Based on a modified diesel-methanol dual direct injection single-cylinder engine, combustion and emission characteristics of the diesel-ignited high-pressure direct injection methanol combustion were experimentally investigated and compared with those of the methanol-diesel dual-fuel combustion with premixed methanol across a wide indicated mean effective pressure(IMEP) load range of 0.4—1.4MPa. The results show that the diesel-ignited high-pressure direct injection methanol combustion can achieve stable combustion at 90%—97% methanol substitution rates over the broad load range. The methanol heat release stage exhibits significant diffusion combustion characteristic at medium to high loads, with the combustion duration during the post-combustion phase remaining nearly constant as load increases. Carbon monoxide and unburned hydrocarbon emissions are both below 1g/(kW·h) at all loads, while nitrogen oxide emissions significantly increase with increasing load. Compared with the methanol-diesel dual-fuel combustion with premixed methanol, the peak heat release rate of the diesel-ignited high-pressure direct injection methanol combustion is only half of that, allowing combustion to commence at earlier crank phases to get an increase of thermal efficiency by more than 4%. While soot, carbon monoxide, and unburned hydrocarbon emissions in all loads are substantially reduced to less than 10% of that, and NO_x emissions are lower at low loads but higher at high loads.

The impact of pre-chamber injection timing and spray angle on combustion and emissions of a WP10H heavy-duty diesel engine was investigated using the numerical simulation software CONVERGE. The results show that under high-load conditions, pre-chamber combustion system improves combustion efficiency, advances the combustion phase, increases the peak cylinder pressure, shortens the combustion duration, and leads to an elevated wall heat transfer loss. Some pre-chamber setups studied effectively reduces both NO_x and soot emissions. The optimized pre-chamber configurations demonstrates that sustained turbulence induced by the pre-chamber disrupts the redistribution of unburnt mixture in the main chamber, decreasing the presence of dilute mixtures in the cylinder and subsequently lowering NO_x emissions. Additionally, with an equivalence ratio near 1, the increased mixture facilitates more comprehensive combustion, resulting in higher temperature in the main chamber during the soot oxidation stage and aiding in soot reduction. The final optimized solution involves selecting a pre-chamber injection timing of 0° CA ATDC and a pre-chamber injection angle of 54.5°. This configuration, compared to the baseline engine, results in a 2.48% reduction in NO_x emissions and a 21.07% reduction in soot emission.

Based on the computational fluid dynamics software CONVERGE, a numerical simulation of the methanol spray auto-ignition process was carried out using the large eddy simulation method. The effect of ambient oxygen volume fraction on auto-ignition characteristics of the methanol spray was studied in a constant volume combustion bomb at an ambient temperature of 1200K and an ambient pressure of 7.77MPa. The results show that when the ambient oxygen volume fraction decreases from 21% to 15%, the ignition delay time(IDT) increases by 2.5%. When the ambient oxygen volume fraction further decreases to 10%, the IDT increases by 8.1%. At 10% ambient oxygen volume fraction, a tiny amount of OH is generated during methanol combustion and always distributed in the periphery of methanol spray. From the perspective of the spatiotemporal distribution characteristics of CH₂O, as the oxygen volume fraction decreases, the temperature range of CH₂O generation narrows, the equivalence ratio range widens, and the spatial distribution range of CH₂O increases and the concentration distribution becomes more uniform. It can be seen that the change of ambient oxygen volume fraction significantly affects the ignition characteristics of methanol spray, and then affects the generation and distribution of its key radicals (CH₂O, OH).

