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Old 15th May 2014, 22:16   #61
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Default re: Oversquare Diesels

Yes, more with Diesel engine, since they ride with high compression.
your experience with two very differently engineered Bikes with different character allowed us to understand the topic practically.
Small info, Hadley engine firing order is unorthodox! Many loves it.
Same F1 rule applies to your Ducati. Inside city, switch to City mode, many parts goes to sleep so less heat & less fuel consuming(I know, Ducati will not allow you to do that).
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Old 16th May 2014, 09:31   #62
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Default re: Oversquare Diesels

Quote:
Originally Posted by narendra.vw View Post
Volume & compression ratio depends on engine design.
As you said for larger engine heater plug is not necessary. They have long stroke.
Stroke really matters.
Stroke and compression are two different things all together. Theoretically and mathematically you can get any compression you like with any stroke. (just change the piston diameter and you will see that it is true!).

The compression ratio for car engines, depends heavilly on the fuel, e.g. petrol (various octane numbers) or diesel. Volume that gets compressed is more relevant for the engine output as it correlates directly to how much fuel can be introduced per compression stroke.

Jeroen
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Old 17th May 2014, 07:14   #63
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Default re: Oversquare Diesels

Quote:
Originally Posted by Jeroen View Post
Stroke and compression are two different things all together. Theoretically and mathematically you can get any compression you like with any stroke. (just change the piston diameter and you will see that it is true!).

The compression ratio for car engines, depends heavilly on the fuel, e.g. petrol (various octane numbers) or diesel. Volume that gets compressed is more relevant for the engine output as it correlates directly to how much fuel can be introduced per compression stroke.

Jeroen
Don't think he mentioned that stroke and compression are related in that respect.

Consider two engines of same capacity, same number of cylinders, but different stroke and dia., C.R., etc.

Now, would the stroke length be important in the way the two engines behave?

Or rather, can you have different stroke lengths and make the engine behavior similar?

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Old 17th May 2014, 10:55   #64
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Default re: Oversquare Diesels

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Originally Posted by gthang View Post
Don't think he mentioned that stroke and compression are related in that respect.

Consider two engines of same capacity, same number of cylinders, but different stroke and dia., C.R., etc.

Now, would the stroke length be important in the way the two engines behave?

Or rather, can you have different stroke lengths and make the engine behavior similar?

Cheers
Absolutely you can, within a certain range of course.

Lets look at some of the statements made earlier:

Quote:
Old generation diesel engine had longer stroke length, meaning higher Compressed air before firing
This is incorrect. Longer stroke doesn't mean automatically higher compression. See my original post. If diesel is your fuel, you need a certain compression ratio. That is a given, you can go about it in different ways, under square, over square whatever.

The stroke of the engine is the result, more to your point, in how the overall engine characteristic need to be (e.g. power, torque, weight, size, cost etc etc). It

Quote:
As you said for larger engine heater plug is not necessary. They have long stroke.
As pointed out by Sutripta, there is no relation between stroke and heater plug.

So I do believe that the context in which stroke is discussed/used is incorrect. And it comes down to some basic fundamentals on how engines actually work.

Jeroen
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Old 17th May 2014, 11:14   #65
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Default re: Oversquare Diesels

Quote:
Originally Posted by Jeroen View Post
Absolutely you can, within a certain range of course.


As pointed out by Sutripta, there is no relation between stroke and heater plug.

Jeroen
A real world example of a shortstroke compression ignition (no heater plug) engine might help understand.

Cheers
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Old 17th May 2014, 17:57   #66
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Default re: Oversquare Diesels

Quote:
Originally Posted by gthang View Post
A real world example of a shortstroke compression ignition (no heater plug) engine might help understand.

Cheers
Here you go have a look at this, back to fundamentals on how a (diesel) works

http://hyperphysics.phy-astr.gsu.edu...mo/diesel.html

Fiddle around with the numbers, note stroke is not in any of the equations!

Q.E.D.

Here's another interesting article about the myth of long stroke/high torque

The author correctly states:
Quote:
So if torque is what accelerates a race car, why donít we use engines with 2-inch diameter cylinder bores and 6-inch long crankshaft strokes? Obviously there are other factors involved.
http://rehermorrison.com/tech-talk-5...ich-is-better/

Another interesting remark:

Quote:
The intake manifold, cylinder head runner volume, and camshaft timing all have a much more significant impact on the torque curve than the stroke Ė and are much easier and less expensive to change.
Obviously, he's talking about hot rod / race engines, but these are generic principles that apply to all engines.

But to my earlier point; stroke is a relevant factor in an engine, but it is a result of a number of engine requirement, rather then a determining factor and it is used out of context in earlier posts.


