One Builder’s Quest to Keep a 3D Printed Rocket Engine from Melting Involves Water

Mr. More Gooder spends his time in the workshop turning everyday ideas into hands-on experiments. This time he decided to tackle a stubborn problem with rocket engines built on standard FDM 3D printers. Plastic parts usually fail quickly once the fuel ignites because the heat softens and melts the material. He came up with a direct fix by routing water through channels inside the printed walls to carry the heat away before the plastic could give way.

He began with a basic propane-burning design, which he expanded upon with a combustion chamber and nozzle created using a standard 3D printer and some common plastic filament. The early versions were a disaster; there was no cooling at all, and when he lit the mixture, the plastic began dripping all over the place almost immediately, and the shape of the chamber would completely fall apart within seconds, as they were all over in a matter of seconds; however, they did identify the point of weakness.

Gooder wasn’t one to give up quickly, so he rethought the entire concept and came up with a two-walled construction with water flowing constantly between the inner wall, which was exposed to the flames, and the outer wall, which contained everything. He put connectors on the sidewalls that connected to a small pump so that the coolant could circulate continuously while the engine was running. He printed all of the new parts in a single piece to limit the amount of seams where leaks could occur. He double-checked the seals for pressure tightness before exposing the engine to an open flame.

The first test with proper cooling resulted in a significant improvement, as the flames remained stable in the combustion chamber and the engine lasted longer than any of the prior ones. Hey, the water flowing through the walls did make a difference, keeping the temperatures low and the cooled areas rock solid. Watching the video, it was clear what was going on, but the uncooled parts lower down in the nozzle were still overheating and sagging, and those plastic droplets were simply falling out of the end of the nozzle.

He went forward with a new design that completely cooled the engine, ensuring that every surface that came into touch with the combustion gasses had water channels behind it. Hey, the following time around, everything seemed extremely promising: thrust was constantly increasing, temperatures were under control, and the water was doing its job. Then a small break appeared in the inner wall, and coolant began to stream into the flames, and the engine died.

Further investigation after the test revealed why the system had struggled: regular 3D printing plastics aren’t particularly good at conducting heat; even when there’s water right behind the surface, the inner layer must still reach melting point before the heat can begin to travel outward. Thinner walls might not have been a horrible idea because they would have helped transport heat more effectively, but they wouldn’t have had the strength to withstand pressure. That increased water tank and pump were pointing to a bigger concern for any future flight version, as the extra weight from the coolant supply was only going to reduce payload and range.
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