Fuel induced deposits

Recent investigation has shown that fuel-induced deposits first form as oxidized compounds which condense onto the surface of the combustion chamber. Continued heating and polymerization results in the formation of a high-molecular-weight liquidlike material. Heat transforms the material into a deposit composed of a crustlike outer layer and liquid underlayer. The crustlike layer can crack and flake off exposing the liquid underlayer. New deposits then form on the underlayer. 

Additive-induced combustion chamber deposits form near the intake valve. The deposit forms directly onto the surface and has a waxy appearance. These deposits do not undergo alterations as do fuel-derived deposits. Also, additive-induced deposits do not readily flake off of the combustion chamber surface. The effect of engine design on combustion chamber deposit formation is being investigated. 

II. Ease of electrical connection Here the main problem is that of efficient electrical current collection, ideally with only two electrical leads entering the reactor and without an excessive number of interconnects, as in fuel cells. This is because the competitor of an electrochemically promoted chemical reactor is not a fuel cell but a classical chemical reactor. The main breakthrough here is the recent discovery of bipolar or wireless NEMCA,8 11 i.e. electrochemical promotion induced on catalyst films deposited on a solid electrolyte but not directly connected to an electronic conductor (wire). 

Thietane and thiophene deposits in shale oil may be used as a future fuel source. Laser-induced fragmentation of these heterocycles in the presence of oxygen could produce a variety of useful gaseous molecules. Unfortunately, these could create a severe pollution problem. ... 

For obvious reasons related to the necessary reduction of the amount of catalyst used in fuel cells, ORR has been studied on thin films of platinum deposited onto glassy carbon or titanium [73, 79] and on small metal particles on carbon [80-82]. The reduction of the Pt film thickness (<1 nm), as well as of the size of the particles (diam. < 3 nm), induces a moderate loss of activity attributed to differences in the adsorption of O2 on the metal surface. 

One of the main problems associated with hydrocarbon steam reforming over Ni is the deactivation of the Ni catalyst as a result of the formation of carbon deposits on Ni. The C-induced deactivation of Ni has been studied extensively [10,18,28-35], For example, Rostrup-Nielsen reported that steam reforming of various hquid fuels on Ni leads to the formation of encapsulating, whisker-like, or pyrolytic carbon on the catalyst [18, 30], To illustrate the problem of carbon poisoning, in Fig. 13.1 we show a transmission electron micrograph (TEM) of a Ni particle taken after steam reforming of propane at steam to carbon ratio of 1.5. The micrograph shows that carbon deposits are formed on Ni [16],... 

Examples for the second group are polymers as fuel in the micro laser plasma thruster (JJ.LPT), PLD of polymers, matrix-assisted pulsed laser evaporation (MAPLE), which is a deposition technique that can be used to deposit highly uniform thin films [26], or laser-induced forward transfer (LIFT) [27-29], which can be used to produce microstructures by transferring an irradiated area of a target film to an acceptor substrate. The polymer can be the transferred material, or just functions as driving force in the transfer. 

In addition to attack by reactive gases, alloys used in practical environments, particularly those involving the combustion products of fossil fuels, undergo an aggressive mode of attack associated with the formation of a salt deposit, usually a sulphate, on the metal or oxide surface. This deposit-induced accelerated oxidation is called hot corrosion. The severity of this type of attack, which can be catastrophic, has been shown to be sensitive to a number of variables including deposit composition, and amount, gas composition, temperature and temperature cycling, erosion, alloy composition, and alloy microstructure. A number of comprehensive reviews on hot-corrosion have been prepared. The purpose of this chapter is to introduce the... 

In discussing the specific case of the high-temperature corrosion of alloys with deposits containing vanadium, the corrosion process will depend on the source of the vanadium. If the vanadium comes from the alloy, then the corrosion process will be similar to that described previously for molybdenum under alloy-induced acidic fluxing. When the vanadium arrives via deposition from the combustion of the fuel, the vanadium component of the fuel is oxidized in the combustion... 

Layers of pure pyrolytic boron nitride are generally prepared by thermally induced chemical vapor deposition (CVD) on graphite substrates. In most cases the reaction is performed using BCI3, NH3, and N2 (sometimes at about 0.5 to 50 Torr) and working at deposition temperatures of 1800 to 2000°C [97 to 111]. The same process is used at lower temperatures (600 to 800°C) for the coating of nuclear fuel pellets with boron nitride [112]. The thermally induced CVD of BN in such systems is not restricted to the formation of boron nitride layers but can be used to prepare compact boron nitride articles such as crucibles [113 to 121]. 

Since both reactions are induced by fast neutrons having energies >10MeV, the total amount of Co released from the materials to the primary coolant of a 1300MWe PWR was calculated to be only on the order of 10" Bq per year (Sie-mens/KWU, unpublished). In this calculation, the essential radionuclide sources were assumed to be corrosion product deposits on the fuel rods as well as corrosion and/or wear from in-core materials. This low production rate raises the question of whether the y rays at 122 and 136 keV occasionally detected in waste water really belong to Co or whether they are caused by side-peaks originating from the decay of other radionuclides present in the samples. 

---