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Old 17th May 2014, 19:29   #67
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Default re: Oversquare Diesels

Quote:
Originally Posted by Jeroen View Post
Here you go have a look at this, back to fundamentals on how a (diesel) works

http://hyperphysics.phy-astr.gsu.edu...mo/diesel.html

Fiddle around with the numbers, note stroke is not in any of the equations!
Are Compression ratio, Expansion ratio, i.e, V1, V2, V3 dependent on stroke length? Yes, you can change volume by piston diameter, but so does stroke length.

Quote:
Originally Posted by Jeroen View Post
But to my earlier point; stroke is a relevant factor in an engine, but it is a result of a number of engine requirement, rather then a determining factor and it is used out of context in earlier posts.


Jeroen
Little bit of Chicken and egg story going on here.

Let's say I want a high revving diesel engine for use in a passenger car. I would use a shortstroke diesel, correct?

Would this engine now need a heater plug to start?

Let's say I need another engine for load carrying. I would use a longstroke diesel, right?

Would this engine need a heater plug to start?

Please explain.

Cheers
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Old 18th May 2014, 09:38   #68
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Default re: Oversquare Diesels

The post said that as time passed and metallurgy advanced, shortstroke engines for passenger cars were developed. Reducing stroke obviously reduced CR.

Now, if your fundamentals say that temperature increase due to compression is not dependent on CR, then you are right.

Yes, in today's diesel engine context, stroke length is not what dictates glow plug. But diesel injection and valve control has advanced quite a bit today.

He was talking historical reason.

Cheers

Last edited by GTO : 19th May 2014 at 15:08. Reason: Quoted post deleted. Thanks
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Old 18th May 2014, 10:58   #69
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Default re: Oversquare Diesels

Quote:
Originally Posted by Jeroen View Post
Here's another interesting article about the myth of long stroke/high torque

The author correctly states:

Quote:
So if torque is what accelerates a race car, why don’t we use engines with 2-inch diameter cylinder bores and 6-inch long crankshaft strokes? Obviously there are other factors involved.
First of all, Stroke does not necessarily decide the amount of torque. It determines the rpm range at which torque is delivered.

Long stroke engines have the ability to provide torque at low rpms, But dont rev high. Ex: Royal Enfield Bikes. They can lug quite a lot of load at low rpms but dont rev so high.

Another consequence of this: Power is product of torque and rpm (Energy*Rate). So long stroke engine do not provide that high power outputs. (high torque*Low rpm)

Short stroke engine can rev relatively high and provide torque (torque figures need not be that high) at those rpms. Ex: The duke 200. It provides almost the same power as the royal enfield, but much lesser torque at the same rpm as the enfield. It provides its torque higher up the rpm band.

Hence the higher power output, (Moderate torque*high rpm).

The reason why race cars dont use a large stroke small bore engine is that race engine need very high power output. That is, they need torque at higher rpms. Except during starting, the race cars travel at very high speeds and do not need low end torque. They need torque at maximum possible rpms. This allows them to harness good amount of energy (not necessarily very high) at Incredibly high rate( very high rpms).

Simplest possible example i can give is the one ive posted else where on this forum but am unable to find.

A cycle with a large peddle can be ridden by a person with a very heavy load at slow speed. Even without the load he will not be able to achieve much faster speeds because of the limit of his leg movement speed (Engine parts inertia).

A cycle with a small peddle can be ridden by the same person at very high speeds, but cannot carry high loads at low rpms (short peddle so very low torque). He will be able to reach very high speeds because his legs dont have to move that big a distance (as compared to big peddles) to turn them at a higher rate.

Quote:
The intake manifold, cylinder head runner volume, and camshaft timing all have a much more significant impact on the torque curve than the stroke – and are much easier and less expensive to change.
This is a very general statement. All of them put together may have (at the very most) an equal effect on torque as stroke. But Stroke determines the very basic and fundamental behavior of the engines.

That is why almost all passenger cars are undersquare (relatively larger load and lower rpm range). Commuter bikes are undersquare for the same reason as well. They do not need high power output, They need good low end torque to minimize usage of high rpms and achieve good mileage.

Extreme examples of this is marine engine. They have VERY high torque outputs at Very low RPMs (Large engines (parts) have high inertia).

Super bikes are oversquare to achieve high power output. Super cars have oversquare engines for the same reason.

Extreme examples of this are Race engines.

Last edited by rangakishen : 18th May 2014 at 11:13.
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Old 24th June 2015, 10:56   #70
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Default Re: Oversquare Diesels

Check out these data for Lombardini Engines;

http://www.lombardini.co.uk/#/lombar...nes/4551573211

They ALL seem to be oversquare
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