Local High-temperature Regions Research Articles

Experimental investigations on the jet flow field propagation characteristics and ignition mechanisms of stoichiometric CH4/O2/N2 premixed turbulent jet flames

The jet flow field (JFF) and flame propagation of stoichiometric CH4/O2/N2 mixtures under variable thermodynamic conditions were investigated experimentally using Schlieren and natural flame luminosity imaging techniques. A two-color method by wavelength integration was used to characterize the temperature field. The turbulent flame velocity (ST), Damköhler number (Da), Reynolds number (Re), and jet flame regime were explored by a combination of experimental data and theoretical calculations. The flame morphology shows that the propagation process can be subdivided into three stages: first, the JFF enters the main combustion chamber, then the flame propagates in the JFF, and finally, the JFF disappears after the flame front and the JFF front coincide. The vortex motion changes the thin reaction zone and the local high temperature region distribution. The normal jet shifts to the Mach disk jet at higher oxygen content. The ignition location changes from the jet tail to the shear layer. The top secondary vortex is more likely to generate at higher ambient temperatures, which enhances the ignition probability on the flame top. In addition, the degree of orifice blockage determines the jet flame type. Since the initial jet flame is more affected by orifice blockage, the variation in ST is strongly influenced by the change in the length-scale ratio. As the jet flame gradually moves away from the orifice, ST is mainly governed by turbulence intensity. Finally, a strong correlation between the Re number and Da number of the jet flame was found.

Dust dynamics in current sheets within protoplanetary disks

Context.Chondrules originate from the reprocessing of dust grains. They are key building blocks of telluric planets, yet their formation, which must happen in strongly localized regions of high temperature, remains poorly understood.Aims.We examine the dust spatial distribution near regions of strong local heating produced by current sheets, as a step toward exploring a potential path for chondrule formation. We further aim to investigate current sheet formation under various conditions in protoplanetary disks in the presence of ambipolar diffusion and Ohmic resistivity and the effect of current sheet morphology on dust dynamics in their vicinity.Methods.We used the RAMSES code including modules for nonideal magnetohydrodynamics and the solution of the dynamics of multiple sizes of dust grains to compute unstratified shearing box simulations of current sheet formation. Through seven models, we investigated the effect of the ambipolar diffusion and Ohmic resistivity strength, the initial density, and magnetic field, as well as the resolution and box size.Results.We find that current sheets form in all our models, with typical widths of 10−3–10−2AU, and that strong dust fraction variations occur for millimeter-sized grains. These variations are typically of an order of magnitude and up to two orders of magnitude for the most favorable cases. We also show that the box size and resolution has a strong impact on the current sheet distribution and intensity.Conclusions.The formation of current sheets that can intensely heat their surroundings near strong dynamical dust fraction variations could have important implications for chondrule formation, as it appears likely to happen in regions with a large dust fraction.

Effects of ambient density and injection pressure on ignition and combustion characteristics in diesel spray under plateau cold-start conditions

Gaining insights into the multi-parameter coupling dominated in-cylinder combustion process takes on critical significance to controlling and enhancing the performance of diesel engines under plateau cold-start conditions. In this study, the effect of varying injection pressure and ambient density on ignition and combustion characteristics of No. -50 diesel spray was investigated through high-speed direct photography and the two-color imaging technique, respectively. Regarding ignition characteristics, the increase of the ambient density led to the variation of the non-monotonic trend of ignition delay time with the rise of the injection pressure to a monotonous decrease, whereas the correlation between the axial ignition location and the injection pressure remained unaffected. Under three different ambient densities, the transition modes of the flame structure varied with the increase of injection pressure, subsequently impacting combustion characteristics. For combustion characteristics, the average level of flame temperature and soot were inversely proportional to the injection pressure for all three ambient densities. Higher ambient density facilitated the heat release from combustion chemical reactions, influencing the impact of increasing turbulence intensity on the ignition and combustion processes of diesel spray. The overall temperature level of the flame displayed an inflection point with the rise of the injection pressure, and this inflection point is delayed with the increase of the ambient density. The local high-temperature regions in flames (＞2300 K) were identified under higher ambient densities, such that soot generation and oxidation were subjected to significant competition. At ρam = 16.6 kg/m3, the oxidation dominant time gradually decreased with the rise of the injection pressure, leading to the integral KL factor maximum at Pinj = 80 MPa case. The optimal fuel injection pressures for cold starting at different altitudes were determined by considering the ignition and combustion characteristics of the flames.

