Fixed fuel-flow system

A fixed fuel-flow system is a simple set-up that is operated to maintain a constant fuel-flow rate. The fuel-rich gas flows out from the gas generator through a choked orifice that is attached at its aft-end. The mass generahon rate of the fuel-rich gas is therefore independent of the pressure in the ramburner. When a projectQe operated by a fixed-flow ducted rocket flies at a constant supersonic speed and at constant altitude, the airflow rate through the air-intake remains constant. Since the gas generahon rate in the gas generator is kept constant, the air-to-fuel raho also remains constant. Ophmized combustion performance is thereby obtained. This class of ducted rocket is termed a fixed fuel-flow ducted rocket . 

However, a change in the flight speed and/or the flight alhtude alters the airflow rate. Then, the air-to-fuel ratio in the combushon chamber is also altered, and the thrust produced by the ducted rocket is altered. Consequenhy the flight envelope of the projechle becomes highly limited. These operahonal characteristics of the fixed fuel-flow ducted rocket reshict its application as a propulsion system. 

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In order to overcome the difficulties associated with the non-choked fuel-flow system and the fixed fuel-flow system, a variable fuel-flow system is introduced the fuel gas produced in a gas generator is injected into a ramburner. The fuel-flow rate is controlled by a control valve attached to the choked nozzle according to the airflow rate induced into the ramburner. An optimized mixture ratio of fuel and air, which is dependent on the flight altitude and flight velocity, is obtained by modulating the combustion rate of the gas-generating pyrolant When a variable fuel-flow-rate system is attached to the choked nozzle of the gas generator, the fuel-flow rate is altered in order to obtain an optimized combustible gas in the ramburner. This class of ducted rockets is termed variable fuel-flow ducted rockets or VFDR . 

A specific fuel cell system is viewed here as having a fixed range of operating temperature between a maximum and minimum heat must therefore be removed in such a manner to maintain the temperature within these limiting values. If heat is removed directly by reactant flows, then the quantity of flow must be adjusted so that inlet and outlet temperatures (as well as... 

As to coal, the gasifiers may be of three types, featuring a fixed entrained or fluid bed. In the first, the bed is moving rather than fixed, the fuel flows by gravity, and ash is removed at the bottom of the reactor by a mobile grid system or in batches. The gases flow in parallel, co- or countercurrent contact, or even perpendicular to each other. 

The Mizushima Oil Refinery of Japan Energy Corporation first implemented an operation of vacuum residue hydrodesulfiirization in the conventional fixed bed reactor system in 1980. We have also conducted a high conversion operation to produce more middle distillates as well as lower the viscosity of the product fuel oil to save valuable gas oil which is used to adjust the viscosity. Vacuum residue hydrodesulfurization in fixed bed reactors mvolves the characteristic problems such as hot spot occurrence and pressure-drop build-up. There has been very little literature available discussing these problems based on commercial results. JafiFe analyzed hot spot phenomena in a gas phase fixed bed reactor mathematically, assuming an existence of the local flow disturbance region [1]. However, no cause of flow disturbance was discussed. To seek for appropriate solutions, we postulated causes ofhot spot occurrence and pressure-drop build-up by conducting process data analysis, chemical analysis of the used catalysts, and cold flow model tests. This paper describes our solutions to these problems, which have been demonstrated in the commercial operations. 

The laboratory reaction system used was a conventional flow system with a tubular fixed-bed reactor as described elsewhere(18). The characteristic feature of this system is its ability to simulate various air to fuel ratios (A/F) of automotive exhaust gases using eight mass flow controllers. In this study, catalytic activity on the catalysts in simulated automotive exhaust gases was measured as a function of X, which is a normalized value of A/F by a stoichiometric one in the simulated exhaust gas, at 300°C and 420,000 h space velocity. The compositions of the simulated exhaust gases for each X are shown in Table 1. Catalytic activity was expressed as percent conversions of NOx(NO+N02), CO, and HC. 

This test method for measuring the high temperature stability of gas turbine fuels uses the Jet Fuel Thermal Oxidation Tester (JFTOT) that subjects the test fuel to conditions that can be related to those occurring in gas turbine engine fuel systems. The fuel is pumped at a fixed volumetric flow rate through a beater after which it enters a precision stainless steel filter where fuel d radation products may become trapped. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

The batch conversion of wood fuels with the following conversion concept overfired, updraft, fixed horizontal grate, and batch reactor, has proven to be highly dynamic and stochastic with respect to mass flow and stoichiometry of conversion gas as well as the air factors of the conversion and combustion system. 

Figure 26 Different flow patterns for batch and continuous fuel beds. The motion of the fuel bed is defined relative to a fixed coordinate system.

As with the flow regimes in fluid dynamic theory, that is, the stagnation, laminar flow and turbulent flow, it is obvious that a solid phase can exhibit the corresponding flow pattern regimes, which herein are referred to as fixed, moving and mixed, respectively. The terms fixed, moving and mixed are defined as the relative motion of the particle phase with respect to a fixed coordinate system (see Figure 26). Examples of commercial PBC systems with different fuel-bed movement are found in section B.3.4. A comparison between theoretical and practical conversion systems. 

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