Abstract:To address the issue of fan blade root fracture during the development of a certain tractor,the combined approach of modal analysis and spectral analysis are employed to identify the root cause under the common operating speed range of a 6-cylinder diesel engine.Based on the findings,an improvement solution is proposed and validated through simulation and endurance testing.The results indicate that the first-order modal frequency of the fan resonated with the third-order excitation frequency of the engine within the common speed range,leading to bidirectional bending fatigue failure at the blade root.By maintaining the fan diameter unchanged and increasing the hub thickness by 2 mm,the first-order modal frequency of the fan is raised from 108 Hz to 150 Hz.The improved fan doesn't break after a 500 h durability test,which indicates that the improvement measures are effective.In the design of rotating machinery systems,it is crucial to control the coupling relationship between the modal frequencies of key components and excitation frequencies.Optimizing structural parameters to adjust modal distribution can mitigate resonance risks while ensuring performance.

Abstract:In order to reduce the pollutant emissions of airport ground handling equipment,a certain international airport is taken as the research object.The types and quantities of ground handling equipment are counted,and the key parameters for emission calculation are determined based on real-time operating data of ground handling equipment.The emissions of five types of pollutants from various ground handling equipment are calculated.The results show that in the ground handling equipment of the airport,the emissions of CO,HC,NOx,PM2.5,and PM10 from the airport's small train(luggage car),conveyor belt car,catering car,de-icing car,aircraft tractor,runway maintenance car,and ground handling commuter car accounted for 78.0％,79.9％,76.4％,79.1％,and 78.7％of the total emissions,respectively.The above mentioned vehicle models are the main sources of emissions for airports and are key to promoting energy conservation and emission reduction.Among various types of equipment,airport small trains(luggage cars)have relatively high emissions of various pollutants due to their large number and the presence of many vehicles that meet the China Ⅱemission standards.Therefore,equipment upgrades should be carried out to meet higher emission standards in order to effectively reduce the airport's pollutant emissions.

Abstract:To investigate the spectral characteristics of the vibration signals of a diesel engine block,the experimental method and signal analysis technology are used.By changing the operating state parameters such as diesel engine speed,torque and oil temperature and the cylinder clearance,the combustion pressure in the cylinder and the vibration acceleration signal of the body are measured.The vibration acceleration signals are decomposed into 16 frequency bands using wavelet packet decomposition(WPD),and the energy distribution of each band is compared with the cylinder pressure signals.The study identifies the variation patterns of wavelet packet energy distribution under different influencing factors and determines the frequency bands sensitive to combustion state and piston slap.The results indicate that:As engine speed increases,the reciprocating inertia force of the piston rises.When the speed increases from 1 000 r/min to 1 600 r/min,the energy of frequency band 16 increases by 3.55 times.With increasing torque,the energy of all frequency bands shows an upward trend.As oil temperature rises,most frequency bands exhibit no significant energy variation,but bands 15 and 16 still demonstrate an increasing trend.With larger piston-to-cylinder clearance,the energy of bands 6,7,8,10,15,and 16 increases significantly.

Abstract:To elucidate the impact mechanisms of testing systems and urea solution quality on secondary particle number(PN)emissions,a China Ⅵ heavy-duty diesel vehicle is tested using two measurement systems,a portable emissions measurement system(PEMS)and a constant volume sampling(CVS)system,along with five types of urea solutions.The experiments are conducted on a chassis dynamometer to investigate the influence of the testing systems and urea solution quality on PN emissions,with comparative analysis performs between the number of particles with a particle size not less than 23 nm(referred to as PN23)and the number of particles with a particle size not less than 10 nm(referred to as PN10)measurements.The results demonstrate that due to differences in particle counting principles and sampling strategies,the PN23 emission measured by different testing systems varies significantly;urea solution quality notably affects PN23 emission.For the PEMS,all contaminated urea solutions(containing calcium chloride,formaldehyde,phosphate,and biuret)lead to a marked increase in PN23 emission,with the peak PN23 emission level from the formaldehyde-added solution being substantially higher than that measured by the CVS system;Ca2+interferes with the electrophoretic particle counting(EPC)method,resulting in significantly elevated PN23 emission from the calcium chloride-added urea solution.Under the CVS system,only urea solutions with added calcium chloride and formaldehyde cause a significant rise in PN23 emission,which may be attributed to the formation and agglomeration of solid particles.Across all test groups,the increase in PN10 emission is more pronounced than that of PN23,which indicates that urea injection primarily augmentes the number of fine particles in the 10～23 nm size range,with biuret exhibiting the most significant promoting effect on particle generation within this diameter range.

