Spray Images Research Articles

Investigation of in-nozzle flow behavior coupled with spray characteristics of waste cooking oil and castor biodiesel

Biodiesel is a promising alternative to conventional diesel. However, it may cause reduced mass flow, higher injector deposits and poor atomization. This study presents the numerical investigation of the effect of in-nozzle flow on fuel spray behavior for castor methyl ester (CME20) and waste cooking oil methyl ester (WCME20) using two different nozzle hole sizes. Two step simulation methodology was adopted where flow inside the nozzle was simulated first, mass flow rate and velocities at nozzle outlet were used as an input for analyzing the fuel spray in a closed vessel. These simulated results of fuel spray were also validated with experimental results from the captured spray images from control volume spray vessel (CVSV). Experimental spray results were also investigated based on light intensity level and macroscopic spray properties. Results revealed higher cavitation intensity for diesel than biodiesel fuels. Smaller nozzle hole (N2) is more likely to cavitate as compared to larger nozzle diameter (N1). In terms of spray behavior, N1 nozzle on average showed longer penetration length (+1.95 %), wider spray cone angle (+6.2 %) and larger drop diameter (+3.1 %) in comparison to N2. CME20, due to its increased viscosity and density showed longer penetration length (+5.9 %), narrower spray cone angle (−21 %) and reduced spray projected area (−19 %) with respect to diesel. WCME20 revealed smaller sauter mean diameter (−4.8 %) as compared to CME20 owing to its lower viscosity.

Flowering Index Intelligent Detection of Spray Rose Cut Flowers Using an Improved YOLOv5s Model

Addressing the current reliance on manual sorting and grading of spray rose cut flowers, this paper proposed an improved YOLOv5s model for intelligent recognition and grading detection of rose color series and flowering index of spray rose cut flowers. By incorporating small-scale anchor boxes and small object feature output, the model enhanced the annotation accuracy and the detection precision for occluded rose flowers. Additionally, a convolutional block attention module attention mechanism was integrated into the original network structure to improve the model’s feature extraction capability. The WIoU loss function was employed in place of the original CIoU loss function to increase the precision of the model’s post-detection processing. Test results indicated that for two types of spray rose cut flowers, Orange Bubbles and Yellow Bubbles, the improved YOLOv5s model achieved an accuracy and recall improvement of 10.2% and 20.0%, respectively. For randomly collected images of spray rose bouquets, the model maintained a detection accuracy of 95% at a confidence threshold of 0.8.

Spray inoculation and image analysis-based quantification of powdery mildew disease severity on pea leaves

Pea (Pisum sativum) is an important agricultural legume crop, but powdery mildew disease caused by the biotrophic fungus Erysiphe pisi regularly limits its annual yield. Assays to evaluate the efficacy of potential antifungal compounds or resistance genes for disease control require a simple fungal inoculation method that provides control over the initial inoculum concentration and enables uniform inoculum distribution within a leaf and across replicates as well as a method for the quantitative assessment of disease severity. Here, we present an easy spray inoculation method for the uniform distribution of a defined concentration of E. pisi conidia on the leaves of pea plants and a semi-automated image analysis-based quantification of disease symptoms. The uniformity in conidial distribution was validated using a novel grading system termed the uniformity index. In addition, RT-qPCR was used to validate the reproducibility of the spray inoculation method and image analysis-based disease quantification. These procedures permit the accurate quantification of powdery mildew disease severity at macroscopic and molecular levels.•Uniform and reproducible inoculum distribution on leaves using a simple and inexpensive spray device•Rapid and reproducible quantification of powdery mildew disease symptoms using open-source software without the requirement of computational expertise

Shadowgraph tomography of a high-pressure GDI spray

An isooctane spray from a high-pressure multihole GDI injector (Bosch HDEV6) was characterised by means of optical extinction tomography, relying on collimated illumination by a focused shadowgraph setup. The tests were carried out in air under ambient conditions at an injection pressure of 300 bar. Spray images were acquired over a 180-degree angular range in 1-degree increments. The critical issues of optical extinction tomography of sprays, related to the strong light extinction by the dense liquid core of fuel jets, were addressed. To mitigate artefacts arising from the reconstruction process, the extinction data were subjected to spatially-variant filtering steps for both raw and post-log data before being analytically inverted through the inverse Radon transform. This approach made it possible to process extinction data at very large optical depths. A nearly complete three-dimensional reconstruction of the spray was obtained, providing significant details of the spray morphology and the internal structure of the jets throughout spray development. Different phases of the atomization process, from the near-field to the far-field regions of the spray, were observed.

