Boosting Technologies and Limits for Small Combustion Engines 2016-32-0077
Two-cylinder engines not only have special demands concerning uniformity and dynamics of oscillating masses and firing order, but also place very different demands on the turbocharger. With two-cylinder engines, the pulsating influence grows and changes the operation of the turbine. In this paper different boosting technologies are compared in small engine applications. Besides turbochargers the potentials and limits of superchargers and electric chargers are compared as well as their combinations. These technologies show differences concerning power supply, operation range and efficiency, and these effects have different implications in small engines. The efficiency of a turbo compressor, for example decreases, rapidly for small dimensions. Results from experiments and engine process simulations are shown based on a two-cylinder engine of 0.8l displacement. The operating condition of a turbocharger turbine in a two-cylinder engine is very specific due to exhaust pulsations. To understand this, a comparison was made with a four-cylinder engine based on numerical analyses. For the boundary conditions of the model, results of models from GT-Power simulations are used. Performing CFD-simulations, the turbine is driven by a two-and a four-cylinder-pulse, whereas both operations use the same specific exhaust enthalpy across one full engine cycle. In this regard, the pulsating operation of a small four-cylinder engine can be simulated and compared with those of a two-cylinder engine. The results show that for the optimization of a two-cylinder engine’s turbocharger, it is necessary to consider the specific pulse characteristics.