Spray Angle Research Articles

Influence of Spray Angle on Scratch Resistance of Cold-Sprayed SS316L Deposits.

In this study, we investigated the effect of spray angle on the microstructure, bonding quality, and scratch resistance of cold-sprayed SS316L coatings on SS304 substrates. The coatings were deposited at spray angles of 45°, 60°, 75°, and 90° using a high-pressure cold spray system. A comprehensive analysis of the relationship between the spray angle and coating properties was conducted, with a particular focus on fracture toughness and porosity. Scratch testing, combined with real-time acoustic emission monitoring, enabled the precise identification of failure mechanisms and the assessment of coating integrity. The results indicate that microhardness and porosity are significantly influenced by the spray angle. The highest microhardness was achieved at a 45° angle, while a 90° angle resulted in the lowest porosity and superior bonding due to superior normal impact velocity. Fracture toughness was found to correlate with microstructural cohesion and particle deformation. Optimizing the incidence angle improved the coating performance by balancing strain hardening and ductility, thereby reducing the risk of premature failure. These findings are particularly relevant for industrial applications, where wear resistance and high-quality bonding are critical, such as in aerospace, automotive, and marine sectors. By adjusting the spray angles, manufacturers can enhance the longevity and reliability of the coated components, thus reducing maintenance costs and improving performance. This research highlights the importance of process parameters in achieving durable, high-quality coatings and emphasizes scratch testing as an effective, sustainable, and semi-destructive evaluation method for coating integrity.

Development, Optimization, and Stability Study of a Yataprasen Film-Forming Spray for Musculoskeletal Pain Management.

Yataprasen (YTPS) remedy ethanolic spray, one of the National Thai Traditional Medicine Formulary, is extensively employed in Thai traditional healthcare to manage musculoskeletal pain and inflammation. Despite its widespread use, the quality and stability of the YTPS formulation, critical to its efficacy, safety, and patient adherence, have not been comprehensively studied. This research developed and optimized a film-forming spray (FFS) formulation of YTPS ethanolic extract and conducted a 6-month stability evaluation. The FFS shares similarities with gel formulations, particularly in its ability to form a cohesive, semi-solid film upon application, enhancing localized drug delivery and prolonged contact time. Key physicochemical properties, including density (0.8450-0.9086 g/cm3), pH (4.72-4.95), spray angle (55.58-60.10°), evaporation time (1.04-1.27 min), and theoretical film thickness (7.72-13.97 µm), were analyzed across varying storage conditions. Active components β-amyrin and stigmasterol demonstrated retention rates of 96.78% and 68.22%, respectively, under refrigerated conditions, with degradation rates accelerating at higher temperatures. Significant variations in density, spray angle, film thickness, and stigmasterol concentration were observed. Additionally, the RP-HPLC method was validated for the accurate and precise quantification of the bioactive compounds such as β-amyrin and stigmasterol, demonstrating excellent linearity within a 10-100 µg/mL range for both compounds with excellent linearity R2 > 0.999. The results confirmed that YTPS-FFS exhibits good stability and that the validated HPLC method is reliable for routine quality control. These findings supported the potential of YTPS-FFS formulation as a standardized and effective dosage form for managing musculoskeletal conditions, advancing its role in modernized traditional medicine.

Development and assessment of a novel single-drive variable angle spraying machine