Experimental study on the penetration and evaporation characteristics of a liquid kerosene jet in the supersonic crossflow

The penetration and evaporation characteristics of a liquid kerosene jet in the supersonic crossflow were experimentally investigated in this study. The experiments were carried out in both cold and high-enthalpy inflows. Detailed spray images were obtained using planar laser scattering techniques. The structures of the spray field were further analyzed on the basis of high spatial and temporal resolution images. The results show that the atomization and evaporation characteristics of a liquid kerosene jet are related to the crossflow temperature, liquid–gas momentum flux ratio, and injection distance. It is found that the breakup process of a liquid jet is accelerated in the high-enthalpy inflow. To accurately describe the maximum flow distance along the direction that kerosene can reach in the state of droplets, the survival distance is defined. It is revealed that the penetration depth and survival distance of the liquid kerosene jet decrease clearly with increase in the crossflow temperature. For the cavity-based combustor, the liquid kerosene jet can mix more sufficiently in the cavity region by reducing the injection distance and liquid–gas momentum flux ratio.

Spray characteristics of different regions downstream of a swirl cup

The spray characteristics of different regions downstream of swirl cups play a critical role in cold start and re-ignition of gas turbines. The spray measurements were performed at the fuel pressures of 0.5, 0.8, 1.0, 1.5, and 2.0 MPa and the fuel temperatures of −23, −13, −3, 7, 17 and 27 ℃, respectively. The droplet size, droplet velocity, droplet number, and instantaneous spatial spray image of sprays from an aviation kerosene Jet-A were measured using a two-component phase Doppler particle analyzer and a digital off-axis holography system. As the fuel pressure and temperature increase, the Sauter Mean Diameter (SMD) and spray non-uniformity of the Spray Shear Layer (SSL) gradually decrease. As the fuel pressure increases, the SMD and spray non-uniformity of the Central Toroidal Recirculation Zone (CTRZ) gradually decrease, and the slopes of these curves both decrease. As the fuel pressure increases, the SMD and spray non-uniformity of the CTRZ rapidly decrease at the fuel temperature of −23 ℃, while slightly decrease at the fuel temperature of 27 ℃. The droplets in the CTRZ come from 3 different sources: simplex nozzle, venturi, and outside the CTRZ. As the fuel pressure increases, the proportion of droplets recirculated from outside the CTRZ decreases. This study proposed the concept of the “pressure critical point” for the swirl cups. As the fuel temperature decreases, the proportion of droplets recirculated from outside the CTRZ increases below the critical pressure, while decreases above the critical pressure. In addition, through the models of liquid film formation and breakup on the curved cylindrical wall, a semi-theoretical model was established to predict the SMD of SSL for swirl cups. The prediction uncertainty of this model is less than 6% for all 14 conditions in this paper.

Flow field reconstruction from spray imaging: A hybrid physics-based and machine learning approach based on two-phase fluorescence particle image velocimetry measurements

The interaction between liquid spray and the surrounding air is crucial in fluid research, especially in the study of fuel spray and combustion. However, the fuel spray–air interaction is a complex process influenced by multiple factors, including fuel type, fuel injection pressure, and fuel temperature. These factors are coupled together, making it challenging and time-consuming to accurately capture the spray–air data using traditional experimental methods alone. The current study proposes a hybrid physics-based and machine learning model for utilizing spray images to reconstruct ambient flow fields. The novelty of this work lies in leveraging the spatial characteristics of spray and airflow data to optimize feature extraction and reduce unnecessary nonlinearity in the model. Consequently, the model offers complementary advantages, improving model interpretability and reducing its reliance on massive data. The training dataset is collected using a combined diagnostic approach, utilizing Mie-scattering imaging and fluorescence particle image velocimetry. The liquid spray and the ambient air velocity field are measured simultaneously under a wide range of experimental conditions, including different fuel types, fuel injection pressures, and fuel temperatures. The reconstruction results are validated against unseen experimental data. In general, the reconstruction results indicate that the model is accurate, fast, and robust for different fuel conditions and injector types. It provides an innovative way to reconstruct airflow fields based on spray images (spray density distribution). These findings highlight the potential of integrating physics-based and machine learning methods for multiphase flow diagnostics, paving the way for broader data-driven applications in fluid research.

