Firing flame temperature

Gun Propellents. Although the stresses on individual gun propellant grains are less severe because of the small size, these propellants must withstand much higher weapon pressures and accelerations. Formulation options are usually more limited for gun propellants than for rocket propellants because the products of combustion must not foul or corrode a gun, should have a low flame temperature, and should exhibit minimum flash and smoke characteristics. Gun propellants are examined microscopically for porosity, are tested for mechanical characteristics, and fired in closed bombs to determine the burning characteristics. 

Fuel-fired furnaces primarily utilize carbonaceous or hydrocarbon fuels. Since the purpose of a furnace is to generate heat for some useful appHcation, flame temperature and heat transfer are important aspects of furnace design. Heat transfer is impacted by the flame emissivity. A high emissivity means strong radiation to the walls. 

The fundamentals of thermal radiation modeling are treated in Chapter 3. The value for emissive power can be computed from flame temperature and emissivity. Emissivity is primarily determined by the presence of nonluminous soot within the flame. The only value for flash-fire emissive power ever published in the open literature is that observed in the Maplin Sands experiments reported by Blackmore... 

Modem fired heaters operate at thermal efficiencies of between 80 to 90 per cent, depending on the fuel and the excess air requirement. In some applications additional excess air may be used to reduce the flame temperature, to avoid overheating of the tubes. 

Several of the combustion-related properties of hydrogen in air, such as its wide flammability limits (4-75 vol%), wide detonation range (20-65 vol%), very low spark ignition energy (0.02 mJ), high heat of combustion (121 kJ/g) and high flame temperature (2050°C) combine to emphasise the high fire-related hazards of the... 

The terrperature of the hot layer in the corridor is shown in Figure 7. In the corridor, the hot gas is untenable for an upright person next to the open fire room door after about 160 seconds. After about four minutes, the radiation from the hot layer would be too high to permit a person to pass. Furthermore, in actual fact, the temperature would be higher than that calculated at the fire room door, because of the fuel which would burn in the corridor, thus providing flame temperature radiation in addition to the hot layer temperature computed here. 

Flash point temperatures are determined using an open-cup apparatus, shown in Figure 6-3. The liquid to be tested is placed in the open cup. The liquid temperature is measured with a thermometer while a Bunsen burner is used to heat the liquid. A small flame is established on the end of a movable wand. During heating, the wand is slowly moved back and forth over the open liquid pool. Eventually a temperature is reached at which the liquid is volatile enough to produce a flammable vapor, and a momentary flashing flame occurs. The temperature at which this first occurs is called the flash point temperature. Note that at the flash point temperature only a momentary flame occurs a higher temperature, called the fire point temperature, is required to produce a continuous flame. 

Convective heating in fire conditions is principally under natural convection conditions where for turbulent flow, a heat transfer coefficient of about 10 W/m2 K is typical. Therefore, under typical turbulent average flame temperatures of 800 °C, we expect convective heat fluxes of about 8 kW/m2. Consequently, under turbulent conditions, radiative heat transfer becomes more important to fire growth. This is one reason why fire growth is not easy to predict. 

Quintiere, J.G. and Rangwala, A.S., A theory for flame extinction based on flame temperature, Fire and Materials, 2004, 28, 387 102. 

Note that the maximum flame temperature appears to be 800-900 °C for these scale fires. For larger scale fires, this flame temperature can increase with diameter e.g. for D 2m,... 

Turbulent fire plume temperatures do not generally exceed 1000 °C. This is well below the adiabatic flame temperature for fuels. Why ... 

Hydrocarbon vapors immediately bum with flame temperatures that are considerably higher than that of ordinary combustibles. For this reason damage from a hydrocarbon fire is much more severe than an ordinary combustible fire. The objective of a fire detection for the petroleum industry is to rapidly detect a fire where personnel, high value, and critical equipment may be involved. Once detected executive action is initiated to alert personnel for evacuation and while simultaneously controlling and suppressing the fire incident. 

A patented water injection system has been devised for extinguishing oil and gas well fires in case of a blowout. The "Blowout Suppression System" (BOSS) consist of finely atomized water injected to the fluid stream of a gas and oil mixture before it exits a release point. The added water lowers the flame temperature and flame velocities thereby reducing the flame stability. In the case where the flame cannot be completely dissipated, the fire intensity is noticeably deceased, preserving structural integrity and allowing manual intervention activities. A precaution in the use of such a device is that, if a gas release fire is suppressed but the flow is not immediately isolated, a gas cloud may develop and exploded that would be more destructive that the pre-existing fire condition. 

The burners are located between tube rows. A larger number of burners reduces the heat release per burner and allows a smaller flame diameter and a reduced lane spacing. A ratio of one burner for every 2 to 2.5 tubes provides a uniform heat release. Most burners are a dual-fired design, firing both PSA offgas and supplemental makeup gas. Low NOx burners are used to meet environmental requirements. Makeup gas can be used to induce flue gas into the flame, reducing the flame temperature and NOx level. In a well functioning unit NOx levels as low as 0.03 lb/MMBtu are possible. 

Flue gas recirculation Flue gas recirculation, alone or in combination with other modifications, can significantly reduce thermal NO,. Recirculated flue gas is a diluent that reduces flame temperatures. External and internal recirculation paths have been applied internal recirculation can be accomplished by jet entrainment using either combustion air or fuel jet energy external recirculation requires a fan or a jet pump (driven by the combustion air). When combined with staged-air or staged-fuel methods, NO emissions from gas-fired burners can be reduced by 50 to 90 percent. In some applications, external flue-gas recirculation can decrease thermal efficiency. Condensation in the recirculation loop can cause operating problems and increase maintenance requirements. 

In order to compute the thermal radiation effects produced by a flash fire, it is necessary to know the flame temperature, size, and dynamics during the propagation. Since flash fires are of very short duration, the effect of radiation is much less than from a jet or pool fire. 

The buoyant gas flow above the fire, including any flames, is typically referred to as the fire plume (see Figure 5-8). Flame temperatures typically range from 900°C to 1200°C, and will vary with the type of fuel, ambient conditions, and oxygen availability. Temperature variations result from the amount of soot particles within the flame (which absorb energy and allow for convective or radiative heat transfer) (Drysdale, 1998). In general, the sootier the flame, the cooler its temperature. 

One effect that a flaming fire has on the surrounding area is to rapidly increase air temperature in the space above the fire. Fixed temperature heat detectors will not initiate an alarm until the air temperature near the device exceeds the design operating point. The rate-of-rise detector, however, will function when the rate of temperature increase exceeds a predetermined value, typically around 12 to 15°F (7 to 8°C) per minute. Rate-of-rise detectors are designed to compensate for the normal changes in ambient temperature [less than 12°F (6.7°C) per minute] which are expected under nonfire conditions. 

Melt and autoignition temperatures for many materials are known, as are normal flame temperatures. Table 8-1 gives selected temperatures of interest to many investigators. Soot will normally not affix itself to surfaces at more than approximately 700°F (371°C). Therefore, areas of high fire intensity may have little or no soot deposits. Flame temperatures are... 

It is denoted by C and depends on the flame temperature, mean molecular mass of the combustion products and propellant formulation. It is a fundamental parameter which gives the energy available on combustion and can be used to compare the efficiency of different chemical reactions independently of the Pc. For propellants, the value of C ranges between 1200 and 1600 ms-1. It is determined by firing a propellant grain in a motor and evaluating the area under the P-t profile and using Equation 4.11. 

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