Aiming at the performance deterioration of the turbocharging mode switching process of a two-stage sequential turbocharging(TSST) diesel engine, a test of turbocharging mode switching was carried out on a modified TSST diesel engine test platform to investigate the influence of engine load and delayed opening time of intake switching valve(ISV) on the switching process. The test results show that the TSST system can reduce fuel consumption rate in the full range of operating conditions, and the switching boundary of different turbocharging modes is set at 65% load with the goal of economic optimization, which can also be broaden based on the consideration of emissions and switching redundancy. As the load rises, the amplitude of boost pressure fluctuation increases during the switching process, and the degree of sudden change in exhaust pressure increases, resulting in the more serious speed fluctuation of the diesel engine. By delaying the opening of the ISV at the outlet of the high-pressure stage compressor of the cut-in branch, the performance fluctuation can be minimized. Under different loads, there exists an optimal delayed opening time of the ISV, which is the time when the pressure before and after the valve is equal without backflow in the compressor, and the optimal value is shortened with the load increases. Through the optimal valve delay control, the surge and backflow phenomena of compressor are significantly alleviated. The decrease of speed fluctuation can be up to 82.47%, realizing the smooth switching of different turbocharging modes.

A lateral-swirl combustion system(LSCS) was used to deal with the challenges of deteriorated combustion performance and increased soot emission after implementing exhaust gas recirculation(EGR) in direct-injection diesel engines. An in-cylinder combustion 3-dimensional simulation of the LSCS and a traditional ω combustion system was conducted under medium and high load conditions at the speed of 1800r/min and 2500r/min, respectively. The results indicate that, under the same NO_x emission levels, the LSCS allows a higher EGR rate compared to the ω combustion system, resulting in an increase of the indicated power from 1.1% to 1.3%. Under the same indicated power conditions, the LSCS can accommodate a higher EGR rate while reducing NO_x emissions by 35.9% to 45.6% and soot emissions by 27.9% to 49.4%, respectively. Furthermore, the results suggest that the wall-flow-guided structure of the LSCS promotes the fuel jet expansion in the cylinder to be fully mixed with the air, enhancing its compatibility with EGR.

An experiment of internal exhaust gas recirculation(EGR) thermal management was conducted on a six-cylinders turbocharged diesel engine equipped with the fully hydraulic variable valve system(FHVVS) at medium load conditions. The cylinder pressure, intake and exhaust dynamic pressure, exhaust temperature and fuel consumption rate were measured to investigate the influence of internal EGR based on secondary opening of exhaust valves on the exhaust thermal management performance experiment. The concept of fuel consumption to temperature rise ratio λ was proposed to represent the additional fuel consumption rate when the exhaust temperature increases by every 100℃ in the certain thermal management mode. The results indicated that the recirculation of the high-temperature oxygen-containing exhaust gas from exhaust pipe during the intake stroke significantly reduces the intake flow rate and increases the exhaust temperature. Compared to thermal management of an intake throttle with the same intake flow rate, the internal EGR thermal management significantly reduces the pressure difference between the exhaust and intake, leading to a pump loss reduction of more than 62.2% and a fuel consumption rate reduction of 4.26%—6.62%. By using the compound thermal management of “internal EGR+throttle”, the exhaust temperature increases significantly to 522℃ under the rotating speed of 1200r/min and medium load condition, and the λ is only 3.0g/(kW·h)·(100℃), while as high as 9.6g/(kW·h)·(100℃) for the throttle mode under the same intake flow.

Based on an externally heated high-temperature and high-pressure constant volume combustion chamber system, an optical diagnostic test on the combustion process of diesel-ignited premixed natural gas was carried out using the natural luminescence method. The effects of different natural gas energy substitution rate(ESR), diesel injection pressure p_inj and diesel injection mass m_inj on the ignition and combustion characteristics were studied. The results show that an increase in ESR leads to an increase in the equivalence ratio of methane to air. Since the specific heat of methane is greater than that of air, the increase in ESR has a promoting effect on diesel ignition. At the same time, the decrease in oxygen makes the increase in ESR, having an inhibitory effect. When the diesel injection mass is small, the increase of ESR has a stronger inhibitory effect on ignition than its promoting effect. When the diesel injection mass is large, the opposite result is presented. With the increase of ESR, the proportion of concentrated soot is increased, but under the diesel injection pressure of 100MPa and the ESR of 94%, there is a stage with a high proportion of concentrated soot. When the diesel injection pressure is higher than 100MPa, the enhancement effect of injection pressure on combustion heat release weakens, and there is no significant increase in the amount of ignited methane. Under the injection strategy of m_inj=10mg, p_inj=80MPa, the ignition delay exhibits a strong linear relationship with the ESR range of 94%—96%.