Drone-mounted remote-controlled arm for monitoring and precision spraying coconut rhinoceros beetle infestations

This paper presents a low-cost (locally-assembled) drone system with a sprayer arm and a remote control for monitoring and precisely applying pesticides to coconut trees infested by the Rhinoceros Beetle. A modified RGB IP camera continuously monitors potential coconut beetle infestation points, capturing real-time spray images, and displaying the results through a smartphone interface. The system provides real-time monitoring, allowing immediate remote control of the spray operation from the ground upon detecting beetle infestations. The drone-mounted sprayer arm is controlled in response to the ground-based signals, to accurately extend or contract while effectively dispensing spray chemicals onto the target areas at the upper canopy of coconut trees. In our tests using Nam-Hom coconut trees, which averaged a height of 10.4 m, the system operated at a speed of 1.25 km/h, achieving a spraying flow rate of 0.333 l/h and a working capacity of 0.352 ha/h. The controlled spraying setup emits a solid jet, ensuring precision and effective atomization of chemicals within a distance range of 1.0 to 4.0 m from the target. The spray quality attributes (droplet size, pattern, and coverage) were not significantly affected by the wind speed. The system could potentially reduce labor costs, chemical usage, and health risks associated with pesticide application.

The Effect of Water Injection on a Naturally Aspirated Spark-Ignited Engine

Water injection (WI) is a well-known technique to mitigate knocking phenomena, reducing the in-cylinder gas temperature with a high heat of vaporization and specific heat of water. In this study, the effect of WI directly into the cylinder on fuel efficiency was investigated using a 2.0 L naturally aspirated (NA), four-cylinder, port fuel injection (PFI)-spark-ignited (SI) engine. Spray visualization of water injection by a commercial gasoline direct-injection (GDI) injector was performed to elucidate the water evaporation characteristics. In engine experiments, combustion characteristics were analyzed by adjusting the WI timing and amount. Synergistic effects with other gas dilution techniques, such as EGR and Lean burn, were also investigated. The spray image of WI showed poor evaporation of water compared to gasoline, even at high fuel temperatures. The optimal timing of WI was advanced up to the early intake stroke due to the harsh conditions of NA engines for water evaporation compared to turbocharged engines. With the combination of EGR, the optimal WI timing was advanced by the compression stroke, and further fuel efficiency improvement was achieved. In lean combustion, WI can improve both combustion stability and fuel efficiency.

Interpreting Image Patterns for Agricultural Sprays Using Statistics and Machine Learning Techniques

The atomization of liquid spray solutions through nozzles is a mechanism for delivering many pesticides to the target. The smallest drop sizes (<150 μm) are known as driftable fines and have a propensity for wind-induced convection. Many agricultural applications include oil-in-water formulations. The experimental metrics obtained from spray images of these formulations include the distance from the nozzle origin to the drop centroid once a drop has formed; the hole location and surface area for holes that form in the liquid sheet (all hole areas approximated as polygons); the angles formed between polygon segments (whose vertices are represented as boundary points); and the ligament dimensions that form from intersecting holes, such as the ligament aspect ratio (R/L), ligament length (L), and ligament radius (width), along with the number of drops a ligament breaks up into. These metrics were used in a principal component regression (PCR) analysis, and the results illustrated that 99% of the variability in the response variable (DT10) was addressed by 10 principal components. Angles formed by the colliding holes, hole distance from the nozzle, drop distance, hole number, ligament number, and drop number were negatively correlated to the atomization driftable fine fraction, while hole area, ligament distance, ligament area, and boundary area were positively correlated. Thus, to decrease/minimize driftable fines, one needs to increase the negatively correlated metrics.

Ethanol Inhomogeneous Lean Combustion Under Different Ambient Temperatures and Pressures with Hydrogen Enrichment

ABSTRACT The effects of different ambient temperatures and pressures on the combustion of hydrogen-enriched liquid ethanol spray were studied in a constant-volume vessel, using experimental and numerical methods. The inhomogeneous combustion experiment was conducted under ultra-lean conditions at an overall equivalence ratio of 0.3 (33% spray ethanol/67% premixed hydrogen). The spray and flame images and combustion pressures were obtained. The spray simulation models used were the RANS k-ε turbulence model, KH-RT model, and wall film interaction model. The experimental results showed that the inhomogeneous combustion of the liquid ethanol spray can be divided into two stages: a rapid-burning and a slow-burning stage. The slow-burning stage was sensitive to changes in ambient temperature and pressure. Combustion duration decreased with elevated pressure and declined temperature. Under low pressure and medium temperature conditions, the flame reached its fastest propagation speed. The simulation results showed that the fuel concentration and concentration gradient around the ignition position are the key factors that affect inhomogeneous lean combustion. When the equivalence ratio was over 0.8 around the ignition position and the gradient of the equivalence ratio increased no less than 0.1/mm, the optimal combustion characteristics were achieved.

