Water Injection: Why did it take so long to enter service?

[rinkol]

The DB 601E and later DB engines apparently had some rather extreme valve overlap see Daimler-Benz

 

[pbehn]

The DB 601E and later DB engines apparently had some rather extreme valve overlap see Daimler-Benz

With 105 degrees of overlap I am surprised they ran at all, no surprise that special measures were needed at low revs.

 

[Koopernic]

On these Aero engines are the intake and exhaust valves open at the same time?

Radical Valve overlap to increase scavenging and bring resonance charging into play is only practically possible with multipoint direct injection as otherwise there is too much fuel-air mixture loss. There was a little overlap on the Merlin but obviously they didn't want to blow the mixture out.

The radical inlet vs exhaust valve overlap was introduced with the DB601E, it also required variable length inlet ports since there is a resonance like "trumpet" effect and the ports had to be lengthened at low rpm to facilitate starting and idling. The DB605A was a Slightly enlarged DB601E with the same bore centres and a new bearing and lubrication system.

Nice article here:
Daimler-Benz

And a comparison with Merlin, DB601A and DB605E here:

As you can see even the Merlin had 43 degrees overlap which is 1 degree more than the 42 degrees of the DB601A but nowhere near the 105 degrees of the DB601E.

Obviously water injection allowed Daimler Benz to get the charge cooling effect before the supercharger without giving up the radical valve overlap that would blow out fuel.

I think the resonance effect actually compressed the air in the cylinder by creating a standing wave node in the cylinder head.

Another reason for water injection was "internal cooling". I recall that in testing of the Ju 388 with the turbo-supercharged BMW 801TJ long climbs that an overstepping of cylinder temperature of 7C or so could occur presumably due to inadequate external cooling flow and that MW0 or MW50 was recommended to keep the heads within authorised limits. This was not to prevent preignition or allow increased boost.

Note for their BMW 802 engine BMW was planning on introducing variable timing on the exhaust valve since I don't think altering inlet port length is practical on a radial engine. Also exhaust pipes are also of varying length.

 

[DarrenW]

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.

...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.

According to America's Hundred Thousand, Republic Aviation began fitting water injection systems on all P-47D-20RE models in November 1943 and by the end of the year most ADI modifications were complete on older aircraft stationed in England. It further states that on November 25th of the same year the 1,551st F4U-1A built by Vought became the first Corsair equipped with WEP from the factory. The book also mentions that 60 percent of all Hellcats had WEP by January 1944.

 

[Mike Williams]

According to America's Hundred Thousand, Republic Aviation began fitting water injection systems on all P-47D-20RE models in November 1943 and by the end of the year most ADI modifications were complete on older aircraft stationed in England. It further states that on November 25th of the same year the 1,551st F4U-1A built by Vought became the first Corsair equipped with WEP from the factory. The book also mentions that 60 percent of all Hellcats had WEP by January 1944.

Regarding P-47 use of water injection in 1943, kits were shipped out in August & September 1943 and received in England by September. http://www.wwiiaircraftperformance.org/p-47/P-47-wi-kits-17sept43.jpg . Encounter Reports from the 8th AF show use of water injection with P-47s in 1943 as well.

 

[taly01]

I have been wondering if their is any external clue if P-47 is fitted with ADI?

The 348th FG in New Guinea also entered combat around August 1943 and were important in developing the P-47 for combat, they also had a better fuel tank than European P-47's got for a long time, the "bathtub" 200 USgal made by Ford in Brisbane North Australia. They used alot of P-47D-2 and D-4's right into 1944, which didn't come with ADI from the Factory.

 

[DarrenW]

I have been wondering if their is any external clue if P-47 is fitted with ADI?

I'm really not sure how to know externally but maybe there was a special access door to the water tank like with the F6F??? It would probably be located at or near the oil tank/hydraulic reservoir access door because the water tank was mounted directly behind and beneath them.

And FWIW Pacific-based Thunderbolts weren't cleared for 64" Hg MP until after May 1944. That's when the kits were authorized:

http://www.wwiiaircraftperformance.org/p-47/p-47-2535hp.jpg

By this time European-based T-bolts were already modified with the new injection kits and were regularly flying at those boost pressures. A week before D-Day 150 grade fuel was being supplied to every unit in the U.K. which allowed the R-2800 to run at 2600 hp without water injection. By the following month it was cleared for 70" Hg with ADI and 150 fuel. Only 130 grade fuel was available in the Pacific theater so the P-47D was limited to 64" Hg there.

 

[MIflyer]

Check this out: NASA Technical Reports Server (NTRS) 19930093190: Effect of internal coolants on the knock-limited performance of an Allison V-1710-99 engine with a compression ratio of 6.0 : NASA Technical Reports Server (NTRS) : Free Download, Borrow, and Streaming : Internet Archive

2310 BHP from a V-1710? Not too shabby!