Combustion intensity condition

In fuel-fired furnaces, heat release rate is usually expressed in heat units liberated per unit of furnace volume in unit time, commonly in Btu/ft hr or MJ/m hr. Closely related to rate of furnace heat release is the combustion volume or flame volume. Generally, the furnace volume should be at least equal to the sum of the maximum flame volume and the maximum load volume. The volume of the flame is a function of the combustion intensity condition discussed with table 3.1 subsequently, and where Fc is a configuration factor to assure that all of any one flame s volume is contiguous. 

TABLE 3.1. Generalized descriptions of six combustion intensity conditions for use in equation 3.1, and In example 3.1... 

Smaller fuel droplet size in spray flames is more desirable, since smaller droplets enhance flame stability and combustion intensity and lead to rapid response to input operational conditions [1-9]. The focus of the present work is to reduce the droplet size by creating high-shear regions within the sprays. 

The WRHA obtained under these conditions has a good quality and may be used as adsorbent, filler of polymers, rubbers, cement, and concrete, or for other purposes. In conclusion, it may be stated that as the high ash content, low bulk density, poor flow characteristic, and low ash melting point makes the other conventional types of reactors unsuitable for rice husks utilization, fluidized bed reactors seem to be a suitable choice. The study of published reports indicates that it is technically feasible to successfully bum the rice husk in a fluidized bed reactor, and combustion intensity of about 530 kg h m can be achieved. 

Figure 5.3 gives an example of a combustion diagram recorded during knocking conditions. This is manifested by intense pressure oscillations which continue during a part of the expansion phase. 

Octane number is a measure of a fuel s abiUty to avoid knocking. The octane number of a gasoline is deterrnined in a special single-cylinder engine where various combustion conditions can be controlled. The test engine is adjusted to give trace knock from the fuel to be rated. Various mixtures of isooctane (2,2,4-trimethyl pentane) and normal heptane are then used to find the ratio of the two reference fuels that produce the same intensity of knock as that by the unknown fuel. 

A flash fire is the nonexplosive combustion of a vapor cloud resulting from a release of flammable material into the open air, which, after mixing with air, ignites. In Section 4.1, experiments on vapor cloud explosions were reviewed. They showed that combustion in a vapor cloud develops an explosive intensity and attendant blast effects only in areas where intensely turbulent combustion develops and only if certain conditions are met. Where these conditions are not present, no blast should occur. The cloud then bums as a flash fire, and its major hazard is from the effect of heat from thermal radiation. 

The methods described in this chapter are meant for practical application background information is given in Chapter 4. If a quantity of fuel is accidentally released, it will mix with air, and a flammable vapor cloud may result. If the flammable vapor meets an ignition source, it will be consumed by a combustion process which, under certain conditions, may develop explosive intensity and blast. 

The consequence of the second approach is that, if detonation of unconfined parts of a vapor cloud can be ruled out, the cloud s explosive potential is not primarily determined by the fuel-air mixture in itself, but instead by the nature of the fuel-release environment. The multienergy model is based on the concept that explosive combustion can develop only in an intensely turbulent mixture or in obstructed and/or partially confined areas of the cloud. Hence, a vapor cloud explosion is modeled as a number of subexplosions corresponding to the number of areas within the cloud which bum under intensely turbulent conditions. 

The excellent detection ability for flames makes UV sensing a good method for remote fire alarm-monitoring. UV radiation after the outbreak of a fire reaches a sensor much faster than heat or smoke. Also, the distance between sensor and fire is less critical. Requirements for the sensor are high sensitivity and excellent selectivity. Radiation intensities at the sensor position may be even lower and the ambient light conditions less restricted than for combustion controlling. When used outside, solar-blindness is a must. These stringent requirements make UV fire alarm monitors expensive, and they are used in industrial environments such as production floors or warehouses rather than in private homes. 

One of the most hazardous conditions a firefighter will ever encounter is a backdralt (also known as a smoke explosion). A backdraft can occur in the hot-smoldering phase of a fire when burning is incomplete and there is not enough oxygen to sustain the fire. Unburned carbon particles and other flammable products, combined with the intense heat, may cause instantaneous combustion if more oxygen reaches the fire. 

Future combustion devices may burn alternative fuels with higher carbon-to-hydrogen ratios and operate at higher pressures. The combustion of such fuels under these conditions will result in more intense turbulence, higher levels of soot formation, and the associated increase in radiative heat loss compared to more traditional fuels burned at lower pressures. Depending upon the design objectives, it may be desirable to control soot levels using predictive capabilities. 

Figure 12.6 Calculated mean temperature fields in the combustor with an open-edge V-gutter flame holder of height If = 10 cm and apex angle of 60°. The isoterms divide the entire temperature interval from To to Tc into 10 uniform parts and correspond to f = 50 ms. The combustor is 1 m long and 0.2 m wide. Combustion of stoichiometric methane-air mixture at the mean inlet velocity Uin = 40 (a), 50 (b), 60 (c), 70 (d), and 80 m/s (e). Other conditions po = 0.1 MPa, To = 293 K, turbulence intensity 2%, fo = 4 mm. The lower boundary of the computational domain is the symmetry plane...

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