A comparative analysis of internal flow and spray characteristics in triangular orifices with diesel and biodiesel

This paper presents an inquiry into the internal flow and spray behavior of diesel and biodiesel in a triangular orifice, using experimental and numerical methods. The inner flow was analyzed through the implementation of Large Eddy Simulation model. Furthermore, two high-speed cameras were utilized to capture spray images of the major and minor axes of the triangle-shaped nozzle simultaneously. The investigation revealed that, in comparison to diesel, biodiesel exhibited a higher discharge coefficient. Additionally, the vorticity magnitudes and turbulence vortex structures for biodiesel were consistently lower than those for diesel. The use of biodiesel can hinder the occurrence of cavitation. Moreover, it was observed that the triangular spray cone angle displayed axis-switching phenomena for both fuels. The axis-switching phenomenon is suppressed by using biodiesel. The research also discovered that the triangular biodiesel spray has a longer spray tip penetration and a smaller angle in all view planes. This could be attributed to the higher viscosity and surface tension of biodiesel, as well as the inhibition of the spray axis-switching during the injection, leading to an increase in the spray tip penetration and a decrease in the spray cone angle for biodiesel.

Spray Characteristics Analysis of Fire Sprinkler Spray with Image Processing

Sprinkler systems are effective in suppressing fires during their initial stages. The ability of a sprinkler to suppress a fire is contingent on the density, size, and velocity of the droplets it emits. In this study, a high-speed camera was employed to measure the size and velocity of droplets generated by a sprinkler head with a K-factor of 80. To capture images of the sprinkler spray, two acrylic partitions were placed 3 cm apart, with the sprinkler head positioned in the center. A light source was positioned behind the spray, and images were recorded at a resolution of 1024 × 1024 pixels and a speed of 4000 fps. During the image processing phase, bounding circles were drawn using the mean of the major and minor axes of the droplets, and these circles were used to calculate the diameter, velocity, and momentum of the droplets. It was observed that smaller droplets were predominantly present closer to the sprinkler head, while larger droplets were more prevalent in regions farther away. The larger droplets exhibited higher velocities and momentum. As the vertical distance increased, droplet velocity and momentum also increased, primarily due to the influence of gravity.

Experimental Investigation on Cross-Impingement Characteristics Under Various Biodiesel-Butanol Blended Proportions and Ambient Conditions

Abstract The cross-impingement phenomenon always appears in several diesel engines with two or more injectors. Meanwhile, the application of biofuels has a great potential in realizing clean and efficient combustion. Therefore, the investigation aims to explore the cross-impingement characteristics at small (10%), middle (30%), and large (50%) biodiesel-butanol blended proportions. Experiments are conducted in a constant-volume combustion chamber with twin injectors. Spray images are captured by optical diagnosis techniques. Several macroscopic parameters are obtained, including diffusion length, collision width, and spray area. Results show that the cross-impingement accelerates the droplet interaction, and the spray presents a “fan-shaped” behavior after the collision, which promotes a more uniform mixing between the fuel and ambient gas. As the twin sprays collide at 120 deg, the vapor-phase vertical diffusion rate is close to the vertical component of the single spray, and the horizontal diffusion rate is about 1.2 times the vertical diffusion rate. The cross-impingement is likely to decrease the spray-wall impingement owing to a change in the diffusion direction. At various blended fuels, the biodiesel blended with 30% n-butanol displays the smallest liquid-phase diffusion length, width, and area. The further increase in the n-butanol mixing ratio leads to larger liquid-phase parameters. Contrary to the biodiesel blended with 10% n-butanol, the biodiesel blended with a higher proportion of n-butanol presents faster vapor-phase diffusion, which promotes fuel-gas mixing.

