Ignition Overpressure Research Articles

Experimental investigation on the development characteristics of high-pressure hydrogen jet flame under different ignition conditions

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice.

Deflector shape impact on aero-acoustic noise generation and propagation

The acoustic pressure level generated during lift-off and the associated vibrations can significantly affect the payload of a launch vehicle. Optimizing the plume deflector is one of the most effective methods to reduce this noise. Considering the Vega launcher as a case of study, different deflectors are studied: flat, inclined at 30°, and wedge. The approach followed is to use the unsteady Navier–Stokes equations to solve both the noise generation and the propagation. First, it has been observed that the blast wave, due to the ignition overpressure, is independent of the deflector geometry. However, the predominant acoustic waves are due to the impact of the jet with the deflectors. The analysis has shown that the flat deflector generates more shock waves and propagates the acoustic waves equally in all directions so that more acoustic loads reach the fairing. The inclined deflector causes a plate shock and intermediate tail shocks and redirects the flow towards one side of the launcher. Finally, the wedge deflector generates a detached shock wave with a higher pressure increase than the inclined deflector. However, as the flow is redirected towards the two sides, a lower OASPL reaches the fairing. In the same way, the pressure distribution over the fairing surface has shown that the wedge deflector is acoustically more efficient for this case of study. The acoustic effectiveness of deflectors has been demonstrated compared to the case without a deflector. Therefore, deflectors are advised to be included on the launch platform to improve payload comfort and reliability on the launchers.

Initial findings from Space Launch System liftoff measurements

This presentation documents initial findings from far-field noise measurements at NASA’s Kennedy Space Center during liftoff of the Space Launch System’s Artemis I mission, which occurred on November 16, 2022. The vehicle— the most powerful ever successfully launched into orbit—consists of four liquid-fueled RS-25 engines and two five-segment, solid-fuel rocket boosters (SRBs). Because this was the first launch, the noise radiation characteristics of this vehicle were previously unknown. Overall sound pressure levels, waveform characteristics, and spectra are described at distances ranging from 1.5 to 8.4 km. The levels due to the SRBs’ ignition overpressure are particularly intense in the direction of the flame trench exit. The post-liftoff maximum one-third octave spectrum has a peak at 20 Hz, and maximum overall levels are greater than described in a pre-launch environmental assessment. These and other findings presently submitted to JASA Express Letters further understanding of super heavy-lift rocket acoustics.

Space Launch System acoustics: Far-field noise measurements of the Artemis-I launch.

To improve understanding of super heavy-lift rocket acoustics, this letter documents initial findings from noise measurements during liftoff of the Space Launch System's Artemis-I mission. Overall sound pressure levels, waveform characteristics, and spectra are described at distances ranging from 1.5 to 5.2 km. Significant results include: (a) the solid rocket boosters' ignition overpressure is particularly intense in the direction of the pad flame trench exit; (b) post-liftoff maximum overall levels range from 127 to 136 dB, greater than pre-launch predictions; and (c) the average maximum one-third-octave spectral peak occurred at 20 Hz, causing significant deviation between flat and A-weighted levels.

Image-Based Analysis of Interactions Between a Steady Jet and an Impulsively Started Jet

Ignition overpressure (IOP) is a principal dynamic load experienced by a launch vehicle during liftoff. The IOP arises due to the sudden ignition of the solid rocket boosters (SRBs) of a launch vehicle. The present work attempts to simulate the ignition of an SRB with an impulsively started supersonic jet generated using a quick-open valve. High-speed schlieren flow visualization is used to document the evolution of an impulsively started jet flowfield that included the characteristic precursor shock wave (that simulates the blast wave causing the IOP) and the following vortex ring. The dynamic interactions between the impulsively started supersonic jet and an established steady supersonic jet from another nozzle () in close proximity are also investigated. Both the precursor shock wave and the vortex ring interact strongly with the established steady-jet column as they proceed downstream from the nozzle exit, thereby introducing new sources of acoustic waves. When a generic jet blast deflector is introduced downstream of the nozzles, the precursor shock wave reflected from it, propagating upstream toward the nozzle exit. The reflected shock wave is recognized as the source of IOP experienced by the launch vehicle. The results show that the quick-open valve presents a unique way to generate impulsively started jets for understanding transients associated with the ignition of the SRB leading to the IOP, without the complexity associated with the use of open-ended shock tubes for carrying out such simulations.

