Spray Impingement Research Articles

Comparative investigation on macroscopic and microscopic characteristics of impingement spray of gasoline and ethanol from a GDI injector under injection pressure up to 50 MPa

Particulate Matter (PM) emissions from passenger vehicles have attracted considerable interest over the last decade. In order to reduce PM emissions, improving maximum injection pressure has been a developing trend for new generation GDI engines. However, comparing gasoline and ethanol impingement spray characteristics from a GDI injector under high injection pressure is still unclear. In this paper, a comparative investigation on both the macroscopic and microscopic characteristics of impingement spray from a GDI injector fuelled with gasoline and ethanol was performed under injection pressure up to 50 MPa, providing new findings to promote a more homogeneous air–fuel mixture and reduce PM emissions. The experimental results show that under the same PI (injection pressure), rebound height of gasoline impingement spray is a bit higher than ethanol. AS (spray area) of gasoline is slightly higher than ethanol under PI=10MPa. However, under PI=30MPa and PI=50MPa, AS of gasoline is gradually exceeded by that of ethanol as time progresses. By increasing PI to 50 MPa, the difference in DN (diffusion distance of the near side) between gasoline and ethanol is greatly reduced, meantime DF (diffusion distance of the far side) becomes weaker than ethanol. For both gasoline and ethanol, with the increase PI from 10 MPa to 50 MPa, VN (average normal component of droplet velocity) and VT (average tangential component of droplet velocity) of incident droplets increase by around 1 m/s. Meantime, there is a slight decrease in the absolute value of VN and VT of reflected droplets. DSMD (Sauter mean diameter of droplets) presents a significant decreasing trend with the increase of PI. Besides, a smaller DSMD can be seen for the gasoline impingement spray compared to ethanol under the same PI.

SPRAY IMPINGEMENT FILM ANALYSIS: CHARACTERISTICS EVALUATION AND CORRESPONDING SIMULATION METHOD

Spray impingement is a process during which discrete spray droplets contact a solid surface and form a continuous liquid film. To thoroughly understand such a process is challenging due to the complex gas-liquid-solid interaction and coupling. The liquid converts from a continuous phase into discrete droplets, and finally back to the continuous phase again on the plate. On the basis of experimental analysis, this work investigates a computational fluid dynamics model in the Lagrangian-Eulerian system to focus more on the film dynamics during the impingement. The impingement criterion is modified to incorporate a more accurate momentum transfer within the liquid film. Furthermore, a submodel of droplet slide is coupled into the numerical model to analyze the effect where droplets with a high horizontal velocity will glide away from the plate without contacting it. The numerical model is validated by free spray experiments in the aspects of spray morphology, droplet size, and droplet velocity. Afterward, film dynamics are validated from experimental film thickness measurement with the high-speed laser-induced fluorescence technique. The results show that the modified Bai-Gosman model in the Lagrangian-Eulerian framework can well predict the motion and characteristics of the impingement film, and incorporating the glide model further improves the approximation in many aspects.

REWETTING AND TRANSIENT HEAT TRANSFER ON THE HEATED HORIZONTAL TUBE SURFACE DURING THE AIR-ATOMIZED SPRAY COOLING

The purpose of this study is to investigate the cooling and rewetting of a heated horizontal tube surface with an air-atomized water spray impingement. Rewetting and transient heat transfer are crucial in nuclear reactor safety during a postulated accident, such as cooling of hot calandria tubes (CT) during the large-break loss of coolant accident (LOCA). The rewetting velocity in the circumferential direction and the rate of cooling of the heated tube surface were determined as a function of nozzle operating parameters. To estimate the local spray impingement density on the tube surface, an in-house mechanical patternator was designed and developed. To record the flow state during cooling, a high-speed video camera was used. The rewetting velocity on the tube surface was determined using the outcome of thermocouples mounted on the heated tube wall and an imaging system used to record the video picture during the runs. The two techniques of calculating rewetting velocity are compared. The highest heat flux removed from the tube surface was estimated as 3.7 MW/m<sup>2</sup>, and the maximum rewetting velocity was found to be 5.58 mm/s. An excellent agreement regarding rewetting velocity has been reported utilizing thermocouples and a high-speed camera.

