Diesel Noise Analysis
 

I've seen postings here about different sounds that are produced by a Diesel engine, and have experienced them all, I'm sure. One thing I would like to see here is a solid set of definitions for these sounds. For instance- what I've noticed from my car-

-Normal warm idle- smooth sewing machine sound- probably no special name for this one, except maybe "all's well"
-Cold Idle on straight Diesel fuel- winter or summer- idle is much more noisey- what causes this in a Diesel but not a gas engine?
-Cold idle with 30% WVO- deep knocking sound- almost like rod bearing failure, but it goes away after 5 mintutes of warm-up. Is this called "nailing" or just "knock"?
-Warm idle with 30% WVO- engine becomes so quiet, you might believe it's not a Diesel. Why does WVO make the engine so much quieter?
-Cruising with straight Diesel, especially winterized fuel- frequent bursts of what sounds exactly like spark knock or pinging in a gas engine, except it happens opposite to gas engine- on trailing throttle, as opposed to accelerating. Should this be called nailing, knock or pinging, and again what causes it?
-Cruising with 30% WVO- absolutely no pinging sounds, smooth drone, seemingly more power. Seems like such a good thing, but again, I can't understand why WVO would cause this.

Dave

1976 300D

Because Diesel designed his engine to run on plant oils!

Possibly just different flame rate spread causes the diferences primarily. On normal diesel the activity of buirn in the cylinder is over a long time before the piston is very far down the bore. I suspect with non petrolem products the period is much longer and translates into much smoother and less noisy power strokes. A softer primary ignition of the fuel is also going to go a long way to reduce knock,The start of the initial burn is much less dramatic but endures longer in my opinion. With gas engines the period of burn lasts a great deal longer than diesel in fact not unusual to get flames out the exhaust headers. WVO should in theory be a lot less punishing to the block. During certain operating loads and rpms there are probably some other complications that are harder for a simple guy like me to understand when wvo is either the fuel or a portion of it. I am probably wrong in what i think but I did not notice a lot of people jump on this thread so thought I would mention one of my thoughts. Still burning petro products myself. Wife hides her canola oil everytime I mention alternative fuels. :D

Unless you have a 603 then it goes; tick, tick, tick, tick. :D

Diesel noise is something I've spent a long time analyzing. A diesel engine makes loud noise when the combustion is sudden but it can be quiet if the combustion is gradual or weak/non-existant, i.e. a quiet diesel doesn't necessarily indicate all is well.

Increased noise at cold idle is caused by delayed combustion which is caused by insufficient combustion chamber temperature. Cold WVO probably delays the combustion even further because of its viscosity, but when heated up it has a higher cetane number than straight diesel, thus it burns quicker and more gradually -> less knock.

A diesel should not have any pinging noises while cruising, otherwise you probably have a bad injector. My 82 developed this problem and I found out #5 injector was just pissing. Replaced the injector and pinging went away, but idle got louder because previously the #5 cylinder wasn't combusting.

My 96 has a very nice sewing machine idle, but when cold there's some pinging while cruising around 3000 rpm. I suspect a bad injector and will try some diesel purge.

My 83 is strange however. It has a quiet idle when cold and semi warmed up, but when fully warmed up it's noticably louder with a slightly varying combustion knock. The only explanation that I can come up with is that when it's cold the combustion temp isn't high enough for complete combustion, thus the lower noise, but there's barely any smoke even when cold. Does anyone have another explanation?

"quicker and more gradually"- that sounds like a self-contradicting statement, but not at all at odds with the mysteries of Diesel combustion. For instance, I've read posts here that say WVO has higher Cetane, hence ignites much quicker. Yet, one would think that a faster explosion would create a louder knock. But I only get a much louder knock when the WVO is stone cold. Once things warm up a bit, the engine gets very quiet on WVO blend.

Note that I don't have a heated tank- the fuel mix gets heated from the rubber return lines from each injector.

Dave

I know it may sound like a contradiction, but it is as described. Think of it this way. Fuel that burns quicker burns with less delay. This means that when combustion starts less fuel has been injected, thus the combustion pressure doesn't rise as suddenly -> less knock. I guess I should have said "with less delay" instead of "quicker".

Aahhh. I think I'm starting to see the light! So, if it ignites more readily, or with less delay, then there is not as much raw fuel sitting in there when ignition finally does happen. This certainly does explain the more noise when cold- and probably the pinging. Pinging would be delayed combustion due to a bad injector- as you said previously. Is this what Dieselheads officially refer to as "nailing"? Interesting again that gasoline and Diesel are opposites when it comes to that particular noise. In a gasser, pinging happens when combustion is too soon, in a Diesel, it happens when it is too late.

I'm pretty sure that the pinging I get only happens with winterized fuel. I don't recall hearing it late last summer when I first got the car. And as I said, once warmed up, the WVO makes it go away completely. On winter fuel however, it really is quite frequent and annoying. It may be a bad injector, but I'm also thinking that fuel is much diferent now than it was in '76. These old injectors would be designed for higher viscosity Diesel fuel than what is being pumped today.

Diesel Engine Noise
 

Would a "hood pad" lower the perceived decibels from my 240D?????
Anyone tried it? Is it worth while??

Yes it will! :)

I have tested the flow from an OM617 injector return line (before the 3 port banjo on the filter) and found that I get 1 litre from the injector return line in 4 000 km. I do not think you will get much heat from that amount of fuel.
Your blend is probably being heated by the heat flow from the head to the injectors, to the fuel and from the IP to the fuel.

Yeah Tony- whatever it is, the fuel definately gets warm. I just changed my filter cartridge last week with the engine hot, and the filter chamber was uncomfortable to touch, to say the least. Good to know that my Canola oil is getting up to the right temp before going to the injector pump while driving. The WVO makes it a little dodgey when started up from stone cold, but after 5 minutes of warm-up on fast idle, the car becomes drivable. I can live with that.

Dave

Toni, Your hood is acting like a DRUM without a hood pad... you will love the difference one makes....