Numerical investigation on the compressor for gas-entraining diffuser EGR

Abstract

Exhaust Gas Recirculation (EGR) is an effective way to reduce nitrogen oxide (NO x) emissions, and the EGR application increases the engine backpressure to some extent. In this paper, a new EGR method named gas-entraining diffuser EGR was proposed to reduce pumping loss. It introduces the exhaust gas into the compressor diffuser inlet where the static pressure is the lowest without blades fouled by exhaust gas. As a result, lower pressure at the turbine upstream can achieve EGR. Then, a newly designed induced structure not only introduces exhaust gas into the compressor diffuser but also reduces the energy loss caused by EGR application. Furthermore, the performance of compressor with different induced angles of the induced structure was investigated using simulation method. Results showed that the compressor’s adiabatic efficiency was the best when the induced angle was 20°. Regarding the induced angle of 20°, the adiabatic efficiency drop of compressor was in the range of 0.8%–12%. Approximately 10% of the adiabatic efficiency drop was caused by the induced structure, the other was mainly from the flow loss and mixing loss in diffuser system. The induced structure mainly affected the static pressure difference between induced structure inlet and impeller outlet ([Formula: see text]). When the impeller mass flow was 0.23 kg/s, [Formula: see text] was 11.21, 13.95, 15.59, 17.18 kPa respectively with corresponding induced angles of 20°, 30°, 40°, 50°. The primary energy loss leading to the adiabatic efficiency drop of compressor with induced structure occurred in diffuser system. It was caused by the mixing process of induced gas and impeller exit gas, and the enhanced effect from the shroud side’s impeller jet-wake and volute tongue.

Effect of the design parameters of induced structures on the sensitivity of compressor efficiency and static pressure of induced structure inlets

“…11 In addition, to meet the stringent requirements of the main emission limits of China VI, 12,13 a higher EGR rate is required for reducing the cost of tail gas after-treatment systems by suppressing NO x generation. To further reduce the pumping loss and increase the EGR rate, a gas-entraining diffuser EGR is proposed in Zhu et al, 14 which introduces exhaust gas into the diffuser inlet where the static pressure is the lowest to achieve HP-EGR without fouling of the compressor blades by exhaust gas. Meanwhile, a new induced structure has been designed to meet the needs of the new EGR so that a large amount of exhaust gas enters the diffuser.…”

“…However, there is a lack of comprehensive studies on compressor performance and energy loss by injection. Regarding the effect of the induced structure on the compressor, Zhu et al 14 only studied the effect of the induced angle on the compressor, and the results showed that the induced gas caused a reduction of up to 7% in the compressor efficiency, the primary loss occurred at the diffuser, and the induced structure had an obvious effect on the static pressure of the induced structure inlet. Therefore, further studies are needed to obtain the best induced structure design.…”