Diesel Spray Research Articles

Microscopic Imaging on Diesel Spray and Atomization Process

Improving diesel engine performance requires a comprehensive understanding of fuel atomization and air–fuel mixing within the combustion chamber. Numerous studies have been conducted to reduce emissions and enhance diesel engines. However, further investigation is required on the detailed diesel spray process. In this study, we adopted extinction measurement to analyze the effects of a fuel injection pressure range of 300 to 700 bar on spray morphology. For the extinction imaging setup, we utilized a high-intensity continuous LED source along with a diffuser to ensure uniform light distribution. The high-speed extinction and image processing results indicate that increasing the injection pressure from 300 to 700 bar effectively produced a smaller particulate size (15% reduction) and a better air–fuel mixing process. Especially at the end of injection, our results show smaller liquid ligaments (50% reduction) and droplets around the injector tip with higher injection pressure cases.

Impact of spray interaction on ammonia/diesel dual-fuel combustion and emission under engine relevant conditions

This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and N2O emissions are sensitive to the diesel/ammonia flame interaction. N2O emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.

Characterization of diesel spray with novel high-speed laser absorption scattering technique under diesel engine-like condition

In Diesel Engines, the injection process plays a decisive role in the combustion efficiency. Hence, the characterization of diesel sprays is very important. Several methods are developed, however, none of them records the temporal fuel distribution throughout the individual injection event and measures the liquid/vapor concentration of an evaporating diesel spray. In this work, two light sources i.e., an ultraviolet LED and a continuous wave laser, were used with two high-speed video cameras. A fuel mixture with the compositions of 97.5 % n-tridecane and 2.5 % of volume-based 1-methylnaphthalene was selected as the test fuel. The fuel was intermittently injected into an inert environment at 4.8 MPa and 800 K by applying a seven-hole injector with a hole diameter of 0.123 mm. The injection pressure was set at 100 MPa and the injection amounts were set as 2.5 and 5.0 mg/hole to observe the effect of the injected mass on the spray characteristics and mixture formation process. Calibration, based on the scattering by non-evaporating sprays and molar absorption coefficients for fully evaporated sprays, indicates a measurement error of 15 %. The findings of the experiments show that, under large injection mass conditions, the liquid phase equivalence ratio is quite low and close to zero just after the end of injection which points out that as the air-fuel mixing quality improves, the majority of the liquid fuel is rapidly converted to vapor. The air-fuel mixture is overall richer at large injected mass compared to the small mass condition. Furthermore, after the end of injection, the high fuel vapor concentration area near the nozzle soon mixes with ambient gas, decreasing the equivalence ratio to low levels, whereas a high-vapor-concentration region is still present at the spray head. This study provides a valuable insights into the behavior of the fuel spray, which could be used to improve the efficiency and performance of diesel engines.

Spray and combustion characterization under an ultra-high-density condition – Multi-fuel comparison

This study reveals for the first time the ignition and combustion characteristics of different fuel properties under ultra-high-density ambient condition. A new pre-burn type optically accessible constant volume combustion chamber was established, allowing for operation at pressures exceeding 300 bar. This chamber was utilized to generate a spray combustion environment at 150 bar and 1000 K, corresponding to a bulk-density of 50.82 kg/m3. Diesel was used as the reference fuel, and three types of primary reference fuel (PRF), i.e., PRF0 (n-heptane), PRF50, and PRF100 (isooctane), were used as the main test fuels. OH* chemiluminescence was utilized to measure the stable flame lift-off length, while the broadband chemiluminescence technique was used to measure the ignition delay time and to capture time-resolved flame development. The results show that the ignition delay of PFR100 is significantly larger than that of other fuels due to its lowest cetane number. Flame visualization results indicate that diesel spray combustion aligns well with the conceptual model proposed by Dec [SAE transactions, 1997: 1319–1348], whereas noticeable wrinkles are observed in the flames of PRF50. The flame lift-off length during the quasi-steady period shows to be independent of fuel properties, but the value has notably reduced to less than 9 mm. Comparison of the multi-fuel luminosity images reveals that diesel experiences the most pronounced combustion recession. Spatially integrated natural luminosity analysis indicates that diesel has the longest combustion duration, chiefly due to a larger rate of injection, whereas the difference in combustion duration between different PRFs is negligible. The heat release rate error range for PRF0 is the largest, suggesting stronger combustion variations. The heat release rate of diesel combustion is the most robust. The peak value of AHRR of PRF50 and PRF100 is marginally higher than that of diesel, which can be attributed to their higher low heating value.

