Nozzle Extension Research Articles

The Research of Diesel Engine Assembly Consistency Influence NOx Emission Based on Uniform Design Method

ABSTRACT Diesel engines need to meet the higher emission requirement according to the Euro VI emission standards, and changes in the assembly tolerance of diesel engines will affect the consistency of nitrogen oxides(NOx) emissions. To study the influence of assembly tolerance on NOx emission, a heavy diesel engine was used as the research prototype. The combustion model of the diesel engine was simulated by the Converge software and calibrated with the bench test data. Because the combustion system parameters have a significant impact on emissions, a three-factor eleven-level uniform design is arranged with three parameters, including compression ratio, fuel injection nozzle extension height and injection advance angle. The regression analysis method is used to obtain the relationship between the parameters and NOx emissions. The R2 test value of the regression equation is 0.916 and the F test value is 43.5, which shows that the results of the analysis are very effective. Then the single factor test method is applied to analyze the varying laws of compression ratio, nozzle extension height and fuel injection advance angle on NOx emissions, and the results reveal the inherent law similar to the regression equation. According to the Euro VI emission standards and the law of diesel engine emission performance consistency, the tolerance variation range of the key dimensions of the assembly parameters is obtained.

Enhancing thermal stability and corrosion resistance of carbon-carbon composites with iridium coatings deposited by electron beam physical vapor deposition

Abstract Carbon–carbon (C−C) composites are extensively used in high-temperature environments such as Combustor Liners and Turbine Blades in jet engines and Throat Inserts, Nozzle Extensions and Exit Cones in rocket engines due to their excellent thermal stability and mechanical properties. However, at temperatures exceeding 800 °C, these composites require additional protection to prevent degradation. This study aims to investigate the behavior of C−C composites when coated with high-purity metallic iridium using Electron Beam Physical Vapor Deposition (EBPVD). The research problem focuses on enhancing the high-temperature performance and corrosion resistance of C−C composites for aerospace applications. The methodology involves depositing a uniform 5.6 microns thick iridium coating on C−C substrates and characterizing the coating’s microstructure, hardness, and corrosion resistance. FESEM micrographs reveal that the iridium coating adheres uniformly to the substrate without any seepage, and XRD analysis confirms an FCC crystal structure with a densely packed grainy surface. Corrosion tests were conducted using a BIOLOGIC electrochemical workstation in a sodium chloride environment indicate a corrosion rate of 0.00307 mm year−1. The Nyquist, Bodo plots, and Taffel plots were constructed for the better understanding of the corrosion mechanism. While the OCP was constructed to understand the stability and the corrosion resistance of the C−C samples. Microhardness of the coating, measured under a normal applied load of 0.20 N, is 702 HV. The coated samples also could withstand thermal shocks between −40 °C and 1500 °C for 40 h without observable damage or color change. These findings demonstrate the potential of iridium-coated C−C composites to maintain structural integrity and performance in extreme aerospace environments, significantly impacting the field by providing a reliable protective solution for high-temperature applications.

The utilization of novel jet extension designs in multi-jet impingement for crossflow mitigation and thermal efficiency enhancement

The aim of this study is to mitigate the distorting effect of crossflow on jet flow and to enhance heat transfer performance in multi-jet impingement heat transfer. To accomplish this objective, novel jet extension designs are proposed: a design with uniform jet extension, a design with linear jet extension in the streamwise direction, a design featuring an initial increase followed by a decrease, a design featuring an initial decrease followed by an increase, and a design where the last five jets exhibit a uniform extension inside the region mostly influenced by crossflow. The effects of various novel jet extension designs on flow and heat transfer are analyzed numerically in this study, focusing on the following: velocity contours, streamlines and velocity vectors, Local Nusselt number variations, variations of the average Nusselt number, friction coefficient, and thermal enhancement factor with Reynolds number. The study findings indicate that the investigated nozzle extension designs yield a notable enhancement of 13.26% in heat transfer. However, it is important to note that these designs may also lead to a substantial rise of 39% in the friction coefficient. In relation to thermohydraulic performance, it is found that all extension designs exhibit better results when compared to the reference state. Notably, the uniform extension design with dimensionless nozzle length of 2 demonstrates a higher degree of thermohydraulic performance.

