Spray Atomization Model Research Articles

Numerical simulation of primary break-up and atomization: DNS and modelling study

This work deals with numerical simulations of atomization with high Weber and Reynolds values. A special attention has been devoted to the modelling of primary break-up. Due to progress of direct numerical simulations (DNS) of two phase flows it is now possible to simulate the primary break-up of a Diesel spray [Menard, T., Tanguy, S., Berlemont, A., 2007. Coupling level set/VOF/ghost fluid methods: validation and application to 3D simulation of the primary break-up of a liquid jet. Int. J. Multiphase Flow 33 (5), 510–524]. The present formulation of the so-called ELSA (Eulerian–Lagrangian Spray Atomization model) [Vallet, A., Borghi, R., 1999. Modélisation Eulerienne de L’atomisation d’un Jet Liquide. C. R. Acad. Sci. Paris Sér. II b 327, 1015–1020] for atomization is presented and evaluated in the dense zone of the spray by comparison to a DNS based on a coupled level set/VOF/ghost fluid method. Once constants and parameters of the model are fixed thanks to comparisons with DNS, the model is tested with experimental data. The liquid and vapour penetrations show a good agreement when they are compared to experiments of Diesel atomization. In particular the influence of the gas temperature is well recovered. For different temperatures, similarly to the experiments, vapour penetrations are unchanged, but the corresponding equivalent ratio fields are strongly modified. Finally, the combustion model ECFM-3Z [Colin, O., Benkenida, A., 2004. The 3-zones extended coherent flame model (ecfm-3z) for computing premixed/diffusion combustion. Oil Gas Sci. Technol. 59 (6) 593–609] is joined to the ELSA model and the effect of gas temperature changes on a Diesel spray flame is reproduced.

Measurement and Prediction of Atomization Parameters from Fixed-Wing Aircraft Spray Nozzles

A survey of spray nozzles used by the agricultural aviation industry identified nozzles and operating conditions that were most commonly used in applying agricultural chemicals in the U.S. Eleven hydraulic nozzles and their typical range of operating conditions were selected from the survey. These eleven nozzles were subjects of a research program to develop spray atomization models that would be easy for aerial applicators to use in adjusting operations to control spray drift from aerial agricultural sprays. Each nozzle was conducted through a series of trials in a spray nozzle test facility equipped with a laser spectrometer to develop a data set for atomization model development. Computer spreadsheet models were developed from the data set with operator selection of a specific spray nozzle and inputs of nozzle orifice size, spray discharge angle, spray pressure, and aircraft airspeed. The model outputs included droplet size parameters, drift potential parameters, and droplet spectra classification. Aircraft speed was the dominating factor influencing atomization from most of the spray nozzle models. Validation studies showed that the models gave useful estimates of the computed parameters for estimating compliance with product label and state regulatory agency requirements for spray drift mediation. The models are available on-line and in a user handbook as well as in the current technical presentation.

CFD prototyping of an air-assisted orchard sprayer aimed at drift reduction

The environmental contamination due to off-target deposition of pesticide droplets can be minimized by using optimum design and operating parameters of sprayers. A three-dimensional computational fluid dynamics (CFD) model was developed and used to evaluate concepts of boom sprayer setup to orchard spraying to reduce drift without a decrease in biological efficacy. To track the path of the droplets, a Lagrangian particle tracking multiphase flow model was used, combined with spray atomization models and taking into account the velocity variation at the fan outlet. The studied sprayer settings included: sprayer ground speed, fan speed (air jet velocity), number, type, size, position and orientation of nozzles and liquid pressure. To account for the speed of the tractor, a moving coordinate system was implemented. For the boom sprayer setup, nozzles were employed that produce a flat fan spray pattern (110° Turbo Teejet and 85° Teejet off-centre air induction nozzles). Boom-type spraying was compared to conventional orchard spraying using 80° hollow cone nozzles. There was a good similarity between the vertical spray distribution profile patterns produced from the boom and orchard sprayer setups; however, the boom sprayer setup produced lower droplet concentration to the highest positions and could therefore offer possibilities for drift reduction at long distance, while providing good coverage at a short range. There was a good agreement between measured and predicted vertical spray distribution patterns.

Development of a Diesel Spray Atomization Model Considering Nozzle Flow Characteristics

Development of a Diesel Spray Atomization Model Considering Nozzle Flow Characteristics

Multidimensional Modeling of Diesel Ignition and Combustion Using a Multistep Kinetics Model

Ignition and combustion mechanisms in diesel engines were studied using the KIVA code, with modifications to the combustion, heat transfer, crevice flow, and spray models. A laminar-and-turbulent characteristic-time combustion model that has been used successfully for spark-ignited engine studies was extended to allow predictions of ignition and combustion in diesel engines. A more accurate prediction of ignition delay was achieved by using a multistep chemical kinetics model. The Shell knock model was implemented for this purpose and was found to be capable of predicting successfully the autoignition of homogeneous mixtures in a rapid compression machine and diesel spray ignition under engine conditions. The physical significance of the model parameters is discussed and the sensitivity of results to the model constants is assessed. The ignition kinetics model was also applied to simulate the ignition process in a Cummins diesel engine. The post-ignition combustion was simulated using both a single-step Arrhenius kinetics model and also the characteristic-time model to account for the energy release during the mixing-controlled combustion phase. The present model differs from that used in earlier multidimensional computations of diesel ignition in that it also includes state-of-the-art turbulence and spray atomization models. In addition, in this study the model predictions are compared to engine data. It is found that good levels of agreement with the experimental data are obtained using the multistep chemical kinetics model for diesel ignition modeling. However, further study is needed of the effects of turbulent mixing on post-ignition combustion.