Waste heat recovery using Organic Rankine Cycle (ORC) systems shows significant potential for reducing CO₂ emissions from ships. This study designs and analyzes ORC systems for recovering multi-grade waste heat from the exhaust gas, jacket water, and scavenging air of a marine two-stroke diesel engine. A thermodynamic model is developed to investigate the effects of working fluid preheating temperature, evaporation pressure, and heat source conditions on system performance. Results show that appropriately increasing the preheating temperature of the working fluid can enhance power output. For hydrocarbons with higher critical temperatures, power output exhibits an extremum as preheating temperature increases, while for fluids with lower critical temperatures, power output increases continuously until the evaporation pressure limit is reached. Increasing evaporation pressure decreases power output but improves thermal efficiency, with a corresponding increase in heat transfer and exergy loss rates in the exhaust gas preheater. Additionally, the temperature of the heat source has an important effect on the energy and exergy balance distribution and power output of the ORC. For every 10 K rise in exhaust temperature, the bottoming cycle power output of cyclohexane increases by approximately 12.3%. This study provides theoretical support for efficient marine waste heat recovery and working fluid selection.

Proton exchange membrane fuel cell (PEMFC) has become one of the new energy vehicle powertrains due to its special advantages, such as no pollution to the environment, high energy efficiency and power density. In order to improve the performance, a three-dimensional simulation model of the actual PEMFC is constructed. Combined with the mathematical models such as the electrochemical model and current conservation model, the model is calibrated by experiments. When the working voltage is 0.64 V, the error of the simulation results is 0.73%, compared with the experimental data. Then, the Taguchi method is used to design a multi-factor and multi-level orthogonal experimental scheme of PEMFC. Based on the orthogonal experimental table, the effects of different anode wave channel distortion, gas diffusion layer thickness and gas diffusion layer porosity on the current density are studied with a simulation experiment. The influence of the above factors on the orthogonal experiment results is analyzed by the signal-to-noise ratio. The regression equation is obtained by calculating the orthogonal experimental data. The t-test results are greater than 3.49, which indicates that each independent variable in the regression equation is important. R² test is 0.915, and the F test is 53.508, indicating that the regression equation is significant and the optimal and worst structural parameter combinations are predicted. The current density reaches 14,190.18 $\mathrm{A}/{\mathrm{m}}^2$ under the optimal structure combination, which is 6.14% higher than the calibrated model. Single factor experiments are carried out on these three different structural parameters to verify the effectiveness of the Taguchi method, and the best combination of structural parameters is obtained.

Multiphase simulations based on the VOF (Volume of Fluid) approach, used in synergy with the cavitation Schnerr-Sauer method and the K-Epsilon turbulence model, have been conducted to study the behavior of an injector nozzle as a function of relevant structural parameters (such as the spray hole diameter and length). The related performances have been optimized in the framework of orthogonal experimental design and range analysis methods. As made evident by the results, as the spray hole diameter increases from 0.10 to 0.20 mm, the outlet mass flow rate grows by 243.23%. A small diameter of the spray hole, however, has a beneficial effect in terms of cavitation suppression. Moreover, rounding the spray hole can effectively increase the outlet mass flow rate and improve the flow characteristics while mitigating the cavitation phenomenon inside the spray hole. In particular, with the optimized nozzle design, the outlet mass flow rate can be increased by 13.33%, while the fuel vapor volume is reduced by 33.53%, thereby, leading to significant improvements in terms of flow characteristics and cavitation control.

A Diesel Particulate Filter (DPF) is a critical device for diesel engine exhaust products treatment. When using active-regeneration purification methods, on the one hand, a spatially irregular gas flow can produce relatively high local temperatures, potentially resulting in damage to the carrier; On the other hand, the internal temperature field can also undergo significant changes contributing to increase this risk. This study explores the gas flow uniformity in a DPF carrier and the related temperature behavior under drop-to-idle (DTI) condition by means of bench tests. It is shown that the considered silicon carbide carrier exhibits good flow uniformity, with a temperature deviation of no more than 2% with respect to the same radius measurement point at the outlet during the regeneration stage. In the DTI test, the temperature is relatively high within r/2 near the outlet end, where the maximum temperature peak occurs, and the maximum radial temperature gradient is located between r/2 and the edge. Both these quantities grow as the soot load increases, thereby making the risk of carrier burnout greater. Finally, it is shown that the soot load limit of the silicon carbide DPF can be extended to 11 g/L, which reduces the frequency of active regeneration by approximately 40% compared to a cordierite DPF.