Effect of atomizer and cross-flows on liquid and gelled Jet A-1 fuel injection

The current study aims to experimentally investigate the effect of atomizer and cross-flow velocities on liquid and gelled Jet A-1 fuels. For gelled Jet A-1, Jet A-1 liquid, Thixatrol® ST and rectified xylene are the base fuel, gellant and solvent, respectively. Gelled Jet A-1 is prepared by adding 85% by weight of base fuel along with 7.5% by weight of gellant and solvent, each at optimum processing conditions. Atomization using a simple-plain-orifice atomizer is investigated to understand its effect on Jet A-1 gel fuel break-up without air cross-flow. Based on the investigation from qualitative flow visualization and quantitative analysis of Jet A-1 gel fuel break-up, a modified simple-plain-orifice atomizer called an internally impinging air-blast atomizer is made. Primary atomization using this new atomizer is studied to understand the break-up of liquid and gelled Jet A-1 gel fuels without any air cross-flow. Secondary atomization of liquid and gel fuel is investigated by transversely injecting fuel into different low-speed subsonic air cross-flow environments. Laser sheet Imaging (LSI) technique is used to capture spray images of both fuels. Break-up mechanisms of both liquid and gel fuels were observed, and the results were compared. Information on the cross-flow air mass flow rate effect on the liquid and gel spray is extracted by developing an algorithm in MATLAB using an image processing tool. Relative droplet size distribution of liquid and gel spray revealed their dependence on cross-flow air mass flow rate. Total droplet count of both liquid and gel fuel decreases significantly as the cross-flow Reynolds’ number increases. At higher cross-flow Reynolds’ number, gel droplets in the flow are observed to be more as compared to liquid fuel.

Experimental investigation of the combined impact of backpressure with the pintle dynamic on the hydrogen spray exiting a medium pressure DI outward-opening injector

A vast scientific literature has shed light on hydrogen as a promising vector for carbon-free mobility. Within this scope, over the last few decades several efforts were directed towards the characterization of hydrogen spray, given its significant influence on the combustion efficiency. Nevertheless, several aspects underlying the hydrogen spray development are still far from being fully understood. This framework prompted the authors to undertake a robust experimental campaign, performing hydrogen injections over a wide range of injection settings. In this study, the schlieren method was utilized to capture the image of jets performed at injection pressure of 3.6 MPa and exiting an outward-opening injector. Afterwards, the spray images were processed by means of an in-home developed Matlab script. In order to assess the spray characteristics, such as the penetration length, area and volume, the analysis of the results was focused on the combined impact of backpressure, ranging from 0.12 to 1.5 MPa, with current profile determining the pintle dynamic. Besides, a qualitative analysis of the injection setting impact on the shock wave position was carried out. In the light of emerged findings, the research serves as a further baseline for forthcoming research activities dealing with hydrogen spray.

Unconventional gasoline spray injection events: Compared evolution of experimental data and numerical simulations

The current homologation standards in the automotive field impose the manufacturers to develop very efficient and clean engines. Low-Temperature Combustion engines have the potential to simultaneously reduce all the pollutants released while maintaining high efficiency. Among them, in Gasoline Compression Ignition (GCI) combustion technology, multiple injections allow to generate a tailored stratified charge which can auto ignite limiting the rough Pressure Rise Rate (PRR) and heat release rate typical of GCI. Therefore, the three-dimensional local distribution of the mixture becomes the key-point which the engine performance depends on. Due to emphasis on the multi-dimensional and local nature of the mixture formation phenomenon, three-dimensional CFD simulations are a promising and attractive method aiming at the design of the injection event features (timing, pattern, etc.). This paper deals with both experimental and CFD campaign on the evolution of a gasoline spray at ultra high-pressure multiple injection as well as high backpressure, typical of Gasoline Compression Ignition engines. The experimental tests have been conducted on a reference Diesel Common-Rail injector which shots in a constant-volume chamber. The hydraulic behaviour of the injector was characterized by means of the Bosch Tube principle whilst the Mie-scattering technique was used to capture the spray images. The numerical methodology is required to predict the Liquid Length Penetration and the jet morphology features (shape, area). Both experiments and simulations were conducted at different values of injection pressure (350, 500, 700 bar), back pressure (1–8 bar), energizing time (350, 600 µs), according to the operations of a real reference GCI test engine. Furthermore, a dedicated sub-model which takes into consideration the effect of the spray dynamics during the injection transient opening stage has been validated. The importance of this approach when dealing with short energizing time (e.g. 350 μs) is shown.Comparing both the experimental and numerical results, the model has proven to efficiently reproduce the spray penetration and morphology features, also under the hypothesis of injector ballistic phase operations, whose determination is crucial in the early development and sustainability of such combustion concept.

