E85 with Water Injection ?
 

Barry Bordes excellent "Rotary Peak Pressure Location ATDC" thread has me thinking, so I would like to light off a discussion on water injection (WI) in ethanol (i.e. E85 - E98) fueled rotary engines. Here's a could of question for "fuel:"

- Should WI setups only run water since the fuel is mostly ethanol?

- Could WI flow rates be reduced while still maintaining the same max timing and knock supression of WI alone?

- At what point (i.e. HP, MAP, Max Cyl. Press., et) would either WI or E85 alone benefit from the max timing and knock supression of the other?

Discuss...

Definitely interested in this topic also...

I'm far from expert, but I've got something in the way of discussion. I'll be using AI to mean auxiliary injection, which can be either water or alcohol (or a mix).

1) I'd say that, yes, you should only run water. As I'm sure you already know, water isn't a fuel. Alcohol/methanol/ethanol/etc, is. Presumably, your tuning sans AI results in an AFR. If you use alcohol, you'll simply be richening your map. Now, if you replace some of your fuel with alcohol, a la HC and BDC, you'll be realizing very little benefit as you're already at 85% alcohol. Essentially, depending on where you inject your alcohol, you'd just be getting reduced AITs. With water, you won't be changing your AFR appreciably (though this point is disputed), you'll just be adding knock resistance to your fuel/air charge. Also, if you inject pre-turbo, which most are only comfortable doing with water, you'll broaden your compressor map and make for more efficient compression.

2) Again, I think that the answer is yes. Alcohol is higher octane than gasoline, so it follows that E85 is as well. Hence, it is already more knock resistant. Therefore the amount of water you'd need to inject to achieve a given level of knock resistance is reduced.

3) Here's where I have no substantive idea, and I'm not aware of any data to help quantify this very well. There are so many variables that would need to be wrapped up into an analysis of available engine data from E85 only engines and WI/gasoline only engines that make it a tough call. Generally, I'd say it'd be "easy" to figure out though, on a given setup. Tune it to your comfortable threshold on E85 only, add some water (say ~100cc), retune, rinse, lather, repeat.

Calculon, thanks for the helpful and sensible response.

Anyone else out there want to contribute or at least concur.... anyone, anyone... Coleman, Coleman... ;-)