Abstract:To improve the vehicle energy utilization rate and meet the diversified electricity needs of heavy-duty truck user,a 48 V mild hybrid system is built based on a tractor.The control strategy of the motor assistance and the braking energy recovery control strategy of the 48 V mild system are analyzed.The China heavy-duty commercial vehicle test cycle for tractor-trailer(CHTC-TT)is used for the dynamometer test,and the working characteristics of the vehicle under the state of pure diesel and mild hybrid are analyzed.The results show that when the vehicle is tested with CHTC-TT in mild hybrid state,the driving efficiency of the motor in assistance mode is 89.0%,and the energy consumption of the motor assistance per hundred kilometers is 2.477 kW·h.The power generation efficiency in the braking energy recovery mode is 79.5%,and the energy recovery per hundred kilometers is 2.924 kW·h.Under the same condition,compared with the pure diesel state,the average engine speed decreased by 117 r/min,the average load of the whole increased by 0.25%,and the fuel consumption rate per hundred kilometers decreased by 4.17%in the mild hybrid state.The 48 V hybrid system can effectively recycle electric energy to assist the engine drive and the electricity consumption of the whole vehicle,and improve the engine operation condition.

Abstract:Through theoretical modeling,simulation analysis,and experimental verification,the power performance and economic performance of fuel cell hybrid commercial vehicles are evaluated.Starting from the dynamics of the entire vehicle,the dynamic relationship between driving force,resistance,and vehicle motion state is analyzed,and the characteristics of fuel cells,power batteries,and motors are combined to establish accurate longitudinal dynamics models of the entire vehicle and multi-level models of the powertrain.A rule-based energy management strategies are designed to achieve dynamic power allocation between fuel cells and power cells.The comparison between the simulation results of actual road spectrum conditions and experimental data shows that the relative errors of the model in terms of vehicle speed,motor power,fuel cell power,power battery power,etc.are less than 5%.The model has high accuracy and effective energy management strategies.The research results can provide reference for the performance optimization and energy management strategy development of fuel cell hybrid commercial vehicles.In the future,we will further explore data-driven power system strategies to enhance the system's adaptability to complex operating conditions.

Abstract:In order to study the evolution law of hysteresis loss in the manufacturing process,the advantages and disadvantages of hysteresis loss calculation methods under natural state and with residual stress are compared and analyzed from the aspects of calculation accuracy,applicability,and computational complexity.The development direction of hysteresis loss calculation methods is also analyzed.The results show that smaller tensile stress can improve the magnetic properties of the material,but larger tensile stress leads to a decrease in the magnetic properties of the material.For ferromagnetic materials with residual stress,the hysteresis loss should be calculated using model parameters that vary with peak magnetic induction intensity and stress.For ferromagnetic materials with plastic strain,expressing the non hysteresis magnetization behavior parameters and magnetic domain wall concentration coefficient of the model as a function of dislocation density can effectively predict the hysteresis loss of ferromagnetic materials.The calculation of hysteresis loss in future ferromagnetic materials should consider the coupled effects of residual stress and plastic strain.

