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THE “Orion” gas-generator turbocompound engine consists of a supercharged, regenerative aircooled, 2-stroke-cycle opposed-piston diesel engine driving two centrifugal compressors. One of these compressors is for combustion air with fine air filtration, while the other is for cylinder cooling with much less filtration. The gas-generator engine has a bore of 4¼-in. diameter and a stroke of 5⅞ in. × 2. The engine turns at 2340 rpm, and the combustion air compressor turns at 37,000 rpm while the cooling air compressor turns 17,000 rpm. The cylinder is cooled with air at nearly the supercharge level and at an equivalent temperature because this air later does work on the turbine. The cooling airflow is about 3½ times the combustion airflow. These two airstreams join in a plenum chamber downstream from the engine, and the mixture temperature is about 500 F. This hot gas stream then goes to the power turbine, which is mechanically free of the gas generator.