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Old 11th May 2005, 17:57   #16
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Post no sparky, diesel

Quote:
Originally Posted by shravan316
Well, now i got a question for you guys... if its easier to ignite fuel with sparkplugs... then why not have diesel engines with spark plugs?? Whats the reason for not using spark plugs in diesel engines??
shravan:
go through these two websites. they'll help in clearing your doubts.

The Diesel Engine
Straight Dope - Diesel instead of Petrol

ads

Last edited by aah78 : 11th May 2005 at 17:58. Reason: aligning content
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Old 11th May 2005, 17:59   #17
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So to make things simpler and fool proof, we use a spark plug to ignite the fuel exactly when required
Exactly, it's the safest and the easiest way to run a petrol engine. A petrol engine might well run without a sprk plug but, it maynot be as reliable as our reguler petrol engines.

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Old 11th May 2005, 18:10   #18
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Hey people is it of any advantage if you use performance plugs on a non modiffied engine???
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Old 11th May 2005, 18:20   #19
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Quote:
Originally Posted by Shan2nu
A petrol engine might well run without a sprk plug but, it maynot be as reliable as our reguler petrol engines.
And there are more chances to see cylinder head blowing out of the bonnet

Some one mentioned about performance lag. Most common example is a 2stroke engine v/s 4 stroke engine. 2 stroke has one "power" stroke in every 2 strokes making more linear power delivery, while for 4 strokes, it is one "power" stroke in every 4 strokes.

But there are lot of advantages of 4 stroke, which is a different story.
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Old 11th May 2005, 18:25   #20
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read up on self detonation in petrol engines also
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Old 11th May 2005, 18:26   #21
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Quote:
Originally Posted by RX135
Some one mentioned about performance lag. Most common example is a 2stroke engine v/s 4 stroke engine. 2 stroke has one "power" stroke in every 2 strokes making more linear power delivery, while for 4 strokes, it is one "power" stroke in every 4 strokes.
But there are lot of advantages of 4 stroke, which is a different story.
Reminds me of motogp when the 500 cc two strokes and 4 strokes used to race together!

Forgot to mention one another thing. Knocking in petrol engine is when the charge ignites before the piston reaches TDC (top dead centre.

In a diesel engine the knocking is because the fuel ignites much after the piston has reached tdc and moves down.

So while in a petrol engine knocking can cause serious damages to the engine and foul with the working of the engine itself, in a diesel engine all that happens is loss of power as the piston has moved down some distance already.

This is why diesel engines are more tolerant to poor quality fuel than petrol engines!

Last edited by Harrie : 11th May 2005 at 18:31.
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Old 11th May 2005, 18:30   #22
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Hey people is it of any advantage if you use performance plugs on a non modiffied engine???
Well, for the OHC, Honda had 2 types of spark plugs. One for low rpm driving (Denso - K16PR-U11) and the other for high speed/rpm driving (Denso - K20PR-U11). I don't know if you can achieve a noticable power increase but, the reliability factor is always there.

Shan2nu

Last edited by Shan2nu : 11th May 2005 at 18:34.
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Old 11th May 2005, 18:48   #23
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Quote:
Originally Posted by Shan2nu
Then how do you explain pre-inginition or knocking. This is caused when the fuel ignites even before the spark plugs light up (due to higher compression than what the fuel was designed for).
This can be caused by carbon build-up inside the cylinder. Since carbon does not conduct heat as well as metal, the areas where the carbon build-up has occurred stay hotter and cause flash ignition of the fuel-air mix. Fuels such as Speed and Power, which contain detergents, wash the carbon residue away and thus reduce the occurrence of knocking.

I'm not saying that it is impossible to build an engine without spark-plugs; just that most modern petrol engines are designed to use them.
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Old 11th May 2005, 18:50   #24
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Quote:
I'm not saying that it is impossible to build an engine without spark-plugs; just that most modern petrol engines are designed to use them.
That's what i'm saying. Not impossible but, not practical at the same time.

Shan2nu

Last edited by Shan2nu : 11th May 2005 at 18:55.
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Old 11th May 2005, 18:53   #25
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There was one instance though, A two stroke petrol engine can run with out a spark plug.

I had come across this when I used to fiddle around with my grand-dad's TVS 50xl.. an old engine rebore with a locally available crowned piston, used to run with out the Ignition key, spark plug cable disconnected....

But used to die if more power is demanded..

Partially, In this scenario of a two stroke engine, there could be a partially continuous supply of charge..
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Old 11th May 2005, 18:57   #26
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Quote:
Originally Posted by Shan2nu
That's what i'm saying. Not impossible but, not practical at the same time.
Shan2nu, it is next to impossible. It would require ideal settings all the time. (By Ideal conditions, I mean, combustion chamber designed in such a way that flame front gradually travels from a ignition point to all other parts of the combustion chamber). So even if someone manufactures it, maintaing those ideal conditions at all the times is almost not possible and can not be controlled by engine designer. Or eventually, one might end up using other fuel like Diesel to make it work.
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Old 11th May 2005, 20:25   #27
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Quote:
Originally Posted by speedsatya
as long as there is a constant fuel supply,why do u need another spark .

even if fuel does not come in a constant spray,once the initial supply is exhausted there should be a lag in performance till the next supply starts.

If there is constant fuel supply what will burn the air and fueL?? spark is required all the time.. its impossible for a petrol engine to run without spark. Diesel on the other hadn work on glow plugs.. which head the mixture during cold starts.. then its the head and the compression that ignites mixture..
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Old 12th May 2005, 00:17   #28
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OK, agree some people really lack basics. Satya this was nt expected from you. I m really surprised.
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Old 12th May 2005, 00:23   #29
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Quote:
Originally Posted by west
OK, agree some people really lack basics. Satya this was nt expected from you. I m really surprised.
haha,
actually this was someone else's doubt.which also got me confused.
as it is i have graduated in electronics and telecommunications.so henceforth dont be surprised if i ask such supposedly stupid questions.
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Old 12th May 2005, 08:53   #30
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Quote:
Originally Posted by RX135
. But there are lot of advantages of 4 stroke, which is a different story.
Which one is more efficient 2 or 4 to the fuel consumed??


and why are deisel engines heavier?? I have seen guys who want to convert petrol into deisel

you need more strenght in walls to with stand higher compression.
we see 4 valves/cylinder , also 5 in ferrari the 5 valve opens up at 120 degree after 2 inlet valves to make the mixture rich. We see this tech only in ferraris think. (doesnt mean there are no 5 valve engines)

Last edited by west : 12th May 2005 at 09:03.
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