Development of a Conceptual Framework for Integrated Vector Management in the Heterogeneous Malaria Ecosystem of Western Kenya Highlands

Malaria heterogeneity in the highlands is due to range of factors including seasonal weather changes, climate variability, land-use changes, topography, drug resistance, and malaria control programs. High coverage of long lasting insecticide treated nets is the basis of vector control in epidemic prone western Kenya highlands. Long lasting insecticide treated nets have effectively controlled malaria in the hypo-endemic zones, but not in meso-endemic and hyper-endemic zones where significant residue of transmission remains despite control efforts. Inadequate policy on integrated vector management application for ecologically heterogeneous ecosystems hinders effective malaria control. Advances in ecological and epidemiological studies have improved our understanding on vector distribution determinants and malaria transmission enabling us to effectively integrate indoor residual spraying into the existing long lasting insecticide treated nets programme. Data on malaria vector abundance and parasite prevalence for different malaria ecosystems within western Kenya highlands before and after mass insecticide treated bed-net distribution campaigns was gathered to assess the efficacy of the long lasting insecticide treated nets based control efforts. Field tests were carried out to determine the impact of combined indoor residual spray and long lasting insecticide treated nets on vector indoor resting densities in zones where insecticide treated nets alone had limited efficacy or zero efficacy was observed. Female An. gambiae s.l resting densities of 0.1 mosquitoes/ house/night were associated with a plasmodium falciparum (pf) prevalence rate of 10% or below. This observation enabled the development of a framework for the inclusion of indoor residual spray in integrated vector management with the suggestion that IRS should be applied in malaria eco-epidemiological zones where An. gambiae s.l resting densities exceeds 0.1 females/ house/ night. Similarly, only those houses with a resting density of 0.1 females An. gambiae s.l and above should be targeted during spraying. Such an approach would significantly reduce the cost associated with indoor residual spray and provides a rationale for judicious integration of indoor residual spray within existing long lasting insecticide treated nets control programmes.

Power consumption and thermal performance of integrated spray and jet array cooling vapor chambers

• Title: Power consumption and thermal performance of integrated spray and jet array cooling vapor chambers. • An integrated arrayed spray impingement vapor chamber (ISVC) is designed. • Two integrated array jet impingement vapor chambers, IJVC-0.8 and IJVC-3.0, are compared with ISVC. • The power consumption of IJVC-0.8 and IJVC-3.0 is 1.36-1.53 and 0.079-0.09 times that of ISVC. • The Nusselt number of ISVC is 33.91% and 52.41% higher than that of IJVC-0.8 and IJVC-3.0. • The maximum temperature difference of ISVC is at least 46.93 % and 56.84 % lower than that of IJVC-0.8 and IJVC-3.0. An integrated arrayed spray impingement vapor chamber (ISVC) is designed for cooling high-power electronic devices. The spray array is arranged on the vapor chamber to measure thermal performance in comparison with the other two integrated arrayed jet impingement vapor chambers (IJVCs) with different jet orifice diameters, named IJVC-0.8 and IJVC-3.0, on the basis of the inlet and outlet diameters of the spray nozzles. Tests have been conducted on pressure drop, power consumption, heat dissipation performance, temperature uniformity, and comprehensive performance. Results show that the pressure drop and power consumption of IJVC-0.8 and IJVC-3.0 are 1.36-1.53 and 0.079-0.09 times those of ISVC. In addition, the heat dissipation performance and temperature uniformity of the ISVC are better than those of IJVCs for given tests conditions. Furthermore, the heat dissipation of ISVC shows more advantage than those of IJVCs as the power is increased. Finally, the comprehensive performance of ISVC is revealed to be superior to that of IJVC if the exit apertures of the spray nozzles and jet holes are equal in diameter. In the IJVCs, choosing larger jet holes is to sacrifice part of the heat dissipation capacity, but compensate for the detrimental effects of high pressure drop, and subsequently improve its overall performance.

