Design and experimental of venturi in EGR system of turbocharged intercooled diesel engine

Abstract: At present, most high-power diesel engines, a majority of diesel engines for automobiles and quite a large proportion of the high performance gasoline engines have adopted the turbocharged intercooled technology. However, owing to an increase of the oxygen content in the mixture after supercharging, NOx emissions in the exhaust will increase. The exhaust gas recirculation (EGR) technology is still a main method to reduce the NOx emissions.Aiming at the practical circumstances of difficulty in introducing exhaust gas recirculation (EGR) with diesel engines under the operating conditions of low speeds and full loads, a venturi was installed after the intercooler in order to improve its introduction ability of EGR. A throat diameter of a venturi was preliminarily obtained by calculating with the help of related formula, and based on this, three sorts of venturi-tubes with different structural dimensions were designed, and then some experimental research was also carried out. The results indicate that with the increase of engine speeds, the gas flow increased and the function of reducing the throat pressure of a venturi was enhanced. The difference between the pressure upstream of the EGR valve and the pressure of inside the throat of the venturi decreased first and then increased along with the speeds, and at the speed range of from 1 100 r/min to 1 600 r/min, this difference value was negative, so it is unfavorable to introduce EGR. At the speed of 2 200 r/min and along with the increase of the engine loads, the pressure upstream of the EGR valve was always greater than the pressure upstream of a venturi and the engine could introduce EGR easily even without a venturi. However, the difference of both pressures decreased along with the increase of engine loads, which led to a lower EGR rate at high loads. The effects of reducing the throat pressure of a venturi increased and the variation of introduction ability of EGR was not obvious along with the increase of engine loads. The difference between the pressure upstream and downstream of the venturi was invariably greater than 5 kPa throughout the test load range. With the increase of engine loads, the introduction ability of EGR of the venturi with three different throat diameters had a rising trend at the speed of 2 200 r/min, but the difference between the pressure upstream of an EGR valve and the throat pressure of a venturi with a smaller diameter was higher than that of the venturi with a bigger diameter, and it is favorable to realize a high EGR rate; while at the speed of 1 600 r/min. The introduction ability of EGR of the venturi with three different throat diameters decreased along with the increase of engine loads. When the engine torque was above 470 N·m, along with the increase of the throat diameter of a venturi, the difference between the pressure upstream of the EGR valve and the pressure of inside the throat of the venturi decreased gradually, and the difficulty in introducing the EGR increased. The research results provide a reference of design and application of venturi in the EGR system of a turbocharged intercooled diesel engine.