NEX Power 15 kW GenSet gas micro-generator | Dossier continuous power output, so the alternator can function purely as a generator – from 60,000 rpm as idling speed, we run up to peak power at 120,000 rpm.” At idle and higher, throttling is performed through levering the fuel input rate up or down, analogously to compression-ignition engines, with that fuel demand being requested and processed via an ECU (as well as a power inverter, both of which we discuss later). “And, ultimately, we can change a lot of this as part of our modularisation approach to enabling low-cost, high-end microturbines,” Mohseni emphasises. “If this simple cycle approach solves their issues, great; if they need two engines in one UAV, also fine; and if they want one batch of aviation microturbines with heat recuperators for longendurance flight, as well as a second batch of micro-CHP turbines because they’re making a bunch of mobile bases for remote power and battery recharging, we have all the first-hand experience needed to do all of that. “We’re even agnostic to the heat source for our combustor. We’ve run it smoothly on Jet-A, natural gas, propane, diesel and solar heat. We’ve also run it on a biomass-powered heat exchanger, and for those really emphatic about zerocarbon, we’ve recently tested this engine on hydrogen, both working successfully.” Gas turbine The compressor forms the first stage of the core gas turbine engine section. It is a conventional centrifugal compressor (also called impeller/radial compressor), consisting of an inlet pipe, a bladed impeller or rotor and a diffuser (this component being bladed/vaned like the impeller but static and mounted to the combustor to further pressurise the air and diffuse it into that subsequent chamber). The impeller is an open-type design, featuring seven inducer blades and seven splitter blades, while the diffuser is designed with 13 blades (and no splitters). “We also have a long nose on the impeller, which helps align it to the main shaft during integration and keep the other components in place,” Najafi says. “Depending on the component, we can weld, bolt or push-fit components onto the shaft, with the latter approach either taking oil or shrink-fitting with different materials. Tightly bolting the impeller’s long nose to the shaft, for instance, keeps it very well aligned.” At the time of writing, the impeller is CNC-machined from aluminium for low weight, although NEX is interested in investment casting as a reliable and repeatable (not to mention far less wasteful) method for large volume production, once demand reaches suitable levels, with Lestercast’s pricing and supplier network making them NEX’s preferred partner for such casting needs. The combustor is designed as a single annular chamber to maximise flame propagation, with the injectors custom designed in-house for optimisation for each fuel. Najafi notes that the injectors can hence be chosen for each customer’s fuel needs if they need such optimisation, although it is not a strict requirement for multi-fuel capability; a hydrogenoptimised combustor could, for instance, still run on natural gas satisfactorily. Stainless steel sheet is bent and formed using custom tooling to achieve the ring-like shape of the annular combustor, before being welded closed, and then the stainless steel housing is bolted directly around the combustor. Like the impeller, the combustor may be cast in the future. Additive manufacturing (AM) could also be an option because the chamber’s hollow 3D shape can be printed as a single piece, eliminating the need to weld it shut, making for simpler overall assembly. Some prospective AM suppliers have also told NEX Power that a printed combustor would give better performance over a longer lifespan than the conventionally formed combustor. A radial turbine sits downstream of the combustor; as mentioned, this is dissimilar to the ‘power turbine’ sections seen in those microturbine engines previously featured because those turbines rotated freely from their 73 Uncrewed Systems Technology | August/September 2025 The engine’s aluminium impeller features seven inducers and seven splitters, with a long nose for ease of integration
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