Transient influence of water injection on the flow field of a hot launch in a W-shaped silo

This study attempts to determine the effect of and mechanisms for the suppression of the ignition pressure and back-flowing exhaust during a hot launch process in a W-shaped silo, considering the missile movement via dynamic mesh technology. The mixture model for the multiphase and the turbulent model employed were experimentally proved to be accurate and reliable. The numerical results show that the injection of water into a missile exhaust can effectively suppress the ignition overpressure, thereby reducing the time of oscillation and oscillation amplitude, and reducing the maximum pressure at missile bottom from 3.68 × 105 Pa to 2.39 × 105 Pa. In addition, water injection makes the back-flowing exhaust remain at the bottom of the launch duct instead of filling the duct, and it cools the missile bottom, thus leading to a reduction in the maximum temperature from 3000 K to approximately 500 K.

Numerical Modeling and Studies of Ignition Transients in End-Burning-Grain Solid Rocket Motors

The ignition-transient process in the end-burning-grain solid rocket motor has been studied. Simplified numerical models for 1) a mass-added ignitor, 2) a grain-propellant combustion, 3) the opening of nozzle closure, and 4) the enhancement of heat transfer on the surface of the solid propellant have been developed. The individual influence of the input of ignitors (energy strength and input time), the physical and chemical properties of propellants (critical burning temperature, burning rate, thermal conductivity, and initial temperature), and the breaking pressure of closure on the ignition transient have been systemically compared. The three stages of the ignition-transient process, namely, ignition induction, flame spreading, and chamber charging, have been successfully reproduced. The interior ballistics agrees with the ground-experimental data. The rapid generation of the initial flame and the creation of the “second peak” of the chamber pressure both contribute to a successful ignition. The results show that the factors that may accelerate the ignition transient do not always increase the second peak of the chamber pressure. The energy input of the ignition gas has greater influence on the ignition transient than do the enhancement of the heating and ignition process of the propellants. The breaking pressure of the nozzle closure has a very weak influence on the chamber pressure’s second peak, but considerably increases the ignition overpressure of the initial flame.

Understanding Ignition Over Pressure During Start Up of Typical Scaled Down Solid Rocket Motors

The Ignition Over Pressure (IOP) is an unsteady pressure wave generated by the ignition of solid rocket motor during launch vehicle lift-off. This wave behaves as a blast or a shock wave followed by a low frequency excitation characterized up to 40 Hz, would cause severe damage to the launch vehicle, its structures and surroundings. However, in case of huge propulsion system, having two solid rocket motors as its boosters, due to the skew in their ignition, during lift-off, the phase difference of the wave from one side of the vehicle to the other could cause a severe moment, which is detrimental to the vehicle. The present paper deals with the occurrence of such blast waves during the testing of various scaled down solid rocket motors. Also, an attempt has been made experimentally to characterize and understand the propagation of the IOP wave causing unsteady pressure oscillations and transient pressure rise in the vicinity of a solid rocket motor. The spectral and directional characteristics of the IOP wave are also highlighted. Typical scaled-down solid rocket motors with and without nozzle shutters have been tested in horizontal firing configuration and the results are compared to study their effect. The resulting shock wave propagation has axial downstream as well as angular directivities. The pressure rise rate in the chamber is found to be directly correlated to the over pressure measured at various locations at the downstream of the nozzle.

Mitigation of Solid Booster Ignition over Pressure by Water Aerosol Sprays

Interaction of acoustic waves with water aerosol layers is analyzed in the context of the problem of solid booster ignition overpressure suppression. In contrast to the conventional approach to ignition overpressure suppression, which aims at using water to quench the sources of the ignition overpressure waves, this study focuses on blocking the ignition overpressure wave propagation, using reflection and attenuation of the wave by the water aerosol layers. The study considers interaction of the waves with aerosol layers of large mass loading for varying sizes of the droplets. The size of the droplets is shown to substantially affect the mechanisms of interaction with the waves. The criteria for the crossover between different mechanisms are established as functions of the droplet size and the ignition overpressure wave parameters. The optimal parameters and designs for water aerosol sprays are proposed that maximize the ignition overpressure suppression. These results were obtained using the nozzle and the exhaust hole geometries similar to those of the space shuttle. Remarkably, it is found that various a priori reasonable designs of the aerosol and water sprays may increase the ignition overpressure impact on the vehicle, increasing the risk of vehicle damage.

Acoustic signature characterization of a sub-scale rocket launch

Georgia Tech Research Institute (GTRI) conducted a flight test of a sub-scale rocket in 2013 outside Talladega, Alabama, to acquire the launch acoustics produced. The primary objective of the test was to characterize the acquired data during a sub-scale launch and compare it with heritage launch data from the STS-1 Space Shuttle flight. Neither launch included acoustic suppression; however, there were differences in the ground geometry. STS-1 launched from the Mobile Launch Platform at Pad 39B with the RS-25 liquid engines and Solid Rocket Boosters (SRBs) firing into their respective exhaust ducts and flame trench, while the GTRI flight test vehicle launched from a flat reflective surface. The GTRI launch vehicle used a properly scaled Solid Rocket Motor (SRM) for propellant; therefore, primary analysis will focus on SRM/SRB centric acoustic events. Differences in the Ignition Overpressure (IOP) wave signature between both due to this will be addressed. Additionally, the classic liftoff acoustics “football shape” is preserved between both full and sub-scale flights. The launch signatures will be compared, with note taken of specific launch acoustic events more easily investigated with sub-scale launch data or supplement current sub-scale static hotfire testing.

