To improve the ignition stability of internal combustion engines in lean-burn mode，the effects of different ignition methods are analyzed from two perspectives：ignition principles and the coverage range of discharge plasma. The potential of the ignition system in combustion rate control and detonation suppression is discussed，and the development direction of advanced ignition systems is summarized. The analysis results show that the ignition system plays a key role in the combustion control process of internal combustion engines. Advanced ignition technology can ensure the ignition stability of internal combustion engines in lean-burn mode. Increasing ignition energy and ignition coverage can enhance ignition stability，but both will lead to a sharp increase in total ignition energy，requiring higher power for the ignition system，increasing system complexity，and reducing engine economy. Currently，the majority of ignition methods generate plasma ignition of the mixture through gas discharge. By adjusting the characteristics of the discharge plasma，the ignition system can flexibly control the combustion heat release throughout the combustion process in the cylinder.

In order to effectively improve the engine exhaust temperature and selective catalytic reduction（SCR）inlet temperature，a certain China VI heavy-duty diesel engine is taken as the research object. Based on the distribution characteristics of exhaust temperature，the combustion control area in the cylinder is divided into several intervals，and differentiated temperature control strategies are formulated for each interval. Based on the experimental verification of the effects of two exhaust thermal management technologies，namely intake throttle valve regulation and combustion parameter optimization，an adaptive exhaust thermal management strategy for the engine integrated with SCR automatic heating mode is designed. Engine bench cold world unified transient cycle（WHTC）tests and high-altitude complex road condition real vehicle verification tests are conducted to evaluate the actual effectiveness of the thermal management strategy. The results show that the influence of post injection quantity and post injection timing on exhaust temperature is significantly greater than that of rail pressure，main injection timing，and pre-injection timing. Furthermore，as the post injection quantity and timing increase，the exhaust thermal management effect gradually strengthens. When the closing degree of the intake throttle valve is not less than 70%，the exhaust temperature shows an upward trend with the increase of the closing degree of the intake throttle valve. When the engine operates at medium to high loads，it can achieve good thermal management effects by optimizing combustion parameters such as fuel injection quantity and timing. Under low load and zero load conditions，the strategy of regulating and coupling combustion parameters through the intake throttle valve can achieve good exhaust thermal management effects. Under cold WHTC conditions，the average exhaust temperature of the engine increases by about 20℃. With a weighted average fuel consumption growth rate of only 4% in cold WHTC，the NOx specific emissions are significantly reduced（by about 30%）. In the case of long downhill slopes on the plateau，the inlet temperature of SCR can be maintained at around 370℃for a long time. The designed engine adaptive exhaust thermal management strategy can enable the engine to have good thermal management effects in harsh working conditions such as refrigeration，high altitude，and low temperature.

In response to the new requirements of the EuroⅦEmission Standard for brake wear particulate matter emissions，the limit values，testing methods，and testing equipment requirements of the EuroⅦEmission Standard for brake wear particulate matter are deeply interpreted，a brake inertia test bench for the EuroⅦemission standard is designed. The bench integrates particulate matter measurement，automatic control system，and mechanical electric inertia hybrid simulation technology，and proposes an overall laboratory layout that is suitable for different site conditions. The practical application results show that the inertia brake platform can accurately measure the number of solid particles，total particle number PM2.5、PM10 . This design scheme not only meets the requirements of EuroⅦEmission Standard，but also improves the accuracy of testing，reduces costs，and optimizes space.

In order to improve the fuel economy of commercial vehicle automatic transmissions during neutral coasting，the fuel injection quality and economic influencing factors of the automatic transmission neutral slip control process are analyzed. The neutral slip control strategy is optimized based on the time-based moving average window method and verified by combining road test spectrum analysis. The results show that the fuel consumption mass is fixed when the vehicle enters and leaves the idle condition，and the total fuel consumption mass during neutral coasting is related to the number of times when it enters and exits neutral coasting control and the duration of a single coasting. Reducing the frequency of entering and exiting neutral coasting control，minimizing short duration neutral coasting，and retaining longer duration neutral coasting can improve vehicle fuel economy. For the road test，the optimized neutral sliding control strategy is adopted to reduce the gas consumption per 100 km from 31.950 kg to 31.728 kg，saving 0.222 kg in gas consumption per 100 km.

