Experimental Investigation and 1D Simulation of a Turbocharger Compressor Close to Surge Operation

Downsizing is widely considered one of the main paths to reduce the fuel consumption of spark ignition internal combustion engines. Some drawbacks usually arise when the engine operates at full load and low speeds, where the compressor experiences close-to-surge operation. In the paper, both experimental and numerical approaches are followed to describe the unsteady behavior of a small in-series turbocharger compressor. The compressor is included in the in-series intake circuit and a pulsating flow is generated by a motor-driven cylinder head fitted with a variable valve actuation system. Different rotational speeds and various valve opening strategies, characterized by different opening durations, are considered. The unsteady compressor behavior is investigated in terms of instantaneous inlet and outlet static pressures, and mass flow rate. The experimental test-rig is schematized in a commercial 1D code. The compressor is described following an enhanced map-based approach, where proper capacities are placed upstream and downstream the compressor to consider the mass and energy storage effects. The model is validated for various rotational speeds and valve lift strategies. After being validated, the methodology is employed to analyze the effect of the equivalent engine speed and valve strategy on the surge resistance.