Wave J-1 | Engine dossier gasoline as standard, although the E85 ethanol-gasoline blend is also compatible with it, and Jet-A or JP-8 configurations are also possible. Additionally, the team worked to establish digital control over the engine via an ECU, with EFI, to ensure that either a crewed aircraft’s fly-by-wire system or a UAV’s autopilot would be able to start, restart and throttle the engine without issue; these subsystems will be discussed henceforth. Today, units of the J-1 have been delivered for trials with prospective customers and the design is in low-rate production, with plans to expand. “It has been a constant process of mostly minor optimisations, bit by bit, and also working on the practical aspects of turning this into a product that people will actually trust and buy for their UAVs. Those have taken the longest; for example, optimising the efficiency in TSFC terms, or improving the reliability of the engine and getting the starting to function robustly and consistently,” Maqbool says. “That last one isn’t trivial either. If you search for pulsejets on YouTube, you see all kinds of weird, convoluted, blowertype systems, so it’s honestly something a lot of technical people struggle with. But you can also see how our starting works, and that it works completely remotely, and only takes a couple of seconds. It’s a very predictable process.” Intake The J-1 is started using a small quantity of electronically controlled, compressed air. “While some gas turbine engines can be started with some sort of electric motor, as reciprocating and rotary engines are, a lot of jet engines actually need compressed air to start, and most often it actually takes quite a lot of air to bring the engine up to operating speed. You can see on YouTube or on some passenger jets just how long it takes,” Maqbool explains. “That also creates a problem for gas turbines in achieving mid-air restarts, because it’s a lengthy process and they can rarely carry a large enough air source to just deliver all the air they need for that. Ours can restart in just a few seconds using a small, onboard air tank, multiple times per flight if needed.” The inlet of either pipe remains constantly open and unobstructed without the need for a throttle to regulate air intake (their exact diameters must remain undisclosed as a key part of the engine’s geometric optimisations). As mentioned, EFI is used for fuel delivery, being a core aspect of modern tech that Wave Engine has brought into the pulsejet realm (the engine can be fuelled without EFI, but this would not yield as fine a degree of control over its operation). “We’ve worked with several ECUs to see how well the results were in terms of fuel and power management, and we customised a range of proprietary ECUs at different levels of simplicity or complexity. The custom design we’ve selected to go into production of the J-1 with is one of the simpler ones, genuinely for the sake of simplicity and reliability,” Maqbool explains. “A more complex ECU and EFI system would be a definite way to get more fuel efficiency, but, at the same time, because this is going to be a new sort of engine for a lot of people, we need to prioritise getting the reliability and ease of integration right. “We do plan on moving to more sophisticated engine management and fuel injection approaches in our future generations though once we’ve established the engine technology among UAV integrators.” While Wave Engine has tried to draw upon standard COTS components where possible, the fuel injectors, fuel lines and associated wiring have been slightly modified into a form factor more suitable for this engine. Fuel/air mixing in the J-1 happens slightly differently than in gas turbine mixing chambers. While gas turbines mix the air and fuel with a steady flow of both, in pulsejets the air moves with an inherently unsteady flow; that is, with a pressure wave almost constantly springing back and forth. “That motion does help with the mixing a bit, but unlike a steady flow environment – like in gas turbines, where you have a lot of time to mix and time to burn – our engine comes with a very limited time to burn,” Maqbool says. 69 Uncrewed Systems Technology | October/November 2024 Another key modern innovation leveraged in the J-1 today is digital control, with an ECU and EFI system enabling UAV autopilots to start, restart and throttle the engine
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