Showing papers on "Burn rate (chemistry) published in 2005"

The influence of fuel structure on combustion as demonstrated by the isomers of heptane: a rapid compression machine study

Abstract: A detailed experimental study of the nine isomers of heptane has been performed in a rapid compression machine Our interest lies in determining the role of molecular structure of the C 7 H 16 hydrocarbons on the rate of combustion of the various isomers Ignition delay times were measured, and their dependence on the reaction conditions of temperature and pressure was studied, and in this way comparative reactivity profiles of the different isomers were obtained Stoichiometric fuel and ‘air’ mixtures were studied in each case, at compressed gas pressure of 10, 15, and 20 atm for the n -heptane study, and at 15 atm for all other isomers, in the compressed gas temperature range of 640–960 K Characteristic negative temperature coefficient behaviour was observed for each of the isomers The more branched isomeric forms of heptane exhibited reduced reactivity, which correlated with the research octane number In addition, the influence of fuel structure on burn rate was also studied It was found that, similar to overall reactivity, the burn rate decreased with increasing octane number

Numerical and Experimental Study of Flame Propagation and Knock in a Compressed Natural Gas Engine

Abstract: One of the major objectives during the development process of new products is to reduce costs and time to market. Increasing computational power and continuous improvements of models for internal combustion engine applications show promise with respect to replacement of some optimisation steps by computer simulations. A prerequisite for such a substitution is that trends can be reasonably predicted and that calculations adequately incorporate the physics. The flame propagation and the knock behaviour of compressed natural gas engines have been studied in the present work. The aim is to improve the physical understanding on one hand and to develop physically based models for cycle simulation tools on the other hand. These models have been used to optimise a new engine concept which combines ultra-low emissions, high efficiency and driveability. An empirical combustion model based on experimentally determined burn rate curves has been developed to predict the engine behaviour for a wide range of operating conditions. It was found that global qualitative trends can be predicted quite well. Some relevant parameters characterising the combustion process the crank angle at 5% burned, the crank angle at 50% burned and the burn duration defined as 5% to 90% burned have been computed and compared with experimental data. The limitations of such a model have been shown by evaluating this model for a different combustion chamber geometry and various operating conditions. Therefore, a new model based on physical formulations has been developed. The phenomenological combustion model dedicated to compressed natural gas engines developed in this work can be used for projections and additionally to support the understanding of experimental results. A characteristic mean flame front area has been defined by applying some submodels describing the laminar flame speed, the turbulent flame speed and the turbulence intensity. Furthermore, the expansion factor describing the flame propagation due to the ratio of the densities of burned and unburned mixture has been considered. Good agreements between experimental data and computed results have been observed by applying this model to a different combustion chamber geometry. The characteristic mean flame front area was redefined for these new geometrical properties. It was shown, that the new flame front area can be approximated based on considerations concerning flame propagation and based on the known mean flame front area. Research and development activities often focus on increasing the efficiency of spark ignited engines, but many modifications leading to higher engine efficiency in part load operation lead to higher risk of knock occurrence at full load operation. These contradictory requirements clearly indicate the necessity of accurate physical formulations of the knock phenomena. The model developed in this work is based on a one step chemistry approach leading to the so called knock integral method. Due to the varying gas composition of compressed natural gas five well-defined compositions of synthetic gases have been tested to investigate the influence of the individual components. Furthermore, the model considers different operating conditions of an engine meaning that intake pressure, intake temperature, engine speed and spark timing have been varied. The differentiation between non-knocking and knocking combustion has been found to be a key factor for the quality of the model and has been thoroughly investigated. The widely used analysis of the maximum amplitudes of the pressure oscillations has been replaced by the analysis of the burn rate, where a new knock detection method has been developed. A clearly defined initiation of knocking combustion was observed. The parameters of the knock model determined finally can adequately describe the dependencies on the gas composition.

