What were to happen if deicing fluid went in to an engine. I have heard that deicing fluid is somewhat flammable. What were to happen if it went in to the engine? Would it combust like fuel?
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$\begingroup$ I edit the question to refer to deicing fluids use on wings and other structure. If this is not what you mean feel free to roll back. $\endgroup$– vasin1987Jun 22, 2015 at 19:27
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$\begingroup$ It would be de-iced, of course. $\endgroup$– Tyler DurdenJun 22, 2015 at 19:42
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3 Answers
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Deicing fluid is inhaled by jet engines nearly every time the truck is called out. The question is how much deice can the engines tolerate?
Turbine engines can accept a rather staggering amount of water, to the point that testing them becomes an exercise in water handling instead of engine handling. The fire department can empty their trucks into an idling engine and not affect it.
Deice does contain various flammable liquids, but the overall mixture is not flammable - rather dangerous although fire would be a quick way to clear the ice.
So, unless you find a way to empty the truck into the engine in less than a few seconds it's simply not an issue.
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Alcohols are typically very effective de-icers (consider that ordinary vodka won't freeze until -17*C, and ethylene glycol, a "diol" or "double alcohol" with two hydroxyl groups, is used as an antifreeze in automotive coolant), but virtually all of them are flammable in some concentration, so it could affect the engine, but unless the engine drew straight deicer through the fuel line it would be unlikely to cause a major problem.
First, it would depend on exactly which deicing compound is being used; the most common are methanol, ethylene glycol, propylene glycol and glycerin. These all have different flash points and different heats of combustion (the amount of energy released by burning them) which will differ more or less dramatically from those of 100LL or Jet A. The closer a compound is in its combustion characteristics to that of the actual fuel, the more it will act like the fuel and thus the fewer problems you'll have; ideally, a compound that is indistinguishable from the aircraft's fuel will simply result in a richer mixture if it's ingested through the air intake (which can be easily corrected with the mixture knob), while if it's fed through the fuel line you'll see no difference at all in the short term (in the long term the de-icer might cause more buildup of combustion byproducts inside the engine requiring cleaning).
If there is a difference in combustion characteristics, you'll see a difference in engine performance relative to the amount being ingested by the engine. A lower flash point for the de-icer means it will ignite before the fuel does and can cause misfires in the engine which is bad (the timescale for exactly how bad depends on the severity and timing of the misfires and the type of engine). A higher flashpoint will cause the engine to lose power, as the de-icer won't burn as efficiently in the combustion chamber, and if ingested through the air intake, will displace oxygen.
De-icer mixed with water is probably the worst case scenario, as under no circumstances will fuel, de-icer and water all sit in a homogeneous solution. Again it depends on how much the engine gets, but the addition of water will act to quench combustion and can cause an engine failure that you're unlikely to recover from in the air (once water gets into an engine it's very difficult to get it back out).
With a jet engine, most of these considerations are reduced by the simple fact that as much as 80% of the air entering the nacelle never enters the actual combustion chamber. So, ground crews at major airports can be much more liberal with de-icer around engine intakes (and should be, as the pressure differentials inherent in and around a jet intake can increase ice crystal formation). Further, commercial jet engines have to be rated to withstand ridiculous amounts of ingested materials of all kinds, including water, birds, dust/sand, etc. A little de-icer is probably the friendliest foreign substance to be introduced into a passenger jet's turbofans during its service life.
Finally, a simple search for "anti-ice" turns up several variants of aviation and automotive fuel with de-icing components mixed in; it's especially important for automotive fuel as most of these fuels contain ethanol which is hygroscopic (it will pull water out of the air) causing ethanol-water ice crystals to form in the fuel lines. AvGas is an older formulation that still uses tetraethyllead and no ethanol, but water contamination is still possible and so a fuel stabilizer (which also typically acts as a deicer) is a common addition to winter fuel tanks. So, aircraft manufacturers know that de-icer will be fed into the engines in some way or other, and they design those engines to be tolerant of it.
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$\begingroup$ The flame in turbine is continuous and hot enough that anything will burn in it. The flash point will have minimal effect on the result. Whatever gets digested and is combustible will burn. $\endgroup$ Jun 22, 2015 at 20:34
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2$\begingroup$ Too much fuel is a big problem for turbine. It increases pressure in the hot section, which can cause a compressor stall, which in turn causes shortage of air and flame out. This is more likely at full power when the engine is running close to the limit of what the compressor can do. $\endgroup$ Jun 22, 2015 at 20:38
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2$\begingroup$ Turbines (and diesels for that matter) don't have mixture knob. They only have power lever which simply controls the amount of fuel injected. Before advent of FADECs, it was important to advance the power levers smoothly, otherwise you could put in too much fuel and flame the engine out, with or without a bang (either compressor stall or the too much fuel would simply not have enough air to burn with and the temperature would drop below the flash point). $\endgroup$ Jun 22, 2015 at 20:42
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$\begingroup$ You seem to talk about what would happen if the deicing fluid got into fuel line of a spark-ignited reciprocating engine, while the question clearly says jet engine and seems to assume ingestion via air intake. $\endgroup$ Jun 22, 2015 at 20:46
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It would not explode it would combust. It would combust at a different rate from jet fuel but unless it was at large quantities (like in the fuel not just sucked off the plane) it should not cause any problems.
Combustion is oxidation and is limited by mass transfer delivering the oxidizing element (oxygen).
In an explosion all the components are in molecular close proximity and the rate is only limited by kinetics. A bomb.
Alcohol is kind of in between as oxidation liberates oxygen but it is still mass transfer limited.