Traditional sprayers are limited to applying spray mixture solely to the upper surfaces of crops. To overcome this limitation, a variable angle spraying machine (VASM) was designed using a linkage system. This machine enables the adjustment of both the spray position and angle through a single input signal, facilitating multi-directional spraying from the top to the bottom of crops. By utilizing ADAMS simulation, the relationship between input signal and output angle of spraying connecting rod was analyzed. The study employs a control variable experimental methodology alongside multiple comparison analysis to investigate various experimental factors, specifically nozzle sweep time (t), spray pump pressure (p), and distance from measurement position to surface (l). The average coverage rate observed in the top, side, and bottom orientations during actual operational conditions serves as the primary evaluation index for experimental analysis. The experimental results indicate that the VASM can achieve comprehensive spraying of crops, effectively covering both the leaf surface and the leaf underside. As the l value increases, the downward spray coverage rate (DSC) gradually rises, while the sideways spray coverage rate (SSC) gradually declines. The upward spray coverage rate (USC) initially decreases before increasing. It was observed that the DSC is lower than both the USC and the SSC due to the influence of gravity, particularly in the surface and middle layers of crops. The VASM can significantly enhance coverage of the underside and inner layers of crop leaves, thereby achieving the objectives of reducing pesticide waste and minimizing environmental pollution.

Experimental investigation on swirling annular liquid film breakup characteristics of prefilming airblast atomizer

In order to further improve the understanding of the liquid film breakup characteristics of prefilming airblast atomizer, the effects of key operating parameters and structural parameters (swirl intensity, diameter and number of injection holes on pilot stage, length of pre-film lip and sleeve angle) on the liquid film pattern of prefilming airblast atomizer were investigated using the high-speed shadow method and the Otsu’s method. The mechanism of liquid film breakage was analyzed, the results show that, with the increase of fuel injection pressure, the spray morphology experiences “columnar-shaped”, “tulip-shaped” and “fully cone-shaped”. Meanwhile, the main fluctuation frequency of liquid film varies from 100.5 Hz in the “columnar-shaped” and “tulip-shaped” to 25.12 Hz in the “fully cone-shaped”. With increasing relative pressure drops of swirler, the film breakup length and film fluctuation frequency decrease, while the film fluctuation amplitude increases. An increase in inner-stage swirl intensities will lead to a reduction in the film breakup distance, while an increase in outer-stage swirl intensities will mainly lead to a larger spray angle. The increase of the diameter and number of injection holes and the length of pre-film lip leads to the rise of the liquid film breakup length, while the decrease of sleeve angle mainly leads to the rise of spray angle, which makes the liquid film more easily broken.

The Structural Design and Analysis of the Multi Nozzle Relay Air-Jet Inserting System by Profile Reed Guiding for 3D Weaving Machine

Introduction: Based on the literature, this article designs a parameterized simulation model of a multi-layer jet weft insertion system by profiles reed guidance for a 3D loom on the PTC Creo9.0 platform, including the main supersonic nozzle, supersonic auxiliary nozzle (relay nozzle), and multi-slot profiles reed components. Method: Based on the existing basic theory, experimental results, and empirical data of turbulent jet, the parameters of the multi-layer jet weft insertion system, as well as the structural parameters and the relative positions of the main, auxiliary nozzle and profile reed components, such as the center distance of each layer's main nozzle, auxiliary nozzle spacing, auxiliary nozzle installation angle, spray direction angle, and spray angle, have been determined preliminarily. Result: Further, the basic flow field parameters, such as the supply pressure of the main and auxiliary nozzles and the shape of multi-layer profile reeds, have been determined optimally on the Virtual Prototype Collaborative Simulation Platform (PTC Creo9.0/ANSYS Workbench/Fluent 2024R1), and the rationality of the structural design also been verified; on the premise of ensuring that the airflow velocity of each layer's profiles groove meets the requirements of weft insertion, the design and simulation calculation is repeatedly modified, and the optimal structural design parameters of the multi-layer weft insertion system and nozzle is finally determined. Conclusion: To explore the feasibility of multi-layer jet weft insertion, the design of threedimensional multi-layer jet weft insertion looms has laid a theoretical foundation, laying a good foundation for the emergence and industrial manufacturing of three-dimensional multi-layer jet weft insertion looms, and providing an important reference for the innovative design of threedimensional multi-layer water jet weft insertion looms.

