68 We featured Michiganbased Strange Development in 2020 (see Issue 33), for its two-stroke, inline, two-cylinder, spark-ignited REVolution engine, integrating a rotary exhaust valve (REV) to leverage forced induction when adjusting its dynamic compression ratio. Since then, the company has continued to operate as a multidisciplinary engineering services house, although ongoing development of its engine technology and REV-based operating cycle (now patented) was moved under a new company, Alpha-Otto Technologies, in 2022. Both Strange Development and Alpha-Otto Technologies are creations of John Krzeminski (CEO of the former and CTO of the latter), as is the newest version of REVolution, styled REV Force. The REV Force remains a spark-ignited, inline, two-cylinder, two-stroke engine with port injection and liquid cooling, today weighing 48 kg and outputting 127 kW (as either shaft power or electric power, thanks to new electric motor-generator integrations), with an expected TBO of 2000 hours – double its predecessor’s lifecycle. Still integrating its exhaust valvebased cycle, five years of r&d have seen the engine reconfigured with a number of innovations, particularly (but not exclusively) about its ancillaries, which have enabled combustion with a greatly broadened range of fuel, including heavy fuels, biofuels and hydrogen. These include a variable forced induction system (which spurred the engine’s renaming), direct injection (DI), and new approaches to combustion, ignition and engine management. All of these are largely encompassed under what Alpha-Otto terms its “low-temperature combustion” (LTC) process. LTC generally refers to techniques aimed at achieving so homogeneous a mixture of air and fuel within the combustion chamber that it may auto-ignite (spontaneous ignition without needing a spark or flame) at a lower temperature than is conventionally required. This would unlock leaner combustions, with reduced and uniform heat distribution throughout the cylinders, and hence lower heat-transfer losses Rory Jackson unpacks a company’s take on low-temperature combustion, through which it is achieving high-efficiency, low-emission operation on a wide range of fuels Multi-fuel futures The REV Force engine uses a multitude of innovations to run on hydrogen, kerosenes and more without necessitating hardware changes between fuel switches (All images courtesy of Alpha-Otto Technologies) April/May 2025 | Uncrewed Systems Technology
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