Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

October/November 2017 | Unmanned Systems Technology 56 Dossier | Continental Motors CD-155 I4 turbodiesel pressure pump as a lift pump that supplies fuel from the tank to a high-pressure pump at 3.0 bar. The high-pressure pump then supplies the fuel rail at 1350 bar. The driver for the single injector per cylinder is integral to the FADEC. The combustion chamber is formed primarily by a bowl within the crown. Often a turbodiesel with four valves per cylinder will have its valves upright and thus a uniformly flat roof to the chamber (assuming the valve feet aren’t dished). In the case of this engine though the valves are slightly canted, with a 12 º included angle in the interest of airflow, but the surrounding chamber roof is flat. The piston has shallow valve clearance notches on the intake side. Valve lift is 8.4 mm. A roller chain drives the intake camshaft with a pair of gears transferring drive to the exhaust side. The cam lobes operate the valves through short roller rockers. In this type of light aircraft/UAV power unit the propeller runs at a fixed ratio of crankshaft speed, and for any given combination of engine speed and load its pitch is varied as appropriate to attain a given amount of thrust. Normally the pilot has three levers to control propulsion – one for throttle setting, one for mixture setting and one for propeller pitch. With the CD-155’s FADEC system there is only one lever; the system takes care of engine plenum pressure and fuelling (a diesel engine has no throttle) and also propeller pitch in accordance with the amount of thrust demanded by the lever setting. Of course, in the case of an unmanned craft there is no physical lever; instead a control signal is sent to the FADEC by the craft’s electronic flight control system. The FADEC and associated wiring loom are produced in-house. It is based on a pair of 32-bit microprocessors, having dual main boards. Two are deployed for reason of redundancy, and these continuously monitor each other. The FADEC incorporates a logger capable of recording more than 100 hours’ worth of data. This is clearly very useful for diagnostic purposes, and the unit itself has the ability to identify sensor malfunction in real time. The key sensors sending data to the FADEC are crankshaft and camshaft speed, plenum air pressure and temperature, fuel rail pressure, coolant temperature, and oil pressure and temperature. The FADEC controls the timing and duration of each injection pulse. At a low-power setting there is a pilot injection prior to the main pulse, which assists cold start and reduces noise. At higher power settings there is only a single injection event. The wastegate controlling plenum pressure is of the conventional diaphragm type, operated by a servo under the command of the FADEC. The FADEC also controls fuel pressure via an electrically operated bleed valve that returns fuel to the high-pressure pump as necessary to obtain the required level. The control of propeller pitch is likewise closed-loop; the FADEC controls it. The engine is equipped with a 1.7 kW electric starter motor. The FADEC controls this and glow plug operation. CD-155 output with altitude Fuel consumption data for the CD-155