Establishment of strain rate‐dependent intrinsic models for short‐cut carbon fiber/nitrile composites in different pyrolysis states

AbstractFlexible nozzle extension technology has been extensively researched throughout the world, but traditional materials cannot meet the growing demands in harsh environments. Short‐cut carbon fiber‐reinforced nitrile rubber (CF/NBR) composites, which are similar to the phenolic impregnated carbon ablator, are currently a hot research topic in this field. The mechanical properties of CF/NBR composites were experimentally tested to study the change in the mechanical behavior of a rocket engine's flexible nozzle extension section under thermal coupling. As indicated by the results, existing models cannot accurately predict changes in materials' mechanical behavior. The theoretical foundation of the nonlinear viscoelastic intrinsic model of rubber is utilized. The uniaxial tensile intrinsic model of CF/NBR composites has been improved by introducing physical parameters, such as fiber reinforcement, strain rate‐dependent correction and temperature‐dependent correction coefficients, and fiber volume fraction. Results show that the intrinsic model developed in this article provides a guide to the uniaxial tensile mechanical behavior of randomly distributed short‐cut CF/NBR composites with known mass‐part formulations and fiber volume fractions at room temperature and under different pyrolysis conditions.

Stage Separation Failure: Model Based Diagnostics and Prognostics


 
 
 Safety of the next-generation space flight vehicles requires development of an in-flight Failure Detection and Prognostic (FD&P) system. Development of such system is challenging task that involves analysis of many hard hitting engineering problems across the board. In this paper we report progress in the development of FD&P for the re-contact fault between upper stage nozzle and the inter-stage caused by the first stage and upper stage separation failure. A high-fidelity models and analytical estimations are applied to analyze the following sequence of events: (i) structural dynamics of the nozzle extension during the impact; (ii) structural stability of the deformed nozzle in the presence of the pressure and temperature loads induced by the hot gas flow during engine start up; and (iii) the fault induced thrust changes in the steady burning regime. The diagnostic is based on the measurements of the impact torque. The prognostic is based on the analysis of the correlation between the actuator signal and fault-induced changes in the nozzle structural stability and thrust.
 
 

Numerical and Experimental Analysis of a Solid Shroud in Multi-arc Plasma Spraying

AbstractPlasma spraying is characterized by high flexibility, but has challenges of high energy consumption and oxidation of the metallic spray particles. Modified plasma spraying processes using a gas or solid shroud have been developed to address these challenges, which aim to reduce the introduction of ambient air into the plasma jet and improve the process efficiency. Prior research mainly focused on single-cathode plasma generators, and the use of a shroud in multi-arc plasma spraying systems has not been thoroughly explored. The primary goal of this study is to analyze the effects of a solid shroud as a nozzle extension on the plasma jet of a three-cathode plasma generator numerically and experimentally. Computational fluid dynamics (CFD) is used to simulate a solid shroud, and the resulting design is constructed for experimental analysis. The experimental setup includes a nozzle extension with a transparent window for diagnostic measurements by a high-speed camera. To isolate the effects of the solid shroud from fluctuations in the power input, current, and voltage measurements are carried out synchronized with the high-speed recordings. Particle diagnostics are also conducted to analyze the properties of the in-flight particles without and with the solid shroud. The developed numerical model can be further used to optimize the shroud geometry for different process parameters.

Performance analysis of expansion – deflection nozzles with reduced lengths of nozzle extension at a high-altitude environment

Performance analysis of expansion – deflection nozzles with reduced lengths of nozzle extension at a high-altitude environment

Design Process and Flow Field Analysis of a Double Divergent Supersonic Nozzle: Enhancing Efficiency and Performance