To improve the combustion process of natural gas，this paper systematically investigates the research progress on ignition optimization and flame propagation enhancement technologies for diesel and natural gas dual fuel engines. By clarifying the core scientific issues of the in-cylinder premixed natural gas combustion acceleration mechanism，the characteristics of three combustion organization modes，regulation of diesel injection，enhancement of in-cylinder flame propagation enhancement，and new combustion mode of induced flame jet are emphatically analyzed. The analysis results indicate that the main technical paths to accelerate natural gas combustion include improving ignition efficiency，enhancing flame propagation speed，maintaining stable flame propagation，and shortening flame propagation distance. The induced flame jet combustion mode represents a potential way to speed up combustion of natural gas by integrating multi-point auto-ignition of diesel with flame jets generated through a throttle ring. In this mode，the combustion flame is injected into the clearance region at high speed，the differences of the start of ignition，combustion duration，and flame propagation distance among different regions in the cylinder will be effectively reduced. To further optimize natural gas combustion performance，the throttle ring structure can undergo additional refinement. Meanwhile，clarifying the mechanism of induced flame jet combustion is essential to promote the technology' s development and practical application.

To reduce the seal failure rate of diesel engine crankshaft oil seals，market failure data of a certain platform's diesel engine crankshaft oil seals is statistically analyzed. Using fishbone diagrams，possible causes of oil seal failure and leakage are analyzed from six aspects：human，machine，material，method，environment，and measurement. The root cause of failure is verified through comparative tests of oil seal reliability from different suppliers and oil seal consistency assessment bench tests. On this basis，the improvement measures to reduce the sealing failure rate are proposed and tracked in the market. The results show that the failure rate of oil seals for cement mixer trucks is the highest，and the failure rate of the rear oil seal is significantly higher than that of the front oil seal. The main failure modes of faulty oil seals include main lip line failure，eccentric wear，and felt fuzzing. The main reasons for seal failure are the insufficient of followability of the oil seal and the inadequate density of the rubber material，defective production assembly process，uncoated end caps and gear shaft end faces，and poor assembly performance of combination oil seals. The oil seal parameters are optimized，as well as the injection vulcanization process，gluing on end caps and gear shaft heads，and assembly processes. After improvement，the failure rate of the oil seal market has significantly decreased.

To address the friction and wear issues of the second land of a forged steel piston in a diesel engine，various pin bore offset solutions，and second land profile solutions are designed under the constraint of maintaining piston rigidity. Dynamic analysis software is used to simulate and study the maximum tilt angle，impact kinetic energy，peak contact pressure，cumulative wear load，blow-by，and oil consumption for different solutions. The simulation results indicate that a 0.5 mm pin bore offset toward the major thrust side，combined with a convex cylindrical profile for the second land，the contact pressure and cumulative wear load are minimized，while keeping blow-by gas and oil consumption within design tolerances. Bench tests verify that the wear of the second land under this optimized solution is approximately 0.027 mm，which meets the engine' s durability requirements.

To improve the performance of hydrogen fuel cell ejectors，the structure and working principle of ejector are systematically analyzed. The classification and characteristics of ejector are described based on gas phase state，nozzle structure，nozzle number，distribution level，and ejection fluid mixing characteristics. Based on this，the future development direction of ejectors is predicted. The analysis results indicate that new structures and technologies such as multi-stage ejector，multi nozzle ejectors，swirl ejectors，and variable geometry ejectors can be adopted，and the problem of poor adaptability to variable operating conditions of ejectors can be solved by optimizing the intelligent control strategy of ejectors. During the design and development process of the ejector，numerical calculations and structural design should be based on actual gas composition and operating parameters to reduce water vapor condensation and ensure the ejector' s ejection performance. With the increasing demand for energy conservation and environmental protection and the development of emerging technologies，the research on ejector is showing a trend of interdisciplinary integration of fluid mechanics，materials science，and intelligent control.

In order to improve the heat dissipation performance of square lithium-ion batteries，a new liquid cooling channel structure is designed. Based on Fluent simulation software，a coupled model of battery heat generation and fluid heat transfer is constructed. The influence of coolant flow rate，inlet temperature，and channel thickness on the cooling effect in the new liquid cooling channel structure is simulated and analyzed. The results show that the new flow channel reduce the maximum temperature of the battery pack by 8.26℃. As the flow rate increases，the maximum temperature of the battery decreases，the temperature difference of the battery does not change much，and the pressure difference of the liquid cooling channel increases significantly. The inlet temperature decreases，the maximum temperature of the battery pack decreases，and the temperature difference is within a reasonable range of variation. As the thickness of the flow channel increases，the maximum temperature of the battery pack rises，the pressure difference decreases，and the temperature difference remains within a reasonable range of variation. To achieve the synergistic goal of higher efficiency and lower energy consumption，a balance needs to be sought between heat dissipation performance and pump functional consumption. A flow rate of 0.4 m/s and a channel thickness of 3 mm are the preferred options.

