Selective catalytic reduction(SCR) technology is the mainstream approach for controlling nitrogen oxide(NO_x) emissions from diesel engines, and urea-water solution(UWS) serves as the key precursor for the reductant. However, the formation of solid deposits due to incomplete decomposition of UWS under low-temperature and transient operating conditions severely impacts the efficiency, reliability, and durability of SCR systems. Recent research progress on the issue was reviewed, the complex composition of urea deposits was systematically summarized and the detailed reaction mechanism was analyzed with isocyanic acid serving as the key intermediate and the liquid film acting as a "micro-reactor". The coupled influence of multiple factors(such as exhaust temperature, injection parameters, and structural design) on deposit formation was emphatically analyzed. Multi-level synergistic mitigation strategies were further comprehensively outlined, including physical process control through optimized spray mixing and thermal management, chemical modification by adding surfactants to alter droplet interfacial properties, and the development of intelligent predictive control. The results indicate that a fundamental solution to the deposit problem requires precise mechanistic understanding, synergistic system-level design and process integration to achieve efficient, stable, and low-maintenance operation of SCR systems across all operating conditions and throughout the lifecycle.

In order to systematically study the impact of inlet flow velocity parameters on the heat transfer performance of intercooler, a three-dimensional numerical model of a two-staged intercooler based on a representative unit was established using computational fluid dynamics (CFD) method. Using the k-ω SST turbulence model, grid independence verification and the comparison between simulation results and experimental data were carried out, and it was confirmed that the model accuracy was able to meet engineering requirements. By analyzing the temperature distribution, heat dissipation, and air-side pressure drop of the first and second stage intercoolers under different water-side inlet flow velocities, the following conclusions were drawn.The optimal water flow rate for the first stage was 10 m³/h, and it should be greater than 2.5 m³/h to prevent coolant vaporization.The optimal water flow rate for the second stage is 20 m³/h; increasing the water-side flow rate could significantly improve temperature distribution uniformity. In addition, it was found that the air-side inlet flow velocity exhibited obvious uneven distribution, and hence it was recommended to control the air-side flow velocity within 1.75 m/s to optimize flow uniformity.

In practical application scenarios such as multi-stage compression, centrifugal compressors often face unsteady pulsating inlet flow induced by the upstream equipment, while the systematic research on the dynamic response of compressors under this condition is relatively scarce. Based on a self-developed experimental platform for centrifugal compressors under unsteady inlet conditions, a flow pulse generator with adjustable pulse frequency and amplitude was designed. For the operating condition of 40 000 r/min, a systematic experimental investigation on the aerodynamic characteristics of a centrifugal compressor was carried out under pulsating inlet conditions, and the influence of pulse frequency and amplitude on the compressor transient response and time-averaged performance were studied. The results show that the transient pressure ratio-flow characteristics of compressor under pulsating inlet conditions exhibit closed slender hysteresis loops. The pulse frequency mainly affects the shape and slope of loop, while the pulse amplitude determines the loop size, and the unsteadiness increases monotonically with the amplitude. In terms of time-averaged performance, pulsating inlet flow reduces the compressor pressure ratio under high flow conditions, and the higher the transient unsteadiness, the more pronounced the deterioration of time-averaged performance. Under low flow conditions, the time-averaged performance approaches the steady-state characteristics. 

To meet the performance-improvement requirements of a China Ⅵ compliant medium and heavy duty diesel engine under full-operating-conditions, a co-optimization of aerodynamic performance and structural reliability was conducted for its matched centrifugal compressor. The meridional contour and blade loading distribution of the impeller were optimized. Three-dimensional flow-field simulation using NUMECA software showed that the optimized compressor achieved synchronous enhancement in pressure ratio and efficiency with a peak-efficiency increase of approximately 3 percentage points. The flow-field analysis indicated that the optimized compressor impeller could achieve a more uniform static-pressure distribution along the flow direction inside the optimized impeller, which effectively suppressed flow losses, especially in the tip-clearance region. Moreover, the mixing loss at the impeller outlet reduced, thereby the diffusion loss in the diffuser reduced. Based on the aerodynamic optimization, the structural reliability design was further performed. The results demonstrated that the stress at critical locations of the optimized impeller decreased by 27% and 67.5% respectively, while the stress at the outlet fillet dropped by more than 10%. A prototype was manufactured via five-axis milling, and the compressor rig tests verified the feasibility of the optimized design. Engine bench comparison tests revealed that the fuel consumption at full-load conditions reduced by 0.6-1.9 percentage points, and the fuel consumption at the best-efficiency-point improved by 1.1 percentage points after using the new compressor. All performance indicators met the technical requirements.

Based on the experimental platform of a visualized constant volume combustion bomb, a computational model was established by using CONVERGE software. Numerical simulation was conducted to investigate the jet ignition of methanol mixture in the pre-chamber and the combustion process in the main chamber. The effects of pre-chamber structures on methanol combustion performance were analyzed, incluidng three structures of without baffle, flat baffle and conical baffle. The results show that the combustion process in the combustion chamber consists of four stages such as the flame propagation stage in the pre-chamber, the jet development stage, the main combustion chamber combustion stage, and the late combustion stage. The pre-chamber jet is a continuous process consisting of cold jet, hot jet and reverse jet. When the equivalence ratio of main combustion chamber is 0.5, the conical baffle pre-chamber structure shows the optimal combustion performance. Compared with the pre-chamber without baffle, the combustion duration for flat baffle and conical baffle configuration shortens by 3.5% and 10.5% respectively. The lean-burn limit of methanol remains 0.4 for all the three pre-chamber structures. When the equivalence ratio of main combustion chamber is 0.4, the pre-chamber without baffle is most favorable for methanol combustion, with a peak heat release rate of 3 329 J/ms.