Infrared radiation response mechanism of sandstone during loading and fracture process

Rock damage and fracture are the fundamental causes of coal mine dynamic disasters such as coal and gas outbursts, rock bursts, and mine water inrush. It is also one of the basic and common scientific problems in the field of rock engineering. Therefore, the reliable precursor information of rock damage and fracture process can be determined for the effective monitoring of the early warning of coal mine dynamic disaster, and early warning of surrounding rock fracture and seepage (water inrush) in mines. In this regard, the researcher failed to describe the mechanism of infrared radiation characteristics for the determination of rock failure precursors quantitatively. Further, the qualitative analysis of the infrared radiation mechanism restricts the use of infrared radiation to characterize the internal damage evolution and permeability characteristics of rocks. Therefore, in this paper, the equivalent plastic strain difference of sandstone is defined based on the plastic strain energy and deformation work conversion equation. The frictional heat effect of loaded sandstone is clarified. According to the Euclidean distance between the plastic zone location and the crack tip, the temperature source density function of the crack plastic zone is characterized. Based on the Fourier law of heat conduction, the thermal effect of crack propagation is deduced and analyzed, and the mathematical model of the infrared radiation response mechanism in the process of sandstone loading and fracture is established. Based on this model, the heat conduction range of sandstone fracture under biaxial loading is determined through the secondary development of finite element software, and the average infrared radiation temperature in the local high-temperature region of loaded sandstone is predicted. The findings of this research can provide a theoretical and experimental foundation for detecting rock failure for the safe and efficient execution of underground engineering projects e.g. mines, tunnels, etc.

One-step in-situ low damage etching of SiC/SiC composites by high-temperature chemical-assisted laser processing

SiC/SiC composites have a promising application prospect in the fields of aero-engine turbine blades and other hot-end components due to their excellent properties. It is difficult to machine SiC/SiC composites by traditional mechanical processing because of the ultra-high hardness and anisotropic character. The routinely laser direct processing in the air produce thermal effect damage, resulting in heat-affected zones and microcracks. Here high-temperature chemical-assisted nanosecond laser processing was investigated to realize one-step in-situ fast etching without causing damage to the structure of SiC/SiC composites. Firstly, the chemical wet etching only occurred in the laser-induced local high-temperature region. There was no additional etching damage to the substrate material in the region where the temperature was relatively low. Secondly, chemical liquid served as a transparent constraint layer, the ablation pressure on the material increased in a liquid confined environment. In comparison with laser direct etching in the air, the exposed fiber was not a needle-like structure and tubular structure but turned into a thin and flat tongue-like structure. The etching behavior of 0° fiber layer, 90° fiber layer, and crossing regions of fibers of different directions at low and high laser intensities were studied. Further, the hardness and friction coefficient of SiC/SiC composites after laser direct etching in the air and high-temperature chemical-assisted laser etching were compared. The chemical elementary composition before and after etching was measured to reveal the oxidized and carbonized characteristics. It was concluded that the action mechanism was the combined result of high-temperature decomposition, laser-induced ablation pressure in the liquid confined region, and local chemical wet etching. The results demonstrate that high-temperature chemical-assisted laser etching has some advantages over traditional laser beam machining and is a potential processing method for SiC/SiC composites.

Research on regeneration characteristics of diesel particulate filter based on fluid-thermal-solid coupling

In order to ensure that the diesel particulate filter (DPF) is not damaged during the regeneration process, a DPF regeneration model based on fluid-thermal-solid coupling is established. The temperature, stress and strain distribution during the regeneration process of DPF are analyzed, and the influence of stress and strain on the solid area of porous media under different carbon loads is revealed. The results show that there is an obvious local high temperature region in the center of the plug section of the intake channel and exhaust channel, and the tangential temperature of the inlet and exhaust outlet gradually decreases from the center to the surrounding. With the increase of carbon loads, the peak reaction temperature in the process of regeneration also began to rise. The thermal stress is mainly distributed near the side corners of the porous medium, and the maximum thermal stress is concentrated at the exhaust outlet end. The deformation is mainly concentrated in the solid center area of the plugs at both ends, the deformation amount decreases from the inside to the outside, and the deformation amount of the exhaust end is higher than that of the intake end. It can be found that the central area of the porous medium is the weak point of the structure, which is prone to thermal damage and cracks.