The dual bell nozzle concept's primary goal is to increase performance through the idea of selfadaptation for two operating regimes without mechanical activation. The dual bell nozzle type known asthe planar double divergent nozzle (DDN) has a rectangular cross section. In this study we propose anumerical method for the design of the nozzle profile with double planar divergent. The design of the doubledivergent nozzle is carried out in two parts. The first divergent is a contour of a two-dimensional supersonicnozzle with a sharp-edged throat that gives uniform parallel flow at the exit. The method of characteristicapplied to the two-dimensional isentropic flow of an ideal gas was used for the design of a supersonic planarnozzle. The contour of the second divergent (nozzle extension) is a polynomial. This is achieved using thedirect method of characteristics. A numerical analysis of a double divergent nozzle, and a planar nozzlewith the same area ratio and the same length using ANSYS-Fluent software. The analysis's findingsindicated that the double divergent nozzle had a weight decrease of 0.61%. The thrust increase is estimatedat 3.88% in the low-altitude operating mode for the double divergent nozzle.

A simplified analytical method for the computation of machine path in filament winding of axisymmetric structures: a case study on a bell-contoured rocket nozzle extension

A simplified analytical method for the computation of machine path in filament winding of axisymmetric structures: a case study on a bell-contoured rocket nozzle extension

Cooling rocket nozzle extensions with supersonic gas injection

Supersonic helium injected into the rocket exhaust boundary layer protects components from extremely hot gas.

Direct numerical simulation of supersonic turbulent flow with film cooling by wall-parallel blowing

An advanced film-cooling application is the thermal protection of the nozzle extension of high-performance rocket engines. The extension wall needs be protected from the hot supersonic thrust gas, very much like the combustion chamber or nozzle throat region, where the flow is, however, sub- or transonic. A reliable cooling modeling for practical applications requires benchmark results for generic cases with accurate flow-field details. To this end, fundamental investigations of the interaction between the thrust and cooling gas have been performed for flat-plate flow using high-order direct numerical simulations for the first time. A cool secondary gas is injected through a vertical slot of height s in a backward-facing step. The thrust-gas flow is steam (gaseous H2O) at Mach 3.3 with a turbulent boundary layer, and a laminar supersonic stream of cool helium is injected. The influence of the coolant mass flow rate is investigated by varying the blowing ratio F or the injection height s at a fixed cooling-gas temperature and Mach number. Several previously unknown effects are found fostering correlation model evolution of the film cooling, inter alia that the upstream wall temperature needs be taken into account and how the turbulent Prandtl and Schmidt number distributions are in the field, essential for improved Reynolds-averaged Navier–Stokes simulations.

Computations of Side Loads in a Thrust-Optimized Parabolic Nozzle During High-Altitude Testing

The present work is to computationally analyze side loads in a thrust-optimized parabolic nozzle during high-altitude testing. The engine startup and shutdown processes of the Korean Space Launch Vehicle II third-stage rocket engine combustor are examined using three-dimensional time-accurate computations. The generation of side loads is closely related to the transition of the separation pattern due to the nozzle shape. However, the results also show that the side loads are significantly affected by the unique flow features of high-altitude testing, such as the flow entering through the gap between the nozzle and the diffuser, as well as the pressure waves produced by the impact of the diffuser flow breakdown. During the engine startup process, the interaction between the nozzle flow and the entrained flow produces unexpected side loads before the transition of the separation pattern. The first transition process generates two side-load peaks. The second transition does not produce any side loads owing to the smooth transition process, which is caused by the entrained flow acting like a nozzle extension. During the engine shutdown process, the initial pressure wave from the diffuser causes fluctuating side loads. The second pressure wave leads to the transition of the separation pattern, which temporarily increases the magnitude of the side loads.

Research on the Influence of Euro VI Diesel Engine Assembly Consistency on NOx Emissions

