Since two-stroke cycle diesels have no intake stroke, they require an external means of forcing air into the cylinders. This can be done with a roots blower (used on many makes and models of diesels), a centrifugal blower (used on the Detroit Diesel 6-110), or a turbocharger with an external drive gear train (as used on EMD turbocharged engines).
A freewheeling turbocharger by itself will not work well, as there is no exhaust energy available at startup, but it can be connected in series with a roots blower. The roots blower provides the air flow for starting, when the turbo has no exhaust energy available to drive it. As load is increased on the engine it powers the turbo which precompresses the air going into the roots blower. This roots blower plus turbo system was used by Detroit Diesel, Cleveland Diesel, Fairbanks Morse, and was also applied to a few EMD engines in experimental installations.
Unlike the others, the EMD engine has the blowers mounted over the generator, and having freewheeling turbochargers and aftercoolers stacked on top of two roots blowers was a nightmare installation, particularly in a locomotive carbody. EMD's unique gear train assisted turbocharger took far less space to do the same job.
A freewheeling turbocharger by itself will not work well, as there is no exhaust energy available at startup, but it can be connected in series with a roots blower. The roots blower provides the air flow for starting, when the turbo has no exhaust energy available to drive it. As load is increased on the engine it powers the turbo which precompresses the air going into the roots blower. This roots blower plus turbo system was used by Detroit Diesel, Cleveland Diesel, Fairbanks Morse, and was also applied to a few EMD engines in experimental installations.
Unlike the others, the EMD engine has the blowers mounted over the generator, and having freewheeling turbochargers and aftercoolers stacked on top of two roots blowers was a nightmare installation, particularly in a locomotive carbody. EMD's unique gear train assisted turbocharger took far less space to do the same job.