Investigation of the effects of compressed air injection directly onto the turbine wheel blades of the turbocharger system on turbo lag

In order to achieve optimum fuel consumption and exhaust emission standards in internal combustion engines, turbocharger systems, which allow engine cylinder volumes to be reduced by increasing the air pressure in the intake line, have become an important element of today's vehicles. However, the most important disadvantage of these systems is that they have long response times due to the nature of the energy transfer between the turbocharger and the engine during the instantaneous change in the load of the engine running at low speeds, known as turbo lag. In this study, the effects of direct compressed air supply onto the turbine wheel blades of the turbocharger system on turbo lag are investigated experimentally and numerically. In order to carry out the experimental studies, firstly, an external nozzle was created near the turbine wheel blades of a variable geometry turbocharger system, and then a cold air flow test rig was set up to measure and record the operating parameters of the turbocharger system. The experiments were carried out in the reference case where the system was operated with only the main air tank and then in the air assisted case where the main and auxiliary air tanks were operated together and the advantages obtained were demonstrated. Within the scope of the study, three-dimensional computational fluid dynamics (CFD) simulations were also performed using ANSYS Fluent to visualize the flow field inside the turbine side of the turbocharger system by applying experimental boundary conditions. The dynamic mesh method with the SST k-ω turbulence model was used to simulate the rotational motion of the turbine wheel. As a result, it was observed that the compressor mass flow rate of the turbocharger system increases in the air-assisted case and a corresponding decrease in the turbo lag time is realized. With the developed system, an increase of up to 8 times in the compressor air flow rate was achieved at the beginning of loading when the turbo lag is at high levels.