The regulation mechanism of ultrasound on iso-octane combustion was analyzed from the macro and micro levels. The three-dimensional computational fluid dynamics model of the original engine was calibrated using the bench test data. Based on the method of physically embedding the dynamic grid sound source surface in the combustion chamber，the ultrasonic with 20kHz frequency and 300μm amplitude was successfully fed into the combustion chamber. Taking the difference between the cylinder pressure with and without ultrasonic wave feeding into the combustion chamber as the ultrasonic radiation pressure disturbance，the effects of ultrasonic field excitation on the ignition delay period，intermediate reaction components and sensitivity analysis of iso-octane were studied. By comparing and analyzing the simulation results of three ultrasonic-fed schemes S₁—S₃ with no ultrasonic-fed scheme S₀，the results show that the S₁—S₃ schemes can advance the combustion phase，and the peak mole fractions of C₃H₆，IC₄H₈ and C₂H₄ in S₂ and S₃ are increased by 42.1%，24.7%，27.5% and 21.5%，9.6%，5.3%，respectively and the iso-octane burnout time of both schemes are advanced by 0.18s. When the equivalence ratio is 1 and the initial temperature is 1300K and 1700K，the ignition delay period is shortened by 31.8% and 6.4%，respectively and both promote to produce a large number of OH radicals.

Combustion performance experiments were carried out on a single-cylinder diesel engine to study the influences of a lateral swirl combustion system(LSCS)and a multi-swirl combustion system(MSCS)on engine performance. Combined with simulation analysis，the fuel-air mixing and combustion characteristics were revealed for the LSCS and the MSCS respectively. Experimental results show that under low loads and high excess air coefficients，the MSCS obtains better combustion performance than the LSCS with the maximum reduction in fuel consumption of 3.6g/(kW•h)，in soot emission of 0.13g/(kW•h)and in combustion duration of 2.6°CA. However，under heavy loads and low excess air coefficients，the LSCS shows better combustion performance than the MSCS with the maximum reduction in fuel consumption of 2.6g/(kW•h)，in soot emission of 0.56g/(kW•h)and in combustion duration of 2.8°CA. Simulation results indicate that，when the engine load decreases or the excess air coefficient increases，the fuel spray penetration ability becomes weakened，and the circular ridge of the MSCS chamber improves fuel-air mixing quality more effectively. However，when the engine load increases or the excess air coefficient decreases，the fuel spray penetration ability is enhanced. The split-flow creation of the LSCS chamber improves the fuel-air mixing quality more evidently，while the circular ridge of the MSCS chamber hinders the diffusion of fuel spray.

The evaporation and micro-explosion characteristics of jatropha oil droplets under high temperature environment(673，773，873，973 and 1073K)were carried out using high-speed backlit imaging technique. The droplet evaporation characteristics of three main components of jatropha oil were analyzed separately. The results show that the micro-explosion of jatropha oil droplets is caused by the pyrolysis of internal components，and the micro-explosion intensity increases with the increase of ambient temperature. At 673K，the jatropha oil droplets undergo stable evaporation，which includes three stages of initial expansion，equilibrium evaporation and residue evaporation. At 773—1073K，the droplet undergoes micro-explosion，which includes four stages of initial expansion，equilibrium evaporation，micro-explosion evaporation and residual evaporation. When the ambient temperature is higher than 873K，the phenomenon of "vapor plume" and "vapor cloud" is observed for the first time，and the droplet evaporation rate significantly increases.

Based on the external heating source regeneration bench and particle loading device，the emission characteristics of outlet gas and particle during active regeneration of diesel particulate filter(DPF)and catalytic DPF(CDPF)under different regeneration temperature and carbon(Printex-U，PU)loading were studied. The results show that the coating of catalyst(Pt)is conducive to the oxidation of PU. Under the same PU loading，CDPF is more likely to produce temperature peaks，and the regeneration efficiency is slightly higher than DPF. DPF regeneration process is accompanied by higher volume fraction CO emission，and a lower concentration nuclear mode particles emission window will appear in the heating stage，and there is almost no particle release in the subsequent regeneration stage. There is almost no CO generation in the regeneration process of CDPF，but a large number of small particles below 30nm will be released in the regeneration stage，and the particle concentration at the outlet of CDPF will gradually increase with the increase of regeneration temperature and PU loading. DPF and CDPF have different optimization windows during regeneration，which is conducive to reducing particulate emissions and maintaining high regeneration efficiency.

The compression pressure and temperature during low-temperature start was analyzed on a V-type 8-cylinder turbocharged diesel engine，and then the ignition characteristics of diesel spray was studied in a constant-volume spray combustion test device with background temperature and density based on the low-temperature start condition of the engine. The relationship between ignition delay period and ignition position under different background temperature and density conditions was studied. It is found that the ignition delay of diesel free spray increases and the ignition stability decreases with the decrease of background temperature. When the background temperature is below 430℃，the success rate of diesel jet ignition is very low，leading to misfire. The research result is of great significance for improving the stability of low-temperature start and improving fuel consumption and emissions for the diesel engine.