INFLUENCE MECHANISM OF STAGNATION-POINT FLOW ON LIQUID-PHASE SPRAY PENETRATION LENGTH UNDER ENGINE-LIKE CONDITIONS

Formulation of liquid-phase spray penetration length (LPL) is one of the basic research works of direct injection (DI) engines. To predict the spray evolution and LPL in the limited space more accurately, the diffused background-illumination extinction imaging (DBI) technology and highspeed schlieren method were employed to detect the liquid- and vapor-phase spray development in a constant volume combustion chamber (CVCC). The experimental results show that the LPL of the impinging spray is significantly smaller than that of the free spray when the LPL is close to the impinging distance. When the LPL is much smaller than the impinging distance, the LPL of impinging spray is the same as that of free spray. Furthermore, based on the CFD simulation and the stagnation-point flow theory, the spatial distribution of velocity, pressure, and density at the near-wall surface was analyzed in detail. Due to part of the spray kinetic energy was converted into potential energy, creating a sharp increase in pressure and density near the stagnation point, which suppressed the movement of fuel droplets, resulting in a significantly smaller LPL. Moreover, a novel LPL prediction model is introduced, which considering the inhibiting effect of wall on spray penetration and demonstrates enhanced predictive capability of experimental results.

Particulate Matter Emissions in Gasoline Direct-Injection Spark-Ignition Engines: Sources, Fuel Dependency, and Quantities

This study investigates sources of particulate matter (PM) from a direct-injected spark-ignition (DISI) engine, all of which are likely the result of poor mixture formation, although through varying mechanisms. Nine unique gasoline formulations, including both oxygenated and non-oxygenated fuels, with varying distillation curves and concentrations of different hydrocarbon classes were employed to investigate the effect of fuel on soot formation. The engine experiments were further supported by reacting and non-reacting experiments in a spray-chamber.The metal-engine experimental results indicated that engine-out PM emissions of the nine fuels generally conforms to their sooting tendency, here quantified by Particulate Matter Index (PMI). Discrepancies with the engine-out PM emissions and PMI were observed under transient operating condition, which is not reflective of the test conditions used to formulate the PMI. A diisobutylene surrogate blend and a high-olefin full-boiling range fuel were investigated further in the optically-accessible engine, showing soot generation from different sources. These differences came from the variation in their spray characteristics, as confirmed in the non-reactive spray-chamber experiments.While the earlier tests were conducted with a fouled injector, the injector was later cleaned and fuels were tested in the optical engine. High olefin fuel and diisobutylene blend showed significantly lower soot emissions with clean injector. E30 fuel exhibited spray impingement and subsequent diffusive combustion, known as pool fire, on the piston top characterized by a yellow flame due to soot luminosity. A final round of experiments in the spray-chamber mimic this pool fire mechanism. A stoichiometric flame was initiated after a spray has impinged on a wall and formed a film. Results showed a large time delay between the flame passing over the fuel film and the formation of soot mass. The slow soot formation via pyrolysis in spray-chamber suggest that pyrolysis may not be a dominating soot-production pathway in SI engines, even for conditions with significant wall wetting. The findings of this study highlight the many considerations which influence the effective design of a combustion system when the minimization of PM emissions is a goal, and the ways in which fuel formulation can change soot-production pathways in DISI engines.

