Micro Gas Turbine

Overview

I am refining a fully 3D-printed micro gas turbine engine with advanced active cooling made from high-heat deflection thermoset resin. The engine is built to be low-cost, IR-suppressed, fast to produce, and with a significantly reduced part count using advanced additive manufacturing. Over the past year I have worked towards designing a 100 N class micro gas turbine engine built as a monolithic polymer structure with regenerative cooling and integrated fuel injection. The static assembly, including the outer casing, diffuser, combustor, and shaft tunnel with radial injectors, is printed in high-heat-deflection-temperature SLA resin, with only the rotating assembly (shaft, turbine wheel) and nozzle guide vanes metallic.

Conventional microturbines rely on sheet metal forming, CNC-machined housings, and brazed fuel systems; this design eliminates all of that, showing that a flight-scale jet engine can be built with nothing more than an SLA printer and off-the-shelf parts. A provisional patent has been filed, hot-fire tests are underway, and SBIR funding is being pursued.

Regarding the regenerative cooling, fuel enters through two inlets on the front face, fills an annular distributor ring with multiple metering orifices, and flows through axial channels down the casing, up the combustor wall, and back down the shaft tunnel. At the tunnel exit, the fuel passes through radial injectors printed into the wall, delivering it into the combustor. This eliminates brass tubing and brazing entirely, since the fuel system is embedded in the printed casing.

A central tradeoff in the design is the size and placement of dilution and liner holes; smaller holes force more air through each jet, improving penetration and flame stabilization but reducing overall wall cooling. Larger holes admit more cooling flow, but at the cost of residence time and combustion efficiency. We iterated through multiple different designs to balance cooling with stability, creating a combustor tailored to a polymer casing while still achieving the target thrust class.

Another key research direction for this engine has been its thermal signature management. Traditional microturbines radiate strongly from hot metal casings. In this design, the fuel-cooled polymer body blocks line-of-sight to the combustor and hot hardware, so the outer surface radiates very little energy. Instead, emissions are biased rearward into the plume. This plume-only IR signature is valuable for seeker calibration and sensor testing, because it replicates what real aircraft engines present to a detector, hot exhaust and a comparatively cold body, rather than the unrealistic signature standard micro gas turbines of this scale emit.

Test variants experimented with different convergence angles, center-body lengths, and sheath offsets, exploiting the Coanda effect, where the high-speed exhaust flow entrains ambient air. This creates a passive insulating layer of cool air around the plume, reducing IR from the nozzle and sheath without active systems.

What I Built / Did

• The channels are tuned so that fuel remains liquid until injection, ensuring pre-heating of the fuel, and targeting phase-change cooling at the injection points along the shaft tunnel.
• Regenerative cooling is what makes a polymer engine feasible, preventing the casing from ever reaching its heat deflection temperature even though the surrounding gas path operates orders of magnitude hotter.
• The combustor is a ground-up design, verified through CFD and airflow simulations.
• To enhance the IR suppression effect, I developed experimental nozzle/sheath combinations consisting of dual-wall nozzles with external sheaths that block direct line-of-sight and entrain ambient air into the annulus and center-body spike nozzles that reshape the exhaust jet and damp acoustic modes.
• The engine design has been validated through CFD of the annulus and channels, transient heat transfer analysis of the casing, and FEA of stresses under combined pressure and thermal expansion. Cold-flow tests confirmed even distribution through the annulus and matched predicted pressure drops.
• For hot-fire testing, I designed a dedicated bench with fuel and ignition systems, a tachometer to measure rotating assembly speed, thermocouples for recording exhaust gas temperature (EGT), turbine inlet temperature (TIT), a thrust load cell, and synchronized IR video.

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