Flyin' Miata : Tech : Water injection

The following data is taken from a 1.8L Miata running an MP62 supercharger with an 8psi pulley, a Link ECU, header and an Aquamist 1s water injection system set to come on at around 130 KPa.

Long datalog (PDF file, will open in a new window)
This is a datalog of almost 4 minutes of driving time. The light blue line is the manifold pressure in KPa. 100 KPa is atmospheric pressure so anything above this is boost. It peaks at around 11 psi at one point. The dark blue line is air intake temperature in Celcius. Green is RPM.

The datalog begins with a hard run through the gears. The water injection is keeping the intake temperature down to a reasonable 45°C (113F) or so, with the temperature climbing as the engine idles for a moment. The driver then starts accelerating again, but just below the threshold where the water injection turns on.The air intake temperature spikes up to 80°C (176F). The driver then accelerates at around 100 KPa and the intake temperature climbs up to a peak of 94°C (202F). The driver then cruises at 3000 rpm with a light throttle and the air intake settles at around 70°C (158F). This car would benefit from having the water injection come on earlier, but it can't run all the time.

Datalog (will open in a new window)
The graph on the left is a run through 2nd, 3rd and 4th gears without water injection. The graph on the right is a run through 3rd and 4th gears with water injection turning on at about 4psi. The important traces are the dark blue trace for the intake air temperature (A Temp on the graph) and the light blue trace, close to the bottom, indicating ignition advance (IADv). Other parameters on the graphs are knock (red, showing simple engine noise in both graphs), MAP (manifold absolute pressure) and RPM.

Both traces for the intake air temperature start above 60°C, typical for a non-intercooled setup such as this one. Once in boost the run on the left shows the intake temperatures climbing to 96°C. With the water injection, the run on the right shows the temperature dropping and then leveling out at about 46°C. We can also run a lot more timing with the water injection thanks to the lower intake temperatures.