uploaded two photos of pistons; one 8.5:1 compression ratio, the other 10:1 compression ratio. If the shape did not matter, why would they affect the compression ratio?

(What I wrote many times was that it was a combination of all the physical factors including shape of piston and chamber)

Well, the "end of the cylinder", as you call it, is called the deck height and the height of the first piston ring.

But you're missing out the shape of the combustion chamber.

For no other reason that it's fun and pretty ... ICE engines are basically air pumps, the purpose of the fuel being to heat the air up to cause it to expand.

Did you know Rudolph Diesel's earliest engines were powered by coal dust? Rolls Royce even used to run in their big aircraft engines with it, and GM demonstrated an engine running on coal again back in the 1980s.

Still flogging that dead 'un convey.

The compression ratio is one thing, and one thing only.

It is the swept volume of the cylinder divided by the volume of the combustion chamber at TDC.

The piston CAN have an effect, but it is only ONE part of the equasion.

Your 8.5:1 piston would be highly unlikely, in my VERY extensive experience, to actually give that ratio. And to find a production engine that has ALL compression ratio's the same is, like Rocking Horse $H1t, is a very scarce thing.

The gasket, combustion chamber, valve recession and even corbon build up ALL affect it.

As I am sure you know, but wont admit.

 

[NotBirdseye]

Ah yes but does the 'shape' of the piston have an effect?

 

[jbweston]

Ah yes but does the 'shape' of the piston have an effect?

Well, the shape of people's heads was once thought to indicate factors like criminal tendencies and intelligence.

Maybe we should study the shape of the heads of posters who carry on saying the same things ad infinitum in the hope of getting the last word.. Perhaps the shape of the head affects brain capacity. Or perhaps it doesn't.

For anyone comng to this thread late in the day, the original poster's question was answered in the first few posts. Just read the first page. The rest is irrelevant, how many angels on the head of a pin argumentifying.

 

[rotrax]

It's sort of irrelevent as petrol engines aren't using compression for the sake of ignition. Without checking Wikipedia, do you have any idea how, how difficult, and how high octane fuel, it would take to manage 14:1 compression? It's like saying all humans run sub-10sec 100m.

Comments, anybody?

FYI convey, the KTM Moto 3 engines are actually running those compression ratios. The oversquare high revving single cylinder engines have a reliable 50 plus BHP from 250cc.

On valve springs. They get away with 14:1 CR because the fuel injection and ignition are elecronicaly controlled to avoid detonation. Detonation is the curse of oversquare engines with big diameter pistons and combustion chambers. Very careful engineering of combustion space and valve to piston clearance is used. Of course, these days, CAD computer programmes assist greatly. My old mate Mervyn S of Rudge 250 fame has cut a cylinder head in half to view what goes on inside. Things have moved on since then.

As the spark plug(s) ignite the fuel/air mix it starts burning. Burning very fast, from the point(s) of ignition outwards. This flame front compresses the unburnt gas at the edges of the combustion chamber which, as you know from Boyles law, reaches the heat of self ignition, and then then ignites.

Two flame fronts, burning at perhaps 4 miles a second, colliding, make a noise - pinking - and can cause serious engine problems and overheating.

That is one reason we dont just stuff a great humpy piston in to give a high CR. The piston is important, but in reallity it is just blocking the cylinder up.

One of the humpiest pistons I know is the 1928 two stroke Levis 250. It has a massive hump but only 5:1 CR.

I wonder if you know why this is?

 

[rotrax]

Well, the shape of people's heads was once thought to indicate factors like criminal tendencies and intelligence.

Maybe we should study the shape of the heads of posters who carry on saying the same things ad infinitum in the hope of getting the last word.. Perhaps the shape of the head affects brain capacity. Or perhaps it doesn't.

For anyone comng to this thread late in the day, the original poster's question was answered in the first few posts. Just read the first page. The rest is irrelevant, how many angels on the head of a pin argumentifying.

Yes, but sometimes it is encumbent on those who know to put those who dont within their area of knowlege.

It is a bugger when they dont - or wont - get it!

 

[RichardS]

For anyone comng to this thread late in the day, the original poster's question was answered in the first few posts. Just read the first page. The rest is irrelevant, how many angels on the head of a pin argumentifying.

Anyone coming to this thread at any time during the last 2 years would have seen the answer.

Richard

 

[VicS]

I uploaded two photos of pistons; one 8.5:1 compression ratio, the other 10:1 compression ratio. If the shape did not matter, why would they affect the compression ratio?

If the change in shape alters the clearance volume the CR will be altered. If it does not the change in shape will not not alter the CR. This is because the CR depends on the volume not the shape.

