Characterisation of supersonic gas jets for different nozzle geometries for laser-plasma acceleration experiments at SPARC_LAB

Plasma-based technology promises a tremendous reduction in size of accelerators used for research, medical, and industrial applications, making it possible to develop tabletop machines accessible for a broader scientific community. The use of high-power laser pulses on gaseous targets is a promising method for the generation of accelerated electron beams at energies on the GeV scale, in extremely small sizes, typically millimetres. The gaseous target in question can be a collimated supersonic gasjet from a nozzle. In this work, a technique for optimising the so generated plasma channel is presented. In detail, a study on the influence of the nozzle throat shape in relation to the uniformity and density of the generated plasma profile is reported. These considerations are discussed first of all from a theoretical point of view, by means of a stationary one-dimensional mathematical model of the neutral gas, thus exploiting the possibility of comparing the properties of the output flow for different nozzle geometries. This is combined with an experimental approach using interferometric longitudinal density measurements of the plasma channel. The latter is generated by a high-power laser pulse focused on a helium gasjet, in the SPARC_LAB laboratories.

Needle-Free Jet Injectors’ Geometry Design and Drug Diffusion Process Analysis

In order to study the injection and diffusion process of the drug in the subcutaneous tissue of a needle-free jet injectors (NFJIs) in detail and understand the influence of different nozzle geometry on the diffusion process of the drug, in this paper, numerical simulations were performed to study the diffusion process of the drug in the subcutaneous tissue of NFJIs with cylindrical nozzle. On this basis, the differences of the drug diffusion process with different nozzle geometries were analyzed. The results show that the drug diffused in the shape of ellipsoid in the subcutaneous tissue. The penetration of the drug into the subcutaneous tissue is deeper under the condition of conical nozzle and conical cylindrical nozzle at the same time. However, it takes longer to spread to the interface between skin and subcutaneous tissue in reverse.

Numerical Investigation on the Performance of Two-Throat Nozzle Ejectors with Different Mixing Chamber Structural Parameters

In this study, the effects of the mixing chamber diameter (Dm), mixing chamber length (Lm) and pre-mixing chamber converging angle (θpm) were numerically investigated for a two-throat nozzle ejector to be utilized in a CO2 refrigeration cycle. The developed simulated method was validated by actual experimental data of a CO2 ejector in heat pump water heater system from the published literature. The main results revealed that the two-throat nozzle ejectors can obtain better performance with Dm in the range of 8–9 mm, Lm in the range of 64–82 mm and θpm at approximately 60°, respectively. Deviation from its optimal value could lead to a poor operational performance. Therefore, the mixing chamber structural parameters should be designed at the scope around its optimal value to guarantee the two-throat nozzle ejector performance. The following research can be developed around the two-throat nozzle geometries to strengthen the ejector performance.

Numerical simulation of cavitating flow in maritime high-pressure direct fuel injection nozzles and assessment of cavitation-erosion damage

The internal flow of Heavy Fuel Oil (HFO) in two maritime direct fuel injector nozzles is studied by 3D flow simulations for the assessment of erosion-sensitive wall regions. The nozzle geometries differ in number, diameter and inclination angle of holes as well as sac wall curvature. Long-term endurance experiments reveal characteristic damage locations for both nozzles. Simulations are performed by a compressible density-based flow solver with a barotropic cavitation model to capture shock wave dynamics. Real geometries and the entire injection cycle with time-dependent rail pressure and transient needle movement are considered. A statistical evaluation of individual collapsing voids in terms of their condensation rate yield an erosion probability that is compared against experimental damage locations. Due to the scatter in the values of viscosity of real fuels a viscosity variation is carried out, which shows that while a lower viscosity leads to a rise of erosion probability, the location of erosion-sensitive wall zones is not significantly changed. The analysis of 3D velocity and void field evolutions motivates the introduction of distinct injection sub-phases of the entire cycle. Erosion probability is separately evaluated within each sub-phase. By this simulation procedure, experimentally found erosion spots are associated with particular sub-phases and can be traced back to characteristic flow and void structures that are linked to particular nozzle geometry features.

Cold emission optimization of a diesel- and alternative fuel-driven CI engine

This paper deals with the emission optimization of a compression ignition (CI) engine during cold ambient operation. Hence, in the present study, the effect of different injector nozzle geometries and pilot injection strategies, but also the influence of intake swirl, rail pressure, exhaust gas recirculation (EGR) as well as EGR cooling on the emission behavior during cold run are investigated. Therefore, test bed experiments under steady-state cold conditions are conducted on a state-of-the-art CI single cylinder research engine (SCRE) with approximately 0.5 l swept volume representing the typical passenger car (PC) cylinder size. The cold charge air temperature of down to −8 $$^{\circ }\hbox { C}$$ ∘ C and a low engine coolant and lube oil temperature represent a cold run close to reality. For emulating the higher friction of a typical 4-cylinder PC engine during cold run, the indicated mean effective pressure (IMEP) is increased according to a specifically developed equation and the turbocharger main equation is solved permanently to adjust the gas exchange loss. To take account of a potential future tightening of emission legislation, in addition to limited exhaust gas emissions, non-limited emissions such as carbonyls are measured as well. Since alternative fuels are able to make a significant contribution to the defossilisation of transportation, an oxygen-containing fuel, consisting of 100 % renewable blend components (HVO, ethers and alcohols) and fulfilling the EN 590 legislation is investigated under the same cold conditions in addition to the research on conventional diesel fuel.