Distribution function and atomization parameters of petroleum fuels sprays: An experimental and numerical study

Heavy fuels are difficult to spray. To investigate the burning of this fuel and create an appropriate combustion chamber, one must first understand the atomization process and spray properties of petroleum fuels. The Diesel spray behavior compared to Mazut fuel spray gives us an understanding of the atomization phenomenon of fuels. The most crucial fuel atomization characteristics include droplet diameter, spray angle, breakdown length, and droplet distribution. The shadowgraphy technique is used to capture images of fuel spray, which are then processed using image analysis software. The size and speed of the fuel spray droplets are predicted using the maximum entropy method. From a pressure difference of 15 bar onwards, the rate of mass flow remains almost constant. The fuels spray cone angle initially increases, and after the flow approaches full atomization, it reaches approximately a constant value. The breakup length and droplets diameter decrease with increasing fuel temperature and pressure, and with the full development of the flow, they tend to almost zero. By raising the fluid's viscosity, the diameter size distribution of the droplets becomes more uniform and smooth (unlike velocity distribution). In this research, an attempt has been made to develop experimental and numerical methods to measure the powdering parameters of a heavy non-Newtonian oil fuel called Mazut and a light petroleum fuel called diesel, as well as to investigate the spray behavior of these fuels.

Quantitative analysis of transient evaporation characteristics in diesel spray by high-speed UV-LAS technique

This paper reports the transient evaporation characteristics of diesel spray in an optical chamber at non-reacting high-temperature and high-pressure conditions. An ultraviolet/visible laser absorption and scattering (UV-LAS) technique was applied for visualizing and quantifying two-phase characteristics. The tip penetration, distribution of vapor mass concentration, equivalent ratio, and the mass of entrained gas was quantitatively obtained. The influence of micro-orifice diameter (0.11∼0.18 mm), ambient temperature (700∼900 K), and density (15∼21 kg/m3) on spatial/temporal results were thoroughly compared. The results showed that the evaporation rate gradually exceeds the injection rate as the mixture temperature increases. The ambient temperature enhances the evaporation rate with a relatively constant entrainment speed and thus further narrows the gap between delivery and evaporation rate. The ambient density and nozzle diameter play a crucial role in the entrainment process by controlling the spray momentum, which dominates the spray volume and eventually influences the evaporation process. These results provide insightful information for understanding and modeling the evaporation process of a diesel spray.

Effects of oxygen enrichment on diesel spray flame soot formation in O2/Ar atmosphere

In this study, diesel spray combustion at oxygen-enriched conditions (oxygen volume fraction of 21–70 %) with argon dilution is experimentally investigated in a constant-volume combustion chamber. Optical diagnostics are employed to study flame development, stabilization, and soot formation at oxygen-enriched conditions. To further verify the experimental observations, two-stage Lagrangian simulations are used to analyze the effects of oxygen on the formation and oxidation of soot precursors, polycyclic aromatic hydrocarbons. Results show that replacing nitrogen in air by argon leads to a 50 % reduction of the flame lift-off length, an increased soot flame temperature by 300 K, and higher soot concentrations. Flame morphology and structure still follow the classic conventional diesel combustion model in the oxygen range of 21–40 %, while changes are observed when oxygen levels are higher than 50 %. The width and length of the soot flame are shortened, and chemiluminescence from intermediate species like CO dominates the flame natural luminosity at the spray head, where the flame temperature reaches near 3000 K. Soot reduction mechanisms at high-degree oxygen-enrichment conditions are investigated. The intrinsic mixing-limited combustion of diesel sprays leads to unavoidable fuel-rich areas locally, but the shortened flame lift-off length and sufficient oxygen supply confines soot-forming conditions to a smaller, upstream region. The residence time of fuel parcels in this confined soot-forming area is shortened due to the larger local spray velocity. Thereafter, fuel parcels enter a high-temperature fuel-lean region, where the formed soot is oxidized rapidly.

