4 ms·

Hijacking (kinda): diesels are vulnerable to a phenomenon called "diesel runaway", where unintended fuel (for instance, engine oil leaks) seems into the intake/

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 4y ago
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.
- namibj 4y ago
  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...
- GeorgeWBasic 4y ago
  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.
- hatsunearu 4y ago
  https://www.team-bhp.com/forum/technical-stuff/188332-explained-why-diesel-engines-need-throttle-body-throttle-plate.html 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 4y ago
    That’s what the injectors are for. It’s for emissions
    - hatsunearu 4y ago
      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.

sokoloff 4y ago

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.

namibj 4y ago
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...
GeorgeWBasic 4y ago
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.
hatsunearu 4y ago
https://www.team-bhp.com/forum/technical-stuff/188332-explained-why-diesel-engines-need-throttle-body-throttle-plate.html 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 4y ago
  That’s what the injectors are for. It’s for emissions
  - hatsunearu 4y ago
    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.