On the turbo diesel DA-42 and DA-62 aircraft there exists a minimum fuel temperature limitation where you may not start or operate the aircraft below that. Does anybody know why this is? It seems strange as the turbo Diesel engines themselves have their own dedicated engine fuel pumps which raise the pressure of the fuel to 19,500 psi prior to infection in the cylinders. This should make the fuel plenty hot for combustion.

Is this minimum fuel temperature requirement typical for all reciprocating Diesel engines?

  • $\begingroup$ Look up diesel gelling to understand what happens to diesel at low temperatures. $\endgroup$ – Ron Beyer Apr 27 '19 at 15:40
  • $\begingroup$ I’m surprised at that considering the airplane runs on Jet A which I don’t believe can gel at that high of a temp. I think the lower limit is something like 21° F $\endgroup$ – Carlo Felicione Apr 27 '19 at 17:12
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    $\begingroup$ "which I don’t believe can gel at that high of a temp" So for the benefit of those of us who don't fly a DA-42 or DA-62, what is this minimum fuel temperature? Also, specifying in the question that the engines are supposed to run on Jet A might be beneficial. $\endgroup$ – a CVn Apr 27 '19 at 19:09
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    $\begingroup$ The DA-62 AFM states that the operational fuel temperature is between -30° to 60° C $\endgroup$ – Carlo Felicione Apr 27 '19 at 23:17

From the DA-42 TDI Approved Flight Manual:

Fuel filter is not heated and can clog if the Diesel fuel flocculates. Jet fuel does not pose same limitations.

AFM section

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  • $\begingroup$ Why is blending diesel and jet fuel in the tanks prohibited? Wouldn't even 50% or so of jet fuel prevent filter clogging (although not as well as 100% jet fuel) by decreasing the freezing point of the mixture below that of pure diesel? $\endgroup$ – Sean Apr 27 '19 at 21:18
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    $\begingroup$ @Sean There are different limits based on which fuel or fuel blend is used, mixing isn’t prohibited but it still carries a limitation. $\endgroup$ – Cpt Reynolds Apr 27 '19 at 21:21
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    $\begingroup$ Jet fuel also has limitations but way lower. Jet A1 and JP 8 are -37C for dispatch and have to stay above -47C in the tanks while flying. $\endgroup$ – John K Apr 27 '19 at 22:59
  • $\begingroup$ Well that’s the thing. I’ve never heard of a DA-42 or -62 operating on Diesel. They only use JET-A or similar jet fuel. $\endgroup$ – Carlo Felicione Apr 27 '19 at 23:03
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    $\begingroup$ @CarloFelicione That's because diesel isn't generally available at most airports, it would be more common in places like South America or China. $\endgroup$ – Ron Beyer Apr 27 '19 at 23:36

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