Investigations of spray breakup Rayleigh–Taylor instability via multiphase lattice Boltzmann flux solver

Poor fuel–air mixing of the diesel spray in low ambient temperature and pressure or thin air leads to intricate fuel breakup mechanism near the nozzle, which still remains worth of study. In this study, a pressure-based modified multiphase lattice Boltzmann flux solver (MLBFS) is proposed to accommodate the fuel spray breakup characteristics of multiphase, multicomponent, and large density ratio, in which the source terms of governing equation are modified emphatically for high injection pressure. Therefore, the characteristics of microscopic diesel spray breakup induced by Rayleigh–Taylor instability are investigated, including spray penetration, spray area, and spray arc length. It is revealed that the spray penetration is increased exponentially with the fuel–air density ratio Rρ. Influenced by air resistance and circulation interference, the roll-up vortex, droplet size, and spray area increase with the decreasing of Rρ (corresponding to high ambient pressure). Affected by entrainment and Rayleigh–Taylor instability, the development of the spray arc length experienced three stages: rapid growth, peak, and violent fluctuation, in which the lower Rρ facilitates development. It is concluded that Rayleigh–Taylor instability is favorable for stimulating the spray internal circulation of spray to enhance entrainment with surrounding air, while improving roll-up and breakup in the spray tail region. Such investigation is conductive to better understanding the micro-breakup mechanisms of fuel spray in the spray-induced internal combustion engine.

Visualization study on the ignition and diffusion combustion process of liquid phase ammonia spray ignited by diesel jet in a constant volume vessel

Ammonia fueled engines applying diffusion combustion mode is expected to further improve the thermal and combustion efficiencies with high burning rate and high ammonia energy replacement. However, there is a lack of the fundamental studies about ammonia diffusion combustion characteristics. Therefore, the fundamental optical experiments of liquid phase ammonia spray and combustion, which is ignited by pilot diesel injection, were performed to investigate the ignition and diffusion combustion characteristics of liquid phase ammonia. According to the high-speed photography, interaction processes between the liquid phase ammonia spray and the diesel spray had been described, and the whole ignition and combustion processes were also recorded in detail. The discussion about the effect of diesel jet ignition location on ammonia ignition process shows that the effective ammonia ignition zone by diesel spray is the region of gas entrainment zone except for the liquid phase ammonia volume under evaporated condition, where the interval on ammonia spray axis is about 16 mm ∼ 35 mm away from the ammonia nozzle exit under the current experimental conditions, and the ammonia spray is failed to be ignited at any region out of the effective ignition zone. Moreover, the ammonia diffusion combustion characteristics under various ammonia injection durations reveals that the entrainment, including both the diesel flame and the surrounding ambient gas, into the effective ignition zone of liquid phase ammonia spray, is the effective way to achieve reliable ignition and the subsequent diffusion combustion of ammonia, which can increase the energy ratio (ammonia to pilot diesel) up to at least 2.9. Finally, based on the control of combustion mode of the pilot diesel, utilizing premixed diesel flame to induce the diffusion combustion of ammonia is proved to be an effective regulation scheme to enhance the performance of ammonia combustion under engine-like thermal conditions.

Visualization study on ammonia/diesel dual direct injection combustion characteristics and interaction between sprays