Performance of combustion process on marine low speed two-stroke dual fuel engine at different fuel conditions: Full diesel/diesel ignited natural gas

In order to deeply understand the combustion process of marine low speed two-stroke dual fuel engine under the background of “carbon neutrality”, MAN B&W 6S50ME-C-GI was taken as the research object, combustion processes of the full diesel (FD) and diesel ignited natural gas (DING) at 100 % load were tested and calculated. The results show that the total combustion duration period (CDP) under DING is 15.5°CA shorter than that under FD. The slow combustion period (SCP) and post combustion period (PCP) under DING were 1.75°CA and 15°CA lower than those under FD, respectively. At the same combustion time, the local high temperature region under DING is reduced by an average of 8 % compared with FD. The radial flame propagation velocity under DING and FD showed a “single peak” law, and the axial flame propagation velocity shows a “fluctuation” law. The difference is that the radial flame propagation velocity under FD shows attenuation to zero twice at 8°CA ATDC and 14°CA ATDC, and the flame propagation velocity of natural gas combustion is faster than that of diesel combustion. The maximum radial flame propagation velocity under DING is 2.5 m/s faster than that under FD. The maximum axial flame propagation velocity under DING is 0.7 m/s faster than that under FD.

Effect of laser shock on lamellar eutectic growth: A phase-field study

Eutectic growth trajectory is a temperature-dependent important behavior that concerns interface stability and subsequent solidification microstructure. In this work, a multiphase-field lattice-Boltzmann method is employed to investigate the effect of thermal shock on eutectic evolution by imposing a laser spot inside the melt. Two morphology feature parameters, average growth velocity and average characteristic path deviation angle of the marginal lamellae, are introduced to quantify the out-of-equilibrium eutectic growth. A multilinear correlation between the feature parameters and the technical factors including laser power, spot radius, cooling rate, and thermal diffusivity capacity is summarized by multiple linear regression analysis. The presence of laser spot bends the solidification front by changing local temperature distribution. The local high-temperature region near the laser spot corresponds to a lower driving force and thus the depression of the solid-liquid interface. Extension to a more general model which can handle large undercooling and phase decomposition is also discussed. The laser shock, static or moving, can be regarded as an efficient tool to obtain the engineered patterns such as curved solidification front or tilt domain.

Three-dimensional heat transfer analysis of flat-plate oscillating heat pipes

• Three-dimensional heat transfer model for flat-plate OHP is proposed. • Model includes both thermal hydrodynamic phenomena and thermal diffusion in casing. • The model is validated with experimental results of Aluminum flat-plate OHP. • Relation of temperature distribution in casing to liquid-vapor behavior is studied. • Novel outcome is that moving hot spots on flat-plate OHP surface are evaluated. This paper presents a three-dimensional heat transfer analysis of a flat-plate oscillating heat pipe (OHP). To enhance implementation of OHPs in various applications, it is important to understand the comprehensive phenomena that include thermal diffusion in the whole structure and thermal hydraulics in the channel. We developed an OHP model that includes the effect of thermal diffusion and thermo-fluid behavior. The model was validated with experimental results of a flat-plate aluminum OHP which has a size of 200 mm × 90 mm × 3.8 mm, a channel diameter of 1.0 mm, and a turn number of 42. The effect of surface roughness in the channel and liquid film thickness on operating temperature is investigated. The relation between thermo-fluid behavior in the channel and temperature distribution of the OHP is analyzed. For aluminum OHP, the temperature difference across the thickness direction is 0.1 °C which is relatively small, whereas, the moving hot spot: local high-temperature region, is found in the planer surface. The maximum hot spot superheat temperature reached 5.4 °C for 200 W. The novelties of this paper are to develop the three-dimensional comprehensive OHP model and to reveal the combined effect of thermo-hydraulic phenomena and thermal diffusion in OHP structure.