Anisole, a second-generation biomass fuel, has a similar molecular structure to toluene in diesel. Blending of biomass fuels with diesel is seen as a viable solution to the energy crisis. Using a liquid fuel combustion system and selecting n-heptane as the base fuel, the flame morphology, incipient soot size distribution, nanostructure, microcrystalline parameters, orderliness, functional groups and oxidation activity of the soot in the flame of n-heptane, n-heptane blended with volume fraction of 10% toluene, 10% anisole, and 5% toluene/5% anisole were analyzed at an evaporation temperature of 160 ℃. Results show that, for the size and nanostructure of soot particles, the average size of soot in the flame becomes larger under the anisole/toluene blending. For the nanostructure of soot, the blend of anisole and toluene changes the morphology of soot particles and accelerates the soot formation. From microcrystalline parameters, the overall soot structure is more organized after anisole/toluene blending, and the effect of anisole in n-heptane flame on the nanostructure of soot is less than that of toluene. For soot ordering, the intensity ratio of the D1 peak to the G1 peak(I_D1/I_G1) increases by 17.3% from T10 to A05 and by 11.5% from A05 to A10, respectively, and the degree of graphitization of soot decreases with the increase of anisole blending. The graphitization of soot in the n-heptane flame is minimized when only anisole is blended.

In order to construct a quality evaluation system of internal combustion engine working cycle with a predictable, measurable and evaluable way, an analysis method of the “quality-quantity” process of cycle fuel energy was elaborated in detail. Based on the results of the one-dimensional simulation software for the engine working process, the entropy change(qualitative change) and enthalpy change(quantity change) of the cycle working fluid were calculated by the temperature-entropy relationship(T-S diagram), the energy loss path of working fluid of internal combustion engines was analyzed from the whole cycle process, and the energy quality loss and quantity dissipation of the working fluid were quantitatively evaluated. Comparing the “quality-quantity” process of the cycle working fluid under the intake pressure of 0.1MPa and 0.2MPa, the results show that the entropy increment of the exhaust working fluid decreases by 5.42%, the energy quality loss is inhibited, the exhaust enthalpy increment decreases by 35.19%, and the energy quantity dissipation decreases under the intake pressure of 0.2MPa. The “quality-quantity” process analysis of the working fluid of the internal combustion engine cycle based on the simulation data can realize the quantitative evaluation of the total cycle course of the energy quality loss and quantity dissipation of the working fluid, which has universal applicability and certain useful value.

A sodium persulfate(Na₂S₂O₈)/urea composite redox removal system using seawater as the solvent was constructed, and a bubbling reactor was constructed. A bubble reactor was used to carry out experimental research on the removal of SO₂ and NO from marine diesel engine exhaust under different Cl^- mole concentrations(0—0.6mol/L), HCO₃^- mole concentrations(0—0.05mol/L), reaction temperatures(30—70℃), Na₂S₂O₈ mole concentrations(0.01—0.20mol/L), and urea mole concentrations(0.1—2.0mol/L). The results show that the presence of Cl^- and HCO₃^- can effectively strengthen the absorption of NO, the increase of the reaction temperature, Na₂S₂O₈ mole concentration, and urea mole concentration can effectively promote the removal of NO, the use of seawater and urea can reduce the competitive role of SO₂ and improve the NO removal efficiency, the increase of the initial volume fraction of NO can inhibit the absorption of NO. The addition of urea can effectively inhibit the generation of nitrate in the solution, and the urea mole concentration of 2.0mol/L can increase the nitrate mass concentration from 25.687mg/L to 15.158mg/L. The Na₂S₂O₈/urea/seawater composite redox removal system not only has a good NO removal ability, but also effectively solves the problem of high nitrate content in washing wastewater.