Ammonia is regarded as a highly promising green fuel. Nevertheless, its auto-ignition temperature is exceptionally elevated, posing challenges for its direct utilization in compression ignition engines. Using highly active fuel as the ignition source seems a solution. In this paper, based on the RCEM experimental platform, the diesel/ammonia diffusion combustion mode was studied in detail. The experimental parameters included the ammonia injection pressure, ammonia and diesel injection interval (including ammonia in advance of diesel and diesel in advance of ammonia), diesel injection pressure, and ammonia nozzle diameter. The results indicated that injecting ammonia on diesel flame contributed to the completeness of ammonia combustion. Injecting ammonia before diesel achieved a higher peak heat release rate but aggravated the incomplete combustion. The injection pressure of diesel had no significant impact on the combustion effect of ammonia. Increasing the ammonia injection pressure resulted in enhanced air entrainment, consequently enhancing the effective combination of fuel with air, which improved the peak heat release rate more effectively. Increasing the diameter of the ammonia nozzle was a necessary way to achieve a high ammonia energy substitution ratio, but a large amount of ammonia sprayed simultaneously caused a portion of the ammonia to not burn in time, resulting in aggravation of incomplete combustion. In addition, the interaction between diesel spray and ammonia spray was also studied. The results showed that, due to the higher quantity of ammonia compared to diesel, the two sprays would gather and develop toward the direction of ammonia injection roughly, and the final development direction of the spray was also related to the fuel injection pressure.

Embedded direct numerical simulation of ignition kernel evolution and flame initiation in dual-fuel spray assisted combustion

The flame initiation process in dual-fuel spray assisted combustion is presently not fully understood. Here, diesel spray assisted combustion of premixed methane/oxidizer/EGR is explored in the post-ignition phase by scale-resolved simulations. The modified dual-fuel ECN Spray A forms the baseline configuration. An extensive local grid refinement (approaching DNS limit) around one of the first high-temperature ignition kernels is carried out in order to examine the validity of hypothesized flame initiation and deflagration. A high quality LES is used to solve the spray dynamics, while the embedded quasi-DNS (eq-DNS) region offers detailed information on the ignition kernel evolution. The finite-rate chemistry is directly integrated, utilizing 54 species and 269 reactions. Local combustion modes are investigated for the ignition kernel development toward spontaneous ignition and premixed flame propagation using various approaches, including the reaction front displacement speed, energy transport budget, and chemical explosive mode analysis. Furthermore, a new criterion based on reaction flux analysis is introduced, which is compatible with dual-fuel combustion. The spatial and temporal scales associated with the ambient methane consumption and consequent flame initiation are characterized. For the first time in dual-fuel spray assisted simulations, numerical evidence is provided on the initiation of premixed flames, and the corresponding timescale is reported. Particularly, there is a transient mixed-mode combustion phase of approximately 0.2 ms after the spray second stage ignition wherein extinction, ignition fronts, and quasi-deflagrative structures co-exist. After such a transient period, the combustion mode becomes essentially deflagrative. Finally, interactions between turbulence and premixed flame front are characterized mostly in the corrugated regime.

Numerical studies of gasoline direct-injection sprays (ECN Spray G) under early- and late-injection conditions using Large Eddy Simulation and droplets-statistics-based Eulerian–Lagrangian framework

This paper presents an approach that uses Large Eddy Simulation under the Eulerian–Lagrangian framework to model the gasoline direct-injection (GDI) spray from Engine Combustion Network (ECN) multi-hole and counter-bore injectors. The approach considers the significant role that cavitation plays in primary atomization due to the counter-bore configuration. The local Weber number (We) and Reynolds number (Re) for GDI sprays are much smaller than those for a diesel spray, which renders conventional diesel spray approaches unsuitable. The proposed one uses a statistics-based droplet distribution function to address this and incorporates necessary information from a DNS inner-nozzle flow simulation. The corresponding models for drag, heat transfer, evaporation, and breakup consider the effects of viscous and distorted spray droplets. The approach has been applied to two different operating conditions, with simulation results that agree well with experimental data. Compared to the blob method assuming the ejected droplets are at the size of the injector diameter, the proposed CFD framework can reproduce a more accurate plume shape in the Spray G3 case. Applying the late-injection condition (Spray G1), the proposed approach improves the projected liquid volume (PLV) extinction compared to the blob method by providing a more accurate droplet evaporation prediction. These findings demonstrate the significance of the proposed approach for modeling GDI sprays and highlight its potential for future research in this area.

Development of a Skeletal Mechanism of a Four-Component Diesel Surrogate Fuel Using the Decoupling Method.