Under the context of increasing rail pressure and reducing orifice diameter for highly intesified diesel engines, the combustion processes of diesel engines with different injection hole diameters were tested and studied under three operating conditions, the combustion and emission results were compared and analyzed, and their working mechanisms were given through the simulation research. The research results show that both the fuel consumption rate and the soot decrease, the fuel consumption rate reduces by up to 2.5% and the soot reduces by 63.9% as the hole diameter decreases from 0.30 mm to 0.25 mm during the test process of the single-cylinder diesel engine. However, when the hole diameter decreases from 0.25 mm to 0.24 mm, the in-cylinder combustion process shows a consistent deterioration trend. The three-dimensional in-cylinder simulation results under the calibration operating conditions show that the matching of hole diameter to operating condition has a range of application, and the combustion shows a deterioration trend for the hole diameter of 0.24 mm and 0.30 mm beyond this range, while for the hole diameter of 0.25 mm, the fuel and gas mixes well, and the thermal efficiency reaches the highest, therefore the optimal combustion is achieved.

Based on the actual road operation data obtained from China Ⅵ remote emission monitoring platform of 385 heavy-duty vehicles, the low-load operating characteristics and NO_x emission features of China heavy-duty vehicles were analyzed by employing techniques such as the micro-trip window method and peak-by-peak fitting according to the U.S. Low Load Cycle (LLC) methodology. The results reveal that the median window load for heavy-duty vehicles in China is below 20%, and the load that remains below 20% during transient operating conditions accounts for more than 57%. Within the load range, the lower exhaust temperature leads to reduced catalytic efficiency of aftertreatment system and obvious increase of NO_x emissions. Furthermore, the window load distribution demonstrates a "single-peak" pattern concentrated between 0% and 40%, which differs significantly from the load distribution of heavyduty vehicles in the United States. Accordingly, an average load of 13% or less is proposed to be set as the upper limit for the low-load operating conditions window for heavy-duty vehicles in China, which provides a reference for establishing low-load operating conditions that are suited to the actual on-road operating characteristics of domestic heavy-duty vehicles. In addition, the current NO_x sensor dew point protection strategy leads to the exclusion of 14.60% to 23.88% of high-emission operating duration from supervision, necessitating urgent attention.

Cooled exhaust gas recirculation (abbreviated as cooled EGR) technology can effectively enhance engine fuel economy and suppress detonation while significantly improve engine emissions. Through numerical analysis, the mechanisms for optimizing the fuel economy of high-compression-ratio hybrid engines equipped with cooled EGR technology were investigated. Comparative analyses of engine performance, fuel consumption and combustion strategy were conducted under  full load conditions of baseline engine and partial load conditions of cooled EGR engine. The lowest fuel consumption point and the corresponding optimal combustion strategy were obtained under different conditions. The study provides a theoretical basis and technical support for the optimization of fuel consumption in hybrid dedicated engines.

With the impending introduction of a new PEMS test methodology in future emission standards, which segments  evaluation into cold-start and thermally stable operation phases, a thorough investigation into the key factors influencing PN emissions at each stage is of significant importance. The PN emission characteristics during both cold-start and thermally stable operation phases under different soot loading conditions were investigated by utilizing an engine bench simulation method for PEMS test. The results indicate that PN emissions exhibit a trend of initial sharp decline followed by a slight rebound with the increase of soot loading during the cold-start phase, attributable to the decisive influence of initial soot cake layer thickness on the physical filtration efficiency of DPF. During the thermally stable operation phase, PN emissions increase significantly with the rise of soot loading, primarily due to the secondary particle generation triggered by soot passive regeneration under high temperatures. Based on the observed patterns, an optimal DPF soot loading window capable of achieving the best balanced PN emissions across the entire operating cycle is further identified.

Aiming at the performance prediction of louvered fin heat exchangers, the predictive capabilities of various machine learning models were systematically compared. A dataset containing 343 data points was constructed through computational fluid dynamics (CFD) numerical simulations, covering three key geometric parameters sucn as fin angle, spacing and length. Heat transfer performance was further evaluated based on the j-factor, f-factor, and jf-factor. A total of 13 machine learning methods were selected, including linear models, tree-based models, ensemble models, and neural networks, with R² and RMSE used as evaluation metrics. The results showed that ensemble learning models, particularly CatBoost, performed best across all prediction tasks, with test set R² values all above 0.997 and the most stable control was RMSE, demonstrating excellent fitting capability and generalization performance. Furthermore, SHAP value analysis was conducted to reveal the influencing mechanisms of different geometric parameters and their coupling on the performance factors, providing insights for the efficient design of future heat exchangers.

As a core component of the proton exchange membrane fuel cell (PEMFC), the performance optimization of claw-type hydrogen circulation pump is crucial for improving the overall efficiency of fuel cell. To enhance the hydrogen supply capacity and working efficiency of claw-type hydrogen circulation pump, multi-objective optimization design was carried out for its structure. A prediction model for the average flow rate and volumetric efficiency of claw-type hydrogen circulation pump was first established based on Gaussian process regression (GPR). Then the model was combined with the non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ) to optimize average flow rate and volumetric efficiency, and the Pareto frontier solution set was substituted into the multi-criteria decision making (MCDM) analysis method to find the optimal combination of structural parameters. The results show that the prediction model based on GPR has a coefficient of determination greater than 0.95 and a root mean square error (RMSE) less than 0.5, which exhibits excellent prediction accuracy and correlation, and can greatly reduce the number of simulation and experiment in practical applications. Compared with the parameters before optimization, the optimal structural parameters obtained by NSGA-Ⅱ have increased the average flow rate of claw-type hydrogen circulation pump by 12.04% and the volumetric efficiency by 2.68% relatively.