Browsing by Subject "Titania"
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Item Catalytic Nanoparticle Additives in the Combustion of AP/HTPB Composite Solid Propellant(2012-02-14) Kreitz, Kevin R.Presented in this thesis is a study of the effects of nano-sized particles used as a catalytic additive in composite solid propellant. This study was done with titanium oxide (titania)-based particles, but much of the findings and theory are applicable to any metal oxide produced by a similar method. The process required for efficiently producing larger batches of nanoparticle additives was seen to have a significant impact on the effectiveness of the additive to modify the burning rate of composite propellant consisting of ammonium perchlorate (AP) and hydroxyl terminated polybutadiene (HTPB). Specifically, titania was seen to be both an effective and ineffective burning rate modifier depending on how the nanoparticle additive was dried and subsequently heat treated. Nanoadditives were produced by various synthesis methods and tested in composite propellant consisting of 80 percent AP. Processability and scale-up effects are examined in selecting ideal synthesis methods of nanoscale titanium oxide for use as a burning rate modifier in composite propellant. Sintering of spray-dried additive agglomerates during the heat-treating process was shown to make the agglomerates difficult to break up during mixing and hinder the dispersion of the additive in the propellant. A link between additive processing, agglomerate dispersion mechanics and ultimately catalytic effect on the burning rate of AP/HTPB propellants has been developed by the theories presented in this thesis. This thesis studies the interaction between additive dispersion and the dispersion of reactions created by using fine AP in multimodal propellants. A limit in dispersion with powder additives was seen to cause the titania catalyst to be less effective in propellants containing fine AP. A new method for incorporating metal oxide nanoadditives into composite propellant with very high dispersion by suspending the additive material in the propellant binder is introduced. This new method has produced increases in burning rate of 50 to 60 percent over baseline propellants. This thesis reviews these studies with a particular focus on the application and scale-up of these nanoparticle additives to implement these additives in actual motor propellants and assesses many of the current problems and difficulties that hinder the nanoadditives? true potential in composite propellant.Item Direct numerical simulation and reaction path analysis of titania formation in flame synthesis(2012-08) Singh, Ravi Ishwar; Ezekoye, Ofodike A.; Raman, VenkatFlame-based synthesis is an attractive industrial process for the large scale generation of nanoparticles. In this aerosol process, a gasifi ed precursor is injected into a high-temperature turbulent flame, where oxidation followed by particle nucleation and other solid phase dynamics create nanoparticles. Precursor oxidation, which ultimately leads to nucleation, is strongly influenced by the turbulent flame dynamics. Here, direct numerical simulation (DNS) of a canonical homogeneous flow is used to understand the interaction between a methane/air flame and titanium tetrachloride oxidation to titania. Detailed chemical kinetics is used to describe the combustion and precursor oxidation processes. Results show that the initial precursor decomposition is heavily influenced by the gas phase temperature field. However, temperature insensitivity of subsequent reactions in the precursor oxidation pathway slow down conversion to the titania. Consequently, titania formation occurs at much longer time scales compared to that of hydrocarbon oxidation. Further, only a fraction of the precursor is converted to titania, and a signi cant amount of partially-oxidized precursor species are formed. Introducing the precursor in the oxidizer stream as opposed to the fuel stream has only a minimal impact on the oxidation dynamics. In order to understand modeling issues, the DNS results are compared with the laminar flamelet model. It is shown that the flamelet assumption qualitatively reproduces the oxidation structure. Further, reduced oxygen concentration in the near-flame location critically a ffects titania formation. The DNS results also show that titania forms on the lean and rich sides of the flame. A reaction path analysis (RPA) is conducted. The results illustrate the di ffering reaction pathways of the detailed chemical mechanism depending on the composition of the mixture. The RPA results corroborate with the DNS results that titania formation is maximized at two mixture fraction values, one on the lean side of the flame, and one on the rich side.