Single-base Propellants Research Articles

Exploration of the combustion characteristic based on the pyrolysis and combustion spectral analysis of single base propellant

Exploration of the combustion characteristic based on the pyrolysis and combustion spectral analysis of single base propellant

A parameter determination method of powder burn model based on Levenberg-Marquardt optimization

ABSTRACT The powder burn model is a mathematical model used to characterize the combustion behavior of energetic materials. In this paper, a parameter determination method for the powder burn model is proposed based on the Levenberg-Marquardt (L-M) optimization algorithm, establishing connections between internal ballistics parameters and powder burn model parameters. Taking a 4/1 single-base propellant as an example, the detailed fitting process is presented, and error analysis is conducted. The fittings of the gas state equation and reaction rate equation of powder burn model converge at the 15th and 22nd iterations, respectively. Both fittings displayed a high level of accuracy, with an R-squared value of 0.999. The comparison with the results of the closed bomb experiments demonstrates excellent agreement between pressure-time curves calculated by the powder burn model and the internal ballistics model, confirming their suitability for describing the combustion behavior of propellants. This method provides a foundation for numerically simulating the internal ballistics combustion behavior of energetic materials.

Aging prediction in single based propellants using hybrid strategy of machine learning and genetic algorithm

This study proposes novel approach that combines optimization and machine learning to predict the aging of single-base propellants in alignment with the high-performance liquid chromatography (HPLC). To obtain aging and reduce HPLC experimentation, the proposed algorithm provides an efficient procedure. A hybrid strategy of genetic algorithm and ML models including support vector machine, ensemble trees, Gaussian process, and regression tree is combined to optimize SBPs aging. The correlation map provides an interdependence table of aging with initial composition, caliber, and environmental factors. The coefficient of determination and RMSE will determine predictive capabilities of ML models. ET-GA is an optimum-performing ML model with a 0.89 coefficient of determination. Partial dependence plots give an overview of the impact on aging by several variables with maximum impact by temperature, humidity, and diphenylamine. ET-GA shows 95% agreement with experimental data. This results in an economically viable interface that reduces experimentation and provides real-time aging prediction.

Study on Pyrolysis Behaviors and Characteristics, Thermodynamics, Kinetics, and Volatiles of Single-Base Propellant, a Typical Energy-Containing Material

The widespread use of single-base propellant may contribute to serious pollution of the environment. The study of single-base propellant pyrolysis could provide an in-depth understanding of the combustion mechanism, reveal the key steps and reaction kinetics of the combustion process, and reduce the damage when using single-base propellant to the environment. In the present study, the pyrolysis behaviors, pyrolysis characteristic parameters, kinetics, thermodynamics, and volatiles of single-base propellant pyrolysis in an argon atmosphere were studied. The results showed that the main temperature ranges of pyrolysis and heat variation were 400–700 K and 450–520 K, respectively. With the increase in the heating rate, the maximum/average reaction rate of pyrolysis increased, the maximum instantaneous heat flow and the heat flow integral increased, the pyrolysis and combustion performance increased, and the thermal stability decreased. The average global activation energy and pre-exponential factor of the pyrolysis were 202.82 kJ and 9.48 × 1021, respectively. Thermodynamic analysis showed that the single-base propellant pyrolysis was a spontaneous endothermic reaction with a low energy barrier and fast reaction rate, which was beneficial to the formation of active complexes. In addition, information on the main volatiles was obtained, including H2, CH4, C2H4, C2H6, H2O, HCN, HCOOH, NO2, HONO, and CO2.

Combinations of essential oils as effective green stabilizers for single base propellants

AbstractNitrocellulose‐based propellants undergo natural (and inevitable) autocatalytic degradation reactions. The presence of a stabilizer is essential to avoid and reduce the degradation reactions by capturing the NOx molecules. Traditional stabilizers, such as diphenylamine, and ethylcentralite, react with NOx through their amine and/or amide groups, leading to n‐nitroso groups, which are known to have carcinogenic, mutagenic and reprotoxic properties. Molecules that are not prone to form by‐products containing nitrosamines have been studied as substitutes, such as guaiacol and curcumin. However, the aromatic rings on these molecules have their acidity augmented when capturing the NOx groups and, paradoxically, increasing hydrolysis rates. In order to find a solution for the problem, we evaluated the use of essential oils containing terpenes and/or phenolic compounds to introduce a buffering capacity. Several propellant formulations with those compounds were subjected to traditional stability tests (German, Bergman–Junk and Storage tests), Pressure Vacuum Stability Test and Heat Flow Microcalorimetry. Finally, industrial batches were produced for the evaluation of real (ballistic) performance. Results indicated that the usage of essential oils increases stability properties not only through a sum of effects, but also in a synergistic way. Ballistic results were also adequate.

