Fuel-flow rate

What is the most meaningful way to express the controllable or independent variables For example, should current density and time be taken as the experimental variables, or are time and the product of current density and time the real variables affecting response Judicious selection of the independent variables often reduces or eliminates interactions between variables, thereby leading to a simpler experiment and analysis. Also inter-relationships among variables need be recognized. For example, in an atomic absorption analysis, there are four possible variables air-flow rate, fuel-flow rate, gas-flow rate, and air/fuel ratio, but there are really only two independent variables. 

By way of example, reducing emissions when firing natural gas to within a 75 ppm limit would require steam or water injection at a rate of 60 per cent of the fuel flow rate. 

In this paper we report the effect of varying loads on a small size DMFC stack (10 cells with 9 cm active-area each). The transient responses of the stack voltage have been investigated upon variable current load conditions to obtain the information on the dynamic characteristics of the stack. Also, the transient responses of the stack current upon changing fuel flow rates have been monitored to obtain the optimal operating conditions for the staek. 

TMs study has shown the dynamic behavior of a 5W DMFC stack when the current loads have changed by pulses and steps. In order to determine the optimum operating conditions of the stack, the dynamic behavior of the stack current has been studied under a constant voltage output of 3.8V, varying the flow rate of 2M methanol solution and air. For the stable operation of the 5W stack, the minimal fuel flow rates are found to be 3 ml/min and 2L/min for 2M methanol and air, respectively. 

In practice, the efficiency of a fired heater is controlled by monitoring the oxygen concentration in the combustion products in addition to the stack gas temperature. Dampers are used to manipulate the air supply. By tying the measuring instruments into a feedback loop with the mechanical equipment, optimization of operations can take place in real time to account for variations in the fuel flow rate or heating value. 

Variable fuel flow is used in burners to throttle or cut back the fuel flow rate, reducing flame size, as the system heating load varies. These burners have conventional steady-state efficiencies and higher seasonal efficiencies. They are available for large apartment boilers and furnaces. 

Fuel flow rate. Your instructor will show you how to vary the fuel flow rate to the burner head and also how to read the flow rate on the flow meter. Measure absorbance values at ten different flow rates, selecting a flow rate range that will maintain a flame while bracketing what the manufacturer s literature or your instructor may suggest as the optimum. 

Oxidant flow rate. Repeat the above, but for the oxidant flow rate rather than the fuel flow rate. Use extreme caution here, since a flashback may result from too much or too little oxidant flow. 

This expression reveals that the height of a turbulent diffusion flame is proportional to the port radius (or diameter) above, irrespective of the volumetric fuel flow rate or fuel velocity issuing from the burner This important practical conclusion has been verified by many investigators. 

Example 10-1 Fuel Flow Rate for 1 Ampere of Current (Conversion Factor Derivation)... 

Example 10-2 Required Fuel Flow Rate for 1 MW Fuel Cell... 

A 1.0 MWdc fuel cell stack is operated with a cell voltage of 700 mV on pure hydrogen with a fuel utilization, Uf of 80%. (a) How much hydrogen will be consumed in Ib/hr (b) What is the required fuel flow rate (c) What is the required air flow rate for a 25% oxidant utilization, Uox ... 

Once the fuel flow rate is determined, the heat release rate is calculated as ... 

The air flow rate was set at 0.3 g/s, and the fuel flow rate was set at 0.9 g/s (above the rich flammability limit). The forcing frequency was chosen to be 592 Hz. This frequency was chosen to coincide with the natural frequency of the air chamber since the resonance would amplify the forcing signal. The amplitude of the forcing is 20% of the mean exit velocity at the nozzle. 

Figure 20.12 shows a stability map of the conical preburner system investigated. In developing the stability map, the fuel flow rate is maintained constant at 0.36 g/s while the primary and secondary air flow rates are varied systematically. The flame is considered to be stable if it could be sustained for a long period of time. As shown in Fig. 20.12, unstable regimes can be noted both for low and high secondary air flow rates. 

Kim, T.K., B. J. Alder, N. M. Laurendeau, and J.P. Gore. 1995. Exhaust and in situ measurements of nitric oxides for laminar partially premixed C2He-air flames Effect of premixing level at constant fuel flow rate. Combustion Science Technology 110-111 361-78. 

Fig. 15.2 Fuel flow rate and Mach number as a function of flight altitude.

Though the specific impulse of a solid rocket is determined by the energetics of its propellant, the specific impulse of a ducted rocket is determined by the mixture ratio of the fuel flow rate from the gas generator and the airflow rate induced from the atmosphere. The ram pressure in the rambumer is raised by the shock wave formed at the air-intake. The combustion in the rambumer further increases the... 

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 . 

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 . 

Fig. 15.4 shows a schematic representation of a nozzle throat area controller used in a VFDR. The mass flow rate from the nozzle attached to the primary combustion chamber (gas generator) to the secondary combustion chamber (ramburner) is changed by inserting a pintle. The high-temperature gas produced in the gas generator flows into the ramburner through the pintled nozzle. The pintle inserted into the nozzle moves forward and backward in order to alter the nozzle throat area. As the nozzle throat area is made small, the mass flow rate increases according to the concept described above. The fuel-flow rate becomes throttable by the pintled nozzle. 

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