The Impact of Fuel Injection Timing and Charge Dilution Rate on Low Temperature Combustion in a Compression Ignition Engine

Using high charge dilution low temperature combustion (LTC) strategies in a diesel engine offers low emissions of nitrogen oxides (NOx). These strategies are limited to part-load conditions and involve high levels of charge dilution, typically achieved through the use of recirculated exhaust gases (EGR). The slow response of the gas handling system, compared to load demand and fuelling, can lead to conditions where dilution levels are higher or lower than expected, impacting emissions and combustion stability. This article reports on the sensitivity of high-dilution LTC to variations in EGR rate and fuel injection timing. Impacts on engine efficiency, combustion stability and emissions are assessed in a single-cylinder engine and compared to in-cylinder flame temperatures measured using a borescope-based two-colour pyrometer. The work focuses on low-load conditions (300 kPa gross indicated mean effective pressure) and includes an EGR sweep from conventional diesel mode to high-dilution LTC, and sensitivity studies investigating the effects of variations in charge dilution and fuel injection timing at the high-dilution LTC condition. Key findings from the study include that the peak flame temperature decreased from ~2580 K in conventional diesel combustion with no EGR to 1800 K in LTC with low-NOx, low-soot operation and an EGR rate of 57%. Increasing the EGR to 64% reduced flame temperatures to 1400 K but increased total hydrocarbon (THC) and carbon monoxide (CO) emissions by 30–50% and increased fuel consumption by 5–7%. Charge dilution was found to have a stronger effect on the combustion process than the diesel injection timing under these LTC conditions. Advancing fuel injection timings at increasing dilution kept combustion instability below 2.5%. Peak in-cylinder temperatures were maintained in the 2000–2100 K range, while THC and CO emissions were controlled by delaying the onset of bulk quenching. Very early injection (earlier than 24 °CA before top-dead-centre) resulted in spray impingement on the piston crown, resulting in degraded efficiency and higher emissions. The results of this study demonstrate the potential of fuel injection timing modification to accommodate variations in charge dilution rates while maintaining low NOx and PM emissions in a diesel engine using low-temperature combustion strategies at part loads.

Spray-wall interaction on n-dodecane spray combustion and soot formation under different wall temperatures

To investigate the effect of the wall on soot formation during spray combustion and to explain the existence of contradictory results, the vapor-phase, ignition, combustion, and soot formation of free- and impingement-spray with different wall temperatures were studied in comparison using optical diagnostic techniques. Results reveal that, compared to free spray, the impingement spray’s vapor-phase spray tip penetration is reduced, and its vapor-phase spray volume is increased by about three times. At conditions where only the vapor-phase impinges on the wall, the impingement spray has a shorter ignition delay time (IDT) for various wall temperatures. Furthermore, the soot formation of the impingement spray combustion is approximately one-third of the free spray, and the increase in air entrainment accounts for this phenomenon. In a comparison of different wall temperature conditions, the higher wall temperature facilitates the spray ignition process with a shorter IDT, and the ignition location is further away from the wall. However, the relationship between wall temperature and soot formation is not linear. The soot formation varies in a pattern of reducing and then increasing as the wall temperature increases due to the high wall temperature accelerating both the generation and oxidation rate of soot.

Engine Combustion Network “Spray G”: Wall heat transfer characterization by infrared thermography

Nowadays, several efforts are being made to design more efficient, cleaner, and economically accessible engines. Spray-wall interactions are strongly related with the fuel–air mixture and emission formation. As such, they are considered as the most important physical processes in engine research. In the present study, the infrared thermography coupled with an inverse heat transfer data reduction is applied to evaluate the wall heat transfer of an iso-octane spray generated by a multi-hole gasoline direct injector (Spray G) impinging on a heated thin foil. The experimental apparatus includes an Invar foil (50μm in thickness) heated by Joule effect and the injector located at 66.66 injector nozzle diameter above the surface. Thermal images of the impinging spray are acquired from the dry side of the foil at several time delays from the start of injection at two different injection pressures (10and 20MPa) and two different wall temperatures (373and 473K). The experimental data are reduced in the dimensionless form in terms of the spray cooling efficiency ξ, which represents the ratio between the spray cooling heat flux and the heat transfer capability of the fluid, by taking into account the area of impact of the spray. Results show a substantial increment of the heat flux and the spray cooling efficiency by increasing the wall temperature. Also, the increment of the injection pressure has an increasing effect on the area of impact, the heat flux, and the efficiency of the spray for both wall temperatures investigated in the experimental campaign. The spray cone angle and the plume jet axis angle were also estimated from the wall heat flux distribution.

