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My thinking is primarily around the idea that in order to see any benefit from water injection, the whole engine design would have to be altered to incorporate water injection under specific conditions, principally at loads that would exceed normal operation parameters.
This is what they did in the aero engines. War Emergency Power conditions meant life expectancies measured in minutes, sometimes even seconds. Remember these aero engines operated at altitudes where atmospheric pressures were less than 1/3 of that at sea level. Running two atmospheres of boost at 30,000 feet versus two atmospheres at sea level is a completely different scenario for power and engine life expectancy.
What I doubt it that there will be a combination of power, economy, and longevity, that any manufacturer would consider selling to the general public.
Now if you went with 16 to one compression on pump gas and supplied just enough water to stabilize combustion at WOT and max vacuum advance you may see a benefit, but the benefit would be a partial throttle openings when the actual in cylinder compression was significantly lower that the maximum available.
I think this is what Mazda is doing with the SKYACTIV engine technology, but instead of water they are using cooled egr to allow much higher compression ratios where part throttle loads can use valve timing and extra egr to minimise pumping losses.
I just wish they would spend as much time and effort at eliminating reciprocation losses.
regards
Mech
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