Gasoline compression ignition engines have the great potential for efficient and clean operation. Based on a self-built gasoline-diesel dual fuel engine test bench and an in-cylinder combustion numerical simulation, the effect of fuel stratification, generated by the gasoline dual or single manifold injection strategies and the diesel single or multiple in-cylinder injection strategies respectively, on gasoline compression ignition combustion at low load was studied. The results show that under the low load condition with a speed of 1500r/min and a fuel calorific value of 610.4J/cyc, the concentration stratification degree of the gasoline single port injection strategy is significantly higher than that of the dual ports injection strategy. The strategy of direct injection of micro diesel greatly increases the activity of the mixture, accelerates the generation and consumption rate of active substance. Under the condition of gasoline premix rate as high as 86%, the average indicated pressure and indicated thermal efficiency(ITE) during early injection(-160°CA ATDC) of diesel fuel reach 0.53MPa and 49.41% respectively, and the emission levels of NO_x, CO and total hydrocarbons(THC) are reduced, but the pressure rise rate exceeds the limit. By optimization of the gasoline injection strategy and use of the diesel multiple in-cylinder injections, the concentration and activity distribution of the mixture can be flexibly adjusted to delay the heat release process and reduce the pressure rise rate. Under the conditions of the first diesel early injection quantity of 1.9mg/cyc and the secondary diesel direct injection of 1.0mg/cyc, the indicated thermal efficiency is further increased to 49.55%.

Four-stroke diesel engines burning heavy fuel oil(HFO) are often used as propulsion devices or power generators for ships. In order to improve the thermal efficiency and reduce emissions, increasing injection pressure and reducing nozzle hole diameter are the trends of injection conditions. The spray and ignition characteristics of HFO with different viscosities under high pressure and micro hole conditions were investigated. Large eddy simulation(LES) was used to solve the turbulent motion and chemical reaction kinetics were coupled. The results show that the liquid penetration length(LPL) of HFO is almost independent of the combustion, while the vapor penetration length(VPL) decreases due to combustion, and the decrease is inversely proportional to the viscosity of HFO. The spray morphology of low-viscosity HFO is similar to that of diesel, while the spray morphology of high-viscosity HFO is narrow and long, having a jagged gas-phase spray edge near the nozzle. The increase in viscosity causes the combustion phase to advance, the heat release rate to slow down and its peak to decrease, the flame lift-off length(FLOL) to shorten and the flame to appear trailing. The flame spread ability and fuel consumption rate during the steady-state combustion phase are independent of the viscosity of HFO. The Sauter mean diameter(SMD) is proportional to the viscosity of HFO, with a slight increase before ignition and a significant increase after end of injection. The decrease rate of the total surface area of droplets is higher than the decrease rate of the total volume of droplets, which is the fundamental reason for the slight increase in SMD after ignition.

The soot volume fraction f_v generation and distribution characteristics of high pressure direct injection natural gas were quantitatively studied on a constant volume combustion bomb under different fuel intake, oil/gas injection interval(STS) and ambient temperature using two-color laser induced incandescence(TC-LII) method. The results show that under the conditions of background pressure of 3MPa, ambient temperature of 800K, oil/gas injection pressure of 32MPa, 31MPa and injection interval of 0.4ms, the high concentration area of soot generated by trace diesel(8.104mg) ignition of high pressure direct injection natural gas(161.500mg) is mainly distributed on both sides of the middle axis of the jet flame. Increasing the amount of fuel increase the f_v in the oil/gas coupled combustion flame, but the increase of diesel combustion intensity can accelerate the oxidation rate of soot in the natural gas jet flame at the later stage of combustion. When the injection pulse width of fuel is 1.1ms, the low concentration distribution interval of soot in the later stage of natural gas combustion is as high as 71%, and the soot discharged with the tail gas is the least. When STS=0.4ms, the peak values of maximum volume fraction(v_max) and average value(v_mean) of volume fraction decreased by 27.2% and 28.1%, respectively, compared with STS=0.8ms, and those decreased by 9.3% and 6.6% compared with STS=1.2ms. The increase of ambient temperature lead to the increase of both v_max and v_mean.