Alkylcyclohexanes with a long alkyl chain account for more than 30% of diesel fuel but seldom used in the oxidation mechanism of diesel surrogate fuel due to the lack of a reduced skeletal mechanism. Hence, a four-component diesel surrogate fuel was developed with n-butylcyclohexane (NBCH) as the representative of alkylcyclohexanes with a long alkyl chain in real diesel. The surrogate fuel can reproduce the physicochemical characteristics of real diesel, especially the distillation range. The reduced mechanism of NBCH was developed, and the skeletal mechanism of the surrogate fuel was formulated including 80 species and 251 reactions based on the decoupling method. The mechanism was validated under a wide range of conditions with the experimental results of ignition delay time (IDT), laminar flame speed, and species concentrations of both pure components and diesel. The accuracy of the mechanism on the spray and ignition performance was further validated against the experimental data obtained in a constant volume combustion chamber system. The calculated results showed a satisfactory agreement, in which the maximum error of flame lift-off length is 7.82 mm and that of IDTs is 0.16 ms. It was proven that the mechanism is suitable to reproduce the physicochemical properties of diesel and further predict the diesel spray and ignition performance.

Experimental observation of the TJI-initiated HPDI gas combustion: Vertically crossed flame jet and methane jet

In the field of natural gas marine engines, the high-pressure direct injection (HPDI) technology is widely used to achieve emission reduction while maintaining equivalent thermal efficiency and power output compared to diesel engines. In these engines, the in-cylinder combustion is primarily initiated by the diesel spray flame near the top dead center (TDC). In the present work, pre-chamber turbulent jet ignition (TJI) is employed to substitute diesel injection to initiate the combustion of HPDI methane jets. The optical experiments of ignition and flame development in the TJI-HPDI system with various injector configurations and injection/ignition control parameters are conducted in a constant-volume combustion chamber (CVCC). It is revealed that with the increase of injection-ignition delay(ti), three ignition modes are observed sequentially: methane jet suppresses ignition, methane jet first suppresses ignition then promotes flame propagation, and direct ignition and promoted flame propagation. The effect of various injection-ignition delays and injection pulse width were explored. The injection-ignition delay significantly influences the combustion characteristics such as heat release rate, while the injection pulse width influences the duration of the lifted jet flame. The flame lift-off length first decreases and then increases due to variations in thermodynamic conditions and oxygen concentration. With a larger-nozzle injector, the critical injection-ignition delay to initiate the main chamber combustion is significantly reduced. Moreover, the use of different nozzle diameters leads to varying levels of turbulent intensity in the methane jet, which in turn affects the combustion behavior.

Characterization of diesel spray combustion under micro-hole and ultra-high injection pressure conditions-analyses of diffused back-illumination imaging and OH* chemiluminescence imaging

This study investigated the spray combustion characteristics of diesel fuel using the Diffuse Back-illumination Imaging (DBI), Direct Photographic, and OH* chemiluminescence methods under different injection pressures (100–300 MPa) and different hole diameters (0.07–0.133 mm). The results indicated that at a certain point, the downstream of the spray, which holds a strong turbulent mixing, starts to disappear gradually without bright flames due to the cool flame combustion process. Based on this process, the ignition timing was determined using the space integral of intensity and optical thickness through the DBI method, which was validated by the OH* chemiluminescence method. The utilization of a micro-hole diameter injector and ultra-high injection pressure can effectively reduce ignition delay. Significant oxidation processes were observed both downstream and upstream for the micro-hole injector under ultra-high injection pressure. A parameter utilizing spatially integrated natural luminosity to OH* chemiluminescence ratio showed that increasing injection pressure and reducing hole diameter effectively reduced soot under unit fuel oxidation conditions. And predicted model results of droplet diameter and equivalence ratio (Siebers' and Hiroyasu's model) were used to analyze the experimental results. These findings contribute to the understanding of spray combustion characteristics and inform the development of efficient and low-emission combustion systems.

