The concept of determining the control function of turbochargers in sequential turbo-charging

Abstract

The sequential turbo-charging consists in using at least two turbochargers that work individually or in a parallel system depending on the changes in engine speed and load. With the right selection of the turbochargers for the engine, each turbocharger can work with greater efficiency in a much wider range of speed and load variations than in an engine using a single turbocharger. However, the benefits of the sequential turbo-charging requires solving the problem of the optimal selection of two different turbochargers and - additional - ensuring the proper conditions for the cooperation between both of them. This is particularly important during the switching over phase of the turbocharger, and thus also for control issues. The paper presents the concept of optimization of the function controlling the switching over of turbochargers in the whole field of engine operation. The operating ranges of the turbochargers were determined on the basis of the economic criterion of the engine operation. For this purpose, the load characteristics of the brake-specific fuel consumption obtained in the mode of operation with one and two simultaneously operating turbochargers were used. The points of intersection for these characteristics determined the work areas of each turbocharger depending on the engine speed and load. The control function determined in this way was used to develop the models and the algorithm of the numerical control system for turbochargers. The correctness of the system operation was verified during tests on the engine dynamometer.