Flash-boiling spray in gasoline direct injection （GDI） engines has the advantage of promoting mixing of oil and gas， but the phenomenon of spray collapse is detrimental to combustion and emission， and studies have found that spray collapse is closely related to single-jet behavior. Therefore， in order to mitigate spray collapse and take full advantage of flash boiling jets in GDI engines， it is extremely important to understand the behavior of flash boiling jet. In this paper， a single-hole fuel injector modified from a five-hole fuel injector is selected， and n-hexane and isooctane fuel are selected to conduct experimental research in a constant volume combustion bomb. The selected fuel temperature is 30 to 130 ℃ and the ambient pressure is 0.2 to 1 bar. By analyzing the relationship between the jet width and different parameters such as superheat degree， nucleation rate， chemical potential and environmental ambient pressure， it is found that the correlation between the jet width and ?\text{?}\mu ·p_{\mathrm{a}\mathrm{m}\mathrm{b}}^{-\mathrm{0.5}} is more than 0.9， which has a good correlation， indicating that the jet width near the nozzle is affected by the phase change potential and the environmental ambient pressure.

In order to predict the particle size distribution of the diesel engine soot emission， 90% mole fraction n-heptane and 10% mole fraction toluene are chosen as diesel substitutes to construct gas phase dynamics mechanism and surface dynamics mechanism respectively， which are coupled to form the diesel substitute mechanism （HTS mechanism）. Combined with the method of moments numeical model， validation of the HTS mechanism is conducted. Then the effect of oxygen concentration on soot particle size distribution is studied by changing the volume fraction of intake oxygen. The results show that the simulation values calculated by the HTS mechanism are basically consistent with the experimental data in terms of ignition delay period， laminar flame speeds， key species and soot particle size distribution in laminar premixed flames， in-cylinder pressure， heat release rate and emissions of the diesel engine. According to the study on the impact of the oxygen concentration on soot particle size distribution by the HTS mechanism， with the increase of oxygen concentration， the average and peak values of soot particle number density decrease， while particle diameters corresponding to the peak particle number density increase. Moreover， the number density of small soot particles （0~50 nm） decreases as oxygen concentration increases.

Hybrid vehicle is an effective solution to reduce vehicle CO₂ emission and pollutant emission. Improving the maximum thermal efficiency of engine and expanding the high thermal efficiency area under common working conditions can effectively reduce the fuel consumption of the hybrid vehicle. According to the requirements of hybrid technology platform， a 2.0T high-efficiency lean burn hybrid engine is developed. The engine adopts an ultra-high compression ratio， large stroke/bore ratio and a deep Miller cycle， and uses a high tumble port design to achieve ultra lean combustion with an excess air ratio of 1.8. With advanced combustion system and friction reduction design， the engine has achieved an effective thermal efficiency of 44%. At the same time， more than 41% of the thermal efficiency area covers the main engine operation points of hybrid engine from 1 000 to 4 000 r/min， ensuring excellent fuel economy of the hybrid vehicle. In addition， the high-efficiency lean burn engine also realizes the maximum power of 115 kW and the torque platform of 240 N·m， which ensures the power requirement of the hybrid system.

In order to study the influence of ash plug formed by ash deposition in diesel particulate filter （DPF） on the trapping characteristics of particulate matter （PM）， a CFD model of DPF channel and ash plug is constructed. The continuous phase coupling discrete phase method is used to study the influence of the blockage ratio， length， position and number of ash plugs on the flow field and PM trapping characteristics in DPF channel. The results show that for the airflow movement in the DPF channel， the position and blockage ratio of the ash plug contribute more to the pressure drop than the number and length， especially the distribution position of the first ash plug plays a decisive role in the pressure drop. The ash plug will change the deposition pattern of PM in the DPF， aggravating the uneven distribution of PM in the recirculation zone at the outlet of the ash plug due to the sudden expansion effect. When the distribution of ash plug in the channel moves forward， the deposition of PM will be uneven. With the distribution of ash plug moving backward， the deposition of PM gradually moves forward and the distribution is more uniform.