The Enhancement of Regression Rate of Hybrid Rocket Fuel by Various Methods

Abstract: Hybrid rocket has been spotlighted recently by its excellent safety in combustion and comparable thrust level although lower density specific impulse and charging efficiency. Thus, many researches have been focused to find the way to increase regression rate. One of the popular methods to increase regression rate is to use a swirl flow of oxidizer. The effect of swirl flow is to extend the residence time of oxidizer in the propellant grain. Meanwhile, it is well known to solid propellant society that the embedded metal wires can increase the burning rate of solid propellant by increasing heat transfer to solid fuel. Thus, metal wires may cause the same effect in hybrid fuel by enhancing the regression rate of solid. In this study, a series of experimental tests is designed to investigate the enhancement of regression rate of solid fuel by embedded metal wires. And fuel grain configuration is adopted to simply increase the burning surface area and to try to induce swirl flow. PMMA with gaseous oxygen is the solid fuel for investigation. Test results show that embedded metal wires are not effective method in enhancing regression rate. Only 3-4% increases in regression rate are observed. However, fuel port configuration yields higher burning performance up to several ten percentages increase in regression rate. And pitch number total impulse can be design variables in determining overall regression rate.

Direct Numerical Simulation of Solid Propellant Combustion in Crossflow

Abstract: A direct numerical simulation (DNS) of a homogeneous ammonium perchlorate/hydroxyl-terminated polybutadiene solid propellant in crossflow was carried out to provide proper boundary conditions to an interior ballistics model. A two-step global finite-rate chemistry model for ammonium perchlorate decomposition and decomposition gas-binder gas reactions was used. An Arrhenius pyrolysis model was used to describe the propellant regression rate. Using strand burn rate data, the DNS model was calibrated by modeling an environment with no crossflow and adjusting thermodynamic properties in the gas/solid to match the measured regression rate. Crossflow Mach numbers were then induced, ranging from At = 0.0 to 0.8, where the calculated regression rates are compared to the base regression rate at M = 0.0. The analysis shows that near-wall vorticity increases with Mach number, but does not significantly reduce the flame to wall stand-off distance. Temperature gradients due to boundary layer compression are shown to dominate the regression rate. The validity of the results was tested by incorporating them into an interior ballistics model to simulate the performance of an actual rocket motor and compare to static test data. A simplified DNS heat-transfer-based analysis is presented and shown to produce similar conclusions.

Plasma Ignition and Combustion of JA2 Propellant

Abstract: Experiments were performed to investigate the effects of various parameters on plasma-driven ignition and combustion of a double-base propellant under closed-chamber conditions. The parameters varied include input electrical energy, nozzle length and inner diameter, nozzle exit to propellant distance, as well as propellant sample thickness. Chamber pressure was measured to determine the ignition delay and to deduce the regression rate. High-speed images of the plasma jets and combustion event were also recorded. At low plasma energies, rapid, plasma-driven burning occurred, but self-sustained burning was not achieved. With moderate plasma energies, combustion of the propellant exhibited a two-stage burning behavior: one stage of plasma-driven rapid burning that occurred during the plasma pulse and a second stage of slower self-sustained burning that occurred with a clear delay after the first stage. When plasma energy was increased further, the two-stage behavior became less distinct and eventually disappeared, leaving only one stage of burning. Nozzle length and diameter affected the ignition and combustion characteristics as a result of energy losses from the plasma as it flows through the nozzle. The propellant burning behavior is also affected by both nozzle-sample distance and sample thickness. High-speed images revealed vigorous motion of gases in the closed chamber, which was induced by the plasma jet. Also, the images showed what appeared to be JA2 fragments; this observation was confirmed by recovery of fragmented propellant after some of the tests.

Direct injection combustion chamber geometry

Abstract: Disclosed is an obstruction for use in a combustion chamber of an internal combustion engine. The obstruction is provided and located within the chamber to generate turbulence and break-up or disrupt the soot rich zone within a directly injected quantity of fuel that is burning. More specifically, disclosed is a ring to disrupt fuel jets directly injected into the combustion chamber that impact on or are influence by the ring. The ring can be suspended from the piston or from the fire deck. Disclosed are obstructions that are posts that help generate turbulence that also are targeted at disrupting the soot rich zone of the burning fuel jets. Disclosed is a method for disrupting the soot rich zone or reducing soot generated within the combustion chamber and increase burn rate by impacting the fuel jets on an obstruction within the chamber.