Effects of boundary conditions on flash boiling ammonia sprays from a twin-fluid atomizer

Ammonia is a carbon-free fuel with a high hydrogen capacity (17.8 wt%) and well-established production and distribution infrastructures, making it a viable option for decarbonized and dispatchable power. In addition, ammonia combustion in its liquid phase is preferred for simplified storage, higher energy density, and compatibility with high-pressure industrial conditions. However, ammonia fuel has drawbacks that must be addressed. This work aims to investigate experimentally the effect of the boundary conditions on the dynamics of an ammonia spray injected by a commercial twin-fluid atomizer in a chamber at room pressure and temperature. A flash boiling analysis was conducted to assess the thermodynamic conditions that promote this phenomenon and the accuracy of existing correlations to predict this transition to flash boiling. The result showed that low injection pressures and preheated atomizing flow promote the formation of bubbles and the subsequent collapse inside the atomizer, creating an unstable spray. Such instabilities are significantly reduced when the injection pressure is increased. Additionally, increasing the atomizing air flow, injection pressure, and atomizing flow temperature improves the fuel breakup, widening the spray angle. However, the spray angle decreases at a certain point, indicating that atomization is more sensitive to thermodynamic conditions than a mechanical breakup.

Influence of adjacent nozzles on flow and fuel atomization characteristics of the central nozzle in a triple-nozzle combustor

This paper examined the influence of adjacent nozzles on the flow and fuel atomization characteristics of the central nozzle in a triple-nozzle model combustor. High-frequency particle imaging velocimetry testing for airflow and phase Doppler particle analyzer testing for fuel particles were employed. Under the central nozzle air intake mode, the momentum exchange between the swirling flow and the surrounding stationary air leads to a seemingly shrinking flow field. While under the triple nozzles air intake mode, the low static pressure at the geometric center between adjacent nozzles attracts the swirling flows to converge, resulting in a larger expansion angle. Confinement has a complex impact on swirling flow. When the angle of the swirling airflow is small, it guides the flow to expand. However, when the angle becomes too large, it restricts further expansion. Observed Sauter mean diameter (SMD) peaks for the tested cases lie within a similar range, suggesting comparable spray angles. Nevertheless, the triple-nozzle air intake mode exhibits consistently higher SMD values and significantly greater spray core penetration depth. Instantaneous flow characteristics deepen the understanding of these differences in atomization results. The large range of airflow oscillation under the central nozzle air intake mode allows the airflow to directly interact with the droplets. While under the triple-nozzle air intake mode, the air flow path is too far away from the spray, resulting in that most droplets do not receive sufficient aerodynamic forces for atomization.

Morphological Modulation of Electrospun PVDF/PVP Nanofibers

ABSTRACTIn electrohydrodynamics, the regulation of the morphology and structures of electrospun nanofibers is crucial for tuning the properties of the final product. In the electrospinning process, the uniform and smooth morphology of polyvinylidene fluoride (PVDF) nanofibers can be obtained by controlling experimental parameters, environmental parameter, and system parameters. However, there is inadequate research on the effect of polymer addition on the morphology enhancement of PVDF nanofibers and the underlying mechanisms. In this study, the effects of the polyvinylpyrrolidone (PVP) molecular weight and content on various process parameters (i.e., Taylor cone length, straight fluid jet length, and spray angle) are evaluated. The obtained electrospun PVDF/PVP nanofibers were further characterized by SEM, EDS, FTIR, and XRD. The results indicate that the solution viscosity, which was controlled by varying the molecular weight and content of PVP, was linearly correlated with the process parameters. As the PVP molecular weight and content increased, the nanofiber diameter increased and the nanofiber morphology became smoother. The EDS results revealed that the nanofibers consisted of PVDF encapsulated by PVP. The FTIR and XRD results indicated that hydrogen bonding between PVP and PVDF weakened the crystallization of PVDF, leading to the formation of smooth PVDF/PVP nanofibers.

Flow Rate Determination of the Nanoflow Sheath Liquid CE-MS-Coupling Applying the nanoCEasy Interface.