Abstract:To address the issues of low integration,weak anti-interference capability,and poor space utilization in traditional centralized control cabinets,this paper proposes a design scheme for a centralized control cabinet based on a three-tier electrical network architecture.The mechanical structure and electrical system components of the control cabinet are designed,and industrial trial verification was conducted.The results show that compared to traditional centralized control cabinets,the cabinet based on the three-tier electrical network architecture achieves reduced volume and mass,improved vibration damping performance,electromagnetic shielding performance,and thermal dissipation performance.Specifically,the space utilization rate of the centralized control cabinet is increased to 85%,the temperature rise of the cooling system is improved by 40%,the vibration attenuation rate of the hyperboloid dampers reaches 78%,and the electromagnetic compatibility meets the standards of the International Electrotechnical Commission(IEC).

Abstract:In order to enhance the noise,vibration,and harshness(NVH)performance of the interior body structure of electric vehicles,a finite element model of the interior body structure of a certain electric vehicle is established based on the ANSA platform.Typical excitation points are scientifically positioned,and the peak response of the vibration transfer function(VTF)at key response points(seat mounting points,steering wheel)is simulated and analyzed.The simulation results show that the peak VTF values at each response point meets the design requirements,and the interior structure exhibits good attenuation effect on vibration transmission under the current layout and connection conditions.This research provides technical support for the virtual verification of NVH performance of electric vehicle bodies and holds significant engineering application value.

Abstract:To improve the efficiency,stability,and service life of proton exchange membrane fuel cell stacks,a typical large-scale proton exchange membrane fuel cell stack is taken as the research object.An equivalent stiffness model is used to analyze the magnitude of the clamping load of the stack and its uniform distribution in the stack components.At the same time,the porosity and contact resistance values corresponding to different stack clamping load are calculated.The optimal clamping load values and selection criteria for fuel cell stacks under different steel strip spacing conditions are proposed.The results show that as the spacing between steel strips increases,the corresponding optimal clamping load shows an increasing trend.Taking the spacing between steel strips of 40 mm as an example,the corresponding clamping load of 32.8 kN is optimal,and the clamping load is judged to be within a reasonable range based on the stress standard deviation and strain standard deviation.At this point,the corresponding contact resistance is 5.35 μΩ,and the porosity is 0.747.

Abstract:To address the cavitation failure of cylinder liners occurring during the endurance test of a new-type engine,the causes potentially leading to cylinder liner cavitation are analyzed,including cylinder liner stiffness,engine torsional vibration and other related factors,and corresponding improvement measures are proposed.Subsequently,the improved cylinder liners are assembled on the engine for a 500 h endurance test.The results show that insufficient cylinder liner stiffness and excessive overall engine vibration are the primary factors causing cylinder liner cavitation,and the coupling effect between the two further accelerates the cavitation process.Increasing the cylinder wall thickness,adopting rolling process on the outer wall and shoulder surface of the cylinder liner,and adjusting the position of cylinder gaskets can effectively improve the cylinder liner stiffness.Optimizing the flywheel moment of inertia can eliminate the main vibration excitation source of the engine and reduce engine vibration.After the engine endurance test,the outer walls of the cylinder liners remain smooth and no abnormal wear is found on the inner walls,indicating that the cylinder liner cavitation failure has been completely resolved.

Abstract:To address the abnormal vibration issues occurring during the trial or production operation of a gas-steam combined cycle generator units,a 9F-class gas-steam combined cycle generator unit is taken as an example.The single-mass,single-degree-of-freedom vibration modes of components such as the foundation plate,columns,and frame in response to disturbance force excitation are analyzed.The generation,transmission,and excitation response processes of the disturbance force are outlined,along with the main causes of abnormal vibration.By comparing the measured results of shaft vibration(relative displacement)and bearing vibration(absolute velocity)with standard limits,the characteristics of abnormal vibration are determined,and corresponding vibration reduction measures are implemented.The results show that the single degree of freedom and natural frequency of the horizontal radial vibration,horizontal axial vibration,and vertical vibration of the base plate of the columns and frame play an important role in the vibration of the generator unit.The vibration of the generator unit's shaft system is a superposition of multiple vibrations;monitoring shaft vibration and bearing vibration can effectively identify abnormal vibrations.Through investigation of the adverse factors causing the abnormal vibrations,it is found that mass eccentricity of the gas turbine rotor is the main cause.Based on the dynamic balancing test,a rectification plan is developed(adding a 700 g counterweight with a key phase of∠60° to the 7th bearing side of the gas turbine;adding an 800 g counterweight with a key phase of ∠240° to the 8th bearing side of the gas turbine;and adding a 1 038 g counterweight with a key phase of ∠220° to the compressor disc of the gas turbine),which effectively solve the abnormal vibration problem.This analytical method can provide a reference for the diagnosis and control of abnormal vibrations in similar generator units.