Performance of AP-Based Composite Propellant Containing Nanoscale Aluminum

Abstract: Several HTPB/AP/Al-based composite propellant mixtures were prepared with and without the addition of small percentages of nanoscale aluminum and burned in a strand burner at pressure up to 5000 psi. The effect of monomodal versus bimodal AP particle size, course aluminum particle size, nano aluminum particle size, and course-to-fine ratios on burn rate and manufacturability were explored. A significant conclusion of the present study is that the addition of nano-sized aluminum does not necessarily increase a propellant's burn rate when prepared using conventional methods. It was observed that, over the range of mixtures and pressures explored, a bimodal oxidizer is required for the nanoscale Al to affect the burning rate, and that a monomodal oxidizer tended to nullify any influence. In some cases, the addition of nano-sized aluminum actually decreased the burn rate. The level of burn rate increase or decrease depended on the bimodal or monomodal AP particle sizes, the coarse Al particle size, and the pressure range.

Combustion system and method for self adaption controllable heat premixing direct jet type diesel engine

Abstract: The invention discloses a kind of self-adaptnig, heat-controllable, pre-mixing and direct-spraying diesel engine burning system and its method, which belongs to the field of internal-combustion engine. The stated burning system incldues multi-hole glib talker, multi connection space burning room and inelt track. The stated multi connection space burning room consists of two or more linking space structure, it can control the transmitting way for pre-mixing burning, and when cooperatnig with the fuel spraying and timing oil support, it can effectively control the space-time distribution of combination gas and fire-starting point and burn rate under different operating modes, thus make the burning system be self-adapting and controllable. The burning room can form multi circulations to promote the forming of the homogeneous combination gas. The vortex ratio O of the stated system is 0-2, glib aperture is 50-180 mum, the oil spraying pressure is higher than 800 bar, it can reduce flame temperature notably, carbon smoke, NOX and HC, improve the combustion efficiency.

Ultrasonic Burn Rate Testing of Bi-Plateau Propellants Under Decreasing Pressure Conditions

Abstract: This paper will present the design of an experiment to measure the burn rate of a bi-plateau composite propellant under a decreasing pressurization rate. It is hoped that by investigating the burning rate characteristics of a bi-plateau propellant under these conditions, some new insights might be gained into the mechanism causing the plateau effect. A bi-plateau propellant is a propellant that has a high and lowpressure region where the burning rate remains constant as the pressure is increased. These propellants are well suited to facilitate propellant energy management and may be less prone to acoustic combustion instabilities. The testing was conducted using a closed combustion bomb utilizing a pulse-echo ultrasonic technique to measure the burning rate. Use of the ultrasonic method allows the burning rate of a propellant to be measured over a large range of pressures during a single test. To measure the burning rate under a decreasing pressure scenario, a novel testing method was developed to release pressure at a controlled rate during the test firing. This is accomplished by use of a custom burst disk and nozzle. A simple numerical model was developed to determine a nozzle throat diameter that would produce a decrease of pressure that would be a mirror image of the pressure increase during the closed portion of the test. Several samples of MURI #4 composite propellant were tested in this manner. Although burning rate data was measured for each of these tests, the data collected to date is not enough to draw any significant conclusions.

Coolant Effect on Gas Generator Propellant

Abstract: The effect of coolants has been studied on the burning properties of low burning rate HTPB/AP composite propellant containing Oxamide or Melamine as coolant for the gas generator. With increasing the content of coolant, the burning rate and the flame temperature could be lowered and the effect on flame temperature was about the same for two coolants. However due to the different thermal decomposition properties of coolant, the burning rate of Melamine propellant was found to abnormally decrease if AP was partially replaced with AP.

Dead Zones in LX-17 and PBX 9502

Abstract: Pin and X-ray corner-turning data have been taken on ambient LX-17 and PBX 9052, and the results are listed in tables as an aid to future modeling. The results have been modeled at 4 zones/mm with a reactive flow approach that varies the burn rate as a function of pressure. A single rate format is used to simulate failure and detonation in different pressure regimes. A pressure cut-off must also be reached to initiate the burn. Corner-turning and failure are modeled using an intermediate pressure rate region, and detonation occurs at high pressure. The TATB booster is also modeled using reactive flow, and X-ray tomography is used to partition the ram-pressed hemisphere into five different density regions. The model reasonably fits the bare corner-turning experiment but predicts a smaller dead zone with steel confinement, in contradiction with experiment. The same model also calculates the confined and unconfined cylinder detonation velocities and predicts the failure of the unconfined cylinder at 3.75 mm radius. The PBX 9502 shows a smaller dead zone than LX-17. An old experiment that showed a large apparent dead zone in Comp B was repeated with X-ray transmission and no dead zone was seen. This confirms the ideamore » that a variable burn rate is the key to modeling. The model also produces initiation delays, which are shorter than those found in time-to-detonation.« less