In recent years, nanoflow sheath liquid (nanoSL) interfaces have been used more commonly for capillary electrophoresis-mass spectrometry (CE-MS) coupling due to their high sensitivity combined with flexibility in CE separation conditions. So far, the exact amount of sheath liquid (SL) and, thus, the dilution effect remain unknown due to the self-supplying type of the nanoSL interfaces. To quantify the SL flow rates, we present here an approach for the determination of the flow rate based on isotopically labeled standards using the nanoCEasy interface. SL and pumped CE flow are spiked with atrazine and d5-atrazine, respectively, enabling the determination of the total flow rate for different electrospray (ES) conditions. Generally, flow rates increase with higher ES voltages. Only at high ES voltages, larger emitter sizes lead to higher flow rates; for low voltages, flow rates are independent of emitter size. Additionally, smaller emitter sizes can generally be operated at lower ES voltages. Visualizing the ES, higher flow rates lead to a larger spray angle. Higher flow rates may decrease the signal intensity by diluting the CE-separated analytes. Indeed, this effect is observed for the flow-injected atrazine analytes and in the CE-MS analysis of an amino acid standard mix under aqueous acidic separation conditions. Therefore, lower flow rates are preferred for low electroosmotic flow (EOF) applications. However, in high EOF applications, higher voltages are required to prevent the accumulation of aqueous background electrolyte (BGE) at the emitter tip, which otherwise leads to peak broadening and inefficient ionization. Overall, the presented data enable the selection of stable and sensitive settings for nanoSL interfaces.

Application and extension of diesel spray theory in analysis of methanol spray characteristics under high-pressure injection conditions

Methanol has received widespread attention as a kind of alternative fuel for internal combustion engines because of its wide range of sources, low price, low combustion emission pollution, and carbon neutrality. Meanwhile, the relatively developed diesel spray theories have a great reference value to theoretical analysis of high-pressure methanol injection. Based on the optical experiment of the methanol sprays under high-pressure injection conditions, the empirical models for predicting spray tip penetration, spray angle, spray area, and spray volume of diesel were used to calculate the parameters of the methanol sprays. These calculation values were then compared with the experimental values to establish empirical models of high-pressure methanol spray characteristics. On this basis, an assessment of the adaptability of the diesel spray similarity theory applied to the high-pressure methanol sprays was conducted under similarity conditions. The results show that Wakuri's model has the best predictive performance on the methanol spray tip penetration (the average relative error is 4.31%), and Inagaki's model provides the most precise predictions on the methanol spray angle (the average relative error is 2.63%). After correcting the constants, empirical models that can describe the methanol spray characteristics in this experiment were proposed. In terms of the similarity theory, the diesel spray similarity theory shows good adaptability to the spray tip penetration and spray angle of the high-pressure methanol sprays with nozzle diameters of 0.12 ​mm and 0.15 ​mm under similarity conditions. The above results can serve as a basis for extending diesel spray theory to methanol and for the upsizing or downsizing design of direct injection methanol engines with different bore sizes of the same series.

Numerical simulation of flow and mass transport in KDP crystal growth using solution alternate jetting method

In response to the limitations of some previous crystal growth method, which cannot generate ‘back-and-forth shear flow’ in rotating-crystal method and the partial realization of ‘back-and-forth shear flow’ in the crystal two-dimensional and three-dimensional motion methods, a novel KDP crystal growth method, named solution alternate jetting method, was proposed. This method can achieve complete coverage of crystal faces with ‘back-and-forth shear flow’. Numerical simulation results indicate that solution alternate jetting method outperforms rotating-crystal growth method and crystal two-dimensional and three-dimensional motion methods in terms of time-averaged supersaturation and its standard deviation on crystal faces. The jet velocity has a significant impact on the magnitude and distribution of time-averaged supersaturation on crystal faces. Other operating conditions, including the vertical distances from the nozzle outlet to the crystal surface, alternate jetting cycle, nozzle spray angle, and special motion velocity, have a relatively minor impact. Crystals grown with less than 50% ‘back-and-forth shear flow’ in the crystal two-dimensional and three-dimensional motion methods had significantly improved quality compared to rotating-crystal growth method. Therefore, the solution alternate jetting method, capable of achieving the ideal ‘back-and-forth shear flow’, undoubtedly holds promising application prospects.

