Investigation of Turbocharger Compressor Wheel Damage Due to Collision with Condensed Water Droplets

The compressor wheels used in turbochargers have typically been made of aluminium alloy for decades. The primary reason is to achieve the lowest possible rotor inertia. However, while in the past this component was only encountered with filtered air, nowadays, due to developments in compliance with tightening emission standards, various fluids also collide with the spinning blades, which can cause mechanical damage. One such fluid is condensed water in the low-pressure exhaust gas channel (LP-EGR) formulated at cold starts and low-load conditions. This kind of design has been developed to reduce the nitrogen oxide emission and is used in both Otto and Diesel engines. This paper presents a testing method - implemented on a component testbench - and its results for this phenomenon. First, the effect of the volume flow of the condensed water colliding with the spinning blades was analyzed, and then, in addition to a constant volume flow, the speed dependence of the degree of damage was also determined. Next to the visual inspections, the physical changes on the blades were also detected by vibration diagnostic tools, mainly by analyzing the amplitude of the order correlated to the number of blades, from which we can deduce the changed balance level of the rotor.