Based on a naturally aspirated four-cylinder and spark-ignition engine, the combustion and nitrogen-based emission characteristics fueled with gasoline/ammonia and ethanol/ammonia respectively, were investigated under different values of excess air ratio ϕ_a at the speed of 2000r/min and the indicated mean effective pressure of 0.64—0.86MPa. The experimental results show that, at ϕ_a=1.0, the addition of ammonia to gasoline can effectively suppress knocking and optimize combustion phase, leading to an increase of indicated thermal efficiency of 3.4%. The nitrogen-based emission patterns of gasoline/ammonia and ethanol/ammonia are similar. The blending of ammonia leads to a notable increase in NO_x emissions. Especially, NO_x emissions decrease with spark timing advance at ϕ_a=1.0, while they increase with spark timing advance at ϕ_a=1.2 and 1.4. Chemical kinetic analysis reveals a positively correlation between fuel-NO_x and temperature, and a negative correlation with pressure, and the impact of temperature on fuel-NO_x is enhanced under lean-burn conditions. The NH₃ emission is controlled by both the crevice mechanism and volumetric quenching effect, with the latter being enhanced as ϕ_a increases. The N₂O emission is controlled by the low-temperature oxidation path of ammonia and tends to increase with delayed spark timing and an increase in ϕ_a. After ammonia blended, the NO_x conversion efficiency of the three way catalyst decreases, while the CO conversion efficiency increases at the stoichiometric ratio.

A dual-stage selective cataiytic reduction(SCR) system effectively reduces NO_x emissions during cold start-up by adding a close-coupled SCR in the upstream position. However, copper-based SCR produces more N₂O in the low temperature section. In order to reduce N₂O emission, a vanadium-based SCR catalyst is selected for the close-coupled SCR, and a copper-based SCR catalyst is selected for the downstream position. This selected aftertreatment system can not only reduce NO_x emissions at low temperatures, but also limit N₂O emission to lower levels. In this paper, vanadium-based and copper-based SCR catalyst models were built using AVL CruiseM simulation software, and N₂O chemical reaction kinetics equations were added to the models. The influence of urea injection amount and NO₂ ratio on NO_x and N₂O emissions was studied by simulation, and coordination control of N₂O and NO_x was verified by experiment. The results show that the co-control of NO_x and N₂O emission can be achieved by selecting the vanadium-based SCR catalyst at the front and the copper-based SCR catalyst in the downstream SCR.

Injection characteristics of a dual solenoid-driven fuel injector under various injection modes was studied, based on controllable fuel injection rate. An experimental platform combining injector inlet pressure and fuel injection rate measurements was developed using the momentum method. By designing the driving current timing control for two solenoid valves(labeled as NCV-1 and NCV-2), various injection rate profiles were achieved, including single-valve rectangular, dual-valve rectangular, ramp, and boot-shaped modes. The results demonstrate that compared to the dual-valve rectangular mode, the single-valve rectangular mode exhibits a 0.23 ms injection timing delay and a lower injection rate growth rate. The ramp mode coincides with the single-valve rectangular mode before NCV-2 activation, after which the injection rate rises sharply. Furthermore, when the actuation interval between NCV-1 and NCV-2 is 1 ms, the ramp injection mode delivers 22% less fuel quantity compared to the dual-valve rectangular mode, while exhibiting significantly reduced fuel injection rate fluctuations during the steady injection phase. The boot-shaped mode demonstrates nearly identical injection delay characteristics to the dual-valve rectangular mode. At a 1 ms interval between the activation of NCV-1 and the subsequent activation of NCV-2, the injection volume reaches over 82% of that in the dual-valve rectangular mode, while fluctuations in the steady injection phase are markedly reduced.

A three-dimensional numerical model for a direct injection hydrogen engine was initially constructed. Subsequently, simulations were conducted to investigate the impact of orifice quantity, installation position, and piston top shape on combustion performance. The results show that the performance of side injector position is better than that of center injector position, and the maximum indicated thermal efficiency is 47.28%. Based on the side injector position, the influence of piston top shape on combustion performance is further studied, and it is found that the shape of piston top shape has a significant impact on the development and distribution of mixture in the cylinder. The mixture concentration distribution formed by the combination of slope head piston and 1-hole nozzle will extend the ignition delay and combustion duration, but it will reduce wall heat transfer loss, increase work capacity, and make the indicating thermal efficiency higher than that of the flat top piston. To further verify the advantages of the slope head piston, the performance under different equivalence ratios was simulated. The result indicates that the maximum indicated thermal efficiency of the slope piston top increases by 0.29%, 0.67% and 0.52% respectively, under the equivalence ratios of 0.3, 0.5 and 0.7.