In order to accurately evaluate the safety performance of a passenger car during a frontal collision，a geometric model of the vehicle is established using CATIA software，and the model is preprocessed using ANSA simulation software. LS-DYNA solver is used to for calculation，and HyperView is used for post-processing and data analysis. The deformation of the front crash beam，energy absorbing box，front longitudinal beam assembly，front wall panel and battery pack during the frontal collision test of the vehicle is simulated and analyzed. The results show that the maximum acceleration of the B-pillars on the left and right sides is 67.325 g（g is the free fall acceleration）and 62.213 g，respectively，both of them meet the standard requirement that the maximum acceleration on both sides should not exceed 72 g. The maximum energy absorption point of the energy absorbing box is located at the front end，with a maximum displacement of 465.281 mm，effectively absorbing collision energy. The front longitudinal beam assembly absorbs energy of 21 kJ，accounting for approximately 27% of the total collision energy，and has a good energy absorption effect. The maximum deformation of the front panel is 24.80 mm，which does not invade the passenger compartment and ensures the safety of the driver and passengers. The maximum deformation of the battery pack bracket is 0.17 mm，which is less than the material deformation threshold（0.20 mm）and meets the evaluation requirements.

In response to the reliability requirements of aluminum alloy wheels for a certain family car，a three-dimensional model of the wheel hub is established using CATIA software. The wheel hub is meshed and simulated using ANSA software，and the natural frequencies and modes of the wheel hub are calculated using post-processing software META. The reliability of the wheel hub design is quantitatively evaluated through the modal separation margin（MSM）index. The calculation results show that the natural frequency of the wheel hub is 383.3 Hz，significantly higher than the excitation frequency of flat road surfaces，uneven road surfaces，and the highest vibration frequency of the engine. The MSM of the wheel hub is 56.5%，far exceeding the minimum safety threshold，effectively avoiding the risk of resonance with adjacent components. The designed wheel hub has high reliability under complex working conditions.

To accurately measure the uncertainty of formaldehyde emission，factors affecting the uncertainty of formaldehyde emission measurement from heavy-duty methanol engines are analyzed from various aspects，such as man，machine，material，method，and environment. A mathematical model of formaldehyde emission is established，and the relative standard uncertainty of formaldehyde emission is calculated using the world harmonized transient cycle（WHTC）test bench. The results show that the uncertainty of formaldehyde emission is related to the repeatability of measurement，the relative standard uncertainty of formaldehyde mass concentration dilution factor，total volume after exhaust dilution，and the relative standard uncertainty of actual cycle work. Among them，the dilution factor had a greater impact. The average formalhyde emission of the cold WHTC test is 41.6 mg/（kW·h），and the standard uncertainty of formaldehyde emission measurement is 1.29 mg/（kW·h），with an expanded uncertainty of 2.58 mg/（kW·h）. This research can provide a technical reference improving the accuracy and reproducibility of emission measurement of unconventional pollutants such as methanol and formaldehyde.

In order to reduce the noise of the crankshaft pulley，the fluid simulation software STAR ccm+ is used to establish a flow field simulation model，and the acoustic software LMS Virtual lab is used to simulate the aerodynamic noise of the pulley and analyze the structural and acoustic cavity modes of the pulley. The simulation analysis results show that when pulley rotates at high speed，the groove flow velocity between the pulley and the front cover of the gear chamber is uneven，and periodic pressure pulsation is generated on the groove surface，which is the main source of aerodynamic noise of the pulley. A relatively closed cavity is formed inside the groove，and the first-order modal frequency of the acoustic cavity is close to the excitation frequency of the noise source，which increases the noise. The optimized scheme with a 5 mm opening on the pulley is used to compare and verify the aerodynamic noise simulation and testing with the original scheme without a hole on the pulley. The results show that compared with the original scheme，the optimized scheme reduces the root mean square sound pressure level of the aerodynamic noise simulation by about 4 dB，and the root mean square sound pressure level of the acceleration condition test by about 2 dB. The simulation and testing data of the original and optimized schemes are basically consistent，and the simulation method could be effectively used in engineering practice.