Influence of the Ignition Method on the Characteristics of Propellant Burning in the Context of the Geometric Burning Model

Mathematical models for the simulation of the operation of various projectile-throwing systems are continuously modified, simultaneously with the development of propellants. For these models, properly determined values of energetic ballistic characteristics of propellants are very important. This paper presents an original test and the results of closed vessel comparative investigations. The study analyses specific combustion characteristics of single-base propellants using conventional black powder ignition, plasma ignition, and gas ignition. The results of the study indicate the need to take into account—in the calculation of the burning rate—not only the dynamics of gas pressure changes but also the real (experimental) form function, which differs from the theoretical one resulting from the assumed geometric burning model. The obtained results allow for a critical analysis of the existing methods used for the determination of values of ballistic characteristics of propellants. Further, it will allow for creating pyrostatic test conditions that would reflect the condition of instantaneous ignition of propellant grains over their entire surface in the most realistic way.

Multi-scale simulation of diffusion behavior of deterrent in propellant

• 1 An onion model is introduced to simulate the diffusion of deterrent in the propellant. • 2 The gap between the experiments and simulation can be bridged by the onion model. • 3 A new time scale is found to describe the diffusion process in the crystalline polymer. • 4 The results of Raman spectra verify the correctness of the onion model. Concentration distribution of the deterrent in single-base propellant during the process of firing plays an important role in the ballistic properties of gun propellant in weapons. However, the diffusion coefficient calculated by molecular dynamics (MD) simulation is 6 orders of magnitude larger than the experimental values. Meanwhile, few simple and comprehensive theoretical models can explain the phenomenon and accurately predict the concentration distribution of the propellant. Herein, an onion model combining with MD simulation and finite element method of diffusion in propellants is introduced to bridge the gap between the experiments and simulations, and correctly predict the concentration distribution of deterrent. Furthermore, a new time scale is found to characterize the diffusion process. Finally, the time- and position-depended concentration distributions of dibutyl phthalate in nitrocellulose are measured by Raman spectroscopy to verify the correctness of the onion model. This work not only provides guidance for the design of the deterrent, but could be also extended to the diffusion of small molecules in polymer with different crystallinity.

Experimental Study on the Thermodynamic Damage Power of Ammunition Deflagration in a Closed Explosive Device

The high temperature and high pressure gas produced by propellant deburning has strong thermal effect,which will produce strong thermal damage effect on the target. In this study, an improved closed explosive device was used to simulate the thermal shock loading of 5/7 single base propellant with a charge mass of 17.4 g, and the change law of heat flow density of propellant in the process of deflagration in a closed environment was tested. The experimental results show that the temperature rises rapidly during the deflagration of the 5/7 single-base propellant, and the maximum heat flow density can reach 17.68 MW/ m2 . The curves obtained from the three tests have good consistency in the change trend, which proves the engineering practicability of the improved closed explosive device in the study.

An approach to detecting diphenylamine content and assessing chemical stability of single-base propellants by near-infrared reflectance spectroscopy

