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enter image description here

This picture shows a fuel ejector of a diesel engine that propels ships.

When the fuel line pressure exceeds 380 bars, the tension of the spring is overcomed and fuel is ejected into the combustion space.

It is common knowledge among engineers and i have read it on manuals that tension of the spring could be adjusted to lift in higher pressures but above this pressure the jet will not penetrate further; instead it will break into smaller droplets.

My question is; Why after a critical value, the surplus energy/pressure we give to a flow does not translate to kinetic energy increase but creates smaller droplets, in other words surfaces?

The flow is sonic, if that is of any help and the speed of the flow is about 500m/sec

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  • $\begingroup$ I couldn't understand what is your question exactly (because of my poor English), but I think your question's answer connect to mach number of flow. $\endgroup$
    – lucas
    Commented Apr 25, 2016 at 8:57
  • $\begingroup$ @lucas. My english is also poor. Yes,you are correct the flow is sonic. Waves propagate in the fuel line at the speed of sound $\endgroup$
    – veronika
    Commented Apr 25, 2016 at 9:30
  • $\begingroup$ A detailed explanation would be very technical. In brief, atomization occurs because of instability of the liquid-air interface : Plateau-Rayleigh Instability. en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability nvlpubs.nist.gov/nistpubs/jres/6/jresv6n3p369_A2b.pdf $\endgroup$
    – sammy gerbil
    Commented Apr 25, 2016 at 9:40
  • $\begingroup$ @sammygerbil. Maybe you want to write kelvin-helmholtz instability. But what i don't understand is why an increase in pressure just makes the droplets smaller instead of making them travel faster/further. Why there is no increase in kinetic energy/momentum. thank you for the link $\endgroup$
    – veronika
    Commented Apr 25, 2016 at 13:30
  • $\begingroup$ Maybe KH. But PR instability describes break-up into droplets, I don't think KH covers that. Possibly I don't understand enough about the details of fuel injection to appreciate your difficulty. It seems intuitive to me that forcing a liquid through a nozzle results in atomization above a critical pressure. Droplets are decelerated much quicker than jets by viscous drag. Wasn't the paper by Castleman any help to you? $\endgroup$
    – sammy gerbil
    Commented Apr 25, 2016 at 14:00

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