The assembly consistency of a diesel engine will affect its nitrogen oxides (NOx) emission variation. In order to improve the NOx emissions of diesel engines, a study was carried out based on the assembly tolerance variation of the diesel engine’s combustion system. Firstly, a diesel engine which meets the Euro VI standards together with the experimental data is obtained. The mesh model and combustion model of the engine combustion system are built in the Converge software (version 2.4, Tecplot, Bellevue, DC, USA), and the experimental data is used to calibrate the combustion model obtained in the Converge software. Then, the four-factor and three-level orthogonal simulation experiments are carried out on the dimension parameters that include nozzle extension height, throat diameter, shrinkage diameter and combustion chamber depth. Through mathematical analysis on the experimental data, the results show that the variation of nozzle extension height and combustion chamber depth have a strong influence on NOx emission results, and the variation of combustion chamber diameter also has a weak influence on NOx production. According to the regression model obtained from the analysis, there is a quadratic function relating the nozzle extension height and NOx emissions and the amount of NOx increases with increasing nozzle extension height. The relationship between emission performance and size parameters is complex. In the selected size range, the influence of the variation of the chamber diameter on NOx is linear. The variation of the chamber depth also has an effect on NOx production, and the simulation results vary with the change of assembly tolerance variation. Thus, in the engine assembly process, it is necessary to strictly control the nozzle extension height and combustion chamber depth. The research results are useful to improve the NOx emission of diesel engine and provide a basis for the control strategy of selective catalytic reduction (SCR) devices.

Active Control of Dual-Bell Nozzle Operation Mode Transition by Film Cooling and Mixture Ratio Variation

A numerical study is conducted to investigate the impact of a film-cooled dual-bell nozzle extension on its operation mode transition behavior. Therefore, unsteady Reynolds-averaged Navier–Stokes simulations of the transition process between the sea level and altitude modes are carried out. The investigated dual-bell nozzle model is fed with hot gas by a combustion chamber using liquid oxygen as oxidizer and gaseous hydrogen as fuel. Upstream of the dual-bell nozzle contour inflection, gaseous hydrogen is injected as cooling fluid for the nozzle extension wall. The numerical studies yield a clear impact of the cooling fluid mass flow rate on the transition nozzle pressure ratio of the dual-bell nozzle. The increase of the cooling fluid mass flow rate leads to a shift of the dual-bell transition nozzle pressure ratio to lower values. Furthermore, the impact of the combustion chamber mixture ratio on the dual-bell operation mode transition is investigated. A clear shift to lower transition nozzle pressure ratio values due to higher propellant mixture ratios can be observed. A combination of the two effects is introduced for an active control of the dual-bell operation mode transition.

Numerical Investigation of Jet-Wake Interaction for a Dual-Bell Nozzle

The turbulent wake of a planar generic space launcher equipped with a dual-bell nozzle is numerically investigated to examine the interaction of the dual-bell nozzle jet and the wake flow. The simulation is performed at transonic freestream condition, i.e., freestream Mach number $Ma_{\infty }= 0.8$ and freestream Reynolds number based on the launcher thickness ReD = 4.3 ⋅ 105, with the dual-bell nozzle operating at sea-level mode. A zonal RANS/LES approach is used and the time-resolved flow field data is analyzed by classical spectral analysis and modal decomposition techniques, i.e., proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). The overall flow topology of the recirculation region downstream of the base and the pressure loads on the outer nozzle fairing are only slightly affected by the modified nozzle shape. However, the changed nozzle flow topology characterized by the flow separation at the nozzle contour inflection leads to a backflow region and an entrainment of the outer flow into the nozzle extension which results in increased pressure loads on the inner nozzle wall. Using spectral, POD, and DMD analyses, the outer wake flow is investigated, revealing a growing and contracting of the separation bubble and an undulating motion of the shear layer similar to the “cross-pumping” and “cross-flapping” motion detected in previous investigations of a configuration with a classical nozzle and a jetless backward facing step setup. The spectral and modal analysis of the nozzle flow shows that the increased pressure loads detected at the inner wall of the nozzle extension are caused by an interaction of the separated shear layer inside the nozzle extension with the shock pattern that leads to a streamwise oscillation of the shock and a pumping or wave-like motion of the shear layer.

