opening of solenoid valve while engine is off

[farooquekhann]

If the injector solenoid opens somehow while the engine is off, what will happen? Will the diesel fuel be admitted to the cylinder in the absence of required compression ratio or some protection will prevent this from happening? How can the fuel be removed from the cylinders if this happens in any case?

 

[dgallup]

Depends on the injection system. On many, nothing at all as there has to be pressure built up to have an injection, the solenoid is not actually opening the injection valve. On others, it is possible to sufficiently fill the cylinder with fuel that on cranking the cylinder will hydraulically lock which could break a piston or bend a connecting rod. About the only thing that can be done is remove the injectors and crank the engine over fast enough to blow the excess fuel out.

You will have to be more specific to get a more precise answer.

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[TugboatEng]

Nothing happens. There isn't enough pressure to lift the needle valve in the injector tip when the engine is not running. Case and point, many engines allow you to cycle the injector solenoids with the engine not running so you can listen for operation. There is no risk of admitting fuel to the cylinder. Also know that injector solenoids usually shut to initiate injection so they all open in order to shut the engine down.

 

[BrianPetersen]

In most cases the actual rail pressure is supplied by a mechanically driven pump. If the engine is not running, that pump is not running. No fuel flow ... no pressure, no issue.

There might be one teeny tiny meaningless squirt of fuel the first instance of opening the first injector due to residual rail pressure if the engine has not been stopped for long enough for the rail pressure to bleed down (which should take on the order of seconds after shutdown). This is of no consequence whatsoever.

 

[PJGD]

TugboatEng: Your answer is not specific enough. On electronic unit injectors (EUI and unit pumps), the control valve is normally open, energize to inject (i.e. close) - as you indicate, but with common rail systems the control valve [solenoid or piezo] is normally closed, energize to inject (i.e. open).

PJGD

 

[TugboatEng]

You are correct, I'm thinking EUI injectors that shut the spill port to initiate injection.