The hydrogen fueled internal combustion engine is an important technical route to promote the green and low-carbon transformation of the automotive industry and achieve the "dual carbon" strategic goal. However, during low-temperature cold start of a hydrogen engine, the water vapor generated by combustion can enter the crankcase and condense into water, causing oil emulsification and seriously affecting the reliability of the hydrogen engine. This study firstly proposed a rapid detection method for oil emulsification of the hydrogen engine. Then, the degrees of oil emulsification under driving conditions of medium and long distance at room temperature and of intermittent and short distance at low temperature, as well as the performance of the emulsified oil at different water contents were investigated. Finally, the effects of oil temperature and ventilation degree on oil emulsification were explored. The results show that the oil discharge weighing method can meet the need of hydrogen engine oil emulsification detection. Oil emulsification does not occur under the medium and long distance driving condition, but mainly occurs under the low-temperature, short and intermittent distance driving conditions. Although the water content of the emulsified oil reaches 25%, it still meets the lubrication need. It is also found that heating the engine oil to above 60℃ can effectively avoid the oil emulsification of the hydrogen engine. By heating the oil mixture to above 93℃, water can be quickly separated from the emulsion. Supplying fresh air at room temperature outside the engine body to enhance crankcase ventilation will accelerate the occurrence of oil emulsification.

In order to solve the problems of over-fitting and low accuracy of the vibration data-driven diesel engine fault diagnosis method caused by the lack of data, a diesel engine fault diagnosis method based on Wasserstein auxiliary classifier generative adversarial network(WACGAN) and Inception residual convolutional neural network(IRCNN) was established from two perspectives of fault data enhancement and diagnosis model optimization. Firstly, Wasserstein distance and gradient penalty were introduced into the auxiliary classifier generative adversarial network, and the WACGAN was established to augment the small-scale training set. Then, the inception structure was introduced into the convolutional neural network(CNN) and continuously differentiable exponential linear units(CELU) were used to improve the feature extraction ability of the model, while residual structure was added to avoid the loss of feature information, and IRCNN model was built. Finally, the IRCNN model was trained with the augmented training set to realize the diesel engine fault diagnosis under small samples. The method was validated by diesel engine fault simulation experiments, which can achieve fault recognition rate of 95% using only 10 operating cycles of vibration data in each fault state. Compared with the traditional oversampling algorithm and the CNN algorithm before and after optimization, the method works best when fault samples are scarce and can achieve fault diagnosis accuracy of 95.47%.

A turbocharger surge identification method based on multi-domain composite features of non-intrusive acoustic signals was proposed on a turbocharged diesel engine. Firstly, the data of surge acoustic signals were collected and relevant database was established through the turbocharger surge reproduction experiment. Then, multiple features were selected and extracted from the time, frequency and cepstrum domains. The contribution of each feature to the wheezing was calculated using the random forest algorithm, and the core contributing features were selected and combined into a multi-domain composite feature, which was used as the sensitive feature of the wheezing acoustic signals for the identification of the turbocharger wheezing. Furthermore, the support vector machine was used to establish a model for the identification of the wheezing, and the whale optimization algorithm was applied to optimize the coefficients of the kernel function of the support vector machine with the objective of the identification accuracy. Finally, multiple acoustic signals were obtained through the turbocharger bench test, and the multi-domain composite features of the acoustic signals were solved to verify the accuracy of the model. The results show that the accuracy of the model can reach more than 99%.