Analysis of counterbore effect in five diesel common rail injectors

[EN] The present work assesses how the nozzle geometry, particularly the counterbore which is used in gasoline direct injection, could improve the fuel mixture when injecting in diesel engines, and ultimately, increase the thermal efficiency of the engine. Five different injector's nozzles are tested using a parametric variation over counterbore dimensions. For this purpose, measurements of the rate of injection, spray momentum and non-evaporative visualization are performed. Comparison of the nozzles performance is assessed by the rate of injection and momentum, nozzle coefficients in the hydraulic part, and in terms of spray penetration and spray angle in the visualization part which describe the macroscopic characteristics of spray development. Minimal variation was found observing at the hydraulic characterization of the injectors. On the other hand, a more notable difference was found in the visualization experiments, in which the modified nozzles presented greater spray angles and smaller penetration than the original one without counterbore. This work provides an insight into the potential effects of using the popular counterbore-used in gasoline direct injection (GDI)-in a diesel injector.The authors would like to express their gratitude to the lab technicians Jose Enrique and Omar and to Sai Vinayak and Alejandro Tortosa for their collaboration throughout the experiments. Part of the experimental equipment was purchased with support from Generalitat Valenciana through project IDIFEDER2018 with title "DIAGNOSTICO OPTICO A ALTA VELOCIDAD PARA EL ESTUDIO DE PROCESOS TERMO-FLUIDODINAMICOS EN SISTEMAS DE INYECCION". Finally, they would like to acknowledge the partnership with CNH industrial.Payri, R.; Hardy, G.; Gimeno, J.; Bautista-Rodríguez, A. (2019). Analysis of counterbore effect in five diesel common rail injectors. Experimental Thermal and Fluid Science. 107:69-78. https://doi.org/10.1016/j.expthermflusci.2019.05.008S697810

An investigation of the validity of a homogeneous equilibrium model for different diesel injector nozzles and flow conditions

In the present work, a methodology for modeling flow behavior inside the fuel injector holes is applied to a number of cases with different geometries and flow conditions. After assessment of the approach results through various experimental studies looking into the flows behavior inside the diesel nozzles, two series of analyses are defined. In the first study, the effect of inlet pressure is investigated by using a series of different rail pressures in both numerical and experimental tests in a single hole industrial injector. Results show a non-cavitating flow and an approximately linear increase of the velocity, turbulence kinetic energy, and turbulence dissipation energy with the increase of pressure difference and linear increase of the mass flow rate with the square root of the pressure difference in this nozzle. The second study is related to the effect of hole geometry on injector performance. The effects of entrance edge rounding and the tube conicity factor are investigated by changing these parameters in a series of geometries from an industrial diesel nozzle. Results show that cavitation occurs in the geometries with a sharper edge and low conicity. The role of the cavitation in emerging flow properties is emphasized in the values of the injector discharge factor and the turbulence properties. The results of this work can be used in the simulation of the primary breakup of fuel spray, and this approach is useful for design and optimization of the injectors for industrial sectors

Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

Computational fluid dynamics represents a useful tool to support the design and development of Heavy Duty Engines, making possible to test the effects of injection strategies and combustion chamber design for a wide range of operating conditions. Predictive models are required to ensure accurate estimations of heat release and the main pollutant emissions within a limited amount of time. For this reason, both detailed chemistry and turbulence chemistry interaction need to be included. In this work, the authors intend to apply combustion models based on tabulated kinetics for the prediction of Diesel combustion in Heavy Duty Engines. Four different approaches were considered: well-mixed model, presumed PDF, representative interactive flamelets and flamelet progress variable. Tabulated kinetics was also used for the estimation of NOxemissions. The proposed numerical methodology was implemented into the Lib-ICE code, based on the OpenFOAM®technology, and validated against experimental data from a light-duty FPT engine. Ten points were considered at different loads and speeds where the engine operates under both conventional Diesel combustion and PCCI mode. A detailed comparison between computed and experimental data was performed in terms of in-cylinder pressure and NOxemissions

Modeling Non-Premixed Combustion Using Tabulated Kinetics and Different Fame Structure Assumptions

