Why do it?

[facthunter]

A lot of operators leave dieses idling. Rail locos are  even kept idling when the wheels are being serviced/machined. Small capacity motors must have minute amounts  injected and some inject twice for each cycle.. The only time you see white smoke (unburned  fuel) is after being started cold at altitude. Nev

[old man emu]

The noise problem is not so much from leaving engines idling, as they don't make much noise when they run slow, and if they are left idling then the noise soon melts into the general background noise, especially in the suburbs. What the real pain comes from is the sudden change in noise level. Remember that all mammals communicate by sound, and one animal in a group making a loud sound alerts the rest. That increase in alertness is  the result of an adrenalin rush, which initiates a flight or fight response. If that rush is repeated frequently, the body tires and is unable to respond. 

 

That is what this revving/shutting down sequence does. The noise alerts us, an on investigation we find no danger to deal with, so we go back to a steady state. Then the noise comes again. This up and down of our heartrate and breathing rate soon tire us and becoming tired, we become aggressive. 

[facthunter]

A good radial rumbling overhead soothes my nerves and makes the hair on the back of my neck stick up.. Better than a Brahm's sp symphony. Sliding van doors in caravan Parks turn me into a raving madman. Nev

[old man emu]

2 hours ago, facthunter said:

A good radial rumbling overhead soothes my nerves and makes the hair on the back of my neck stick up

You are not wrong there. Some lucky bastard was committing aviation the other day out of Camden using a round engine. Roll over Beethoven.

[ClintonB]

The annoying sound you described in initial post, is like the annoying sound trail bikes make when ridden in small yards-full throttle, off throttle, repeat. It’s enough to make one feel murderous.

 

[Yenn]

I used to service diesels years ago and from what I read here either the whole system has changed or I never knew anything. Do modern injectors work slowly at low speed instead of only opening when the pressure lifted them. You could tell the quality of an injector by the noise of its injecting and that was on a test stand at very low rpm.

[facthunter]

They are triggered electronically with a small shot during the initial upstroke and a bigger one when it fires, This gives a quieter engine than the earlier types, one high pressure pump feeds all the injectors. Nearly all engines are four valve heads and get their torque at 1300- 2300 rpms and are rarely bigger than 2.4 litres Four Cyl. run intercoolers and use EGR.  ALL injectors make SOME noise. There's no linkage to any throttle. It's electronic. Nev 

[onetrack]

Virtually all current model diesels utilise electronic injection and a common rail, whereby the rail is supplied with fuel at extremely high pressure by a simple high pressure pump - and the electronic injectors are fired by commands from the engine ECU. Many of the current diesels utilise multiple injections over a short period to reduce diesel "clatter" or knock, and to improve fuel burn.

 

The fuel in common rail systems is constantly circulating between tank and engine, often at rates of up to 80L/hr. This is done to dissipate the major heat levels imparted to the diesel when it is pressurised to the 25,000-30,000psi (172-206Mpa) held in the common rail.

Virtually all the common rail diesels also have a fuel cooler in the line back to the fuel tank to assist in heat removal from the diesel.

 

But the Cummins engines I spoke about earlier, are the non-electronic Cummins engines utilising the patented Cummins "Pressure-Time" fuel system, which was designed before WW2, and which fuel injection system served Cummins admirably until the late 1990's.

In the PT system, the injector is operated directly by a rocker from the camshaft, and the injector does both fuel metering and fuel injection. I won't describe the entire fuel system in detail - the link below provides that detail, if you're interested.

 

But the weak point of the Cummins PT fuel system is that at idle, the metering and atomisation of the fuel is not as good as it is at higher engine speeds - purely due to the PT system design. As a result, the fuel spray from a PT injector at idle results in poorer fuel atomisation and fuel burn, and this results in increased smoke, increased ring blowby, and more engine emissions. 

All other, older, mechanical, Bosch-style, inline fuel injection systems do not suffer from poor fuel atomisation at idle, as much as the Cummins engines with the PT fuel system do. However, the engines fitted with Bosch fuel injection systems still do suffer from it, to a certain extent.

 

https://co-mach.com/cummins-pt-fuel-system-introduction-2/

[old man emu]

9 hours ago, onetrack said:

the electronic injectors are fired by commands from the engine ECU

And when you are at the back of Bullamakanka and your ECU packs it in, you are stuck with a very expensive white elephant, massive repair costs and long down time. I wonder which is cheaper - a reliable, but poorer fuel consumption mechanical fuel metering system or a box of magic that you zip-tie your wallet to and throw down a wombat hole.

[facthunter]

Diesel particulates are deadly toxins. That soot has to go.  Most have a limp home mode. The efficiency of these engines is remarkable as well as the low speed torque and quietness. and general driveability, The immobiliser system on any of them can be a disaster if someone keep s trying to fiddle with starting it.   Clean fuel essential. Absolutely NO water allowed. and no broken radiator hoses..Motors putting out a lot of power need the coolant system to be right. Nev

[Yenn]

I used to work on Bosch and CAV mainly and they had no electronics, just pure pressure to open them.

My Prado has electronics and it is amazing, I got an air inlet blockage, which I thought could be a waste gate problem. Just a lack of power and no black smoke. I used to reckon an air inlet problem always resulted in black smoke.

The newer engines may have expensive gear when it needs fixing, but it goes a lot further before that happens. I never met a Leyland, AEC or Scammel that had 400000km on the clock.

[facthunter]

Diesel particulates are deadly toxins. That soot has to go.  Most have a limp home mode. The efficiency of these engines is remarkable as well as the low speed torque and quietness. and general driveability, The immobiliser system on any of them can be a disaster if someone keep s trying to fiddle with starting it.   Clean fuel essential. Absolutely NO water allowed. and no broken radiator hoses..Motors putting out a lot of power need the coolant system to be right. Nev

[facthunter]

The Post above has sat for a while.  I had a bit to do with AECs as well as many others Albion GM diesels scammels  AEC's generally broke a crank at around 450,000 miles or more. There was always a discussion as to whether it had been lugged or revved too much  by the particular driver. High Mileage motors like these are not reliable  as the modern trucks are. I think a lot still depends on the driver. Nev