A combined measurement method was proposed and applied to the study of transient dual fuel injection rate of a high-pressure nature gas and diesel co-direct injection engine. Firstly，since the traditional "momentum method" could only obtain the injection pattern but not the accurate injection rate，a parallel test method was proposed to obtain the circular injection quantity by collecting and testing the pressure change in the cavity，and the accurate gas injection pattern curve by combining the transient momentum signal. Then，the measurement and time characteristics of the injector were verified. Finally，the common working conditions of the diesel-natural gas dual fuel injector were tested. The results show that the method solves the problem that two-phase fuel injection rates are difficult to measure in the same field，and achieves the accurate measurement of the instantaneous injection rate of diesel and natural gas in the dual fuel injector. The test error of injection mass is not more than 5%，and the test error at the start moment and end moment of injection is not more than 0.113ms. Besides，the fluctuation rate of diesel injection mass and natural gas injection mass is not more than 1.4% and 2.9%，respectively. With the increase of injection pressure，the opening period of the injector decreases and the closing period increases，and the opening and the closing speeds of the internal diesel needle are greater than those of the external gas needle. The injection of diesel injection affects the gas injection mass by affecting the duration of the gas injection，and the gas injection mass fluctuates up and down with the gas-only injection.

Based on the linear stability analysis method，considering the liquid viscosity，the coaxial rotating motion and compressibility of the surrounding airflow，a mathematical model describing the viscous liquid jet in the coaxial rotating compressible airflow was established and verified，and the effects of the dimensionless rotation intensity of the airflow and the physical properties of the fluid on the unstable form of the liquid jet were studied. The results show that when the rotation speed of the surrounding airflow is small，it promotes the jet stability，continues to increase the dimensionless rotation intensity of the airflow，and begins to promote the splitting of the jet. With the increase of airflow rotation intensity，the jet disturbance develops along the circumferential direction，and the jet column becomes highly asymmetric. In the range of parameters studied in this paper，gas compressibility and gas-liquid density ratio surface tension can promote the instability of the jet and affect the spatial shape of the jet，especially in the circumferential direction，it can change the dominant mode of the jet and enhance the asymmetry of the jet. Both surface tension and liquid viscosity are conducive to the jet stability.

In order to solve the problem of cold start struggling and failing of engine，comparative experiments were conducted on a diesel engine with integrated starting/generator technology fueled with -50^# diesel A0(fuel oxygen content 0%)，A1(fuel oxygen content 2.05%) and A2(fuel oxygen content 4.40%). Experimental data were collected on an engine cold start test cell of high plateau conditions at -43℃. Effects of different fuel oxygen contents on the processes and combustion of the diesel engine under cold start conditions were examined. The results show that comparing with A0，starting times of the diesel engine fueled with A1 and A2 are shortened by 36.64% and 42.71% respectively. The amount of fuel consumption during cold start periods is reduced by 47.8% and 60.6% respectively and the speed fluctuation rate is reduced by 25.3% and 43.8% respectively in the first 60 s of idle operation. With the increases of fuel oxygen content，the in-cylinder combustion temperature and in-cylinder pressure of the first diesel cycle，the heat release rate and the peak pressure rise rate all are increased. The CA50 is advanced and the combustion duration is shortened. And the lower the number of cycles is during the starting speed rise，the higher the average maximum cylinder pressure，and the better the combustion stability during the starting process.

Based on the self-developed variable-mode valve actuation system，a combined simulation of the valve actuation system and the engine used was carried out to study their coupling operation characteristics，which provides a theoretical proof for vehicle application. The results show that there is a strong coupling relationship between the in-cylinder pressure and the valve operation，especially in the exhaust valve operation stage near top dead center(TDC) and below the engine speed of 2300r/min. The higher the engine speed is，the greater the valve dynamic lift loses，and the higher the maximum cylinder pressure is. While their change degree is gradually reduced at engine speed over 2300r/min. Adding a transitional lift on the exhaust brake cam after TDC can eliminate the exhaust valve recoil，and further improve contradiction relationship between the braking power and the maximum in-cylinder pressure. Compared with the ideal four-stroke brake，braking power of the two-stroke brake is obviously increased，and the maximum in-cylinder pressure is obviously reduced. The actual two-stroke braking power is increased by 35.94%，45.61% and 27.54%，and the maximum in-cylinder pressure decreased by 45.42%，27.20% and 7.35% at 1600，1900 and 2400r/min，respectively.

The influence of different inlet conditions on the oil film cavitation phenomenon of connecting rod bearings of a heavy-duty diesel engine was explored through the dynamic boundary calculation. A method of slotting on the bearing bush was proposed to suppress the cavitation phenomenon during the bearing movement. The effects of the number，depth and form of grooves on the suppression of oil film cavitation were further analyzed. It is found that the increase in the number and depth of grooves can improve the effect of oil grooves to inhibit cavitation，but the degree of improvement of the inhibition effect decreases accordingly. If cavitation occurs and collapses frequently，it will be more likely to destroy the bearing bush surface and cause obvious cavitation erosion compared with the stable cavitation state. Compared with the full-groove model，the half-groove model has a higher suppression effect，which can reduce the maximum gas phase volume fraction of the oil film from 0.94(ungrooved)to 0.39. Combined with the reliability requirements of the overall structure of the bearing bush，selecting a half-ring single groove with an appropriate groove depth can effectively suppress the cavitation of the oil film during the bearing movement.