Analysis of spray penetration models applied to high pressure diesel spray cases for different injector nozzle geometries

Darlington Njere, Nwabueze Emekwuru

Research output: Chapter in Book/Report/Conference proceedingConference proceedingpeer-review

Abstract

An analysis of the applicability of existing diesel fuel spray penetration models to results from the experimental evaluation of the fuel spray penetration of high-pressure diesel spray cases for different injector nozzles is presented. The experimental test conditions include injection pressure values of up to 2000 bar. The results indicate that the assumptions behind the development of these fuel spray penetration models are not always valid for the in-cylinder spray conditions encountered in the present study. The results will form part of the basis for the development of appropriate correlations for high pressure diesel spray penetration models. Introduction The concern over the stringent emission legislations against diesel engine and the probability of outright ban across some developed cities of the world have made combustion and emission characteristics an active research area. Studies [1,2] have shown that these attributes are significantly influenced by diesel fuel injection and atomization characteristics. One way of optimising these events is by controlling the spray injected into the combustion chamber through increasing injection pressure. The evolution of diesel injection equipment from the jerk pump system to common rail system (CRS) has facilitated the increase in Injection pressure. With the CRS, injection pressure of 3500 bar is possible [3], and prediction of up to 4000 bar by 2020 [4]. This improved capacity is supporting the development of deeper understanding of the processes related to spray behaviour, which is responsible for the progress made thus far in reducing diesel emissions. However, the demand for accuracy and wish for more detail continue to grow with the increase in understanding. Spray formation is a complex process. Extensive studies [5-7] on the process have been conducted, there are still details that are yet to be understood. For example, studies [8] suggest fairly good consensus on which physical quantities have an effect on spray characteristics, but there are some discrepancies. This could be due to: wide range of injection systems, engine-related configurations (e.g. combustion system design), flow field characteristics, operating conditions (e.g. pressure and temperature levels) and fuel quality/composition. However, the analysis of spray penetration is crucial, especially in the design of high speed direct injection (HSDI) diesel combustion chamber. While under-penetration of (liquid) spray may result in poor air utilization, over-penetration may cause impingement on cool surfaces with little air swirl, reducing mixing rate and producing unburned fuel [9]. The effect of impingement can be linked with engine operations. At light loads and low speed conditions, unburned hydrocarbon emissions will be reduced if the contact between (liquid) spray and combustion chamber walls is avoided. In contrast, fume emissions will be reduced if this contact exists at heavy loads and high-speed conditions. It is therefore desirable to optimize fuel distribution within the combustion chamber together with high fuel air mixing rate. The main factors that are driving spray propagation studies include: the practical importance of spray penetration (e.g. optimization of spray penetration in internal combustion engines); spray penetration is easily measurable, which is useful for spray model validation; and the correct prediction of the spray penetration can indirectly reveal the correctness of complex models of spray formation. Investigations [5,10] have shown significant dependence of spray penetration on in-cylinder pressure and injection pressure. Spray penetration was defined to be a primary function of spray angle, nozzle hole diameter, and other conditions including the ambient gas density, temperature, injection pressure and injection duration [11]. Overall, several studies have tried to correlate spray penetration with time, injection pressure, ambient gas pressure and temperature. Some of these correlations are simplified and derived from the first principles, while others are from experimental results. The two groups are complementary, and are sometimes applied in parallel. Computational Fluid Dynamics (CFD) codes use these correlations in modelling. However, this work focuses on the former models, since they usually facilitate the development of better insight into the physical background of the processes. Much from these simplified group of models have been presented/compared in the literature [5, 10, 13, 14]. Though there was a general agreement on key parameters that exert considerable influence on spray penetration, some of these studies differed on which proportions were important. Spray (cone) angle, which is strongly influenced by (characteristics) of nozzle design, is an important part of spray characterisation. Together with spray penetration, the cone angle
Original languageEnglish
Title of host publicationICLASS 2018, 14 th Triennial International Conference on Liquid Atomization and Spray Systems, Chicago, IL, USA, July 22-26, 2018
PublisherInstitute for liquid atomization and spray systems - ILASS
Number of pages7
Publication statusPublished - 22 Jul 2018
Event14th Triennial International Conference on Liquid Atomization and Spray Systems - Chicago, United States
Duration: 22 Jul 201826 Jul 2018
https://ilasseurope.org/events/iclass-2018/

Conference

Conference14th Triennial International Conference on Liquid Atomization and Spray Systems
Abbreviated titleICLASS 2018
CountryUnited States
CityChicago
Period22/07/1826/07/18
Internet address

Keywords

  • diesel
  • Spray
  • Penetration
  • models
  • Optical engine

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