[tempnow987]

I was boating and same issue - broke to full throttle on a gas engine. So I just came flying in and killed engine. I could have restarted probably if needed. These things are almost always stoppable.

Another boat had a diesel. This boat had serious flooding and I went over to help ($1M+ boat, owner had backed it hard into concrete pier and not noticed a transom crack that opened). Engine would not shut off (electrical all shorted out). That diesel engine was running full tilt almost totally submerged - was pretty impressive. Eventually someone got a mask and snorkel and dove to fuel cutoff before it ingested a bunch of water through air intake (which I'm sure would have stopped it). With diesels I always liked knowing where manual fuel cutoff was after that.

[hatsunearu]

Hijacking (kinda): diesels are vulnerable to a phenomenon called "diesel runaway", where unintended fuel (for instance, engine oil leaks) seems into the intake/cylinder. The engine is controlled by how much fuel is injected, so if you just add an extra amount of fuel it will start increasing torque all on its own, and in the worst case, will cause unintended acceleration.

Nowadays diesels actually come with throttle bodies for emissions reasons which I think also will serve a safety function against runaways.

[sokoloff]

A major part of diesel efficiency comes from a lack of a throttle plate. I’d be surprised if adding one was beneficial for emissions. Do you have any reference here? I couldn’t find one with a quick googling.

[GeorgeWBasic]

I don't know if it's for emissions reasons, and I doubt it does anything for emissions, but Volkswagen diesels have a throttle that's there to make engine shutoff much less shaky. It's called the anti-shudder valve, and it activates every time the engine is stopped, and it would stop a runaway diesel.

[namibj]

I'd guess too-lean combustion in idle is bad, and throttling the intake so that it starts out with reduced pressure and at the fixed compression ratio, won't reach as-high pressures (which waste power by some of the adiabatic heating coupling to the cylinder walls). Might only work on individual cylinders, as it seems like it'd easily prevent ignition, but still...

[hatsunearu]

https://www.team-bhp.com/forum/technical-stuff/188332-explai...

from what i understand it's mostly to have a control over the air fuel ratio.

[gonzo]

That’s what the injectors are for.

It’s for emissions

[hatsunearu]

what the heck are you talking about, if you're at partial throttle, by design a normal diesel has no control over how much air is entering the engine, so your only way of modulating torque is changing the injection. This means your air fuel ratio will be uncontrolled, which is bad for emissions.

[moron4hire]

A place I worked years ago was a manufacturer of industrial lifting cranes. They had a problem one particularly hot summer of the diesels in the cranes starting up in their own.

These were massive engines. The block was bigger than my whole car. Terrifying watching one of them run away. They tended towards "violent, unscheduled disassembly" if they couldn't be shut down.