Microturbine Relies on 3D Printed Housing to Preheat Fuel

KW Micro Power of Miami, Florida, is developing a microturbine generator that company president Enrique Enriquez expects to deliver the highest power density ever realized in a generator of this class. The 30-inch by 15-inch-diameter generator coming to market soon will be capable of 30 kW, an output that today might require a device around twice these dimensions. Additive manufacturing is essential for producing the intricate components that allow a large power output from a small volume. And because AM is also enabling lightweighting of the same components, the 150-pound generator will offer a previously unattained power-to-weight ratio as well, Enriquez says.

The company has gone component by component through its generator design looking for engineering wins it could achieve through AM. An earlier success involved a 10-inch-diameter ring-shaped component with elaborate internal passages for channeling exhaust gas. Now, the component seen here is an even bigger success — bigger in terms of volume, and in terms of the many interrelated benefits the additive design achieves. This housing for the turbine features internal passages and large internal spaces not only for lightweighting, but also for cooling the system and preheating the fuel by passing the fuel through the housing structure.

Enriquez says, “How do you raise the power efficiency? Stop letting parasitic losses get away.” When a generator gets hot, this means energy is being lost to heat rather than work. Flowing the generator’s fuel through open passages in the housing allows the fuel itself to capture that energy. The fuel gets preheated from room temperature to 130°F, reducing the additional energy needed for combustion. Meanwhile, subtracting mass from the housing by adding the internal passages and cavities reduced its weight from 23 pounds for the original solid housing design to 13 pounds, while the cooling effect saves cost. Running cooler allows the housing to be made from an aluminum alloy (F357) instead of a more expensive heat-resistant material.

Software from nTopology was used to create the housing design. Load modeling determined where material could safely be removed. The software generated a hollow shell design with variable wall thickness, and it smoothed the internal geometry to ensure it could be 3D printed without support structures. Wagner Machine of Champaign, Illinois, made the part for KW Micro using a Sapphire laser powder bed fusion system from Velo3D. Wagner, a full-service metalworking contract manufacturer, performed the part’s CNC machining as well.

Aircraft are among the potential applications for the generator — it can serve as an auxiliary power unit where space and weight constraints are critical. But Enriquez says ground-based applications are promising, too. “Instead of a massive 1 MW turbine, what if 30 of these microturbines were daisy-chained to deliver the same output?” Units could then be turned on and off as needed, he notes. There would be significant power available, combined with the chance to generate only the amount of power that is required.