Parametric modeling and analysis of intake phases for side-ported Wankel rotary engines

This research presents a novel port parametric modeling technique using three-dimensional computational fluid dynamics for the design and optimization of intake and exhaust phases in side-ported Wankel rotary engines (WREs). Definitions for the port phases encompass parameters such as port start opening, port full opening, port start closing, and port full closing timings. The four port phase control arcs are obtained by translating and rotating the rotor flank to satisfy the high control accuracy. Further, the shape of the port is further smoothed and varied by four auxiliary circular arcs. Moreover, the influence of port full closing timing and the size of auxiliary circular arcs (R1, and R3) on the intake characteristics is studied. The results show that the novel method can flexibly and effectively control the phases and shapes. The early port full closing timing reduces fluid backflow and improves volumetric efficiency (VE) but increases intake loss (IL). The small size of R1 facilitates to increase the VE and reduce IL. A larger or smaller size of R3 is not conducive to reducing IL, and the smaller size of R3 improves the VE. The novel generation method proposed in this paper provides a theoretical basis to optimize the design of various sizes of side-ported WREs and guidance for practical manufacturing.

Improving accuracy of quantifying nitrate removal performance and enhancing understanding of processes in woodchip bioreactors using high-frequency data

Woodchip bioreactors have gained popularity in many countries as a conservation practice for reducing nitrate load to freshwater. However, current methods for assessing their performance may be inadequate when nitrate removal rates (RR) are determined from low-frequency (e.g., weekly) concurrent sampling at the inlet and outlet. We hypothesised that high-frequency monitoring data at multiple locations can help improve the accuracy of quantifying nitrate removal performance, enhance the understanding of processes occurring within a bioreactor, and therefore improve the design practice for bioreactors. Accordingly, the objectives of this study were to compare RRs calculated using high- and low-frequency sampling and assess the spatiotemporal variability of the nitrate removal within a bioreactor to unravel the processes occurring within a bioreactor. For two drainage seasons, we monitored nitrate concentrations at 21 locations on an hourly or two-hourly basis within a pilot-scale woodchip bioreactor in Tatuanui, New Zealand. A novel method was developed to account for the variable lag time between entry and exit of a parcel of sampled drainage water. Our results showed that this method not only enabled lag time to be accounted for but also helped quantify volumetric inefficiencies (e.g., dead zone) within the bioreactor. The average RR calculated using this method was significantly higher than the average RR calculated using conventional low-frequency methods. The average RRs of each of the quarter sections within the bioreactor were found to be different. 1-D transport modelling confirmed the effect of nitrate loading on the removal process as nitrate reduction followed Michaelis-Menten (MM) kinetics. These results demonstrate that high-frequency temporal and spatial monitoring of nitrate concentrations in the field allows improved description of bioreactor performance and better understanding of processes occurring within woodchip bioreactors. Thus, insights gained from this study can be used to optimise the design of future field bioreactors.