Enhancing high-density battery performance through innovative single-phase spray technology in immersion cooling systems

The flow field organization in liquid-cooled BTMS (Battery Thermal Management System) is crucial to the thermal performance of lithium-ion batteries. This study introduces an innovative single-phase spray technology to optimize the flow field and enhance thermal characteristics in BTMS. Using Computational Fluid Dynamics simulations, key factors such as dielectric fluid type, nozzle diameter, spray angle, and nozzle position are analyzed. Novec 7500 is identified as the optimal dielectric fluid, with thermal conductivity and viscosity playing significant roles. Response Surface Analysis and the entropy weight TOPSIS (Technique for Order of Preference by Similarity to the Ideal Solution) determine optimal conditions: a 0.47 mm nozzle diameter, 0 mm nozzle offset, and an 88.16° spray angle. These parameters reduce the maximum battery temperature to 25.43 °C and minimize the temperature gradient to 3.41 °C, achieving reductions of 14.20 % and 57.74 %, respectively, compared to non-spray systems. Furthermore, the system reduces the maximum temperature of a 36-cell battery module by 27.28 % to 25.33 °C and the maximum temperature difference by 69.39 % to 4.35 °C. The optimized spray cooling technology is effective for smaller battery stacks and demonstrates the potential to maintain high cooling efficiency in complex systems, providing a solution for BTMS.

FORMULATION AND CHARACTERISATION OF RISEDRONATE SODIUM SUBLINGUAL SPRAY

Objective: To formulate a propellant-free sublingual spray of Risedronate sodium, addressing issues of gastrointestinal side effects associated with current oral formulations and improving patient compliance. Methods: Initially, a fractional factorial design was used to screen variables, followed by a face-centered central composite design for optimization. Formulation batches were characterized by spray pattern, spray angle, leak test, prime test, drug delivery uniformity, drug content per spray, and ex-vivo permeation study. Results: The optimized batch O1 exhibited an ovality ratio of 1.1, a spray angle of 640, and a drug permeation percentage of 4. In vivo absorption analysis revealed that the relative bioavailability of optimized batch O1 was 2.27 times higher than that of the plain drug solution. Compatibility of the product pack with excipients and the drug was confirmed through stability studies of batch O1. Conclusion: The study concluded that Risedronate sodium sublingual spray presents a promising alternative to oral administration, potentially reducing gastrointestinal side effects and enhancing patient compliance.

Comprehensive Theoretical Formulation and Numerical Simulation of the Internal Flow in Pressure-Swirl Atomizers Type Screw-Conveyer

The present work shows the development of a comprehensive theoretical formulation for its application in the study of the internal flow of pressure-swirl atomizers with helical channels: “screw-conveyer”, which are characterized by presenting in their inlet channels, an angle of incidence or helix angle ψ. This angle originates a trigonometric factor (cosψ) that must be considered in the geometrical characteristics parameter of pressure-swirl atomizer (Ah), which consequently involves other geometric parameters, such as the annular section coefficient (φ), discharge coefficient (Cd), spray angle (2α), etc., being relevant in the internal flow study and design of the pressure-swirl atomizers type screw-conveyer. This theoretical formulation integrates an internal ideal flow model (Abramovich theory) with a model that considers the influence of the liquid viscosity (Kliachko theory) and hydraulic resistance of Idelchik. For the validation of this theoretical formulation, numerical simulation was used, considering the commercial software Ansys Fluent 2023 R2 furthermore, hexahedral meshes were generated with the ICEM CFD software 2023, for four cases of helix angle ψ (15°, 30°, 45° and 60°), with application of the RNG k-ε turbulence model and VOF multiphase model (volume of fluid) for the location of the liquid-gas interface and spray angle visualization.