Thermal performance and flow pattern of an immersion spray array cooling vapor chamber

An immersion spray array cooling vapor chamber (ISVC) is proposed for high-power electronic devices. Experimental and numerical studies on thermal performance and flow pattern have been conducted. It is shown that increasing the inlet temperature of the coolant facilitates the heat transfer performance and temperature uniformity of the ISVC within the safe working temperature range of electronic devices. The immersed spray impingement process includes a stage of velocity reduction from the nozzle exit to the target surface, a process of velocity boundary layer formation on the target surface, and a flow collision region formation process of adjacent sprays. As the inlet flow rate increases, the effect of the spray on the target surface is enhanced and the interaction between adjacent sprays is stronger. The perturbation effect of the spray on the fluid in the impingement cavity is positively influenced by the inlet flow rate. The spray array has a strong stirring effect on the water in the spray chamber in the XY, XZ and YZ planes. The heat transfer capacity of the ISVC is enhanced with a larger inlet flow rate due to the enhanced spray effect and larger spray coverage area. The temperature uniformity of the ISVC is improved with an increase of flow rate. The ISVC operating limit heating powers of 2.0 L/min, 4.0 L/min and 7.0 L/min flow rates are 531 W, 575 W and 600 W. Compared to the existing integrated heat sink combined vapor chamber and array jet impingement, the operating limit heating power of ISVC is increased by at least 68%.

Development of a hybrid Lagrange–Euler transition model for the film formation and dynamics of an impinging liquid spray

This paper proposes a hybrid Lagrange–Euler transition model that fully describes the injection and film formation process with different transition sub-models to balance accuracy and efficiency under the incompressible framework for spray cooling of electric machines. When the liquid phase is far away from a wall or film, a Lagrange discrete particle modeling method is employed to track liquid phase motion, which then transforms into a Eulerian droplet when a particle is close to a wall or film. Thereafter, the volume-of-fluid (VOF) method is adopted to simulate the processes of impingement, wall film formation, and dynamics. The transition model is implemented with the CONVERGE code package and validated against several available experimental data ranging from single droplets to spray impingement. The results indicate that the hybrid Lagrange–Euler transition model exhibits excellent mass and momentum conservation under different mesh resolution conditions and can well reproduce film formation and dynamics behaviors. In addition, detailed comparisons between the transition model and particle-based thin film modeling (TFM) are made for wall film formed by spray impingement. The transition model predicts a smaller film area and a better film shape than the TFM model compared to the measurements. Overall, the transition model coupled with the VOF method shows a higher sensitivity to mesh resolution, whereas the TFM model is more easily affected by semi-empirical splash models.

Impact of Foliar Spray with Some Nutrients on Growth and Nutritional Status of Pomegranate Trees

Impact of Foliar Spray with Some Nutrients on Growth and Nutritional Status of Pomegranate Trees

Investigation of the Behaviors of Methanol Spray Impingement and Wall Wetting

Port fuel injection is an important technical route in methanol engines. To obtain a theoretical basis for injector arrangement and injection strategy development in methanol engines, an optimal experimental platform based on diffuse back-illumination and the refractive index matching method (RIM) was designed and built in this study. The experiments on the behavior of low-pressure methanol spray-wall impingement and wall film were carried out and the influence of the three boundary conditions of spray distance (Dimp), wall temperature (Twall), and injection pressure (Pinj) were analyzed comprehensively. Results showed that with the increase of Dimp, the overall shape of spray before impinging the wall changed from conical to cylindrical. The impinging spray height Hi and impinging spray width Wi increased with the decrease of Dimp and the increase of Pinj. Adhesive fuel film mass Mf increased with the increase of Dimp due to the decrease of kinetic energy during wall impact. In addition, the increase of the wall temperature Twall reduced Mf due to evaporation, but when Twall reached 423 K, Mf rebounded due to the Leidenfrost effect. The results of this study are helpful to improve the accuracy of the numerical methanol engine model.