Diphenylamine (DPA) as a stabilizer component plays an important role in maintaining the chemical stability of single-base propellants (SBPs). This work investigated the feasibility of rapidly detecting the content of DPA in SBP by near-infrared reflectance spectroscopy (NIRS). The quantitative NIR model was developed by intervals selection, spectral pretreatment and factor number optimization. The optimal spectral intervals were determined to be 1081 nm ∼ 1280 nm and 1378 nm ∼ 1602 nm based on the characteristic spectral peaks of DPA. By comparing the performance of the developed models with different preprocessing methods, the best preprocessing method was standard normal variate transformation (SNV) + de-trending (Dr) + Smoothing. The optimal number of factors was 6 for DPA model. Partial least squares (PLS) regression was used to establish the calibration models of DPA. For the developed model, the determination coefficients of calibration and prediction (Rc2, Rp2) were 0.9907 and 0.9884, respectively. The root mean square errors of calibration and prediction (RMSEC, RMSEP) were 0.0310 and 0.0342, respectively. The samples in the prediction set were predicted by the developed model, and the average absolute error of the proposed and reference method was only 0.0265. The developed model can be applied in rapid monitor the content of DPA in SBP. In addition, vieille test have demonstrated that the chemical stability of SBP became worse with the decrease of DPA content. The content of DPA contained in the SBP with qualified chemical stability is not less than 0.8753%. Thus, the developed model can be used to judge whether the chemical stability of SBP is qualified or unqualified.

Numerical Simulation and Experimental Study of Internal Ballistics Parameters for Howitzer Field Guns

Howitzer Gun is a type of large-caliber artillery gun that typically utilizes a mixture of propellant grain shapes to control the burning inside the gun, and to impart the prescribed velocity to the projectile with the smallest mass of charge without exceeding the maximum allowable pressure. In this paper, a mathematical model has been developed to predict the main internal ballistic parameters i.e., Maximum Pressure (Max. P) and Muzzle Velocity (MV) for artillery howitzer guns. The propellant charge utilized is a single-base propellant using a mixture of dual-shape grain namely, tubular and multi-tubular seven-hole shapes. The mathematical model was solved numerically using the Runge-Kutta method in MATLAB environment for a 130 mm howitzer field gun which was chosen as a test case. The simulation results were obtained in terms of several plots showing the effect of grain shape and grain mixture ratio on the Max. P and MV along the gun barrel. Furthermore, the optimum mixture ratio gives a slightly reduced MV with a significant reduction in Max. P has been determined graphically and compared with experimental data taken from the test firing of the gun. The simulation results showed good agreement with the experimental ones (less than 10% numerical error). The proposed model can be used in the analysis and optimization of other similar gun systems taking into account the right input data for both guns, and propellants.

A New Method for Correcting Deviation of Volatiles Content and Chamber Pressure for Single Base Propellant

In this study, special treatment was applied to two production batches of single-base propellant to correct three of the most important properties in the final product. These properties are internal and external volatile content (IV%, EV% respectively) and chamber pressure, the special treatments depend on mixing two batches with different percentages of mixing starting with sieving and ended with blending to guarantee the homogeneity of the final batch. The batches under study (A and B), batch A with (IV% 0.53%) which must be not less than 0.6%, so it deviated from standard requirement and Bach B with (IV =0.88%), the treatment applied for these batches to generate (C and D) batches. Batch C was a mixture composed of (25% of batch A and 0.75% of batch B). batch D was a mixture composed of (50%batchA and 50% of batch B). Six samples were subjected to sieving and blending according to calculations to correct internal and external volatile content and chamber pressure. For all samples lab, ballistics test, and executive calculations were done. After the test observed that no significant difference between the test and the results of calculations for all samples with different mixing ratios either volatiles content or chamber pressure so according to the result achieved the procedure (Method) was dependable for correcting the deviation of volatiles content and chamber pressure. The selectivity of the optimum mixing ratio can be controlled by using the equation used in this study. The importance of this study in reducing material losses due to the non-conformity of the final product with the specification.

Analysis of Application of Plasma Ignition in Closed Vessel Tests

This paper presents the results of a comparative investigation into the effects of the ignition method on the ballistic properties of three types of propellants: a single-base propellant, a double-base propellant and a low vulnerability (LOVA) propellant, as determined via closed vessel tests (CVT). Conventional gunpowder ignition and plasma jet ignition methods were used. The influence of the ignition method on the values of the propellant characteristics obtained in CVT was analysed. It was found that the method of ignition has an influence on the values of propellant characteristics, determined in CVT. An analysis of the experimental form functions showed that plasma ignition is not a solution to the problems inherent to the process of determining the ballistic properties of propellants in which the burning process deviates from the geometric burning law.

