Effect of Changing the Integral Parameter of the PI Controller on the Quality of Speed Control in a Helicopter Diesel Engine

Turboshaft aircraft engines, commonly used in helicopters have lower overall efficiency than the compression-ignition internal combustion engines currently used in road vehicles. The differences are mainly due to the operating principle of the two power units. Despite the advantage, in terms of overall efficiency, compressionignition engines are not widely used in the aerospace industry today. The main limitation is the high value of the engine’s weight/power ratio expressed in $\mathrm{kg} / \mathrm{kW}$. The aerospace industry is witnessing the rapid development of propulsion systems to reduce fuel consumption, emissions, and noise. One direction is the study of the possibility of using traction internal combustion engines as the main source of propulsion in helicopters. Within the framework of such a solution, several problems of adapting a diesel engine to a helicopter can be distinguished. One of them is controlling the engine’s crankshaft speed under the variable operating conditions to which helicopters are exposed during flight. The most popular and widely used algorithm for controlling the speed of internal combustion engines is the PID-type algorithm. As part of the research carried out at the Lublin University of Technology, the author analysed the effect of changes in the value of the integral parameter I on the quality of speed control in a compression-ignition engine operating under helicopter variable load conditions. The tests were performed on an engine dynamometer equipped with an Andoria ADCR diesel engine. It is a compression-ignition power unit equipped with a common-rail fuel supply system and a turbocharger with a charge air cooling system. The engine has a displacement of $2636 \mathrm{~cm}^{3}$ and generates a mechanical power of 85 kW at a crankshaft speed of 3700 rpm. Load shifting on the test bench was carried out by activating an additional electrical load system on the engine’s alternator. The value of the step change of the load was selected based on previous simulation studies, which analysed the effect of crosswind gusts on the power demand of the main rotor of a light-class helicopter. The stand enabled control of the accelerator pedal position percentage, thanks to the use of National Instruments actuators and the development of a control and recording program in the LabVIEW environment. The test plan included changes in the setting of the integral parameter I in the case of constant values of the settings of the proportional parameter P and the differential parameter D. One representative value of the engine crankshaft speed at 2000 rpm was selected for the tests. The results of the tests were presented in the form of time courses of speed and accelerator pedal position. On the other hand, the analysis of the test results included a comparison of the average errors of diesel engine speed control. As shown, there is an apparent effect of changes in the setting of the integrating member I on the speed control error of the crankshaft of an internal combustion engine operating at variable load.