Laser Ignition of an Experimental Cryogenic Reaction and Control Thruster: Pre-Ignition Conditions

In the frame of an experimental study conducted to assess the feasibility of laser ignition for implementation on cryogenic reaction and control system and orbital and maneuvering system thrusters, fluid flow structures and phenomena affecting ignition have been examined. This paper presents a qualitative analysis of the impact of preignition pressures, propellant injection conditions and injection phenomena such as flash evaporation, the local chamber flowfield, and propellant mass flow stability on altitude ignition. The use of test sequences and encountered phenomena to control the ignition delay and energy deposition and ignition overpressure is addressed.

Numerical Analysis of Ignition Overpressure Effect on H-IIB Launch Vehicle

A numerical simulation was conducted to investigate the ignition overpressure mechanism generated by the Japanese H-IIB launch vehicle. A simplified benchmark problem and analysis of a free jet exhausted from a single solid booster were used to verify the present numerical method; the unsteady Reynolds-averaged Navier–Stokes simulation was found to be essential for determining the typical features of ignition overpressure, such as the shock wave generated in front of the plume and following starting vortex. Comparing with the measured pressure history at the launch complex, the numerical result agreed reasonably. The correlation between the wave pattern measured at the launch complex and the ignition overpressure mechanism was clarified. The effect of ignition overpressure on the launch vehicle can be reduced by shielding the inlet of the flame duct with a mobile launcher; however, severe impact on the launch complex is unavoidable. The numerical technique and knowledge obtained in this study are applicable in the preliminary design of a launch pad to mitigate the impact of ignition overpressure.

Numerical Study of Solid-Rocket Motor Ignition Overpressure Wave Including Infrared Radiation

The ignition overpressure wave generated during the pressure build-up of a solid-rocket motor is numerically investigated in this study. Numerical simulations are compared to the LP10 experiments, consisting of the horizontal firing of a scaled-down model for the Ariane 5 P230 booster. The present work aims at the prediction of the main characteristics of the ignition overpressure in the far field and the assessment of afterburning influence on both its formation mechanisms and its alteration by the jet plume. Two three-dimensional large-eddy simulations are performed, one considering inert flow and one modeling the afterburning. Infrared images of the plume are also computed with a dedicated radiation transfer solver. An overall good agreement with the experimental results is reported on amplitude and duration. Nevertheless, the reactive case is found to provide better results on amplitude and directivity. The signature is also better reproduced on the microphones near the jet centerline, and the emitted infrared intensity is well captured. Computations indicate that the formation of the shock wave is obtained by coalescence of compression waves emitted by the accelerating jet at early times. For the reactive case, computations show an increased interaction between the jet and the overpressure wave.

Method for Optimally Controlling Unsteady Shock Strength in One Dimension

This paper presents a new formulation and computational solution of an optimal control problem concerning unsteady shock wave attenuation. The adjoint system of equations for the unsteady Euler system in one dimension is derived and used in an adjoint-based solution procedure for the optimal control. A novel algorithm is used to satisfy all necessary first-order optimality conditions while locally minimizing an appropriate cost functional. Distributed control solutions with certain physical constraints are calculated for attenuating blast waves similar to those generated by ignition overpressure from the shuttle’s solid rocket booster during launch. Results are presented for attenuating shocks traveling at Mach 1.5 and 3.5 down to 85%, 80%, and 75% of the uncontrolled wave’s driving pressure. The control solutions give insight into the magnitude and location of energy dissipation necessary to decrease a given blast wave’s overpressure to a set target level over a given spatial domain while using only as much control as needed. The solution procedure is sufficiently flexible such that it can be used to solve other optimal control problems constrained by partial differential equations that admit discontinuities and have fixed initial data and free final data at a free final time.

Scale model acoustic test overview

Launch environments, such as lift-off acoustic (LOA) and ignition overpressure (IOP), are important design factors for any vehicle and are dependent upon the design of both the vehicle and the ground systems. LOA environments are used directly in the development of vehicle vibro-acoustic environments and IOP is used in the loads assessment. The Scale Model Acoustic Test (SMAT) program was implemented to verify the Space Launch Systems LOA and IOP environments for the vehicle and ground systems including the Mobile Launcher (ML) and tower. The SMAT is currently in the design and fabrication phase. The SMAT program is described in this presentation.

