Water injection test for exhaust gas cooling

On Atex compliance Zone engines there are requirements for different parts, surfaces and fluids to meet certain temperatures. In this application and Atex zone, the required temperature for the exhaust gas is 200 Celsius and although this engine (at 160hp) meets the requirement with a maximum gas temperature of 192 Celsius but that was deemed to be too close to the limit.

Many alterations have been made to the existing cooler design to attempt bring the temperature down along with a few different configurations. All with varying degrees of success.

At this point my suggestion for some water injection to further cool the exhaust gases was accepted for an experiment. After some simple calculations with the nozzles that I could choose from the amount of energy taken from the exhaust gasses could be anywhere between 2 and 50kJ, assuming the water temperature is 93 Celsius (top hose temperature)  and that all the injected water is converted to steam (but then no more heating is done).

As the suppliers of the misting nozzles didn't reply to me with costings I made one instead. Making a nozzle (Fig 1 and 2) integrated into the system it was found that there was not a spray pattern but more of a jet (a second hole shown as the drill bit snapped in the first one), in order to rectify this some wire was soldered onto the blanking plate to help vaporise the jet (Fig 3 and 4), this worked surprisingly well for to the point that it was desired in the first place.

Fig 1 - Nozzle with a hole shown.

Fig. 2 - Nozzle jet at 0.5 bar.

Fig 3 - 'Vaporisation' wire after 1 run up.

Fig 4 -  0.5 bar past the vaporisation wire.

In order to do the test I wanted the engine to get up to temperature for the exhaust gas and then start the water injection process to show the difference in the temperature. In Figures 5 to 8 you can see the installation in the system

Fig 5 - Injector screwed into the cooler blanking cap.

Fig 6 - Whole cooler with the blanking plate attached.

Fig 7 - Tank mainly filled ready to be hooked up to the airline.

Fig 8 - Whole engine all wired up for various testing.

In Figure 9 you can see the trace for the test that was carried out. After the second start up when the exhaust gas temperature reached ~195 Celsius the system was plugged in. Initially this was run at 1.5 bar (then shortly thereafter reduced to 1 bar) and saw the gas temperature reduced to around 50 Celcius, unfortunately this is a false reading as it is 'over cooling' by pouring water onto the temperature sensors and not necessarily a true reading of the temperature.

Then the pressure was dropped which saw the temperature rise back up again. Then the injection was resumed at 0.5 bar leading to a gas temperature of ~130 Celsius with fluctuations due to the pressure regulator and other users on the gas lines. This is a more realistic reading with the amount of water that is entering the system. Once shut off again the temperature can be seen to rise again, showing that the system was actually making a difference to the gas temperature.

Fig 9 - Temperature traces for the test.

Bonus picture in Fig 10, what happens when you leave the airline plugged in and take the tank up to 3x its working pressure (4.5bar), by accident, but there was a very large bang and thankfully it was outside at the time and no one was hurt.

Fig 10 - Bonus picture!