Study on leading-edge trenched holes arrangement under real turbine flow conditions

Turbine guide vane faces extremely high thermal load, especially on the leading edge region. In order to enhance cooling performance, the present study investigates the effects of leading-edge film cooling arrangements by adiabatic and aero-thermal coupled simulation. The three-row cooling design of the 25° inclined angle with the trenched holes is used to replace five-row showerhead holes. The model is employed after conducting the numerical validation. The results show that at coolant mass flow of 0.00171 kg/s, three-row showerhead film cooling with trenched holes can provide higher laterally averaged adiabatic cooling effectiveness than three-row round holes. It can also improve cooling performance in most of the leading-edge regions, compared with five-row showerhead cooling arrangements. The three-row cooling design with trenched holes can still obtain the highest area-averaged effectiveness on either the suction side or the pressure side of the leading edge. Besides, the trenched holes are also beneficial to the reduction of the aerodynamic losses. In the aero-thermal coupled simulation, the improvement of the three-row cooling design with trenched holes decreases because of the internal cooling effect. It is also proved that the transverse trench would not lead to a local high temperature region on the metal surface. The trenched configuration above can be used on the first-stage turbine vane to increase turbine inlet temperature, improve engine efficiency, and prolong engine life.

Numerical evaluation of pulverized coal swirling flames and NOx emissions in a coal-fired boiler: Effects of co- and counter-swirling flames and coal injection modes

A numerical evaluation was performed to investigate the effects of swirl arrangement (co-swirling and counter-swirling flows) and coal injection mode (non-, fully-, and partially-premixed with swirling flow) on the flame structure, coal particle uniformity, burnout performance, and nitrogen oxide (NOx) emissions in a 16-kWth coal-fired boiler. The co-swirling flame exhibits a tulip-shaped inner recirculation zone (IRZ), which increases the coal particle residence time: 1.61 s and 1.45 s for co-swirling and counter-swirling flames, respectively. In addition, the high uniformity of coal particles is maintained in all horizontal cross-sections. The total amount of NOx emissions at the boiler outlet are 205.0 and 551.2 ppm (@6% O2) for the co-swirling and counter-swirling flames, respectively; the deNOx efficiency is 62.8%. An exhaust tube vortex (ETV) structure with a tulip-shaped IRZ is observed in the non-premixed swirling flame injection mode; however, the ETV structure is not observed in the other injection modes. The ETV structure enhanced the coal particle uniformity and expanded the reaction zone, consequently reducing the area of the local high-temperature region. Although the non-premixed injection mode has a slightly lower burnout performance than other injection modes, it is determined to be more effective in reducing the total amount of NOx emissions.

Local high-temperature phenomena within magnetic clouds

In this study, three methods were used to analyze 17 large-scale local high-temperature regions with durations exceeding 2 h within magnetic clouds (MCs) observed by advanced composition explorer from 1998 to 2008. Results show that five of these large-scale regions may have been caused by flare heating; seven of the regions may have been caused by non-uniform expansion when MCs propagated in the solar-terrestrial space; four large-scale high temperature regions may likely result from combined non-uniform expansion and flare heating; and only one large-scale local high-temperature region was not related to either flare heating nor non-uniform expansion. No evidence indicated that magnetic reconnection occurred or had occurred within the high-temperature regions. Based on our results, we infer that such local high-temperature phenomena within MCs are caused primarily as a result of flare heating and non-uniform expansion, either separately or jointly, and that magnetic reconnection plays only a minor role in the formation of high-temperature regions.

FGM을 이용한 에탄올 연료의 MILD 연소특성에 대한 수치해석 연구

MILD combustion has been considered as one of the promising combustion technology for high thermal efficiency and reducing nitrogen oxides and carbon dioxide emissions. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas-phase fuel MILD combustion. Therefore further study on MILD combustion using liquid fuel is needed. In this work, we will focus on the numerical simulation of the effects of diluted gas velocity on the formation of liquid fuel MILD combustion using FGM using ethanol fuel as a carbon-neutral fuel. A two-stage combustion structure similar to ‘Deft jet in hot co-flow’ configuration was used to study the formation of liquid fuel MILD combustion for the validation purpose. The diluted burnt gas velocity from the first premixed combustion chamber can be controlled by an open ratio of the nozzle between two combustion chambers. The results show that the local high-temperature region was decreased and the flame temperature was uniformly distributed due to the intense mixing by the higher momentum of ejected diluted burnt gas from the venturi type nozzle considering atomization and vaporization of the injected liquid fuel.

