78 throttle control over the engine exhaust and scavenging. “That essentially means that, instead of our normal operating cycle, where the REV shuts the exhaust port at piston BDC, so that the supercharged air can flow freely, and the compression and power stages last just as long as each other, we can phase the valve 180° and create an Atkinson-cycle in which the power stage lasts longer than the compression stage,” Krzeminski explains. “This could work especially well for VTOL transitioning aircraft, where for 5% of the time they’re in VTOL and need peak power output, and don’t care so much about thermal efficiency, but then they’re cruising for 95% of air time and need the high-efficiency mode for that.” Combustion control We previously wrote that the REVolution ran on a Cosworth ECU, and the REV Force uses the same solution for standard spark and injection timing. Since then, however, Alpha-Otto has engaged in developing its own proprietary control algorithms and controllers in Simulink as an alternative means of engine management, for which the Michiganbased outfit is mulling over the use of a different, more aviation-oriented ECU that is better suited to both LTC management and UAV applications. “Some newer Cosworth ECUs would be capable in this regard, and we’re certainly not about to become an ECU manufacturer, but REV Force operates so differently to normal engines that it’s very difficult to use an off-the-shelf solution. In most of our bench tests, we’ve actually been using a PC directly wired into the engine to run it,” Krzeminski says. The principle challenge that AlphaOtto undertakes in this development is combustion control, in which the engine detects either the fuel type and quality or monitors combustion (the company having looked into many approaches for that), and responds by switching between fuel-specific calibrations or mappings embedded in the ECU. “If you look at the profile or tracings of pressure sensor data in a cylinder, it tells you a ton about what’s happening in its combustion chamber: you can see clearly if you’re getting detonations, if ignitions happen too early or too late, and so on,” Krzeminski says. “So, in future, instead of prioritising the analysis of conventional things, like throttle position, CHT and so on – which are, of course, very important – we’re going to really be studying combustion analysis, and what we need to see in TPS, rpm, CHT, EGT, MAP, or what have April/May 2025 | Uncrewed Systems Technology Dossier | Alpha-Otto REV Force The company’s proprietary ECU algorithms will enable fine combustion control, as well as future optimisations such as AI-powered, real-time combustion tracking Additional future work will hone the electrical and electronic subsystems, particularly through real-world trials of new components and applications
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