Diesel knock and overall sound

[alltherage]

Why are some brands of engines louder in terms of knock than others? It seems like I've seen pretty drastic differences at times.

 

[JimRB]

If you were talking about a 1997 Dodge Cummins and a 2004 Dodge Cummins, or a 2003 VW TDI and a 2004 TDI, both models used the same style of pump and injectors in the early years. The later years used different injectors and different pumps. Lots of noise from the pump itself on the earlier Cummins and VWs using the Bosch VE pump. In any event the pump is one source of noise.

Second source of noise or variability it the injection timing. On my VW with the VE pump when I change the static timing you can hear a difference in tone.

Next issue is sound deadening. My little JD has some fairly dense foam on panels surrounding the engine that help quiet things down a bit.

I also think but am not sure that worn injectors sound different than injectors that are within spec.

 

[Professor Marvel]

a lot of things can effect sounds from equipment. temp, is there snow, do I have a hat on, am I near a building, am I aggravated, do the trees have leaves on, is the tractor just starting up or has it warmed up etc

 

[alltherage]

My brother in law had a NH tc29 and the shibaura was really quiet. My father in laws older kubota is the same. Our yanmar has a louder knock and I've heard others that are even louder. Just curious.

 

[jimmysisson]

My 1993 2120 is a raucous old thing: hearing protection absolutely required. I never thought I might be able to quiet it down by altering the timing. Hmmm
Jim

 

[RalphVa]

Our 220D, 240D Benzes and first two JD tractors were essentially the same in starting up cold: lots of diesel rattle and some shake/shudder when cold. Whereas, our 2010 VW TDI and Isuzu 12.5 kw diesel generator do not sound like diesels at all. No rattle or shake/shudder.

Drove an Opal and a Fiat diesel rentals in Italy. They sounded much like the Benzes.

Ralph

 

[Dan Hunter]

Indirect injection into pre cups, such is in the 6.5 chevy diesel, is noisy compared to direct injection.

 

[narampa]

Manufactures have increased the injection pressures for a whole pile of reasons pollution being one.
This makes for a much quieter combustion.
The noise is all about how it burns in the combustion chamber.
Ever listen to an International WD 9 starting on gas and switching over to diesel?
That music is a thing of the past.

 

[Raspy]

It's not pre-combustion vs. direct injection. One of the noisiest diesels ever made was the mid '90s Cummins 5.9 with direct injection.

The main reason modern diesels are so quiet is because they have electronic injection, similar to a gas engine, but at much higher pressure. The timing can be adjusted by the computer, but most importantly, the system allows multiple injection events, per power stroke. So, at idle, the computer will inject a very small amount that cannot make much noise, then add several more shots to continue the burn. The injectors are simply "on" or "off" and are always supplied with high pressure fuel. With mechanical injection, the entire amount to be injected is done in one shot and causes a very abrupt and powerful pressure rise. A "knock". Also, if either system is not clattering as much as expected, it probably meas the timing is retarded for emissions. And that probably means it is running less efficiently than it might. Possibly cleaner, but at the cost of using more fuel. Diluting the air charge with exhaust, EGR, also slows and cools the burn, which may quiet it some too.

 

[Raspy]

Manufactures have increased the injection pressures for a whole pile of reasons pollution being one.
This makes for a much quieter combustion.
The noise is all about how it burns in the combustion chamber.
Ever listen to an International WD 9 starting on gas and switching over to diesel?
That music is a thing of the past.

Those Internationals are funny beasts. The one I worked on absolutely would not start on diesel. It could be up to temperature and working at full throttle. Shut it off and immediately try to re-start on diesel. No way. But would not miss a beat if started on gas and switched over. It might have been because of in-direct injection, or maybe just low compression. Dunno.

That thing would sometimes develop a miss on gas. The old coot working with me would reach in and touch each of the spark plug wires at the plugs to see which one was not firing. Made him jump a bit, but he could tell me which one it was.

Actually, compression pressures have been lowered quite a bit in recent years. Direct injection does not require as high of compression as indirect injection and direct systems are better for turbocharging. Old Mercedes engines wire about 21 to 1, modern Cummins are only about 16.5 to one. Higher compression contributes to more Nox and more sudden combustion, not quieter running. Mazda is experimenting with even lower compression systems for future designs that can be run below the near minimum of 16 to 1.