In searching of optimum electrospray ionization using both spray image and electric current measurement

Electrospray image and spray electric current measurement were used to experimentally characterize the optimum operating condition of the electrospray ionization process under different operating conditions, including electrospray flow rate (Q), solution electric conductivity (k) and the organic solvent content in the sample solution (Ro). It was first observed that a special cone-jet mode electrospray with extremely high stability could be obtained when the electrospray voltage was operated in a specific range (the optimum voltage range). In this mode, the spray current remains independent of spray voltage and the angle of electrospray (the optimum spray angle) was much larger than the ones in other modes of electrospray. The experimental results also showed that the optimum voltage range was dependent on multiple factors. The average value of the optimum voltage range (the optimum voltage) increased slightly as Q was increased and decreased significantly as Ro was increased. In addition, the optimum voltage would increase initially with the increase of k and become essentially independent of k at a sufficiently high solution electric conductivity. In contrast to a rather complicated parametric dependence of the optimum voltage range, the optimum spray angle was found to only depend on Q. It would increase initially as the increase of Q and remain to be constant when Q was higher than a specific value. The experimental results in this study allow one to maintain an optimum electrospray ionization under different operating conditions as required by the actual method of mass spectrometry analysis.

The effects of sub/supercritical conditions on the spray interface characteristics of alkane fuel

ABSTRACT Alkane fuels are widely used in engines. The spray characteristics in supercritical environments are very different than in subcritical environments, and supercritical environments significantly impact the formation of the gas mixture in the engine. In this paper, the spray images of n-heptane and n-tetradecane in subcritical (500K-2MPa) and supercritical (700K-4MPa, 800K-6MPa) environments were obtained on the constant volume spray test platform. The effects of the supercritical environment and carbon chain length of alkane fuel on spray characteristic parameters were investigated. The results showed that the carbon chain length and ambient pressure are the main factors of penetration. The ambient pressure is the main factor of the spray cone angle and the spray non-liquid layer thickness. Compared with n-heptane, in the 500K-2MPa (subcritical) environment, the cone angle of n-tetradecane was reduced by 2°, the penetration was increased by 10 mm, and the spray non-liquid layer thickness was reduced by about 1 mm. In the 800K-6MPa (supercritical) environment, the cone angle of n-tetradecane was increased by 2°, the penetration was increased by 10 mm, and the spray non-liquid layer thickness was increased by about 1.2 mm. In addition, the calculation model of alkane fuel spray penetration in sub/supercritical environments was modified and achieved 95% prediction accuracy.

Experimental investigation on collision characteristics of dual-spray with different physical-chemical fuel properties: A case study of butanol-biodiesel fuel combination

The dual direct injection strategy can flexibly control the reactivity distributions and equivalence ratio, which shows a great potential in realizing clean and efficient combustion. However, the sprays’ collision is inevitable when the fuel sprays are injected into the combustion chamber simultaneously owing to limited in-cylinder space, which is rarely investigated. The investigation aims to explore the atomization and combustion characteristics of collision between biodiesel and butanol sprays at different injection delay times of biodiesel (0, 0.5, 1, 1.5, 2 ms). Experiments are conducted in a constant volume combustion chamber. The collision spray and combustion images are captured by optical diagnosis techniques. Several macroscopic parameters are obtained, including spray behavior, spray area, ignition delay, ignition location, flame behavior, flame lift-off length, and natural luminosity intensity. Results show that the variation of injection delay time can effectively change the spray distribution and realize the concentration stratification. The liquid-phase diffusion region increases with an increased premixed charge of butanol spray, but the total evaporation time has a tiny difference. The sprays’ collision can promote the ignition process, but the ignition location is slightly affected by the injection delay time of biodiesel. A trade-off relationship between the vapor-phase diffusion area and combustion characteristics is found. When the injection delay time exceeds 0.5 ms, a longer injection delay time can lead to a larger vapor-phase area, which causes smaller equivalent ratio, longer flame-off length, and lower luminosity intensity. However, a longer injection delay would lead to an uncomplete combustion of the n-butanol spray. At the experimental cases, the injection delay time of biodiesel should be 1/2–2/3 injection duration to realize complete combustion and small emissions.