High-efficiency spray cooling of rough surfaces with gas-assist atomization

Spray impingement heat transfer experiments were conducted to assess the role of surface roughness on heat transfer performance. Surfaces covered with arrays of micro-pillars with diameters in the range 0.8–50 μm were fabricated using standard lithography technique and etching processes. A recently developed air-assist nozzle was used to produce fine droplets of de-ionized (DI) water. Experimental results obtained indicate that the heat transfer performance is better for length scales in the 5–10 μm range than for sub-micron scales. Heat transfer coefficients in the two-phase evaporative regime were calculated by subtracting the sensible heat. Accounting for the enhancement in surface area allows for assessment of the effects of capillary wicking and thin film flow. Surfaces with bigger pillar size and larger spacing (∼20μm) exhibits greater heat transfer coefficient values due to higher permeability for wicking flow. The effect of nozzle/target spacing, porosity and liquid/air flow rates were also studied. At the highest liquid flow rate of 120 ml/min, a CHF value of 969 W/cm2 was observed, which is among the highest values documented in the literature, and suggests the potential for further enhancement at higher flow rates.

Combined experimental and numerical study on fuel deposition characteristics of an impinging PFI spray with different impingement geometries

This paper presents a combined experimental and numerical study on the fuel deposition characteristics during the Port fuel injection (PFI) spray impingement process. The numerical models mainly consisted of a newly developed atomization model, the Senda spray impingement model, and the Bai-Gosman liquid film model. A group of measurement methods were used to hierarchically calibrate and validate the numerical models. It was found that the calibrated models were able to predict the time-resolved morphology of the impinging spray, as well as the shape, area, and thickness distribution of the deposited fuel film with a good reliability. Then the calibrated models were used to study the effects of impingement distance ( Lw) and impingement angle ( θw) on the fuel film deposition. The results showed that as Lw increases, the film area ( Af) and film mass ( mf) rise faster and reach higher final values. As θw increases, Af and mf grow slower, and their final values are hugely reduced. Increasing Lw and decreasing θw can effectively reduce the average film thickness ( hf,a). Af is mainly affected by the contact area between the spray plumes and the impinging wall, while mf is also affected by the dominant droplet-wall interaction regime.

Rainwater chemistry composition in Bellsund: Sources of elements and deposition discrepancies in the coastal area (SW Spitsbergen, Svalbard)

Discrepancies in rainfall chemistry in Bellsund were found to be influenced by the orographic barrier and related to the variability in the inflow of air masses as well as to the distance of sampling sites from the sea and thus the extent of sea spray impact. This study covers measurements of rainfall (P) and air temperature (T), physicochemical parameters (pH, specific electrolytic conductivity (SEC), major ions (Cl−, NO3−, SO42−) and elements (Na, Ca, Mg,K), as well as trace elements (i.a. As, Cd, Cr, Fe, Co, Pb, Ni, Zn) and dissolved organic carbon (DOC) in 22 rainfall samples collected in August on the Calypsostranda marine terrace and in the forefield of a land-terminating glacier (NW Wedel Jarlsberg Land). The comparison of chemical parameters in the samples revealed major discrepancies, including statistically significant higher rainwater pH and SEC, and the levels of Ag, As, Bi, Ca, Co, Fe, Li, Mn, Mo, Ni, Pb, Sb, and V, deposited near the seashore (Calypsostranda) than in the glacier forefield. Cluster analysis (CA) showed that elements deposited in lower concentrations at the glacier forefield site came from predominately anthropogenic sources. Conversely, CA results of metals and metalloids deposited on the Calypsostranda marine terrace indicate both natural and anthropogenic sources. A correlation matrix and principal component analysis (PCA) permitted identifying two primary factors affecting rainfall chemistry at each of the study sites. In Calypsostranda, these were the inflow of relatively unpolluted cold air (F1 = 35.1%) and sea spray (F2 = 27.6%), while in the glacier forefield the factors were an orographic barrier (F1 = 37.3%) and the inflow of polluted warm air (F2 = 25.2%).

