Author Topic: Water Injection  (Read 169 times)

Offline Mongoose

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Water Injection
« on: January 29, 2023, 09:47:45 AM »
Someone in game was asking about water injection, and why it was used.  I found a couple of articles that might help explain it.

I am also including an article about War Emergency Power as used in American planes.
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Offline icepac

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Re: Water Injection
« Reply #1 on: March 12, 2023, 10:26:51 AM » has amazing studies on water/methanol injection......often by the guys who invented it.


Offline Arlo

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Re: Water Injection
« Reply #2 on: March 12, 2023, 05:13:51 PM »

Offline TryHard

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Re: Water Injection
« Reply #3 on: March 13, 2023, 08:21:35 PM »
Also the Germans used Nitrous Oxide to boost high altitude performance (because nitrous is essentially a chemical supercharger with out raising manifold pressure) in addition to MW50 injection (MW-50 is 50% methanol 50% water)

GM-1 raises EGT and Cylinder head temperate and requires the ignition timing to be retarded, while MW-50 does the opposite allowing you to run more boost and or ignition timing with out preignition or detonation.
Preignition is when the air fuel mixture being compressed in the cylinder ignites before the spark plug fires causing very high combustion chamber temperatures that will melt pistons in short order.
Detonation is when the air fuel mixture once ignited rapidly explodes inside the cylinder rather than burning in one smooth downward moving flame front causing multiple pressure waves to collide inside the cylinder and rattling, that's where that "marbles in a tin can" sound from detonation comes from.

Preignition is rare and unless you really know whats going on almost impossible to detect before its too late. Detonation is common and almost every good running engine will have slight "pinging" (another word for detonation) especially during rapid throttle movements as rapidly opening the throttle will produce a lean mixture for a split second. Detonation will destroy the engine eventually if its happening for a while under a high load low RPM situation usually destroying the connecting rod bearings and or breaking ring lands off the pistons. This is what was destroying so many of the Allision engines in the early P38s was the intake manifold design caused the far cylinders to run lean compared to the middle of the engine, as such during a cruise condition with the engine at 2200 RPM and 30 inHg MAP auto lean mixture the outer cylinders are on the ragged edge of detonation. If the pilot is bounced by an Enemy he must in this order:

1: Set mixture to AUTO-RICH
2: Set RPM to 3000 RPM
3: Open throttle to power required (full combat power)

If the pilot in a panic opens the throttle before bringing the RPM up and setting the Mixture to rich when the throttle opens and the engine takes a nice big gulp of air with not enough fuel to quench the combustion chamber the end cylinders begin to detonate and if boost is high enough or RPM is low enough it will almost always in the case of the Allision destroy the rod bearings and pistons. This problem was greatly reduced when the Allision engineers redesigned the intake manifold and Lockheed installed better intercoolers to keep intake air temperatures lower. Its worth noting the pilot of a FW-190 needn't worry about any of this because he has an analog computer decide how to run the engine for him, all he needs to do is slam single throttle lever to the firewall.