Long-Run Testing of Model Nozzle Extensions Made of a Carbon-Carbon Composite Material in a Liquid-Propellant Rocket Engine Operating on Hydrogen and Oxygen

Results of a series of firing tests of two model nozzle extensions made of a carbon-carbon composite material are reported. This material can be used to fabricate nozzle extensions for a large-scale liquid-propellant rocket engine. The tests are performed in an experimental setup operating on oxygen and hydrogen. It is shown that the thermochemical loads on the nozzle material in model tests are greater than those under real conditions. The temperature of the outer surface of the nozzle extension is measured in each experiment by thermocouples and an infrared imager. The level of wall material ablation during the entire test period is determined. It is demonstrated that the results of firing tests can be used for estimating the operation performance of a large-scale engine. A simple analytical dependence is derived for recalculating the results of model tests on material ablation to full-scale conditions.

Effect of Pouring Conditions and Gating System Design on Air Entrainment During Mold Filling

Air entrainment during mold filling is a major source of oxide inclusion formation in metal casting. A model was recently developed by the authors to predict the volumetric air entrainment during pouring of metal castings. In the course of validating the model with experimental data for plunging liquid jets, it was shown that the air entrainment rate during mold filling depends fundamentally on the velocity and diameter of the jet formed by the pouring stream. In this study, the effect of more complex pouring conditions and gating system design on air entrainment is examined. Simulations are performed investigating the air entrainment characteristics of castings filled without a gating system, and with bottom-gated and side-gated filling systems. Results indicate that reducing the head height and pouring time, and the addition of a nozzle extension significantly reduces the air entrainment. In addition, using an offset pouring basin with a stopper and pressurizing the gating system further reduces the volume of entrained air. Simulation results also show that the generation of vortex flows inside the filling system is beneficial in reducing free surface turbulence, which results in less air entrainment and oxide inclusion formation during mold filling.

Simulation of Air Entrainment during Mold Filling: Comparison with Water Modeling Experiments

Oxide inclusions form during pouring of metal castings as a result of air entrainment. Recently, a model was developed by the authors to predict the volumetric air entrainment during pouring. It was found that the velocity, diameter, and turbulence intensity of the liquid stream affect the air entrainment rate during pouring. In this study, the developed air entrainment model is validated with water modeling experiments. In the water modeling studies, water was poured using a bottom pour ladle. The effects of nozzle opening, head height, nozzle diameter, and nozzle extension are simulated. The predictions compare favorably with the experimental measurements. Results indicate that low head height and short pouring time have a beneficial effect on reducing the air entrainment during pouring. In addition, a fully open nozzle and the use of a nozzle extension further reduce the amount of entrained air.

On-Demand Multi-Resolution Liquid Alloy Printing Based on Viscoelastic Flow Squeezing.

Recently, high-resolution patterning techniques of stretchable electronics advanced extensively. An important trend is to fabricate complex circuits with varied sizes in a small area, which is a technical challenge to current conductive ink printing technologies. Here, we introduce a new strategy for multi-resolution liquid alloy printing, which can tune the resolution of printed liquid alloy trace in real time with the squeezing effect of compound viscoelastic flow. A newly developed coaxial nozzle with the inner nozzle extension (CNINE) is used to wrap and squeeze liquid alloy steadily and effectively. By controlling the working parameters and compound flow properties, liquid alloy patterns with different widths are obtained continuously. This work offers a new way to rapidly manufacture complex stretchable electronics patterning in multi-resolution.

Thermo Structural Analysis of Carbon-Carbon Nozzle Exit Cone for Rocket Cryo Engines

Launch and space vehicle structures are required to be extremely weight efficient. The need to achieve the performance required for the engine in the upper stage of a launch vehicle, increase the payload capacity drives rocket engine manufacturers to seek higher thrust level, specific impulse and thrust to weight ratio. The use of high temperature C-C composite materials is an efficient way to reach these objectives by allowing use of high expansion ratio. Nozzle extensions benefiting of the outstanding thermal, mechanical and fatigue resistance of these materials to decrease mass and featuring high temperature margins. A three-directionally reinforced (3D) carbon-carbon (c-c) material nozzle exit cone is selected for the current study. C-C composite exit nozzle must possess excellent stability and strength under extreme conditions for a specified amount of time. Carbon-carbon composites are appropriate materials for applications that require high specific strength at elevated temperatures. The paper describes the thermo structural analysis of a typical c/c nozzle exit cone.