Turbocharging Systems Development for Aircraft Propulsion

This chapter illustrates a procedure having as a goal the definition of the supercharging architecture of a 2-Stroke diesel engine for general aviation and Unmanned Aerial Vehicles (UAV) propulsion. At the beginning, the engine platform (a six-cylinder uniflow engine) is modeled coupled with different supercharging solutions – single turbocharger, double turbocharger, single turbocharger combined with a mechanical compressor, with intercooler or aftercooler. A comparison of fuel consumption under different configuration is provided after the ability in reaching the target power was assessed. Afterwards, the potential of increasing the engine output power at take-off or decreasing the fuel consumption at highest operating altitude has been explored running a multivariable optimization process on the engine supercharged by two sequential turbochargers and an aftercooler per bank. In order to make a comprehensive analysis, many design and operation parameters have been selected as input parameters for the optmization procedure, i.e. exhaust valves opening and closing angles and maximum valve lift, scavenging ports opening angle, distance between bottom edge of the scavenging ports and bottom dead center, area of the single scavenging port and number of ports, engine volumetric compression ratio, low and high pressure compressor pressure ratios, air/fuel ratio. These parameters have been varied on a wide range of values. It is demonstrated that, with a proper design and control of the engine, it is possible either to increase the output power at sea level of about 42% or to save about 7% fuel with the engine operating at highest altitude. Finally, the benefits in engine performance have been assessed deriving from the utilization of: an electrically assisted turbocharger on the low pressure side; thermoelectric generators. Results show that the former technology is more effective at low operating altitudes and high engine speed, basically due to the higher availability of energy at the engine exhaust, exceeding that required by the compressors to compress the air and reach the target values of power. A fuel saving up to 3.6% could be achieved at sea level and rated engine speed.