As a result of global warming， attention has been paid to greenhouse gas emitted by vehicles. In order to quantify the effect of temperature on vehicle CO₂ emission， WLTC test cycle of a light-duty E10 gasoline vehicle is carried out at the ambient temperatures of -10， 0， 23 and 40 ℃ in this study. It is found that the CO₂ emission factors of -10 and 0 ℃ at hot-start are 10.4% and 20.8% higher than those at 23 ℃， respectively. For cold-start engine， achieving full warm-up is longer than 300 s， which is required by China 6 standard. The relative deviation factor RF of the vehicle with full warm-up is close to 1， and 23 and 40 ℃ are close to 1 at \mathrm{R}{\mathrm{F}}_{\mathrm{4}}\text{?}and\text{?}\mathrm{R}{\mathrm{F}}_{\mathrm{3}}， respectively， indicating that the higher the ambient temperature， the shorter the time required to achieve full warm-up. The absolute deviation factors \mathrm{A}{\mathrm{F}}_{\mathrm{1}} and\text{?}\mathrm{A}{\mathrm{F}}_{\mathrm{2}} at -10 ℃ are 1.98 and 3.63 times higher than those at 23 ℃， respectively， which quantifies the difference of CO₂ emission of cold-start vehicles in winter and summer. There is a strong correlation between cumulative CO₂ emission and idle CO₂ emission factors， which can be used to establish or modify microscopic CO₂ emission models， and it is suggested that the change of ambient temperature should be taken into account when evaluating vehicle CO₂ emission.

In this paper， the influence of valve overlap angle formed by variable intake timing （IVT）， variable exhaust timing （EVT） and variable intake and exhaust timing strategy （IEVT） on combustion and particulate emission of the direct injection gasoline engine is studied. It is found that the increase of positive valve overlap angle under the three timing strategies under low load will lead to the increase of residual exhaust gas in the cylinder，prolonged ignition delay and increased combustion duration， and reduce fuel consumption and HC emissions at first and then increase， and reduce NO _x emission. At the same valve overlap angle， EVT has the largest amount of residual exhaust gas， while IVT can improve the pumping loss by 15.6%. Compared with IVT and EVT， IEVT still burns stably at the overlapping angle of 60 ° CA and reduces heat transfer loss and exhaust loss， with reduction offuel consumption by 8.67%， reduction of NO _x by 96.57%， and reduction of the total number of particles by 89.43%.

In order to meet the RDE （real driving emission） sampling requirements of 160，000 km in-use vehicles stipulated in China 6 emission regulations， the aggressive RDE test cycle on test bench is carried out on two durable aging vehicles under the critical environment of 1 ℃. By adjusting the engine control strategies， the operation parameters of two extreme working conditions with high NO _x emission are optimized： rapid acceleration after cold start and rapid acceleration to super high vehicle speed after hot start， then the comparative verification tests between the new and old strategies in variable emission combinations include roller cycles and RDE are carried out. The results show that the VVT， excess scavenging coefficient， lambda target value and aging catalyst window control have great impact on NO _x emission of durable aging vehicle under cold and hot engine’s high load conditions. Appropriate control strategies can reduce the total NO _x emission by more than 40%. It is an effective RDE development method to firstly carry out the emission development based on durable aging vehicles under aggressive RDE cycle， and then validate it on the real road.

Premixed combustion and diffusion combustion are the basic combustion modes of diesel engines. In this paper， the two typical combustion chambers of the reentrant combustion chamber and flared combustion chamber of high-pressure common-rail direct injection diesel engine are selected to study the mixture formation mechanism based on the entrainment effect under different background airflow conditions by simulation calculation. The results show that the entrainment effect caused by the small-scale vortex on the surface of the oil spray is the main reason for the formation of the pre-mixture when the oil spray penetrates the background air flow at the initial stage of injection. The entrainment effect is directly affected by different background airflow under certain injection condition. For the reentrant combustion chamber， at the initial stage of injection， there is strong entrainment effect and a fast premixing rate. Most of the fuel is rapidly diffused and combusted under the action of strong tumble inside the combustion chamber. Therefore， it belongs to the premixed diffusion combustion mode （PDC）. Although the proportion of premixed combustion is small， the high-temperature zone is wide. For the flared combustion chamber， although there is relatively weak entrainment effect and a low premixed combustion rate at the initial stage of injection， a secondary premixing process is formed after the oil spray impinges on the wall convex platform， which extends the formation duration of the pre-mixture and increases the proportion of premixed combustion to form a double-premixed diffusion combustion mode （DPDC）. Through the DPDC combustion mode， the high-temperature area is reduced， thus effectively inhibiting the generation of NO _x .

To study the causal relationship between the multi-frequency pressure fluctuations and the characteristics of the internal flow of nozzle， as well as the influence mechanism on the near-field spray， the high-speed microscopic imaging technology is used to carry out visualization experimental study on the real-size tapered hole nozzles during the multiple injection process under different common rail pressures. At the same time， the high-pressure sensor is used to measure the pressure fluctuation data of the nozzle inlet. The research results show that the spray cone angle shows a boot-shaped trend in the main injection process， which consists of the development period， the transformation period， the stable period and the decay period. The overall trend is affected by the injection pressure， and there is a change of cavitation form in the process. In the process of small fuel injection such as pre-injection and post-injection， there are obvious inconsistencies caused by the fluctuation of the needle valve lift. The pressure drop at the nozzle is positively correlated with the level of cycle fuel injection quantity， and the cavitation characteristics affect the frequency characteristics and propagation speed of the pressure fluctuation. When the geometrically induced cavitation forms， the pressure fluctuates at a low frequency.Whenline cavitation forms， a high frequency pressure fluctuation trend occurs.

