CALCULATION OF THE IGNITION DELAY TIME OF METALLIZED SOLID PROPELLANT BY A CONVECTIVE HIGH-TEMPERATURE FLOW

This paper presents a mathematical model and methodology to calculate the ignition delay time and the stationary combustion formation of a metallized solid propellant with aluminum additives ignited by a convective high-temperature flow.

ОПТИМІЗАЦІЯ КОНСТРУКЦІЇ ФАКЕЛЬНОГО ЗАПАЛЬНИКА ГТД ЧИСЕЛЬНИМ МЕТОДОМ

Solved the problem of gas-turbine engine combustion chamber flame igniter efficiency increasing by increasing the flame temperature via optimizing the body design. To determine the influence of the igniter body various geometric parameters, affecting the formation and combustion of the fuel-air mixture, a parametric model was developed. This model together with the developed project in the ANSYS Workbench software package made it possible to automate the modeling process. The influence of the geometric parameters of the igniter body and external factors on the average flame temperature has been studied via a numerical model of the stationary combustion process of the air-fuel mixture formed inside the igniter of the combustion chamber of a gas turbine engine by evaporation and spraying particles of aviation kerosene in the air stream. The adequacy of the numerical simulation results was confirmed by the implementation of a series of full-scale experiments using the Fisher criterion.The uniformity of temperature and adequacy of the average temperature estimation algorithm was established using the correlation analysis of the results of measured temperature at various points of the flame. To determine the degree and nature of their influence, sequentially screening (fractional), as well as full-factor experiments with varying factors at two and three levels were implemented. Based on the results of the analysis of variance, the most statistically significant factors were selected. A regression dependence was established that relates the diameter of the air inlet orifice and the air pressure drop to the flame temperature. A qualitative and quantitative assessment of the influence of the considered factors on the process of formation of a hot air mixture and its combustion has been performed. The optimal values of the geometric parameters of the igniter body and its operating conditions are determined under which the maximum flame temperature at the stationary combustion stage is ensured. Relationships between design features, igniter operation mode, and the temperature of the flame are established. This allows expanding the range of stable ignition of gas turbine engine combustion chambers in accordance with the design of the igniter, the starting fuel supply mode, and the air pressure drop.

MATHEMATICAL MODELING OF THE METALLIZED SOLID PROPELLANT IGNITION BY A HIGH-TEMPERATURE CONVECTIVE FLOW

This paper presents a mathematical model and a methodology to calculate stationary combustion of a metallized solid propellant with aluminum additives ignited by a hightemperature convective flow. The study considers the ignition of a semi-infinite slab of the metallized solid propellant which is blown over by an unlimited high-temperature flow. A boundary-layer approximation is used to develop the ignition model. The high-temperature blowing effect is taken into account in the model by means of turbulent heat and mass transfer. The paper provides a numerical and theoretical analysis on the impact of the velocity and temperature of the convective flow on the ignition time delay and the stationary combustion mode establishment. The analysis shows that the proposed approach allows calculating the time of the ignition delay and stationary combustion mode establishment for the metallized solid propellant. Moreover the ignition delay and the period of the stationary combustion mode establishment are found to be controlled by both the velocity and temperature of the convective flow.

First long-term and near real-time measurement of atmospheric trace elements in Shanghai, China

Atmospheric trace elements, especially metal species, are an emerging environmental and health concern with poorly constrained on its abundances and sources in Shanghai, the most important industrial megacity in China. Here we continuously performed a one-year (from March 2016 to February 2017) and hourly-resolved measurement of eighteen elements in fine particles (PM2.5) at Shanghai urban center with a Xact multi-metals monitor and several collocated instruments. Independent ICP-MS offline analysis of filter samples was used to validate the performance of Xact that was based on energy-dispersive X-ray fluorescence analysis of aerosol deposits on reactive filter tapes. Mass concentrations (mean ± 1σ; ng m-3) determined by Xact ranged from detection limits (nominally 0.1 to 20 ng m-3) to 14.7 µg m-3, with Si as the most abundant element (638.7 ± 1004.5), followed by Fe (406.2 ± 385.2), K (388.6 ± 326.4), Ca (191.5 ± 383.2), Zn (120.3 ± 131.4), Mn (31.7 ± 38.7), Pb (27.2 ± 26.1), Ba (24.2 ± 25.4), V (13.4 ± 14.5), Cu (12.0 ± 11.4), Cd (9.6 ± 3.9), As (6.6 ± 6.6), Ni (6.0 ± 5.4), Cr (4.5 ± 6.1), Ag (3.9 ± 2.6), Se (2.6 ± 2.9), Hg (2.2 ± 1.7), and Au (2.2 ± 3.4). Metal related oxidized species comprised an appreciable fraction of PM2.5 during all seasons, accounting for 8.3 % on average. As a comparison, atmospheric metal pollution level in Shanghai was comparable with other industrialized cities in East Asia but one or two orders magnitude higher than the sites in North America and Europe. Here our high time-resolution observations over long-term period also offer a unique opportunity to provide robust diurnal profiles for each species, which are useful in determining the sources and processes contributing to the fluctuation of atmospheric trace elements. Besides, various mathematical methods and physical evidences were served as criteria to constrain various solutions of source identification. Results showed that atmospheric trace elements pollution in Shanghai was the interplay of local emissions and regional transport, and different sources of metal species generally have different variation patterns associated with different source regions. Specifically, V and Ni were confirmed as the prominent and exclusive tracer of heavy oil combustion from shipping traffic. Fe and Ba were strongly related to brake wear, and exhibited significant correlation with Si and Ca, suggesting that Si and Ca in Shanghai were primarily sourced from road fugitive dust rather than long-distance dust transport and local building construction sites. Stationary combustion of coal was found to be the major source of As, Se, Pb, Cu and K, and the ratio of As / Se was used to infer that coal consumed in Shanghai likely originated from Henan coal fields in Northern China. Cr, Mn and Zn were the mixed result of emissions from stationary combustion coal, ferrous metals production, and nonferrous metals processing. Ag and Cd in Shanghai urban atmosphere were also the mixture of miscellaneous sources. Collectively, our findings in this study provide baseline data with high detail, which are needed for developing effective control strategies to reduce the high risk of acute exposure to atmospheric trace elements in China's megacities.