The fourth stage of China’s fuel consumption limits for heavy-duty commercial vehicles has set higher requirements for the brake thermal efficiency(BTE). Based on a 7.7L diesel engine, a one-dimensional simulation was firstly conducted with experimental verification, and the mechanism of the influence of Miller-cycle coupling compression ratio on the BTE was explored through exergy analysis. The results indicate that the irreversible combustion loss and exhaust loss decrease with the increase of Miller degree. Under the equal torque conditions, an increase in the compression ratio can reduce the exhaust loss. The use of two-stage turbochargers increases the intake flow rate and total heat capacity in the cylinder, which helps to reduce the heat transfer loss and the exhaust loss. Under high combustion pressure targets, compared to the late intake valve closing strategy, the early intake valve closing scheme increases the heat transfer loss and exhaust loss. Then, an actual engine development plan was completed based on the above calculation results. Engine test was run under the speed of 1200r/min and the torque of 1200N·m. The BTE increases by 4.0% and the brake specific fuel consumption rate(BSFC) decreases by 16g/(kW·h), when the intake valve closing angle is delayed by 40°CA, the compression ratio is increased from 17.2 to 20.5 and the peak combustion pressure is increased from 16.5MPa to 25.0MPa.

To investigate whether hybrid electric vehicles can achieve energy savings and emissions reduction in plateau regions, real driving emissions(RDE) tests were conducted using a portable onboard emissions measurement system in two cities on extended-range electric vehicles(E-REV), plug-in hybrid electric vehicles(PHEV), and gasoline vehicles compliant with China Ⅵ emission standards. The study analyzed the actual emission characteristics and fuel economy of hybrid electric vehicles in plateau regions. The results indicate that lower coolant temperatures and higher values of the product of speed and acceleration(v·a) result in higher instantaneous emissions of carbon monoxide(CO) and nitrogen oxides(NO_x). After excluding cold start emissions, the reduction proportions of CO and NO_x emissions during the cold start phase are greater than those of carbon dioxide(CO₂) emissions. The pollutant emissions of hybrid electric vehicles are less affected by plateau environments. As the altitude increases, CO emissions rise for PHEVs and gasoline vehicles, while CO emissions decrease for E-REV. The CO₂ emissions for E-REVs, PHEVs, and gasoline vehicles increase, and NO_x emissions decrease. Compared to gasoline vehicles, the NO_x reduction of E-REV and PHEV in plateau regions is mainly observed in suburban and highway conditions. The fuel consumption(FC) of E-REV increases with altitude, and PHEVs demonstrate better fuel economy compared to E-REV.

Urea deposits in a selective catalytic reduction(SCR) system can be effectively suppressed by adjusting injector parameters, adding mixers, and coating catalysts on the pipe wall. Based on samples of urea deposits in a marine SCR system, V₂O₅-WO₃/TiO₂ catalyst and pure urea(CH₄N₂O), etc., the urea catalytic decomposition characteristics and the chemical composition of samples were firstly analyzed using characterization techniques such as thermogravimetric analysis(TGA) and Fourier transform infrared spectroscopy(FT-IR). Secondly, based on density functional theory(DFT), a detailed urea decomposition mechanism was proposed, which complemented the formation and decomposition path of cyanuric acid(C₃H₃N₃O₃) and its homologue. Finally, a non-catalytic and catalytic coupled kinetic model of urea was developed using TGA experimental data and chemical reaction kinetics methods. The results showed that the main chemical components of urea deposits in marine SCR system are cyanuric acid and its homologue, and ammelide(C₃H₄N₄O₂). Increasing the quantity of catalyst can accelerate urea decomposition, thereby blocking the conversion of urea and biuret(C₂H₅N₃O₂) to cyanuric acid. However, as the decomposition temperature of the by-products increases, a greater amount of catalyst is required.

