Control strategy optimization exploration of a novel hydrogen-fed high-efficiency X-type rotary engine hybrid power system by coupling with recuperative organic Rankine cycle

This paper proposes an innovative hydrogen-fed high-efficiency X-type rotary engine (XRE) hybrid system by combining with recuperative organic Rankine cycle (RORC). The off-design model is established based on optimal thermo-economic parameters. Furthermore, the effects of key operation parameters on system off-design performance are revealed. Two novel ignition advance angle - crankshaft rotational speed (IAA-CRS) and equivalence ratio - crankshaft rotational speed (ER-CRS) control strategies are proposed by adjusting dual-variables. Meanwhile, the modified sliding pressure control strategy is adopted for RORC to obtain constant final XRE exhaust temperature. Finally, the part-load performance superiorities of novel strategies are revealed. The results show that the novel hybrid system thermal efficiency and LCOE could be improved by 24.2% and declined by 22.2% comparing with standalone XRE, respectively. Compared with crankshaft rotational speed and ignition advance angle, XRE peak cylinder gas temperature and pressure are the most sensitive to equivalence ratio. With decreasing XRE load, the optimal ignition advance angle drops firstly and then keeps constant under IAA-CRS strategy, while the optimal equivalence ratio of ER-CRS strategy drops. The novel ER-CRS strategy is the optimal control strategy, which could perform 2.06% and 7.95% higher thermal efficiency than IAA-CRS and traditional CRS strategies at most.