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Old 07-29-2005, 05:28 PM   #1
6000LE
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Diesel

Why was it when I was drivinf a diesel jetta is sounded like a tractor
From what i know diesel engines have no spark plugs
but what difference does that make the car sounded like a broken airplane starting up and it was BRAND NEW!!
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Old 07-29-2005, 05:32 PM   #2
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huh? whats your question?
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Old 07-29-2005, 06:34 PM   #3
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diesels run on detonation.

Serioulsy, when your normal gasoline car knocks or pings from detonation, that's because the compression is causing the fuel to ignite in the alraedy hot cylinder before the spark plug sparks.

Diesels run specifically on having high compression (usually between 16:1 and 20:1), compressing the air and fuel until it ignites on it's own. the cylinder has to be hot for this to happen, so they have glow plugs that warm up the combustion chamber befor eyou start it.

But this is why they always sound like a gasoline car that is knocking from overheating.
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Old 07-30-2005, 09:02 PM   #4
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Also, if I might ad, modern Diesel engines are becoming more and more refined. For example, a brand new Merc or BMW diesel will have next to no knocking

I'll move this, seeing as it's about Diesel in general!
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Old 07-31-2005, 12:37 AM   #5
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Quote:
Originally Posted by 6000LE
Why was it when I was driving a diesel jetta is sounded like a tractor

Because I stole the TDI engine and replaced it with a tractor engine.

EDIT: Im sorry, don't listen to my rambling. Listen to chris.
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Old 08-01-2005, 01:20 AM   #6
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Quote:
Originally Posted by ChrisV
the cylinder has to be hot for this to happen, so they have glow plugs that warm up the combustion chamber befor eyou start it.

I have read this in many places; however I am puzzled. How do you heat the engine up? A battery could not possibly heat the engine up enough to do this without killing itself, right? And it seems like it'd be really inconvienent to plug it in to a 110vAC or 220vAC outlet.

How's the engine warm up? Where to the glow plugs get power?
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Old 08-01-2005, 02:58 AM   #7
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Quote:
Originally Posted by ChrisV
Serioulsy, when your normal gasoline car knocks or pings from detonation, that's because the compression is causing the fuel to ignite in the alraedy hot cylinder before the spark plug sparks.
How does a gasoline engine prevent the compressed air-fuel from igniting before the sparkplug???
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Old 08-01-2005, 05:31 AM   #8
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Quote:
Originally Posted by moostang104314
How does a gasoline engine prevent the compressed air-fuel from igniting before the sparkplug???
It will only ignite on its own if you compress it too much. That's why engines with high compression ratios run premium fuel. The premium fuel has a higher octane number, which means it will withstand more compression before it ignites. Like Chris said, diesels run higher compressions ... they are designed to work like this ... fuel engines aren't, so they generally have lower compression ratios.
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Old 08-01-2005, 07:37 PM   #9
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Quote:
Originally Posted by windsonian
It will only ignite on its own if you compress it too much. That's why engines with high compression ratios run premium fuel. The premium fuel has a higher octane number, which means it will withstand more compression before it ignites. Like Chris said, diesels run higher compressions ... they are designed to work like this ... fuel engines aren't, so they generally have lower compression ratios.
ooo... thanx a lot!
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Old 08-01-2005, 07:50 PM   #10
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Quote:
Originally Posted by Jon_K
I have read this in many places; however I am puzzled. How do you heat the engine up? A battery could not possibly heat the engine up enough to do this without killing itself, right? And it seems like it'd be really inconvienent to plug it in to a 110vAC or 220vAC outlet.

How's the engine warm up? Where to the glow plugs get power?

The heat is caused by compression, as you compress anything, heat builds, when the heat reaches a point high enough it ignites the fuel.
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Old 08-01-2005, 07:55 PM   #11
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Quote:
Originally Posted by Jon_K
I have read this in many places; however I am puzzled. How do you heat the engine up? A battery could not possibly heat the engine up enough to do this without killing itself, right? And it seems like it'd be really inconvienent to plug it in to a 110vAC or 220vAC outlet.

How's the engine warm up? Where to the glow plugs get power?

A glow plug is essentially a controlled direct short. And yes, a battery can easily do the job (you can arc weld with a fully charged 12V battery, due to the high amperage). the glow plug starts out drawing a fairly high amperage to heat up (often glowing white hot) and slowly stabilizes (usually taking about 10-15 seconds from completely cold).



Once this is hot enough, the cylinder warms up. Then the high compression of the pistons does the job. Remember, air generates heat just from being compressed. So you combine a heated up cylinder with high compression 9usually considerably higher than gasoline engines can handle) and you get ignition. the high compression is the main reason the engines make so much torque, and the fact that they effectively run on detonation is teh reason they dont' rev very far (relying on compression alone to provide ignition is not reliable at elevated rpm, and in fact, simply stops happenning with regularity at higher rpm, becoming it's own rev limiter).
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Old 08-01-2005, 08:00 PM   #12
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And Chris Demonstrates how to properly answer a question, And how I am dumb...
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Old 08-01-2005, 08:01 PM   #13
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Quote:
Originally Posted by Zalight
And Chris Demonstrates how to properly answer a question, And how I am dumb...
Ya but its okay to be shown up by Chris lol.
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Old 08-01-2005, 08:31 PM   #14
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I tend to like it, Because I learn more that way.
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