Influence of non-uniform inflow swirl and hot streak on turbine vane

The turbine vane bears higher and higher temperature of upstream flow with the higher requirements for the engine thrust. The heat resistance of turbine vanes is a severe problem for the lifetime of turbine vanes. Therefore, it is essential to study the flow field and heat transfer of the vane to find better ways to improve the heat resistance of the turbine and increase the thrust of the engine. To improve the efficiency of the turbine vanes, the present paper conducted researches on the heat transfer and the pressure loss of turbine vanes under different radius ratio of swirl and hot streak. The numerical applies CFD 3D RANs solver with the SST turbulent model to get the influence of non-uniform inflow velocity and temperature distribution on turbine vanes. The present numerical model utilizes turbine vane C3X. Considering the viscosity of the fluid causes shear stress on the wall, the paper set the boundary layers mesh in the numerical model. The size of the first boundary layer mesh is 10–6 m. The results show that the hot fluid on the suction side migrates towards the hub, and the hot fluid on the pressure side migrates towards the shroud while there are coupling effect of the swirl and hot streak. The larger the radius ratio of the hot streak and the swirl (RHS) is, the higher the temperature of the local high-temperature regions exist on the suction side of leading edge and the pressure side of the trailing edge is, and the higher the pressure loss is.

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.

Experimental and numerical study of the effect of injection strategy and intake valve lift on super-knock and engine performance in a boosted GDI engine

For four-stroke turbocharged gasoline direct injection engines, the improvement of pre-mixture homogeneity and the reduction of wall wetting are beneficial to improve combustion performance and emission characteristics, and specifically effective to suppress super-knock because of the decrease of oil dilution and soot formation. This paper investigated the effect of injection strategy and intake valve lift (IVL) on super-knock frequency and engine performance through experimental study. The validated numerical models revealed the mechanisms behind experimental results. The results showed that using late second injection under high-IVL condition and early single-injection under low-IVL condition reduced wall wetting and improved mixture homogeneity. This restrained the formation of pre-ignition origins (oil dilution and soot formation were decreased). The tendency of hot-spot self-ignition (local high-temperature region was narrowed) and end-gas detonation combustion (end-gas reactivity was reduced) was suppressed as well. These factors contributed to the reduction of the actual super-knock frequency in experiment. Further, late second injection under high-IVL condition and early single-injection under low-IVL condition also accelerated the flame propagation and promoted the complete combustion of fuel. Thus the dynamic and economic performance improved. CO and soot emissions also reduced, only NOx emission increased. Two-stage injection played the opposite role in engine performance respectively under high-IVL and low-IVL condition. In general, the combination of low-IVL and early single-injection showed the lowest super-knock frequency and best engine performance.

Numerical and experimental study on heat transfer and flow features of representative molten salts for energy applications in turbulent tube flow

This article investigated the heat transfer performance and flow friction of molten salts in turbulent tube flow, where four salts including Hitec, Solar Salt, NaF-NaBF4, and FLiNaK were studied. A computational model was developed to analyze the flow and heat transfer features of the salts in the tube, and experiments were conducted to test the heat transfer performance of a representative salt Hitec in the tubes of a salt-oil heat exchanger. Comparison of simulation results with the experimental data shows that the average errors are smaller than ±4%, which validates the simulation model. Based on the model, firstly the influences of heat flux uniformity at the tube outer wall were examined. The results show that the non-uniform wall flux can lead to local high-temperature region but influences little on the flow friction coefficient and the heat transfer performance. Then, the model was utilized to investigate the friction and heat transfer features of the salts under broad ranges of the temperature and the velocity. Comparisons of the simulated heat transfer results with Hansen’s, Sider-Tate’s and Gnielinski’s correlations show that the largest errors can reach +25%, +13% and −15%, respectively. Furthermore, the errors between the simulated friction coefficients and the Filonenko’s correlation are smaller than ±2%, which indicates that this correlation is suitable for predicting the friction of the salts. Finally, to predict the heat transfer performance more accurately for these representative salts, a new correlation was developed. It was found that the errors between all simulation results and the proposed correlation are smaller than ±5%, while the corresponding values for 80% experiment data of three salts are also lower than ±5%. The current study can offer beneficial results and correlation for the applications of molten salts in energy systems.