단기추진제 저장수명 예측을 위한 온도분포형태 영향성 분석

추진제는 “1회성 시스템(one-shot system)”으로 수명주기 동안 장기간 저장된다. 단기추진제의 주요성분인 Nitrocellulose는 저장 중 온도, 습도 등의 환경요인에 의해 분해되는 성질이 있어 초기의 품질수준 유지가 어렵다. 이러한 추진제의 특성을 고려하여 추진제 전순기(Total Life Cycle) 동안의 품질 신뢰성 확보가 필요하고, 추진제의 정확한 수명 예측을 위한 다양한 연구가 진행되고 있다. 본 논문은 저장환경의 온도분포형태가 단기추진제의 저장수명에 미치는 영향에 관한 연구논문이다. 탄약 저장시설 내의 온도분포를 여러 형태로 가정하였고 분포형태를 확률밀도함수로 근사, 저장수명의 기댓값을 도출하였다. 평균온도는 25 ℃로 동일하지만 온도분포형태에 따라 기대되는 저장수명은 114년에서 217년으로 큰 차이를 보인다. 이를 통해 동일한 평균온도를 가지더라도 저장소가 위치한 환경에 따라 다양한 형태의 온도분포형태에로 인해 저장수명에 영향을 미칠 수 있으며, 낮은 온도의 비율이 높을수록 저장수명의 기댓값이 커질 수 있음을 확인하였다. 온도분포형태별 확률밀도함수를 누적분포함수로 나타내면 저장환산온도는 누적분포함수의 40 %에 해당하는 온도와 11 % 이내의 편차를 가진다. 보다 정확한 저장수명을 예측하기 위해선 평균온도만이 아닌 온도분포를 고려하는 것이 타당할 것으로 판단된다.

English

In this work chemical changes in 42 years old single base propellant induced by natural aging were evaluated. The sample was stored for a long time under uncontrolled conditions. The chemical stability was tested using High performance liquid chromatography (HPLC), High-performance thin-layer chromatography (HPTLC), the vacuum stability test (VST), SEM/EDX and visual analysis by Stereo Microscope. Heat flow calorimetry (HFC) method was used for analysis of thermal behavior of the sample. Visual changes in appearance of the 42 years old propellant sample surface were apparent. HPLC analysis showed that the sample contains very low effective stabilizer content (<0.2%) and VST measured very high gas release (ΔVST gas >2 ml/g). Therefore, the propellant is classified as very unstable. Although the effective stabilizer is almost completely consumed, the sample demonstrated very good thermal properties measured using HFC where the heat flow limit of 114 μW/g was not exceeded. The presence of inorganic stabilizers which could contribute to stability was examined using SEM/EDX. The results showed only presence of C, O and N and traces of Si. It could be assumed that even though all the parent DPA is almost consumed, the remaining daughter stabilizer products continue to protect the propellant from possible self-ignition for a long period of time. Key words: Propellants, natural aging, chemical stability.

Effects of module number and firing condition on charge thermal safety in gun chamber

Thermal safety of modular charge which is fed into and retained in the chamber after gun fires consecutively is first investigated with cook-off method. A two-dimensional cook-off model of modular charge in gun chamber is established and the cook-off process of modular charge in gun chamber is numerically simulated. Then the effects of module number and firing condition on charge thermal safety are evaluated by researching the cook-off response characteristics of modules. The results show that, under conditions of different module numbers the cook-off responses all occur on the module closest to the boundary of missile, and the single-base propellants located at the inner surface of cartridge ignite first. When the number of loaded module changes from 1 to 6, the cook-off response temperatures vary little, only in a small range of 478.1 K–482.4 K. The cook-off response times decrease logarithmically in the range of 211.2 s–166.7 s with the increasing length of residual air gap in gun chamber. The simulation results are well matched with the experimental data. Furthermore, different firing conditions have great influence on the cook-off response time, minor influence on the initial response position and little influence on the response temperature. Under the three conditions of consecutive 32 launches with 5 rounds/min, 43 launches with 1 round/min, and 41 launches with different firing frequencies, the cook-off response temperatures are 479.2 K, 481.1 K and 479.9 K respectively and the response times are 709.2 s, 211.2 s and 214.4 s respectively. The response position is near the middle area of the inner cartridge surface in the former condition and near the right area in the latter two conditions.