Pulse-echo measurements of unsteady propellant deflagration

Abstract: This article discusses a laboratory test method for the measurement of nonsteady deflagration rates and combustion-stability properties of solid propellants. The method combines ultrasonic pulse-echo measurement, fluidic pressure modulation, and digital signal processing techniques to compute the real and imaginary components of pressure-coupled response functions of solid propellants. A description of the apparatus identifies the major components and their functions. A section on the experimental procedure illustrates the steps necessary to conduct a test, and a section on the data reduction technique describes the sequence of steps employed to compute the nonsteady burn rate and the pressure-coupled response. A detailed implementation of the technique as it applies to two representative tests follows, in which graphs and tables illustrate the intermediate data reduction steps. Details of the evaluation of the uncertainties associated with the technique and the data reduction algorithms are also presented.

Cross-sectional functionally graded propellants and method of manufacture

Abstract: Methods of making cross sectional, functionally-graded munitions propellants exhibiting various distributions of particle concentrations and burn rate, including having a fast burning core and slower burning outer layer(s). Unlike prior art methods of preparing such munitions, propellants prepared according to our inventive method(s) may be performed substantially as a single extrusion step or as a few processing steps, without requiring the time, expense and/or difficulties that characterized familiar, laminating methods and methods which use multiple extruders. Our inventive method advantageously employs a demixing phenomenon that, prior to our inventive application and teaching, has been considered quite undesirable in the preparation of propellants where uniformity and well-mixedness have been propellant attributes widely sought after.

Measurements and ALE3D Simulations for Violence in a Scaled Thermal Explosion Experiment with LX-10 and AerMet 100 Steel

Abstract: We completed a Scaled Thermal Explosion Experiment (STEX) and performed ALE3D simulations for the HMX-based explosive, LX-10, confined in an AerMet 100 (iron-cobalt-nickel alloy) vessel. The explosive was heated at 1 C/h until cookoff at 182 C using a controlled temperature profile. During the explosion, the expansion of the tube and fragment velocities were measured with strain gauges, Photonic-Doppler-Velocimeters (PDVs), and micropower radar units. These results were combined to produce a single curve describing 15 cm of tube wall motion. A majority of the metal fragments were captured and cataloged. A fragment size distribution was constructed, and a typical fragment had a length scale of 2 cm. Based on these results, the explosion was considered to be a violent deflagration. ALE3D models for chemical, thermal, and mechanical behavior were developed for the heating and explosive processes. A four-step chemical kinetics model is employed for the HMX while a one-step model is used for the Viton. A pressure-dependent deflagration model is employed during the expansion. The mechanical behavior of the solid constituents is represented by a Steinberg-Guinan model while polynomial and gamma-law expressions are used for the equation of state of the solid and gas species, respectively. A gamma-law model is employed for the air in gaps, and a mixed material model is used for the interface between air and explosive. A Johnson-Cook model with an empirical rule for failure strain is used to describe fracture behavior. Parameters for the kinetics model were specified using measurements of the One-Dimensional-Time-to-Explosion (ODTX), while measurements for burn rate were employed to determine parameters in the burn front model. The ALE3D models provide good predictions for the thermal behavior and time to explosion, but the predicted wall expansion curve is higher than the measured curve. Possible contributions to this discrepancy include inaccuracies in the chemical models, integration of the momentum equation, and representation of the interfaces in the gaps. Two model problems were used to explore the effects of parameter variations on the fracture and fragmentation of AerMet 100 tube sections driven by the deflagration of LX-10. For the range of parameters considered, the model fragment sizes are of the same scale as the measured sizes.

