Abstract
High pressure EGR systems recycles the exhaust gases upstream of the turbine to downstream of the intercooler. Modern EGR configurations are equipped at least with a compact cooler, an EGR-valve and a bypass-valve to control the mass flow rate and the temperature of the recirculated exhaust gases. These systems are placed in a severe environment, exposed to favorable fouling conditions, strong temperature gradients and pressure waves wich may reduce their performance and reliability over their lifetime.
This paper is focused on the study of pressure pulse propagation by experimentation. Dynamometer experiments were conducted on a modern four cylinders turbocharged engine with the two bypass-valve operational positions for full load for engine speeds varying from 1000 to 4500 rpm. The instantaneous crank-angle resolved pressure data were acquired in two locations at both sides of the bypass valve with two piezoresistive transducers.
The results showed that both sides of the bypass valve are exposed to different arrival times and magnitude of the blowdown pulse and EGR reflected pulses. As a consequence the stress load applied to the valve and the torque necessary to switch the valve position may be underestimated during the design process.
Keywords: HP EGR system, dynamometer test bench, exhaust pulses, bypass valve, dynamic loads