With the increasingly serious problems of environmental pollution and energy consumption， the search for clean alternative fuels and new combustion technologies has gradually become the focus of engine research. In this paper， a diesel natural gas hydrogen three fuel RCCI internal combustion engine is numerically simulated， and the effect of different hydrogen ratios on the engine performance is discussed. The results show that with the increase of hydrogen addition ratio， the combustion rate of the in cylinder mixture is significantly increased， the peak pressure in the cylinder gradually increases， and the phase of the peak value is advanced， with the average temperature in the cylinder increased. Meanwhile， the indicated thermal efficiency of the engine increases， and the equivalent indicated fuel consumption rate decreases， which improves the fuel economy of the engine. Because the pressure rise rate and the sound intensity are within the allowable range， the engine operates well. In addition， the exhaust gas temperature decreases with the increase of hydrogen addition ratio， and the exhaust gas energy shows a downward trend. In general， appropriate increase of the hydrogen addition proportion is beneficial to improve the overall performance of the engine.

For the cold start of heavy-duty diesel engine in low temperature environment， an intake preheating scheme using spray ignition by hot wall impinging combined with flame stabilization by recirculation is proposed. Based on the self-designed and built preheating experiment apparatus， the temperature rising and combustion characteristics under different inflow speed， fuel spray targeting and injection strategy are studied， and CFD numerical simulations are conducted. The experimental results show that ignition and temperature rise are strongly sensitive to spray targeting， and there is an optimal position of heating plate， with the mean temperature rising rate reaching 4.24 ℃/s at the inflow speed of 10 m/s. To balance the temperature rising rate， combustion efficiency and maintenance cost， the injection strategy with an injection period of 20~25 ms and injection pulse width of 1~3 ms should be adopted at high inflow speed. The fast droplets rebound and break up after impinging the heating plate， which falls in the Leidenfrost breakup mode. The simulation results show that a recirculation region with local flow speed of lower than 5 m/s is formed by the spoiler， which promotes evaporation and fuel-air mixing， and it is conducive to ignition and flame stabilization. For appropriate match between the injection mass with injection frequency， it is essentially to make the combustion duration suitable with injection period， so as to make full use of fuel and increase temperature rise and heat release rate.

In this paper， the turbulent flame propagation speed model is used to describe spark ignition （SI） combustion. For a single self-ignition point， the turbulent flame propagation speed model is still used， the sum of the equivalent turbulent flame speed of all self-ignition points is considered as the total equivalent turbulent flame speed， which is used to describe compression ignition combustion and then a spark-assisted compression ignition （SACI） quasi-dimensional combustion model is established. The air and external exhaust gas recirculation （EGR） dilution SACI based on this model is studied， and the simulation and experimental results match well. The calculation shows that the flame propagation speed of SACI is higher than that of SI， which increases with ignition advanced.， with the flame propagation speed of external EGR dilution lower than that of air dilution. Delaying ignition or increasing external EGR can lead to an increase in the peak area of the flame front， a slowing down of the decay rate and a weakening of the isovolumetric combustion. The thermal efficiency of air dilution is higher when the dilution ratio is comparable， but the exhaust aftertreatment of external EGR dilution is easier.

A study is conducted on a three-cylinder 1.5TGDI turbocharged direct injection engine， in terms of the effect of triple spark plug （TSP） ignition on the lean combustion performance. The results show that TSP can effectively extend the lean burn limit， with compression ratio of 15， the TSP can achieve stable combustion at lambda 1.95 for the specific operating condition of 2 000 r/min 8 bar BMEP， with the minimum brake specific fuel consumption （BSFC） reduced by 5 g/（kW·h） compared with that of the single spark plug， and raw NO _x emission reduced to about 50×10^-6. At this condition， the limit for a further lambda increase is mainly due to the boost capability. When the compression ration increases to 16， the minimum BSFC improvement is not obvious compared with that of the compression ratio of 15， and the lean burn limit decreases. The TSP has little benefit for reducing the knock tendency， but can increase the lean mixture combustion rate obviously， at the same lambda condition， its combustion duration can be 3-6°CA shortened compared to single spark plug， and increase by only 2°CA at lambda 1.95 compared to stoichiometric combustion. Through a further investigation on the potential maximum thermal efficiency， it shows that with the compression ratio of 15， the TSP can finally achieve 45.02% maximum brake thermal efficiency.