Yes, I'd agree with Hilife too. Thought it would add an unnecessary complication to my post, so thank you for bringing it out. All that luggage and maintenance is a pain if you don't really need it. There might still be a case for the hot/hi though, especially military jets operating at edges of envelope.
And you're right, I did interpreted the previous post as for some form of jacket or external spraying.
Re the injection into the combustion chamber, IIRC that's the preferred method for a more conventional axial flow jet, because it gets a more even distribution through the mixture and because it's possible to pump a lot more in, faster and more effectively. I went for the soft option to illustrate. I should have known better than to over-simplify on PPRuNe!!
Nevertheless, I think you may still be referring to the cooling effect on the inlet air to the combustion chamber (laws of thermodynamics and physics will do it anyway), though, rather than other cooling effects. I can see a case for cooling the turbine though (as opposed to inlet).
The only other possibility I can see - but I think it unlikely- is to use the water to improve the boundary layer around the combustion chamber, so that higher temps can be maintained in the burn.
I'm a bit sceptical because it would probably have been easier to design the larger boundary layer with inflow air from the start rather than augment it in some way. But if there's a RR designer watching, by all means pronounce me wrong (but put us all out of our misery with the answer too please!).
Last edited by GlosMikeP; 10th Dec 2006 at 17:18.
Reason: Turbine addition.