{"title":"Modeling and investigating the fuel heating in injector nozzle hole under action of pressure drop and viscous friction","authors":"","doi":"10.1016/j.ijthermalsci.2024.109296","DOIUrl":null,"url":null,"abstract":"<div><p>Due to the high pressure difference during injection, the fuel in the nozzle hole of common rail injectors is accompanied by significant temperature changes, which has an important impact on the injection characteristics of the injector and the combustion performance in the engine cylinder. In this paper, a mathematical model of fuel heating in nozzle hole is proposed considering the combined effect of pressure drop and viscous friction, and the calculation accuracy of the model is verified based on the experimental data in the literature. The transformation characteristics of fuel heating and cooling under different discharge coefficients <em>C</em><sub>d</sub> of nozzle hole are analyzed, and the influence and mechanism of fuel type and nozzle hole structure parameters on fuel temperature increase in nozzle hole are studied. The result demonstrates that a large pressure drop is formed at the inlet of the nozzle hole, and the fuel may be cooled in this pressure drop area; as the high-speed flowing fuel passes through the nozzle hole, viscous friction causes the fuel to be heated, the fuel heating or cooling state at the nozzle hole outlet depends on the balance between frictional heating and cooling at the inlet. In the case of small <em>C</em><sub>d</sub>, the fuel in the nozzle hole is heated. There is a critical flow coefficient <em>C</em><sub>d-crit</sub>, and the fuel transitions from being heated to being cooled once <em>C</em><sub>d</sub> surpasses this critical value. The value of critical discharge coefficient increases with the increase of injection pressure difference, which shows that the fuel in the nozzle hole is more easily heated under higher injection pressure. The degree of fuel heating and cooling is related to both <em>C</em><sub>d</sub> and the injection pressure difference. Within the range of <em>C</em><sub>d</sub> from 0.55 to 0.95 and injection pressure difference from 80 MPa to 200 MPa, the maximum temperature increase and drop at the outlet cross-section of the nozzle hole can reach up to 65 K and −4 K, respectively. As the diameter or length of the nozzle hole decreases, the fuel temperature increase at the hole outlet increases, and the structural parameters of the nozzle hole have a more significant impact on fuel heating at higher injection pressure differences. Compared with winter diesel, standard fuel ISO 4113 has a more significant heating in the nozzle hole due to different physical properties.</p></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":null,"pages":null},"PeriodicalIF":4.9000,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Thermal Sciences","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1290072924004186","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, MECHANICAL","Score":null,"Total":0}
引用次数: 0
Abstract
Due to the high pressure difference during injection, the fuel in the nozzle hole of common rail injectors is accompanied by significant temperature changes, which has an important impact on the injection characteristics of the injector and the combustion performance in the engine cylinder. In this paper, a mathematical model of fuel heating in nozzle hole is proposed considering the combined effect of pressure drop and viscous friction, and the calculation accuracy of the model is verified based on the experimental data in the literature. The transformation characteristics of fuel heating and cooling under different discharge coefficients Cd of nozzle hole are analyzed, and the influence and mechanism of fuel type and nozzle hole structure parameters on fuel temperature increase in nozzle hole are studied. The result demonstrates that a large pressure drop is formed at the inlet of the nozzle hole, and the fuel may be cooled in this pressure drop area; as the high-speed flowing fuel passes through the nozzle hole, viscous friction causes the fuel to be heated, the fuel heating or cooling state at the nozzle hole outlet depends on the balance between frictional heating and cooling at the inlet. In the case of small Cd, the fuel in the nozzle hole is heated. There is a critical flow coefficient Cd-crit, and the fuel transitions from being heated to being cooled once Cd surpasses this critical value. The value of critical discharge coefficient increases with the increase of injection pressure difference, which shows that the fuel in the nozzle hole is more easily heated under higher injection pressure. The degree of fuel heating and cooling is related to both Cd and the injection pressure difference. Within the range of Cd from 0.55 to 0.95 and injection pressure difference from 80 MPa to 200 MPa, the maximum temperature increase and drop at the outlet cross-section of the nozzle hole can reach up to 65 K and −4 K, respectively. As the diameter or length of the nozzle hole decreases, the fuel temperature increase at the hole outlet increases, and the structural parameters of the nozzle hole have a more significant impact on fuel heating at higher injection pressure differences. Compared with winter diesel, standard fuel ISO 4113 has a more significant heating in the nozzle hole due to different physical properties.
期刊介绍：
The International Journal of Thermal Sciences is a journal devoted to the publication of fundamental studies on the physics of transfer processes in general, with an emphasis on thermal aspects and also applied research on various processes, energy systems and the environment. Articles are published in English and French, and are subject to peer review.
The fundamental subjects considered within the scope of the journal are:
* Heat and relevant mass transfer at all scales (nano, micro and macro) and in all types of material (heterogeneous, composites, biological,...) and fluid flow
* Forced, natural or mixed convection in reactive or non-reactive media
* Single or multi–phase fluid flow with or without phase change
* Near–and far–field radiative heat transfer
* Combined modes of heat transfer in complex systems (for example, plasmas, biological, geological,...)
* Multiscale modelling
The applied research topics include:
* Heat exchangers, heat pipes, cooling processes
* Transport phenomena taking place in industrial processes (chemical, food and agricultural, metallurgical, space and aeronautical, automobile industries)
* Nano–and micro–technology for energy, space, biosystems and devices
* Heat transport analysis in advanced systems
* Impact of energy–related processes on environment, and emerging energy systems
The study of thermophysical properties of materials and fluids, thermal measurement techniques, inverse methods, and the developments of experimental methods are within the scope of the International Journal of Thermal Sciences which also covers the modelling, and numerical methods applied to thermal transfer.
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