In order to meet the future emission regulations for diesel engines, dual-injection selective catalytic reduction(SCR) system has become an important means, in which the urea uniformity on the cross section of the close-coupled SCR(cc-SCR) is crucial for NO_x conversion. A transparent after-treatment test bench was established and a particle image velocity(PIV) optical method was used to measure the urea droplet velocity field and droplet concentration distribution of the cc-SCR. A computing simulation of the urea distribution was also conducted and validated by the measurement. Results showed that, when the injection pulse width is less than 1.00s, there has no urea droplets on the cross section of the cc-SCR within 1.00s, which leads to a decrease of NO_x conversion efficiency under the condition of low ammonia storage. The velocity field at different cross-sections presents double vortices. The simulation results are found to be consistent with the experimental results. In addition, different nozzles with different particle sizes were tested on the bench under the temperature of 215℃ and the air flow rate of 1250kg/h and 360kg/h, respectively. It is found that the distribution uniformity of urea droplet depends on the exhaust air flow rate. This phenomenon is also well explained through simulation results.

Diesel density is an important parameter that must be set in design and simulation of a modern diesel engine fuel system. Diesel density varies greatly with temperature and pressure, and the accuracy of density is an important guarantee for the correctness of fuel system design and simulation. The wave velocity of national standard No.0 diesel under high temperature and high pressure was measured using a self-designed test platform of fuel pressure wave velocity, and the corresponding diesel density was derived and calculated. The law of variation of diesel density with temperature and pressure was obtained. The results show that the diesel density decreases with the increase of temperature and increases with the increase of pressure, and the influence of pressure on diesel density is much greater than that of temperature. Every increase of 10K in the temperature of 300—360K, the average density decreases by 0.004043—0.006038g/mL, and the higher the pressure, the smaller the density decreases with temperature. In the pressure of 20—200MPa, the density increases by 0.003844—0.004509g/mL on average with every increase of 10MPa. The higher the temperature, the greater the density increases with the pressure.

Aiming at the problem that it is difficult to extract the relative information of multi-interface oil film thickness with the ultrasonic liquid phase thickness measurement technology monitoring the lubricating state of the piston ring-cylinder liner friction pair of the internal combustion engine for the echo superposition, a mathematical model was proposed for measuring the oil film thickness of the four layer medium based on ultrasound, and a corresponding finite element model was established using the finite element simulation software, the sound pressure fields under different probe emission frequencies, coating thickness, and oil film thickness were simulated. The effects of ultrasonic probe parameters, coating thickness and preset oil film thickness on the simulation results of oil film thickness were analyzed. The sound pressure response with oil film thickness of 0.5—10.0μm at different emission frequencies was calculated. Results show that the calculated oil film thickness is in good agreement with the preset oil film thickness. The accuracy of this method in determining the thickness of coated piston ring oil film is further confirmed by practical measurement experiments.

Casing treatment improves the flow stability of turbocharger centrifugal compressors，but often leads to additional aerodynamic losses. Based on the optimal Latin hypercube sampling，radial basis function(RBF) neural network and gradient mutation hybrid optimization algorithm，a coupling optimization of the impeller and the casing treatment for a turbocharger centrifugal compressor was implemented by taking the efficiencies of the large-flow-rate condition，the design condition and the near-stall condition as the optimization objectives. Results show that the efficiencies of the large-flow-rate condition，the design condition and the near-stall condition are increased by 3.90%，3.02% and 1.10%，and the pressure ratios are improved by 9.28%，6.38% and 4.49%，respectively. The choke flow rate is increased by 1.13%，and the stable operating range is expanded by 0.83%. Compared with the solid casing compressor，the efficiencies of the design condition and the large-flow-rate condition are improved by 1.70% and 0.68%，respectively. The coupling optimization realizes the improvements of aerodynamic performances of the compressor in all operating conditions，and solves the problem of the traditional optimization that the aerodynamic performances of the design condition or the large-flow-rate condition decrease after introducing the casing treatment. By combining the global sensitivity analysis of the design space and the comparative analyses of the flow fields before and after optimization，the mechanisms of stability and efficiency improvements of the centrifugal compressor are obtained.