Abstract:In order to reduce the vibration and noise problems caused by meshing impact,load bias and transmission error of the electric drive axle of heavy-duty vehicles,a model of a two-stage gear reduction system for a certain electric drive axle is established based on the analysis software.The tooth profile modification and tooth direction modification are combined to minimize the fluctuation of transmission error and the contact stress on the tooth surface as the optimization goal,and the modification parameters such as involute slope,involute convexity,tooth direction slope,and tooth direction convexity of the first and second stage reduction active gears are determined,and the simulation analysis is carried for verification.The results show that the modification parameters of the first and second stage reduction active gears are determined by the multi-objective optimization method,with the involute slopes being 1.82 and 2.33μm,the involute convexities being 2.01 and 0.15 μm,the tooth direction slopes being 0.704 and-3.200 μm,and the tooth direction convexities being 0.185 and 0.443 μm,respectively.The simulation analysis of the modified gear shows that the maximum reduction of the peak-to-peak transmission error is 82.5％,the maximum reduction of the maximum contact stress on the tooth surface is 18.8％,and the maximum reduction of the load per unit length is 21.4％.The stress and load distribution on the modified tooth surface are more uniform,which effectively reduces the vibration and noise of the gear meshing in the transmission system.

Abstract:To solve the problem of difficult start of proton exchange membrane fuel cell(PEMFC)in ultra-low temperature environment,a solution to the difficult cold startup of hydrogen cells is proposed.By generating high-temperature gas with a hydrogen burner,the coolant is heated by a heat exchanger,and the stack temperature is improved by a small cycle coolant to reduce the cold startup time and improve the cold startup performance of fuel cells.The computational fluid dynamics(CFD)method is used to establish a three-dimensional model of the shell-and-tube heat exchanger based on AVL_FIRE software,and the heat exchange performance of the heat exchanger is numerically analyzed.In view of the low heat exchange efficiency and uneven temperature distribution of the initial model,four optimization schemes are proposed,including shortening the length of the heat exchanger inlet and and adjusting the distribution of copper tubes,setting baffles to change the airflow path,increasing the diameter of the fluid inlet pipe,and reducing the length of the heat exchanger to eliminate the low-efficiency heat exchange area at the tail.The simulation results show that the fourth optimization scheme increases the temperature of outlet cooling water by 36 K compared with the inlet temperature,which meets the requirements of the cold start system for the temperature rise of the cooling water and is the best option.

Abstract:In order to enhance the reliability of airtightness testing for engine cast aluminum components and reduce the leakage failure rate during test runs,a test plan is designed to analyze the reliability of collaborative airtightness testing using water inspection and differential pressure testing methods,as well as high-temperature water inspection method.The results show that the initial pressure difference range for qualified cast aluminum parts is 336-354 Pa,and the retest pressure difference range is 260-281 Pa,with a significant difference.There are inconsistencies between the leakage results determined based on pressure difference and the observed results.The collaborative airtightness testing using water inspection and differential pressure testing methods had low reliability and is not suitable for airtightness testing of cast aluminum parts.As the water temperature increased,the leakage phenomenon of cast aluminum parts intensified,and new leakage points are identified,effectively improving the reliability of airtightness testing for cast aluminum parts.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract: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.