Modeling the impact of spray drying conditions on some Maillard reaction indicators in nano‐filtered whey

AbstractThe objective of this study was to develop a mathematical model to predict the loss of available lysine and the formation of Maillard reaction (MR) compounds in sweet whey during spray drying process. The heat damage and other spray drying process‐related variables were estimated with the compartment model coupled to the drying kinetics of droplets. The model was adequate to determine the outlet temperature of air and the final moisture content of the product. The model predicted available lysine losses like those found experimentally. However, the model predicted a higher furosine concentration than that found experimentally. The browning index exhibited no significant increase for experimental and calculated results during the spray drying, possibly because the MR did not reach the final stages. The model showed to be comparable to those reported in the literature, with the advantages of being computationally less time‐consuming and providing confidence intervals for the response variables.Practical applicationsThis work presents the integration of several mathematical models to predict the loss of available lysine and the formation of some heat damage indicators during the spray drying of whey. The model contributes to the understanding of relevant variables—such as residence time distribution, global heat transfer coefficient of the dryer, thermal properties of the drying media, glass transition temperature, drying kinetics, drying air inlet, and outlet temperature among others—on the loss of food quality regarding the thermal process. This information could help the decision‐making process that can lead to the optimization of spray drying to obtain food with minimal thermal damage and therefore the maximum amount of available nutrient content.

Effect of single and split injection on combustion process of diesel spray injected into 2D piston cavity

The flame characteristics of wall-impinging diesel fuel spray at single injection and split injection strategies were investigated in a high-temperature high-pressure constant volume combustion vessel. The 2D piston cavity has been used to form the impingement spray flame and the two-color method has been used to analyze the flame process. Results reveal that 2nd ignition delay can be defined in a specific area surrounded by single and split injections when the 1st injection proportion is from 25% to 75%. The KL factor and distribution area of a single injection are smaller than that of a split injection at EOI + 0.2 ms. The soot oxidation area is far away from the wall surface. However, the soot formation area is mainly concentrated along the cavity groove. The soot oxidation area proportion plays a decisive role in the emission of soot. The split injection interval has a key role in the soot formation dominant process at the initial stage of ignition. The initial mean flame temperature changes slightly, the mean flame temperature decreases earlier, the soot oxidation degree becomes higher, no interaction or small interaction between the 1st and 2nd injection, and the maximum degree of soot formation and oxidation dominant process occur when the 1st injection proportion equals 50%. The mean flame temperature drop time of the single injection is advanced. The total flame area and the soot formation and oxidation dominant process before and after EOI + 0.2 ms were also discussed. The total flame area of split injection is larger than single injection after EOI + 0.2 ms.

Evaluation of impingement effects on high-power diesel engine mixing process with an optimized stochastic combustion model

• The mixing-controlled combustion can be modelled by a stochastic combustion model. • The impingement is evaluated by a volume ratio between squish part and total spray. • The modeling is classified into different types according to the impinging location. • The spray impingement significantly enhances the mixing rate. Spray impingement has been proved to have remarkable influence on the mixing process, and particularly for high-power diesel engines, where the dominant diffusion combustion is mixing-controlled. Therefore, in this paper, the stochastic combustion model, which has the capability to indicate the heterogeneity of the fuel–air mixing, was optimized to account for the influence of spray impingement. The combustion chamber was divided into squish region and non-squish region, and by judging the location of the spray/wall impingement, the spray was correspondingly divided into squish part and bowl part. After that, a parameter that was defined as the volume ratio between squish part and the total spray was introduced to evaluate the influence of impingement on spray mixing rate. Finally, the optimized stochastic combustion model was validated by a single-cylinder high-power-density diesel engine to have the ability to estimate the influence of spray impingement on the mixing rate of mixture and the performance of diesel combustion with a pretty good accuracy, and the results showed that, spray impingement significantly enhanced the fuel–air mixing rate, contributed to leaner and more homogenous mixture and hence optimizing the combustion.