But you're missing out the shape of the combustion chamber

.

The shape of the combustion camber is irrelevant. What matters is its volume

For no other reason that it's fun and pretty ... ICE engines are basically air pumps, the purpose of the fuel being to heat the air up to cause it to expand.

Did you know Rudolph Diesel's earliest engines were powered by coal dust? Rolls Royce even used to run in their big aircraft engines with it, and GM demonstrated an engine running on coal again back in the 1980s.

You dismiss the definition of compression ratio in a standard reference book.
What is your definition of compression ratio? ..................A straight question that requires a straight answer.

 

[penberth3]

……..You dismiss the definition of compression ratio in a standard reference book.
What is your definition of compression ratio? ..................A straight question that requires a straight answer.

I've already asked three times if we agree CR = Total Volume/Clearance Volume. No answer.

 

[VicS]

I've already asked three times if we agree CR = Total Volume/Clearance Volume. No answer.

He dismisses an equation like that which is why I am asking for a definition.
asking him to fill in the missing words:

Compression ratio is the ratio of ................... to ................... .​

​

 

[convey]

If the change in shape alters the clearance volume the CR will be altered ... The shape of the combustion camber is irrelevant.

Those appear to be two contradictory statements. How can it be irrelevant is changing the shape of the combustion chamber alters the clearance volume? Perhaps you've never worked on an engine whose chamber has been re-shaped, blueprinted or performance tuned an engine?

Volume does not exist. It is literally just space. Without the shape of the containing vessel, it is nothing, therefore it is the shape that determines the CR.

What you're doing again here, as I've point out before, in an attempt not to lose face over your simplistic understanding, is try and move the goal posts from shape (dimensions), to 'kind of shape' (e.g. to be more realistic; flat, wedge, hemi-, D etc) but in each kind of shape, the same would applies.

It is the shape (dimensions) of the various components that determines the CR, not the equation. It simply cannot be anything else.

 

[convey]

I've already asked three times if we agree CR = Total Volume/Clearance Volume. No answer.

That's because we're long past that point and it was always an irrelevant question.

What determines the Clearance Volume?

Let's just remind ourselves of where this all started, it was the incorrect or misleading statement that

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

--
BTW, just as an aside, I started this morning off reading the instructions included with a Mahle/Volvo piston and, funnily enough, they said precisely what I wrote about and was told was wrong, i.e. apply a bridge to hold the cylinder/s down, use a micrometer to measure. No mention of using "the proper tool" as another member wrote.

It seems even the manufacturers are wrong and don't know what they are talking about to this crowd.

 

[Beneteau381]

FYI convey, the KTM Moto 3 engines are actually running those compression ratios. The oversquare high revving single cylinder engines have a reliable 50 plus BHP from 250cc.

On valve springs. They get away with 14:1 CR because the fuel injection and ignition are elecronicaly controlled to avoid detonation. Detonation is the curse of oversquare engines with big diameter pistons and combustion chambers. Very careful engineering of combustion space and valve to piston clearance is used. Of course, these days, CAD computer programmes assist greatly. My old mate Mervyn S of Rudge 250 fame has cut a cylinder head in half to view what goes on inside. Things have moved on since then.

As the spark plug(s) ignite the fuel/air mix it starts burning. Burning very fast, from the point(s) of ignition outwards. This flame front compresses the unburnt gas at the edges of the combustion chamber which, as you know from Boyles law, reaches the heat of self ignition, and then then ignites.

Two flame fronts, burning at perhaps 4 miles a second, colliding, make a noise - pinking - and can cause serious engine problems and overheating.

That is one reason we dont just stuff a great humpy piston in to give a high CR. The piston is important, but in reallity it is just blocking the cylinder up.

One of the humpiest pistons I know is the 1928 two stroke Levis 250. It has a massive hump but only 5:1 CR.

I wonder if you know why this is?

I do! Question is does smarty pants?

 

[rotrax]

I do! Question is does smarty pants?

I should not think so!

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

 

[RichardS]

I do! Question is does smarty pants?

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

Richard

 

[VicS]

Those appear to be two contradictory statements. How can it be irrelevant is changing the shape of the combustion chamber alters the clearance volume?

What I said was, " If the change in shape alters the clearance volume the CR will be altered. If it does not the change in shape will not not alter the CR. This is because the CR depends on the volume not the shape. "
There is nothing contradictory in that!

Volume does not exist. It is literally just space.

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


ANSWER the question ........................... What is your definition of compression ratio ?

Begin with the words "Compression ratio is the ratio of.............