Enhancement of Fixed-bed Flow Reactions under Microwave Irradiation by Local Heating at the Vicinal Contact Points of Catalyst Particles

The formation of local high temperature regions, or so-called “hot spots”, in heterogeneous reaction systems has been suggested as a critical factor in the enhancement of chemical reactions using microwave heating. In this paper, we report the generation of local high temperature regions between catalyst particles under microwave heating. First, we demonstrated that reaction rate of the dehydrogenation of 2-propanol over a magnetite catalyst was enhanced 17- (250 °C) to 38- (200 °C) fold when heated with microwave irradiation rather than an electrical furnace. Subsequently, the existence of microwave-generated specific local heating was demonstrated using a coupled simulation of the electromagnetic fields and heat transfer as well as in situ emission spectroscopy. Specific high-temperature regions were generated at the vicinal contact points of the catalyst particles due to the concentrated microwave electric field. We also directly observed local high temperature regions at the contact points of the particles during microwave heating of a model silicon carbide spherical material using in situ emission spectroscopy. We conclude that the generation of local heating at the contact points between the catalyst particles is a key factor for enhancing fixed-bed flow reactions under microwave irradiation.

Initiation of Explosive Transformation of High Explosives under Low-Velocity Mechanical Impacts and Weak Shock Waves Due to Formation of Viscoplastic Flows

A key issue for explaining bursts and explosions of high explosives (HEs) under low-velocity mechanical impacts with registered time delays is the formation of local high-temperature regions. It is demonstrated by an example of HMX that the required temperatures should significantly exceed the HMX melting point and can be obtained only due to the work of viscosity forces in the liquid phase. In this case, however, it is necessary to ensure HE flow velocities greater than the primary impact velocities by several orders of magnitude. A mechanism of generation of such velocities is proposed: squeezing of the HE, which is heated on shear strains and plasticized, from the shear layer under the action of the pressure difference along the layer. Conditions of fast decomposition of the HE in the shear layer and conditions of an explosion of the surrounding HE are formulated.

Computational optimization of fuel supply, syngas composition, and intake conditions for a syngas/diesel RCCI engine

By utilizing the promising alternative fuel of syngas, and the syngas/diesel dual-fuel reactivity controlled compression ignition (RCCI) is a potential combustion strategy for internal combustion engines. However, the optimal operating parameters for syngas/diesel RCCI engines under wide operating conditions have not been investigated. In this study, the operating parameters include fuel supply, syngas composition, and intake conditions of a syngas/diesel RCCI engine were optimized under wide load by integrating the KIVA-3V code and the non-dominated sort genetic algorithm II (NSGA-II). The results indicated that nitrogen oxides (NOx) emissions can be controlled in considerably low levels, and the efficient combustion of the premixed syngas in the squish region can be realized with high premix ratio and early pilot injection of diesel. Equivalent indicated specific fuel consumption (EISFC) and ringing intensity (RI) are the major issues for the optimization at low and mid load, respectively. The double diesel injection strategy with the relatively late main injection timing is an effective way to both improve combustion efficiency at the low load and reduce RI at the mid load. For the double diesel injection, the ratio of pilot injection is controlled in a narrow range to provide sufficient high reactivity fuel in the piston bowl and to avoid the local high-temperature combustion region simultaneously. With the restrictions of EISFC and RI, the optimal H2 fraction in the syngas is 60–80%. Based on the optimal fuel supply and intake conditions, a syngas with 75% H2 and the diluent factor C of 0.8 is capable of realizing the high efficiency, moderate combustion, and low emissions for the RCCI engine at full load range.