Search results for "Combustion"

One-year characterization of organic aerosol markers in urban Beijing: Seasonal variation and spatiotemporal comparison

2020

Abstract Organic aerosol (OA) is a major component of fine particulate matter (PM); however, only 10%–30% of OA have been identified as individual compounds, and some are used as markers to trace the sources and formation mechanisms of OA. The temporal and spatial coverage of these OA markers nonetheless remain inadequately characterized. This study presents a year-long measurement of 92 organic markers in PM2.5 samples collected at an urban site in Beijing from 2014 to 2015. Saccharides were the most abundant (340.1 ng m−3) species detected, followed by phthalic acids (283.4 ng m−3). In summer, high proportions (8%–24%) of phthalic acids, n-alkanes, fatty acids, and n-alcohols indicate dom…

Solution to Urban Air Pollution – Carbon Free Transport

2016

Abstract The analysis of the results of long-term air quality monitoring in Riga is presented, which shows that in city centre throughout the measurement time (2004-2014) according to the guidelines defined by the European Union directives and Latvian laws the limits of small particles PM10 and nitrogen dioxide (NO2) are exceeded. From the nature of appearance of pollution and from the research of morphology and composition of fine dust particles it was concluded that in the city centre where the monitoring was performed the main air pollutants are caused by internal combustion engine vehicles. The measures to reduce air pollution performed by two Action Programs (2004-2009; 2011-2015) of t…

Optical diagnostic of temperature in rocket engines by coherent Raman techniques

2004

Abstract This article reviews the study of Raman line shapes of molecular species involved in reactive media, such flames or engines, at high temperature and high pressure. This study is of interest from a fundamental as well as from a practical point of view with regards to the CARS temperature diagnostic of GH2–LOX combustion systems. We will particularly draw attention to recent investigations by means of Stimulated Raman Spectroscopy (SRS) in H2–H2O mixtures at temperature up to 1800 K. Whereas H2–X systems usually exhibit large inhomogeneous effects, due to the speed dependence of the collisional parameters, the absence of such apparent inhomogeneous signatures in the H2–H2O system all…

Improvement of Biomass Gasification/Combustion Characteristics by Microwave Pretreatment of Biomass Pellets

2021

Loop seals in circulating fluidized beds – Review and parametric studies using CPFD simulation

2020

Abstract Loop seal is a robust particle recycling technique used in circulating fluidized bed (CFB) reactors. The rate and the location of the loop seal aeration exert a significant impact on the rate of particle circulation (GS). The standpipe balances the cumulative pressure drop across the rest of the CFB by adjusting its particle height or gas-particle slip velocity. Higher fraction of the loop seal aeration naturally flows down to riser. Increased pressure drop in the standpipe results in high rate of particle circulation. Computational-particle-fluid-dynamic (CPFD) code is customized for multiphase flow modelling. The inbuilt tool of “BC connectors” was incorporated to downsize a CFB …

Controllable Solid Propellant Rocket Motor Stability: Deep and Rapid Variable Thrust Operations

2008

When flow and combustion processes couple with the acoustic modes of the combustion chamber, the solid rocket motors experience unsteady gas motion and associated thrust oscillation and motor vibration. The operations of the variable nozzle introduce relevant dynamic changes in the chamber flow and combustion. This article proposes a non-linear approach for the analysis of the effects of severe nozzle manoeuvres on the controllable solid rocket motor stability and provides the evidence that the acoustic wave amplitude evolution is influenced by the nozzle manoeuvre severity, shape and direction. The additional complexity in the problem of the combustion stability analysis introduced by the …

Alkylated dibenzothiophenes in pine needles from pulp and paper mill environment

1998

Abstract Concentrations of alkylated dibenzothiophenes (C n DBTs) in pine needles in a recipient area of the emissions from a pulp and paper mill where also waste combustion was done were measured. The concentrations (ng/g dry weight) of C 1 DBTs were in the range of 2 DBTs in the range of 3 DBTs in the range of 3 DBTs] > [C 2 DBTs] > [C 1 DBTs]. The pulp mill could not be shown to be the source of C 1 C 3 DBTs in the pine needles. Other possible sources are situated in the vicinity of the pulp and paper mill. Long-range transport, either, cannot be excluded as a possible source.

Structure evolution and reaction mechanism in the Ni/Al reactive multilayer nanofoils

2014

Abstract The extremely rapid gasless reactions in binary Ni/Al reactive multilayer nanofoils (RMNFs) are investigated both experimentally and theoretically. The quenching technique is used to study the dynamics of structural transformation on the micro- and nanoscales. The experimentally obtained patterns of structural evolution related to the heterogeneous reactions are compared with the results of molecular dynamics simulations carried out for the same reactive system. Based on the obtained data, the intrinsic mechanism of the reaction in Ni/Al RMNF is considered, which adequately explains the unusual parameters of a gasless combustion wave in such a system.

Assisted self-sustaining combustion reaction in the Fe–Si system: Mechanical and chemical activation

2007

Abstract This work presents original investigations carried out to improve the activated self-propagating high-temperature synthesis (SHS) process in the Fe–Si system: different ignition modes are tested (volume heating as opposed to a local ignition source), and the use of additive is considered in order to enhance the SHS type reactivity in the Fe–Si system. When 20 wt.% of KNO 3 is added to the reactive mixture, the fast (>20 mm s −1 ), stable and self-sustaining combustion reaction produces a very fine FeSi + α-FeSi 2 structure. Infrared thermography (IR) as well as post-mortem analysis (SEM, EDXS, XRD) was used to understand the mechanism behind the chemical activation process when KNO…

Microstructural study of titanium carbonitride elaborated by combustion synthesis

2007

Abstract The self-propagating high-temperature synthesis (S.H.S.) process, which is promising for the fabrication of ceramic materials, was chosen to elaborate titanium carbonitride materials. The influence of parameters such as nitrogen gas pressure and carbon ratio on the microstructure was studied. A single phase product of Ti(C,N) is obtained for a carbon ratio under 15 at.% and a nitrogen pressure of 36 MPa. The increase of the carbon ratio corresponds to a decrease of the maximum temperature reached during the synthesis. Time resolved X-ray diffraction measurements (TRXRD) with the synchrotron radiation were used to determine the reaction mechanisms. We could observe that the synthesi…