Optimal Control of Shock Wave Attenuation using Liquid Water Droplets with Application to Ignition Overpressure in Launch Vehicles

This paper presents the first solution of an optimal control problem concerning unsteady blast wave attenuation where the control takes the form of the initial distribution of liquid water droplets. An appropriate two-phase flow model is adopted for compressible homogeneous two-phase flows. The dynamical system includes an empirical model for water droplet vaporization, the dominant mechanism for attenuating the jump in pressure across the shock front. At the end of the simulation interval, an appropriate target state is defined such that the jump in pressure of the target state is less than that of the simulated blast wave. Given the nature of the non-linear system, the final time must also be a free variable. Anovel control algorithm is presented which can satisfy all necessary conditions of the optimal system and avoid taking a variation at the shock front. The adjoint-based method is applied to NASA's problem of Ignition Overpressure blast waves generated during ignition of solid grain rocket segments...

5% Ares I scale model acoustic test: Overpressure characterization and analysis

During the ignition of a ducted solid rocket motor (SRM), rapid expansion of injected hot gases from the motor into a confined volume causes the development of a steep fronted wave. This low frequency transient wave propagates outward from the exhaust duct, impinging the vehicle and ground structures. An unsuppressed overpressure wave can potentially cause modal excitation in the structures and vehicle, subsequently leading to damage. This presentation details the ignition transient findings from the 5% Ares I scale model acoustic test (ASMAT). The primary events of the ignition transient environment induced by the SRM are the ignition overpressure (IOP), duct overpressure (DOP), and source overpressure (SOP). The resulting observations include successful knockdown of the IOP environment through use of a space shuttle derived IOP suppression system, a potential load applied to the vehicle stemming from instantaneous asymmetrical IOP and DOP wave impingement, and launch complex geometric influences on the environment. The results are scaled to a full-scale Ares I equivalent and compared with heritage data including Ares I-X and both suppressed and unsuppressed space shuttle IOP environments.

Simulation of acoustics for Ares I scale model acoustic tests

The Ares I Scale Model Acoustics Test (ASMAT) is a series of live-fire tests of scaled rocket motors meant to simulate the conditions of the Ares I launch configuration. These tests have provided a well documented set of high fidelity acoustic measurements useful for validation including data taken over a range of test conditions and containing phenomena like Ignition Over-Pressure and water suppression of acoustics. To take advantage of this data, a digital representation of the ASMAT test setup has been constructed and test firings of the motor have been simulated using the Loci/CHEM computational fluid dynamics software. Results from ASMAT simulations with the rocket in both held down and elevated configurations, as well as with and without water suppression have been compared to acoustic data collected from similar live-fire tests. Results of acoustic comparisons have shown good correlation with the amplitude and temporal shape of pressure features and reasonable spectral accuracy up to approximately 1000 Hz. Major plume and acoustic features have been well captured including the plume shock structure, the igniter pulse transient, and the ignition overpressure.

Overview of the Ares I scale model test program

Launch environments, such as lift-off acoustic (LOA) and ignition overpressure (IOP), are important design factors for any vehicle and are dependent upon the design of both the vehicle and the ground systems. LOA environments are used directly in the development of vehicle vibro-acoustic environments and IOP is used in the loads assessment. The NASA Constellation Program had several risks to the development of the Ares I vehicle linked to LOA. The risks included cost, schedule, and technical impacts for component qualification due to high predicted vibro-acoustic environments. One solution is to mitigate the environment at the component level. However, where the environment is too severe for component survivability, reduction of the environment itself is required. The Ares I scale model acoustic test (ASMAT) program was implemented to verify the Ares I LOA and IOP environments for the vehicle and ground systems including the mobile launcher (ML) and tower. An additional objective was to determine the acoustic reduction for the LOA environment with an above deck water sound suppression system. ASMAT was a development test performed at the Marshall Space Flight Center (MSFC) East Test Area (ETA) Test Stand 116 (TS 116). The ASMAT program is described in this presentation.

Ares I Scale Model Acoustic Tests Instrumentation for Acoustic and Pressure Measurements

The Ares I Scale Model Acoustic Test (ASMAT) was a development test performed at the Marshall Space Flight Center (MSFC) East Test Area (ETA) Test Stand 116. The test article included a 5% scale Ares I vehicle model and tower mounted on the Mobile Launcher. Acoustic and pressure data were measured by approximately 200 instruments located throughout the test article. There were four primary ASMAT instrument suites: ignition overpressure (IOP), lift-off acoustics (LOA), ground acoustics (GA), and spatial correlation (SC). Each instrumentation suite incorporated different sensor models which were selected based upon measurement requirements. These requirements included the type of measurement, exposure to the environment, instrumentation check-outs and data acquisition. The sensors were attached to the test article using different mounts and brackets dependent upon the location of the sensor. This presentation addresses the observed effect of the sensors and mounts on the acoustic and pressure measurements.