Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Musing on water injection I get the first dates of deliver to service squadrons for Water Injection in WW2 as being no earlier than 1944.
1 Me 109G6AM and Me 109G6ASM about February or March 1944.
2 P-47 Probably January 1944 though P-47 had provision for the 15 gallon tank about 1 year earlier. (long wait?)
3 Hellcat and Corsair. Sometime in 1944 as well, probably latter rather than sooner.
4 Fw 190D9 about November 1944. Ta 152 maybe Jan 1945.
5 Some sources credit the Fw 190A9 in late 1944. BMW801 is a bit cryptic as some sources say it was tried in Fw 190A5 in 1943 but caused micro cracks in the heads but at that time the Luftwaffe was upgrading its C3 fuel and the engines were injecting C3 as a rich mixture so why bother with MW50? Some sources speak of BMW801 on bombers getting it for takeoff.
Japanese aircraft I have no knowledge.
Hence 1944.
I had thought that water injection would be an aggressive modification but studying this curve of the Me 109G14AM I note that even above the sustainable full pressure altitude of 1.3 atmospheres the DB605A of 6600m/22000ft that the Water is providing about 3% (10mph/16kmh) more speed which must be 10% or 100 extra hp all without any additional boost and the negative effects of higher temperatures. The late service entry is even more puzzling regrading German aircraft given their lack of high octane fuels.
This is perhaps why the V-1710-9 on the P-51H received this. It would have given 150hp even without boost.
View attachment 471965
Water injection will cool the air, thereby increasing its density at any given boost pressure. So some power gain could be expected even without an increase in boost pressure. Note that there would be an increase in fuel consumption on top of the water used.
Which is pretty much the route taken by Formula 1 engine manufacturers in the first turbo era exploiting the questionable definition of 'petrol' in the regulations. Water injection was not permitted so this is the way they went. It prompted rumours of the carcinogenic properties of some of the chemicals thrown into the brews. They reached @85% toluene by the end.Tthe Germans were forced to boost the octane primarily by mixing in $$$ aromatic hydrocarbons (e.g. benzene, toluene).
The limited development resources available in the US were focused on exploiting increases in fuel octane first. The benefits of water injection were known since the late 1800s, but it has some significant downsides for aircraft. Not only do you have to carry the water injection/storage equipment and the water itself, but also additional fuel to exploit the hp increase. High octane gives more horsepower at comparatively cooler temperatures and reduced fuel consumption. It was the lowest hanging fruit that everyone pursued first.
Water injection wasn't really utilized until thermal limits were reached. It was a way to generate more horsepower beyond the cooling capacity of an engine. Air cooled engines were a natural beneficiary. Liquid cooled engines tended to have a higher reserve cooling capacity. The P-51 didn't get water injection until the H model when 90" of boost was approved.
The German's were in a more unique situation due to their available fuel. High performance aviation fuels were produced through the hydrogenation of coal, which gave a product consisting mostly of straight chain alkanes having an octane rating of ~72. This fuel responded poorly to additions of tetraethyl lead due to the lack of branched chain alkanes, so the Germans were forced to boost the octane primarily by mixing in $$$ aromatic hydrocarbons (e.g. benzene, toluene). Their 87 octane fuel contained ~15% aromatics and their 95-97 octane contained ~40%. Aromatic hydrocarbons burn with a flame type that radiates more heat into the cylinder walls/pistons than branched/straight-chain alkanes. The result was that their engines ran hotter than allied models. Another issue they faced was that aromatics tend to dissociate at a faster rate than branched alkanes at elevated temperatures. So while their lean octane rating was high, their full rich octane stayed about the same. The net result was that Germans were willing to pay the weight penalty of water injection sooner because they were the first to run out of development potential.
Which is pretty much the route taken by Formula 1 engine manufacturers in the first turbo era exploiting the questionable definition of 'petrol' in the regulations. Water injection was not permitted so this is the way they went. It prompted rumours of the carcinogenic properties of some of the chemicals thrown into the brews. They reached @85% toluene by the end.
In actual practice (and it depends a bit on which engine) many engines actually used a de-enrichment circuit in the carburetor when the water injection was switched on. Some radial engines, in particular, had been using large amounts of fuel as an internal coolant, well over what was needed for combustion.
The R-2800-8W in the Corsair for example used 45 gallons an hour less gas when using war emergency power than when using take-off or full military power despite making 250 more hp (with aux blower in neutral).
Please note the P-47 and Navy two stage engines were using all three methods to reach high boost.
1.High performance number fuel
2. Intercoolers.
3. water injection
Take one away (or reduce it's contribution) and you won't get the same result.
Trying to use water injection to make 100PN fuel act like 130PN fuel is going to require a lot of water.
I would note that the specific fuel consumption of the navy engines was over 0.70 at full power.
So while their lean octane rating was high, their full rich octane stayed about the same
This fuel responded poorly to additions of tetraethyl lead due to the lack of branched chain alkanes, so the Germans were forced to boost the octane primarily by mixing in $$$ aromatic hydrocarbons
The result was their engines ran hotter than allied models
I'm fundamentally questioning whether 100/130 fuel mixed lean will have any different response to plain 100 fuel mixed lean when used with water injection. In the plain air it doesn't make any difference lean by definition nor should it make any difference lean in the presence of water from water injection. Also, the presence of the alcohol antifreeze is going to push the mixture towards rich. Unless the gasoline is substantially de-enriched there are going to be uncombusted alcohols and/or fuels in the exhaust.