Methane(CH₄) catalytic oxidation can effectively deal with CH₄ slip from liquefied natural gas(LNG) ships, but it also catalyzes the oxidation of NO in the exhaust gas. In order to study the impact of CH₄ oxidation unit on the selective catalytic reduction(SCR) system of LNG ships, a joint catalytic reaction system based on Mn-Ce-O_x catalyst and commercial vanadium based catalyst was constructed on a self-built denitrification experimental platform. The effects of reaction temperature, catalyst type, space velocity and impurity gas interference on the catalytic oxidation of NO and catalytic reduction of NO_x by Mn-Ce-O_x were studied. The results indicate that, when the NO volume fraction is elevated from 0.05% to 0.20% and the O₂ volume fraction is decreased from 17.00% to 5.00%, the oxidation efficiency of NO slightly declines. Under the same conditions, Mn-Ce-O_x significantly enhances the denitration efficiency of SCR. Under conditions of a reaction temperature of 180℃, a space velocity of 21356h^-1 and a mole ratio n(NO)/n(NH₃) of 1.0∶1.1, the denitration efficiency can reach 86.80%, and the overall catalyst volume can be reduced by 50.7%, thereby reducing the occupied space of the SCR system.

The evolution characteristics of the squeezing flow field in atmospheric diesel fuel were studied using high-speed squeezing flow device. Effects of four kinds of armature structures, including round hole and sector hole, on the squeezing flow characteristics in the gap between solenoid valve and armature under the high-speed condition of 29.9—67.4m/s² were simulated using Fluent software. The armature structure with ideal squeezing flow characteristics was obtained and verified by high-pressure fuel supply system. The results show that when the acceleration of the armature increases from 29.9m/s² to 67.4m/s², the maximum pressure of the fluid on the armature surface increases from 0.12MPa to 0.24MPa, the jet velocity at the armature edge, and hole edge and the vorticity at the armature side wall increase, thus the flow at the diversion hole becomes more chaotic. When the square armature is replaced by the round armature, the flow path between the gaps is short, the area of the high-pressure zone is reduced by 6.6%, and the liquid between the gaps can be discharged faster. Compared with round hole and guiding trough, the fan-shaped hole on round armature has weak influence on the jet flow in the middle of the hole, the pressure on the surface of the armature is the least, the resistance is the weakest, and the response speed is the fastest. The experimental results show that the closing delay of guiding trough and sector hole armature is 0.610ms and 0.405ms respectively at the speed of 400r/min, and the former is 50.6% longer. At the speed of 1250r/min, the closing delays of the guiding trough and the sector-hole armature are 0.850ms and 0.720ms, respectively, and the former is 18.1% longer.

In order to effectively evaluate the anti-deposition ability for aftertreatment system(ATS) of diesel engine, an evaluation method that is based on NH₃ distribution uniformity testing and simulation results, liquid film temperature simulation results, steady-state and transient-state deposition risk testing results was proposed. Several influences were also considered in the method including engine emissions and exhaust temperature characteristics, urea injection temperature calibration and transient injection control parameters calibration. This method can not only quantitatively evaluate the overall anti-deposition ability of ATS, but also quantifies the degree to which the overall anti-deposition ability is affected by urea injection system, mixing system, ATS software calibration, engine emissions and exhaust temperature characteristics, which indicating the specific optimization directions for improving the anti-deposition ability of ATS clearly.

To investigate the mechanism of water-cooled valve seat sealing failure on the high-temperature exhaust side of the cylinder head of marine diesel engines due to progressive thermal deformation during long-term service, a finite element simulation method incorporating temperature history effects was proposed, based on a thermal viscoplastic constitutive model. The Chaboche nonlinear combined hardening equations and the Norton-Bailey creep equations were utilized to describe the nonlinear deformation induced by thermal fatigue and creep, respectively, and investigate their coupling mechanism. On the basis, introducing the load attenuation to analyze the impact of creep fatigue loading on structural stiffness degradation, thereby elucidating the evolution of valve seat sealing performance. Research findings reveal that the average error in deformation of cylinder head valve seat holes is approximately 16%, with a 19% improvement in calculation accuracy compared to existing methods. Moreover, the maximum attenuation of the sealing load for the valve seat hole reaches 75%, resulting in sealing failure and water leakage. Progressive deformation is primarily controlled by plastic strain during the heating and cooling stages of the thermal cycle, with influence from the creep-enhanced plastic deformation mechanism during the high-temperature holding stage. This underscores that progressive plastic deformation over long-term service periods is the fundamental cause of valve seat sealing failure.