Principle and Realizable Approach of Variable Burning Rate Propellant

Abstract: According to the interior ballistic performance of guns, a concept of variable-burning rate propellant was put forward, the fundamental principle of this propellant was discussed and the technologic way to realize the principle was explained.In order to realize the variable-burning rate ,the propellant has two layers ,inner layer's burning rate is higher than the outer layer's. The results show that two-layered variable-burning rate propellant has wishful discharge rule and good properties of progressive combustion.The propellant has the advantages of high energy,universal applicability and high security.

Burn rate profiles for compression ignition engine model

Abstract: This study was done in order to show general trends as user-defined burn profiles are changed for Wave model of naturally aspirated compression ignition engine. The recent advances would have been impossible without the help from the computer-aided engineering (CAE) methods. For the processes governing engine performance and emissions, two basic types of models have been developed. The presented measurements of cylinder pressure and computation of its predicted equivalent have shown that user-defined burn profile should be established using gross (chemical) heat release rate. Such approach offers better accuracy then the net heat release profile which is by definition a simplified measure of combustion process.

Propellant composition and methods of preparation and use thereof

Abstract: The invention relates to propellant compositions comprising a solid inorganic perchlorate oxidizing agent, a nitrogen-containing fuel, and a burn rate catalyst. Such compositions may be used as a propellant material, (e.g., in rocketry), a pyrotechnic material, an explosive material, a light generating material, a heat generating material, or a sound generating material.

Method and system for controlling oxygen levels in exhaust gases emitted from an i.c. engine for particulate filter regeneration

Abstract: A method and system for controlling oxygen levels in exhaust gases emitted from an i.c. engine adjusts the amount of cooled EGR and non-cooled EGR to allow the temperature of the exhaust gases to be controlled in order to achieve a desired temperature for regeneration of a particulate filter. The exhaust gas recirculation may be directed and controlled through an EGR cooler, an air cooler, as well as a cooler bypass to achieve the desired exhaust gas temperature. Also disclosed is a method which includes controlling the oxygen levels as a function of the soot burn rate of the filter, and a method which includes monitoring these rates during regeneration to prevent an uncontrolled soot burn rate condition.

Effect of Components of Fuel-rich Boron-based Solid Propellant on the Burning Rate in Low Pressure

Abstract: Effects of components of fuel-rich boron-based solid propellant on burning rate in low pressure and explosive heat were investigated by measuring its burning rate with standard burner method and explosive heat with calorie meter of oxygen bomb. The results show that enhancing the concentrations of AP, adding burning catalyzer and increasing the concentration of superfine AP will increase the burning rate, and increasing the boron content increases the explosive heat and decreases the burning rate. Thermal analysis results show that the burning rate increasing in low pressure can be attributed to the condensed-phase reaction.

Development of Ionic Liquid Monopropellants for In-Space Propulsion

Abstract: A family of new, low toxicity, high energy monopropellants is currently being evaluated at NASA Marshall Space Flight Center for in-space rocket engine applications such as reaction control engines. These ionic liquid monopropellants, developed in recent years by the Air Force Research Laboratory, could offer system simplification, less in-flight thermal management, and reduced handling precautions, while increasing propellant energy density as compared to traditional storable in-space propellants such as hydrazine and nitrogen tetroxide. However, challenges exist in identifying ignition schemes for these ionic liquid monopropellants, which are known to burn at much hotter combustion temperatures compared to traditional monopropellants such as hydrazine. The high temperature combustion of these new monopropellants make the use of typical ignition catalyst beds prohibitive since the catalyst cannot withstand the elevated temperatures. Current research efforts are focused on monopropellant ignition and burn rate characterization, parameters that are important in the fundamental understanding of the monopropellant behavior and the eventual design of a thruster. Laboratory studies will be conducted using alternative ignition techniques such as laser-induced spark ignition and hot wire ignition. Ignition delay, defined as the time between the introduction of the ignition source and the first sign of light emission from a developing flame kernel, will be measured using Schlieren visualization. An optically-accessible liquid monopropellant burner, shown schematically in Figure 1 and similar in design to apparatuses used by other researchers to study solid and liquid monopropellants, will be used to determine propellant burn rate as a function of pressure and initial propellant temperature. The burn rate will be measured via high speed imaging through the chamber s windows.

Burn rate nanotube modifiers

Abstract: Nanotubular structures of high energy materials are used in high energy compositions, such as propellants.