4 ms·

I'm not an engine expert, but I thought a substantial disadvantage of water injection was incomplete combustion (see for example the billowing smoke here: https

by ahh 10y ago

I'm not an engine expert, but I thought a substantial disadvantage of water injection was incomplete combustion (see for example the billowing smoke here: https://en.wikipedia.org/wiki/File:Boeing_KC-135_J57_wet_takeoff.jpg https://en.wikipedia.org/wiki/File:Boeing_KC-135_J57_wet_tak... They may be more efficient, but is there a pollution concern?

hausen 10y ago
I'm no expert either, but according to https://en.wikipedia.org/wiki/Water_injection_(engine) https://en.wikipedia.org/wiki/Water_injection_(engine), it actually reduces emissions.
- qplex 10y ago
  In turbine aircraft engines that is not the case though. Injecting water inside turbine engine causes fuel to go unburned, hence the black smoke.
aidenn0 10y ago
I'm also no expert, but a bit of a hobbyist... Water injection will reduce the temperature of the combustion chamber. If you take an engine already tuned for the temperature of minimum emissions and inject water, then obviously you will upset that equilibrium. If you took an engine properly tuned and just add boost (by boost, I mean increasing the pressure of the air at the intake manifold, which allows more oxygen into the combustion chamber), then you will increase engine knocking and raise the temperature of the engine, thus increasing NOx formation. If you then add water injection, that can balance things out again. Obviously all of the above is an extreme simplification, and in addition, you have to deal with the case where there is no water to inject. Previously this would have been a real concern, but with modern computer controlled engines, it is possible to reconfigure the engine while it is running for some combination of reduced boost, less aggressive timings (including late intake valve timing, if your engine is setup for that; this effectively reduces the compression ratio of the engine), and richer fuel-air mixture.
kls 10y ago
With modern computers the combustion process can be controlled to such a degree that this is a non-issue, but with that said, see my post above on water methanol mixture, incomplete combustion can be solved by the addition of methanol. As well there is already a ready source of methanol/water mix at every gas station as that is the formula for windshield wiper fluid.
- aidenn0 10y ago
  Windshield fluid is made from all sorts of various formulae. In areas with cold winters it may be methylated ethanol, or ethylene glycol. In Southern California, it's mostly water.

by ahh 10y ago

hausen 10y ago

I'm no expert either, but according to https://en.wikipedia.org/wiki/Water_injection_(engine) https://en.wikipedia.org/wiki/Water_injection_(engine), it actually reduces emissions.

qplex 10y ago
In turbine aircraft engines that is not the case though. Injecting water inside turbine engine causes fuel to go unburned, hence the black smoke.

aidenn0 10y ago

I'm also no expert, but a bit of a hobbyist... Water injection will reduce the temperature of the combustion chamber. If you take an engine already tuned for the temperature of minimum emissions and inject water, then obviously you will upset that equilibrium. If you took an engine properly tuned and just add boost (by boost, I mean increasing the pressure of the air at the intake manifold, which allows more oxygen into the combustion chamber), then you will increase engine knocking and raise the temperature of the engine, thus increasing NOx formation. If you then add water injection, that can balance things out again. Obviously all of the above is an extreme simplification, and in addition, you have to deal with the case where there is no water to inject. Previously this would have been a real concern, but with modern computer controlled engines, it is possible to reconfigure the engine while it is running for some combination of reduced boost, less aggressive timings (including late intake valve timing, if your engine is setup for that; this effectively reduces the compression ratio of the engine), and richer fuel-air mixture.

kls 10y ago

With modern computers the combustion process can be controlled to such a degree that this is a non-issue, but with that said, see my post above on water methanol mixture, incomplete combustion can be solved by the addition of methanol. As well there is already a ready source of methanol/water mix at every gas station as that is the formula for windshield wiper fluid.

aidenn0 10y ago
Windshield fluid is made from all sorts of various formulae. In areas with cold winters it may be methylated ethanol, or ethylene glycol. In Southern California, it's mostly water.