Avoiding blocked injectors.

[Driver]

Hello,
Much is written on these forums about blocked injectors, especially on Common Rail, and the possibility of engine damage. There seems to be more of us content to cruise our rocket ships more slowly now. The unanswered question is, how low can you go with engine speed without risking such disasters.
I have the feeling that 1500 revs/min on my Volvo D9 575s might be OK, but its only a feeling, can anybody give a more scientific answer, please?

 

[jfm]

Gut feeling answer = you will be fine. But I would have the injectors serviced as recommended on D9, because it's the only engine I ever had fail catastrophically on me when I was driving a boat - a hosing injector destroyed a piston.

Scientific answers:
1. I see no logic in "especially on common rail" comment: an electronic injector is agnostic about whether it is fed fuel from a common rail or a unit injector.
2. I don't see how blockage will generally tend to result from running at modest speeds. Dirt shouldn't be getting to the injector in the first place, but it feels unscientific to think that the higher fuel flow at 2300rpm will flush out dirt that the lower fuel flow at 1500rpm won't.
3. You'll get LESS injector wear at 1500rpm than 2300 rpm, AOTBE, because there is less flow of fuel and so less frictional wear.
4. Remember nearly all European 50Hz generators run at a fixed 1500rpm, often at a much lower loaded state (and hence with less fuel flow) than a propulsion engine at 1500rpm and they are not prone to blockage.

 

[Driver]

Point taken regarding injector servicing on D9s. I read that CR injector tips differ by having multiple tiny canuli and at lower speeds carbon build up (due to less heat?) can cause them to "hose".

Interesting about the generators, do any of them use D9s?

 

[jfm]

The modern multiple nozzles/multiple injection events and all that are features of modern diesel engines with electronically controlled injection, not features of the common rail method of distributing the fuel. The injectors are indifferent/ don't even know whether the high pressure fuel comes from a common rail or from cylinder-specific high pressure pumps (so called "unit injectors").

A Volvo D9 isn't a common rail engine. It has unit injectors, which means a local high pressure pump for each cylinder, thwacked by the camshaft to create the pressure. That high pressure fuel is then injected by modern fully electronically controlled injectors. Nothing at all unusual or bad about any of that. Same iirc for D11, D12, D13 engines.

Yes lots of generators use the D9 engine.

 

[Momac]

I keep my boat on a river which is speed restricted.
Boats here with planing hulls designed for sea use are common. They don't seem to suffer from mostly going slow .

At mostly slow speed I have clocked up over 850 hours in my present boat since 2014 and 650 hours in my previous boat between 2008 and 2014 and never had any issues with fuel or injectors.
That's mechanical injection kad32 diesels.

I do get to go fast when we go to tidal/salty water which is a very few times a year but that's a relatively small number of hours overall.
Must admit the engines always feel better after a good blast , even if its a 20 minute blast. But no issues as far as I know.

The last couple of years I use a fuel additive which claims to keep the fuel system clean.