A numerical simulation study was conducted on the co-optimization of injector configuration parameters and injection strategies for diesel-piloted high-pressure direct-injection ammonia combustion. Results indicate that reducing injector offset increases the proportion of effectively-ignited ammonia spray, improving combustion efficiency and thermal efficiency. Under high load conditions, the ammonia-first-diesel-later(AD) injection strategy leads to obstruction of the diesel flame by the ammonia spray, preventing full effective ignition of ammonia, with maximum combustion losses reaching 27.62%. Using a two-stage ammonia(ammonia-diesel-ammonia, ADA) injection strategy or optimizing the side injector nozzle insertion distance effectively avoids interference between the ammonia spray and diesel flame distribution, enhancing the ignition and combustion processes. The optimal solution features: side nozzle offset of 10mm, insertion distance of 6mm, diesel-first-ammonia-later(DA) injection strategy at low load(thermal efficiency of 49.68%), and AD injection strategy at high load(thermal efficiency of 50.75%). The sub-optimal solution adopts a side nozzle offset of 10 mm with other parameters unchanged: DA injection strategy at low load(thermal efficiency of 50.26%) and ADA injection strategy at high load(thermal efficiency of 49.93%).

A numerical simulation model was developed for an ammonia-diesel dual-fuel two-stroke low-speed marine engine using the 3D simulation software Converge, and the accuracy of the model was also validated. The effects of two injector arrangements, namely close arrangement and uniform arrangement, and different fuel injection timings on engine performance and emissions were investigated under 112r/min speed and 75% load operating conditions. The results show that the dual-fuel injector arrangement directly influences the fuel mixture formation and development, leading to different combustion modes and variations in engine performance and pollutant emissions. Under high-pressure direct injection dual-fuel conditions, NO_x emissions are reduced by 45.71% to 59.63% compared to those of diesel-only operations, while greenhouse gas emissions are decreased by 91.38% to 98.12%. Advancing diesel injection timing to -4°CA facilitates faster ammonia ignition and combustion, but further advancing it to -6°CA shows an opposite trend. It is found that advancing liquid ammonia injection timing significantly improves work output of the engine, but NO_x emissions increase. Delaying the liquid ammonia injection timing to 3°CA, NO_x emissions reduces to below 3.4g/(kW·h), meeting the Tier Ⅲ emission regulation requirements.

In order to solve the cold start difficulty for diesel engines on the plateau, an experimental study on the effect of flame intake preheating on the starting performance of diesel engine at 5km altitude was carried out on a plateau environmental test chamber. The results show that under the altitude of 5km and the intake temperature of 303K without intake preheating, the diesel engine falters in the speed range of 400—500r/min at the coolant temperature of 303, 318 and 333K, respectively. At the coolant temperature below 318K, the diesel engine falters for a longer time and even cannot go to idle condition. After analyzing, it is found that at 200r/min, large amount of residual gases from the last cycle results in misfire. At 400r/min, no misfire happens. When the engine speed goes above 500r/min, the misfire cycle rate increases significantly due to the increased ignition delay period, leading to faltering at 400—500r/min. Under the altitude of 5km, when a flame intake preheating device was used and set its preheating power to 0.84kW at 200r/min and 400r/min, 1.25kW at 600r/min and 2.10kW at 800r/min, respectively, the misfire cycle rate drops to 0% across all speeds. Experimental results show that the flame-assisted intake preheating system used with a precise fuel control can effectively improve the starting performance of the diesel engine at plateau, reducing the engine starting time to within 4s at the altitude of 5km.

Diesel spray characteristics under hydrogen atmosphere were researched by employing backlighting techniques in a virtual high-pressure constant-volume vessel under an environmental pressure of 2MPa and an environmental temperature of 293K. The effects of hydrogen volume fraction λ_H and fuel injection pressure p_inj on the macroscopic and microscopic characteristics of diesel spray were discussed in detail. Furthermore, based on the spray characteristics results, this study clarified the effect of micro-addition of hydrogen on diesel combustion characteristics. The results indicate that the spray penetration increases with λ_H, but the curves overlap when p_inj≥120MPa. The spray cone angle initially decreases and then slightly increases with λ_H, but when p_inj≥120MPa, the spray exhibits intense fluctuations, and the angle changes irregularly. Small amounts of hydrogen addition(λ_H≤9.0%) significantly reduce droplet size, and the sauter mean diameter(SMD) decreases by 1.45% when λ_H=9.0% compared to that of no hydrogen addition. Excessive hydrogen addition(λ_H≥25.0%) inhibits secondary atomization of the spray, resulting in an increased droplet size. Due to the vortex effect, droplet size first decreases and then increases radially at lower λ_H, while at higher concentrations, it increases slowly along the radial direction. Microaddition of hydrogen in the atmosphere alters the diesel ignition delay time. The ignition timing is 3.55ms after the start of injection(ASOI) when λ_H=1.5%, and 2.70ms when λ_H=3.0%. As λ_H increases, intensity of combustion first decreases and then increases, while the duration of large-area combustion extends, leading to a more uniform distribution of diesel ignition points.