Gas-liquid mass transfer intensification for bubble generation and breakup in micronozzles

The local gas-liquid mass transfer was characterized during bubble generation in T-contactors and in an adjacent micronozzle. A colorimetric technique with the oxygen sensitive dye resazurin was investigated to visualize gas-liquid mass transfer during slug flow, bubble deformation, as well as laminar and turbulent bubble breakup in the wake of a micronozzle. Two optimized nozzle geometries from previous studies were evaluated concerning volumetric mass transfer coefficients for low pressure loss, narrow residence time distribution, or high dispersion rates. Highest values in kla up to 60 s−1 were found for turbulent bubble breakup and an optimized micronozzle design in respect to pressure drop and dispersion rate. The achieved mass transfer coefficients were correlated with the energy dissipation rate within the micronozzles and with the inverse Kolmogorov time scale in vortex dissipation in good agreement for laminar and turbulent breakup regimes. Graphical abstract

An investigation of the interaction between a travelling shock wave and a solid rocket motor nozzle

A gasdynamic mechanism has been identified as a potential source of combustion instability in solid-propellant rocket motors (SRMs). This mechanism involves the reinforcement of a reflected shock wave in the nozzle convergence region of an SRM's exhaust nozzle. A shock tube apparatus was developed for the experimental component of this study. Various factors, such as the effect of different nozzle geometries and driven channel pressures, were examined. Also, a model of the shock tube was developed for computational fluid dynamics (CFD) simulations. These simulations were generated for comparison with the experimental results and to provide additional information regarding the nature of the flow behaviour. A gasdynamic mechanism has been identified as a potential source of combustion instability in solid-propellant rocket motors (SRMs). This mechanism involves the reinforcement of a reflected shock wave in the nozzle convergence region of an SRM's exhaust nozzle.A shock tube apparatus was developed for the experimental component of this study. Various factors, such as the effect of different nozzle geometries and driven channel pressures, were examined. Also, a model of the shock tube was developed for computational fluid dynamics (CFD) simulations. These simulations were generated for comparison with the experimental results and to provide additional information regarding the nature of the flow behaviour.Experimental and numerical pressure-time profiles confirm the appearance of transient radial wave activity following the initial incidence of the normal shock wave on the convergence region of the nozzle. The results establish that the strength of this activity is markedly dependent upon the nozzle convergence wall angle and the location within the shock tube

An investigation of the interaction between a travelling shock wave and a solid rocket motor nozzle

A gasdynamic mechanism has been identified as a potential source of combustion instability in solid-propellant rocket motors (SRMs). This mechanism involves the reinforcement of a reflected shock wave in the nozzle convergence region of an SRM's exhaust nozzle. A shock tube apparatus was developed for the experimental component of this study. Various factors, such as the effect of different nozzle geometries and driven channel pressures, were examined. Also, a model of the shock tube was developed for computational fluid dynamics (CFD) simulations. These simulations were generated for comparison with the experimental results and to provide additional information regarding the nature of the flow behaviour. A gasdynamic mechanism has been identified as a potential source of combustion instability in solid-propellant rocket motors (SRMs). This mechanism involves the reinforcement of a reflected shock wave in the nozzle convergence region of an SRM's exhaust nozzle.A shock tube apparatus was developed for the experimental component of this study. Various factors, such as the effect of different nozzle geometries and driven channel pressures, were examined. Also, a model of the shock tube was developed for computational fluid dynamics (CFD) simulations. These simulations were generated for comparison with the experimental results and to provide additional information regarding the nature of the flow behaviour.Experimental and numerical pressure-time profiles confirm the appearance of transient radial wave activity following the initial incidence of the normal shock wave on the convergence region of the nozzle. The results establish that the strength of this activity is markedly dependent upon the nozzle convergence wall angle and the location within the shock tube

Automated removal of carbon fiber reinforced plastic layers for the repair by adhesive bonding

For the industrial repair of carbon fiber reinforced plastics (CFRP), scarfing is used to re-establish the load path. In the industry today, the state of the art removal of CFRP layers for a repair process is done mainly manually, leading to a time-consuming process. Therefore, an automation of this process is desirable. Today, vacuum suction blasting is used to pre-treat CFRP surfaces only for the superficial removal of impurities or the removal of the cover layer before bonding. With the common used blasting agents and nozzle geometries, the even removal of larger areas together with the fiber was not possible. This work shows that the technology of vacuum suction blasting was adapted to be used as an automated scarfing method. A combination of blasting parameters, especially the nozzle geometries together with a blasting agent were found to be able to remove CFRP layers precisely, detecting and correcting errors in-line with a line scanner-measuring unit. The presented method allows treating large-scale surfaces, scarfing the area one single layer at a time, increasing the removal rate in comparison to common blasting. With vacuum suction blasting the grinding dust emissions and process forces are low, post cleaning or further surface activation are not necessary and the removal results can directly be controlled. Challenges still exist with inaccurate removal due to interruptions in the blasting program and the generation of sharp edges for a stepped scarf.