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Originally Posted by mwebb
watch out for thermal shock
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This is not a major issue at all. A properly-dimensioned water injection is just like some sort of "chemical intercooler".
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on the theory that there will be no liquid h2o in the exhaust stream , it will all be in vapor state due to the heat / temperature in the exhaust
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It vaporizes while it absorbs latent heat from the intake air. When some alcohol is added to the water, usually methanol but it could also be ethanol (even the good old Everclear may serve as it's quite similar to the E96h used as a motor fuel in my country), it vaporizes quicker.
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you do not want to crack the substrate in the DPF or the thimbles in the lambda sensors
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Water injection won't lead to a risk of cracking the DPF core or the lambda sensors. Otherwise, it would already be an issue to drive on a rainy day, which does a roughly similar effect to water injection.
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EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .
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EGR may have some benefits under certain conditions, but it doesn't prevent water injection to fare better on other conditions. By the way, while EGR has been pointed out to increase particulate matter emissions, water injection can decrease both NOx and particulate matter simultaneously.