Based on a self-built optically visualized constant volume combustion chamber system, the effects of injection duration(3.0, 6.0, 8.6ms), injection pressure(30, 40, 50MPa), and ambient temperature(880, 910, 940K) on n-butanol spray flame were studied. The flame development process and combustion characteristics were revealed by flame self-illumination high-speed imaging method. Results show that the n-butanol spray flame shows a yellow-white flame as a whole, and there is a small amount of light blue flame upstream of the spray. Under small injection duration(3.0ms), a partial flame-quenching phenomenon presents after n-butanol ignites. As injection duration increases, the soot lift-off length shortens, and the flame brightness, ignition delay and combustion duration increase. As injection pressure increases, the flame brightness and flame backtracking phenomenon weaken, and the soot lift-off length increases. At the same time, the ignition delay is prolonged, but the combustion duration is shortened. The ambient temperature has a significant effect on the stable ignition of n-butanol spray flame. With an increase in ambient temperature of only 60K, the ignition delay of n-butanol spray flame is notably shortened by 4.16ms, while the flame brightness is obviously enhanced and the flame shape is more stable.

Aiming at the pyrolysis and coking of RP-3 aviation kerosene at temperatures above 1000K and ambient pressure around 1.8MPa, optical imaging and time series sampling of RP-3 aviation kerosene soot formation process under oxygen-free environment were conducted using a new sampling method to study the formation rate and morphology evolution route of soot. The results of optical imaging indicate that the higher the ambient temperature, the faster the growth rate of soot and the higher the soot peak mass. By comparing the transmission electron microscopy images of soot at different times, it is found that soot could complete the whole process from fuel pyrolysis to mature aggregate formation within 8 ms at 1200K. After the soot matured, the particle size distribution and internal structure no longer change over time. However, even though the total mass of soot has stopped increasing, the average particle number of soot aggregates continues to increase with time.

In order to study the influence of the distribution of double-layer in-wall coatings with different thickness ratios and up-down orders in the wall thickness direction on the filtration performance of gasoline particulate filter(GPF), two layers of coatings with different coating amounts were applied in the filtration wall thickness direction, and six different double-layer in-wall coated GPF were formed by changing the up-down orders and thickness ratios. The filtration performance, particle deposition and porosity distribution at the end of filtration of these six GPF and two single-layer in-wall coated GPF were simulated. The results show that the higher the proportion of the coating thickness of the coating with the larger amount of coating to the thickness of the filter wall, the larger the initial filtration efficiency of the GPF, and the upper and lower order of the coatings has no effect on this. The initial filtration efficiency of the GPF increases by 2.50% in the case that the proportion of the coating to the filtration wall thickness increases from 1/4 to 3/4 when a larger amount of coating is located on the top, and the initial filtration efficiency of the GPF increases by 2.52% in the same case when the coating is on the bottom. Both cases of placing a larger amount of coating on the top and having a larger percentage of thickness of this coating enhance the growth rate of filtration efficiency and pressure drop of the GPF during filtration, but the former effect is more pronounced than the latter. For the design of double-layer in-wall coatings, it is recommended to place the larger amount of coating on the top and keep the thickness ratio of the coating smaller, such as 1/4 or 1/2.

To improve the response characteristics of a no-static-leakage injector, an electronically controlled injector was designed with a three-orifice plate structure. Its performance was optimized and evaluated through simulation modeling. In the performance analysis, the leakage ratio was introduced as a standard to assess the fuel leakage level of the injector in order to eliminate the evaluation error caused by cyclic injection volume. In the optimization phase, a fitness function was constructed based on three performance indicators: Leakage ratio, opening response time, and closing response time. The non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ)with an elitist strategy was used for multi-objective optimization. The optimization results indicate that, under a rail pressure range of 100MPa to 200MPa, compared to the original model designed for the operational conditions, the closing response time of the designed injector is reduced by up to 11.46%, the opening response time is reduced by up to 1.68%, and the leakage ratio is increased by up to 11.23%. The application of this algorithm effectively improves optimization efficiency and enhances the overall performance of the injector.

Based on the multi-input and multi-output model of a supercharged direct injection engine and vehicle, which was provided by the internal combustion power intelligent control algorithm challenge, a joint decoupling controller was developed by combining back propagation neural network(BPNN), particle swarm optimization(PSO) and proportional-integral-derivative(PID) control. In order to reduce the coupling error and achieve both target tracking and decoupling control for the exhaust gas recirculation(EGR) valve and the turbine vent valve, the PSO algorithm was employed to optimize the PID control parameters to control the opening of the EGR valve. Meanwhile, the BPNN algorithm was utilized to iterate the PID control parameters of the equivalent flow diameter of the turbine vent valve through the method of error backpropagation. The control effectiveness of the combined decoupling controller with respect to different driving speeds was evaluated on the Simulink platform. The results show that compared with the BPNN-PID algorithm, the mean integrated absolute error of the boost pressure and EGR rate of the combined BPNN-PID and PSO-PID algorithm is reduced by 31.86% and 2.46% respectively, and the controller demonstrates excellent performance under different driving speeds.

In order to deal with the challenges in predicting the high cycle fatigue(HCF) crack initiation life of cast Al-Si alloy cylinder head, the impact of pore characteristics on the mechanical response of cast Al-Si alloy was investigated through a representative volume element model containing the pore. The relationship between pore size and the non-local maximum plastic shear strain amplitudewas established. The HCF strength of the cylinder head was evaluated based on the obtained model. The findings reveal a significant level of stress concentration at the local complex concave and convex positions of large pores. The harmfulness of pores is primarily determined by their size. With the increase in pore size, experiences an accelerated growth. The HCF life of samples extracted from the cylinder head can be predicted within ±2.5 times dispersion band using the crack initiation model driven by. The bottom plate, the inlet and the exhaust walls are the main parts of the cylinder head with high mechanical stress. The combination of high stress and large pores results in a low HCF life of the inlet wall.