Nowadays, detailed kinetics is necessary for a proper estimation of both flame structure and pollutant formation in compression ignition engines. However, large mechanisms and the need to include turbulence/chemistry interaction introduce significant computational overheads. For this reason, tabulated kinetics is employed as a possible solution to reduce the CPU time even if table discretization is generally limited by memory occupation. In this work the authors applied tabulated homogeneous reactors (HR) in combination with different turbulent-chemistry interaction approaches to model non-premixed turbulent combustion. The proposed methodologies represent good compromises between accuracy, required memory and computational time. The experimental validation was carried out by considering both constant-volume vessel and Diesel engine experiments. First, the ECN Spray A configuration was simulated at different operating conditions and results from different flame structures are compared with experimental data of ignition delay, flame lift-off, heat release rates, radicals and soot distributions. Afterwards, engine simulations were carried out and computed data are validated by cylinder pressure and heat release rate profiles

Model-Based Control of Torque and Nitrogen Oxide Emissions in a Euro {VI} 3.0 L Diesel Engine through Rapid Prototyping

In the present paper, a model-based controller of engine torque and engine-out Nitrogen oxide (NOx) emissions, which was previously developed and tested by means of offline simulations, has been validated on a FPT F1C 3.0 L diesel engine by means of rapid prototyping. With reference to the previous version, a new NOx model has been implemented to improve robustness in terms of NOx prediction. The experimental tests have confirmed the basic functionality of the controller in transient conditions, over different load ramps at fixed engine speeds, over which the average RMSE (Root Mean Square Error) values for the control of NOx emissions were of the order of 55-90 ppm, while the average RMSE values for the control of brake mean effective pressure (BMEP) were of the order of 0.25-0.39 bar. However, the test results also highlighted the need for further improvements, especially concerning the effect of the engine thermal state on the NOx emissions in transient operation. Moreover, several aspects, such as the check of the computational time, the impact of the controller on other pollutant emissions, or on the long-term engine operations, will have to be evaluated in future studies in view of the controller implementation on the engine control unit

The significance of Lactobacillus crispatus and L. vaginalis for vaginal health and the negative effect of recent sex: a cross-sectional descriptive study across groups of African women

Background: Women in sub-Saharan Africa are vulnerable to acquiring HIV infection and reproductive tract infections. Bacterial vaginosis (BV), a disruption of the vaginal microbiota, has been shown to be strongly associated with HIV infection. Risk factors related to potentially protective or harmful microbiota species are not known. Methods: We present cross-sectional quantitative polymerase chain reaction data of the Lactobacillus genus, five Lactobacillus species, and three BV-related bacteria (Gardnerella vaginalis, Atopobium vaginae, and Prevotella bivia) together with Escherichia coli and Candida albicans in 426 African women across different groups at risk for HIV. We selected a reference group of adult HIV-negative women at average risk for HIV acquisition and compared species variations in subgroups of adolescents, HIV-negative pregnant women, women engaging in traditional vaginal practices, sex workers and a group of HIV-positive women on combination antiretroviral therapy. We explored the associations between presence and quantity of the bacteria with BV by Nugent score, in relation to several factors of known or theoretical importance. Results: The presence of species across Kenyan, South African and Rwandan women was remarkably similar and few differences were seen between the two groups of reference women in Kenya and South Africa. The Rwandan sex workers and HIV-positive women had the highest Gardnerella vaginalis presence (p = 0.006). Pregnant women had a higher Lactobacillus genus mean log (7.01 genome equivalents (geq)/ml) compared to the reference women (6.08 geq/ml). L. vaginalis (43%) was second to L. iners (81.9%) highly present in women with a normal Nugent score. Recent sexual exposure negatively affected the presence of Lactobacillus crispatus (<0.001), L. vaginalis (p = 0.001), and Lactobacillus genus (p < 0.001). Having more than one sexual partner in the last three months was associated with an increased prevalence of Gardnerella vaginalis (p = 0.044) and L. iners (p = 0.001). Conclusions: Although the composition of species across the studied African countries was similar, the presence of protective species i.e. Lactobacillus crispatus and L. vaginalis in women with a normal Nugent score appeared lower compared to non-African studies. Furthermore, Lactobacillus species were negatively affected by sexual behavioural. Strategies to support protective Lactobacillus species are urgently needed