A new aerosol delivery approach for enhanced long-term respiratory care in resource-poor settings

Continuous aerosol therapy is safe, superior, and the mainstay in the therapy of patients with severe asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), and coronavirus disease (COVID-19). However, continuous nebulization has been perceived as highly expensive and labor-intensive, which often requires specialized medical equipment. Moreover, it is difficult to maintain consistent aerosol output and particle size delivery over an extended period without operator intervention. This work proposes a simple and reliable continuous nebulization method using a conventional gas jet nebulizer and intravenous (IV) bottle/bag. The present work reports detailed experimental studies on a gas jet nebulizer with Particle image velocimetry (PIV), Particle/droplet Imaging Analysis (PDIA), and Mie scattering techniques to demonstrate the feasibility of the proposed technique. The preliminary investigation shows that the proposed method provides continuous liquid output delivery without external supervision. The liquid delivery rate and mass median diameter (MMD) of the nebulizer mainly depend on the gas flow rate and suction height. The MMD of the primary generated droplets is reported to vary between 100 and 230 μm for a ± 10 cm suction height and 500–1000 mlph nebulization gas flow rate. Most importantly, the nebulizer spray angle, stability, droplet size distribution, and the axial and radial velocities of the droplets are marginally affected by the suction height. Therefore, the proposed system is a versatile, safe, and cost-effective method of continuous nebulization therapy, especially in resource-poor countries or contagious disease outbreak situations.

Experimental investigation on the application of cold-mist direct evaporative cooling in data centers

The rapid development of the internet era has driven the construction of numerous data centers worldwide. In hot climate, data centers consume significant energy for cooling. Cold-mist direct evaporative cooling offers a natural cooling solution that can help reduce this energy consumption. This study investigates the temperature and relative humidity changes of natural high-temperature air after being cooled using a cold-mist direct evaporative cooling test bench. The effects of several control factors such as spray angle, spray flow rate, and air speed on the cold-mist direct evaporative cooling performance was systematically examined. The findings revealed that: (1) the optimal spray angle for cold-mist direct evaporative cooling treatment air is 65°; (2) high-temperature air between 27 °C and 37 °C can be cooled to 23.57 °C – 25.58 °C after cold-mist direct evaporative cooling treatment, with relative humidity levels of 67.0 % – 78.8 %, meeting the air supply requirements for data centers; (3) the proposed approach could reduce the data center energy consumption by 14 % – 41 %, while extending the annual natural cooling period by 3.16 % – 20.45 %.

Computationally cost-efficient analysis of the flow behavior of twin-fluid atomizers using computational fluid dynamics

In industrial-scale operations, wet electrostatic precipitators (WESPs) are used to minimize particulate matter, employing atomizers such as single-fluid and twin-fluid atomizers (TFAs). While TFAs provide several benefits over single-fluid atomizers, quantifying their spray characteristics is more complex, necessitating comprehensive case studies to design the internal structure of the spray and achieve desired properties. This study employed computational fluid dynamics (CFD) to simulate the internal and external flow phenomena of TFAs in industrial-scale WESPs, aiming to facilitate various parametric studies by reducing the high computational costs associated with analyzing high-speed internal flows and particle dynamics within the spray system. To decrease computational costs, the simulation was divided into two parts using stepwise segregated scenarios: Part I focused on the high-cost internal flow analysis, examining the spatiotemporal evolution of internal flow until it is fully developed, followed by droplet size distribution estimation at the nozzle. Part II computed the external flow of the spray, assessed potential cost reductions by examining the interactions between dispersed droplets, and validated the spray angle, penetration, and coverage against experimental data. The segregated strategy employed mapping techniques to integrate the two parts seamlessly. The simulation results closely matched the experimental benchmarks for spray angle, penetration, and coverage within a minimal error margin (< 5 %), demonstrating the model’s accuracy in capturing actual spray phenomena in TFAs. This approach significantly reduced the computational cost by more than twentyfold compared to conventional one-step solvers, offering a viable method for conducting various case studies in spray CFD simulations.

