Impact of diffuser width on performance of variable gas-entraining compressors

Abstract

This paper is a continuation of the previous work, which studies a new exhaust gas recirculation (EGR) technique called “gas-entraining diffuser EGR (DEGR),” focusing on improving the induced air compressor (IGC)’ efficiency. Therefore, two IGC schemes with variable diffuser width (VIGC) are proposed. A numerical simulation was conducted to compare the compressor efficiency and static pressure at the induced structure inlet of two schemes and original IGC (ID1 scheme). The findings indicate that the compressor efficiency of the two schemes surpasses that of the ID1 scheme. However, in contrast to the ID1 scheme, Scheme A does not exhibit a decrease in inlet static pressure at the induced structure. Instead, the enhancement in efficiency and the reduction in inlet static pressure at the induced structure vary inversely with the diffuser width. Conversely, Scheme B demonstrates a lower static pressure at the induced structure inlet compared to ID1. Notably, when the diffuser width is increased by 5 mm, Scheme B achieves the most significant improvement in compressor efficiency. As the IR increases, the VIGC efficiency rises by 1.6%, 1%, 1%, and 0.5%, respectively, while the inlet static pressure at the induced structure decreases by 1.0, 1.8, 3.5, and 6.5 kPa. Finally, the flow field at various cross-sections of the VIGC casing, with an incremental diffuser width of 0.5 mm has been analyzed. High entropy regions are observed at the outlet of the induced structure, indicating energy loss due to the mixing of induced gas and compressed air. The entropy levels within the casing’s cross-sections are found to be lower in Scheme A compared to Schemes B and ID1. Nevertheless, the static pressure at these cross-sections is noted to be less in Scheme B.