Hi All,

After some struggles with EGT (measured just after the manifold/turbine flange) on a somewhat undersized hotside (FM2 manifold, GTX2860 0.64, 2.5" exhaust, Built VVT) for my goals (max out my cooled AZ6 ~280whp on track, 93 octane fuel - 99 UK RON), I installed an AEM water injection kit, along with a solenoid controlled by the megasquirt to only come in above 5000rpm.

I started with the recommended 500cc nozzle, but the combination was starting to misfire and seemed a rather high ~30:100 ratio water to fuel so I dropped to the 250cc nozzle for ~15:100.

With the 250cc nozzle, I can't see any EGT improvement from the WI in the data on track as shown below. Please note this data was only at a nominal 170kPa and the laps aren't too consistent with traffic, but the back straight that is marked shows the lack of effect. Both setups stabilise around 870C EGT.




Is the nozzle still too large? Or maybe my 11:1 base AFR on gas needs leaning for any benefit to be seen?

Does anyone have any WI vs EGT data they could share?

Thanks.

 

I thought WI was more for improving effective octane and reducing detonation than lowering EGTs? Did you advance the timing after adding the water?

--Ian

 

Hmmm, I know it improves effective octane, but I thought it burned cooler. I did not advance timing. Maybe that's where I'm going wrong... But it is already at mbt at that boost level.

 

Something to keep in mind is that there is literally 100 times the mass of air as the mass of water in your system. Even though the latent heat of vaporization of water is high, this would mean that in a perfectly ideal world where everything went according to some simple model of the first-order effects, your maximum EGT reduction would be maybe 15 degrees Celsius.

Second-order effects, including the significant fact that the water has evaporated before combustion starts and before the charge is done equilibrating with the engine's temperature, are all aimed in the direction of making the gap even smaller.

 

That is a good point, but I would have thought the combustion is key.

15C is less than half a lambda point, and I'm adding a lot more water than the difference in fuel between 11.0 and 11.5:1.

 

The difference is that adding more fuel when significantly rich of peak actually results in less fuel (in absolute terms, not just as a proportion) burning.

In other words, the drop in temperature at higher AFRs is not just from evaporating fuel absorbing heat — the energy of changing phases is small compared to that of chemical reactions. The benefit from WI (and the place “extra fuel cooling” is the main effect of rich AFRs) is, as Ian said, during the compression stroke.

 

Have you tried moving the water injection to the exhaust side?

 

Perhaps a better question would be, has anyone successfully (or otherwise) used water injection to lower EGT? If so, how?

 

Water injection could presumably lead to reduced EGT by allowing the timing to be advanced. Fuel and timing are the biggest EGT ***** you can turn.

 

Do you mean knock limited spark advance rather than mbt spark advance?

Just I would be surprised if you are able to run actual MBT timing figures at 170kPA even on premium.

What I am getting at is dependant on your WI setup you may now actually be able to advance timing to MBT rather than what I suspect you run currently without WI - knock limited best timing.

As others have already stated being able to optimise timing to MBT or near it is what will net you the EGT reductions.

If you do find MBT please report back I would be very interested! Currently installing a WI system on my supercharged car and will be on the hunt for it also