Effect of nitrate nitrogen content on properties of modified single-base propellant

In order to investigate the effect of nitrocellulose (NC) nitrogen on the performance of modified single-base propellants, modified single base propellants with different nitrogen content (12.8%, 12.7%, 12.6%, 12.4%) were prepared by solvent extrusion. The mechanical properties of the modified single-base propellant were tested using a universal material testing machine and a simply supported beam impact tester; the impact section was observed by a scanning electron microscope; and the combustion performance of the modified single-base propellant was tested by a closed explosive device test. The results showed that the higher the nitrogen content of nitrocellulose, the worse the swelling effect, the worse the cotton’s dissolving ability, and the worse the mechanical properties of modified single-base propellant; as the nitrogen content increases, the burning rate and force capacity of the propellant gradually increase.

Effect of ageing on the combustion of single base propellants

This paper shows how the combustion properties of single base nitrocellulose propellants are affected by degradation by ageing. A single base gunpowder sample containing methyl centralite and ethyl centralite as stabilizers was artificially aged by 10, 20 and 25 years. Closed vessel experiments were performed to evaluate the burning rate, the dynamic vivacity, the maximum pressure, the force, and the covolume of the gases produced. The propellant degradation was characterized by the Bergmann-Junk test, heat flow calorimetry test (HFC), high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC). Gel permeation chromatography was especially useful to describe the degradation process. The results found for the burning rate suggest the existence of two phases during ageing: intensification and passivation. The intensification phase occurs while the propellant samples maintain the chemical stability and the passivation phase was observed for the unstable samples.

Research on the Combustion Performance of Mixed Charge of the Super-porous Coated Propellant

In order to study the constant volume combustion performance of the mixed charge of super-porous propellant and super-porous coated propellant, 37-hole nitroguanidine propellant and 37-hole nitroguanidine coated propellant containing flame retardant TiO2 were prepared. At high temperature(50°C), normal temperature(20°C), low temperature(-40°C), a constant volume combustion experiment was performed on a mixed charge with a mass ratio of 1: 1 for the 37-hole propellant and the 37-hole coated propellant. The research results show that the constant volume combustion performance of the mixed charge is different from a single coated propellant and a single base propellant. The p-t, dp/dt-t and L-B curves of the mixed charge were between the coated propellant and the base propellant, but mixed charge has the greatest progressive combustion. And the temperature dependence of the progressive combustion of mixed charge is small, which has a certain low temperature effect.

On Influence of Mechanical Properties of Gun Propellants on Their Ballistic Characteristics Determined in Closed Vessel Tests.

The geometric burning law of gun propellants is widely used in computer codes used for the simulations of the internal ballistics of guns. However, the results of closed vessel tests prove that the burning process of some propellants deviates from the geometric law. Validation of the hypothesis that observed deviations can be attributed to the cracking of propellant grains was the aim of this work. In order to verify the hypothesis, three types of gun propellants were chosen with considerably differing mechanical strengths: a single-base propellant, a double-base propellant, and a composite propellant. The mechanical properties of the gun propellants were tested using a quasi-static compression method with strain rate values of the order of 0.001 s−1 and the Split Hopkinson Pressure Bar technique with the strain rate in the range of 1000–6000 s−1. The mechanical responses of the propellants were assessed on the basis of the true stress–strain curves obtained and from the point of view of the occurrence of cracks in the propellant grains specimens. Moreover, closed vessel tests were performed to determine experimental shape functions for the considered gun propellants. Juxtaposition of the stress‒strain curves with the experimental shape functions proved that the observed deviations from the geometrical burning law can be attributed mainly to the cracking of propellant grains. The results obtained showed that the rheological properties of propellants are important not only from the point of view of logistical issues but also for the properly controlled burning process of propellants during the shot.

Experimental Study on Plasma Ignited Single-base Propellant using SEM and EDS

To explore the reaction mechanism in the plasma-propellant interaction, plasma ignition and conventional ignition experiments are carried out on a single-base propellant. The samples after ignition are analyzed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Results show that the plasma jet brought a variety of high enthalpy flows into the propellant and deposited them on the surface of the propellant. These high enthalpy particles reacted with the propellant on the surface rapidly and produced voids and cracks different from the surface melting mode in the conventional ignition process. These voids provided microchannels for ignition and heat transmission. The area of ignition and combustion increased accordingly.