Effects of Non-Uniform Center-Flow Distribution and Cavitation on Continuous-Type Pintle Injectors

In this paper, the flow characteristics of a continuous-type liquid–liquid pintle injector are described, focusing on the differential impact of a non-uniform center-flow distribution on single- and bi-injection methodologies as well as the cavitation effect on the spray angle. Using cold-flow experiments, jet-type flows of the center propellant caused by a non-uniform flow distribution were observed during a single injection. This resulted in an augmented pressure drop, as opposed to the flow characteristics of uniform single-film injection. By contrast, bi-injection modalities exhibited a substantial reduction in the pressure drop of the center propellant, underscoring a more equitable flow distribution. Moreover, the occurrence of cavitation in the center propellant was found to markedly affect the spray angle. By considering the injection exit area reduction caused by cavitation, the spray-angle prediction accuracy increased. The findings of this study are expected to reveal the interplay between flow distribution and pressure drop as well as that between cavitation and the spray angle in pintle injectors. Through this understanding, this study provides crucial considerations for the development of more efficient propulsion systems.

Analysis of Atomization Performance of Linear Laval Nozzle under Varied Water Pressures Based on VOF and DPM Models

Particulate matter from coal and stone operations is a primary air pollution source. The traditional nozzle requires high-pressure conditions, and the atomization droplets are large and uneven. This paper aims to study a linear Laval nozzle and investigate the impact of water pressure on atomization performance. The volume of fluid (VOF) model and discrete phase model (DPM) of Fluent are used to simulate the internal and external fields of the nozzle and analyze the velocity, droplet size, and atomization angle. The results show that the optimized water pressure parameters are 0.1 MPa with an air pressure of 0.5 MPa. Droplets in the middle are smaller, while those on the sides are larger. Compared to traditional nozzles, the water pressure is reduced by over 90%, and the Sauter mean diameter (SMD) decreases by over 50%. Moreover, the theoretical spray angle increases by approximately 150%.

Numerical study on the effect of injection strategy on combustion and NO emission from different sources in a diesel/ammonia RCCI engine

Diesel/ammonia operation is one of the ways to efficiently utilize ammonia and reduce carbon emissions, however, the increase in fuel NO introduces serious emission problems. To explore the generation mechanisms of fuel NO and oxidant source NO, a multi-component diesel/ammonia chemical reaction mechanism was constructed in this study, and based on 3D CFD simulation and N-element tracking method, the combustion and different source NO emission characteristics of diesel/ammonia reactivity controlled compression ignition (RCCI) engine at low loads were investigated by pilot injection timing (SOI1) and pilot injection ratio (PIR). In addition, the effect of different first injection spray angle (SA1) and double injection spray angle (SAtotal) on the engine operation was investigated. The results showed that high PIR and delayed SOI1 enhanced the engine IMEP but led to high PRRmax. At a PIR of 15 %, total NO emissions increased as SOI1 advanced, and the trend was reversed when the PIR was higher than 15 %. Fuel NO was produced earlier than the oxidant source N∗O. In terms of 1 spatial distribution, high concentrations of both NO and N∗O were distributed in and around the secondary diesel fuel ignition location, and fuel NO began to be reduced where the oxidant source N∗O was rapidly formed. The reduction mechanism of NO in the cylinder was a multi-path reduction mechanism incorporating Thermal DeNOx, NO Reburning, and inverse reaction pathways for NO formation from the oxidant source. Appropriate reduction of the SAtotal can significantly reduce the total NO emission while maintaining no significant reduction in IMEP. When SAtotal was 82°, the total NO emission was only 16.3 % of the original spray angle and PRRmax was further reduced. After optimization, when a narrow SAtotal of 82°, SOI1 of −15° CA, and PIR of 35 % were used, the IMEP of the engine increased by 5.9 %, and the total NO emission was reduced by 86 %, while PRRmax did not exceed the PRR upper limit.