Optical Study on Spray and Two-Stage Ignition Characteristics for Diesel Spray Under Low Ambient Temperature and Density Conditions

Optical Study on Spray and Two-Stage Ignition Characteristics for Diesel Spray Under Low Ambient Temperature and Density Conditions

Very low soot formation with modulated liquid length and lift-off length of diesel spray flame

The vehicle diesel engine has entered the ultra-high injection pressure era. In order to study the spray and combustion characteristics under ultra-high pressure, the liquid length and combustion characteristics of multi-hole injectors (10 holes) with different hole diameters and different injection pressures were studied via experimental methods. The results show that increasing the injection pressure can effectively increase the slope of liquid length, while the hole diameter has little effect on it. However, during the stable stage, increasing hole diameter increase the liquid length, while the injection pressure has little effect on it. Different from the liquid length, the lift-off length during the stable stage is mainly affected by the injection pressure. F. Dos Santos’ model and the parameters of Siebers can more accurately predict the liquid length and lift-off length, even if the injection pressure has been increased to 300 MPa. Increasing injection pressure and reducing hole diameter can reduce the interference between liquid length and lift-off length. When the liquid length is less than the lift-off length, it can effectively inhibit soot formation. The value of LL/LOL has a fine linear relationship with stoichiometric air percentage. An equation of the relationship between the injection pressure and the hole diameter was established by the predicted model. Using this equation, we can get the range of LL/LOL less than 1 under different hole diameters or different injection pressures. The determination of this equation provides guidance and suggestions for the selection of hole diameters and injection pressure for diesel engines.

Experimental study on radial diffusion characteristics of diesel–pentanol spray

It is always a hot topic to find alternative fuel for diesel. Pentanol is a potential alternative fuel for diesel. In this study, different volume ratios of fuel were obtained by adding pentanol to diesel. On the high-pressure common rail experimental platform, the spray processes of pure diesel and diesel–pentanol blends were observed and analyzed, and the differences of radial diffusion capability between different experimental fuel sprays were evaluated. The maximum radial diffusibility was analyzed through the maximum width and the maximum width corresponding to the axial position. The radial diffusion capacity of the whole was analyzed by means of the average width and spray cone angle, and the area of the gas entrainment area was analyzed. The results showed that the addition of pentanol enhanced the radial diffusion ability and gas entrainment ability of diesel sprays.

Advanced Research on Internal Combustion Engines and Engine Fuels

Internal combustion (IC) engines serve as power devices that are widely applied in the fields of transport, engineering machinery, stationary power generation, etc., and are evolving towards the goal of higher efficiency and lower environmental impacts. In this Editorial, the role of IC engines for future transport and energy systems is discussed, and research directions for advancing IC engine and fuel technologies are recommended. Finally, we introduce the 14 technical papers collected for this Special Issue, which cover a wide range of research topics, including diesel spray characteristics, combustion technologies for low- and zero-carbon fuels, advanced combustion mode, fuel additive effects, engine operation under extreme conditions and advanced materials and manufacturing processes.

Numerical study on the effect of a two-stage pilot injection strategy on the performance of medium-speed diesel/natural gas dual-fuel marine engine

The need to reduce marine engine emissions continues to grow with the implementation of stricter emission standards. Numerical simulations were conducted to study the effect of a two-stage pilot diesel injection strategy on combustion and emissions in a medium-speed diesel/natural gas dual-fuel marine engine. A comprehensive analysis was performed on the start of the first pilot diesel injection (SOI1) and the proportion of the first pilot diesel injection (POI1), identified as two coupling factors of the injection strategy. The results indicated a significant improvement in indicated thermal efficiency (ITE) of over 48% and a reduction in nitrogen oxide (NOx) emissions of over 50% compared to the baseline single-stage injection strategy can be achieved through the use of high POI1 and delayed SOI1. In addition, the first pilot diesel spray covered the squish and piston bowl regions, enhancing the reactivity of the fuel-air mixture in these regions. The mass fraction of CH2O and H2O2 radicals determined the distribution of reactivity in different regions and characterized the transition process from low-temperature reaction to high-temperature reaction. The strategy of high POI1 and delayed SOI1 resulted in a better low-temperature reaction distribution, reducing combustion duration, improving ITE, and decreasing NOx, HC, CO emissions at medium load condition.