Burner

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In Fenix+ 3, a burner can be created in several ways.

Burner as element at a combustible object

The first method is to place in the script an object with a horizontal top surface (Wall, Solid, Platform, Slab) made of combustible Material, and place the Burner element on this object.

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In this case, an object made of a combustible material can have an arbitrary shape, and the Burner element placed on it will always be rectangular. This is because the VENT parameter group in the FDS input file that Fenix+ 3 uses to simulate a Burner is rectangular. The size of the rectangular Burner can be arbitrary, but no more than the maximum rectangle inscribed in the contours of the object on which the Burner is placed.

Burner on the Solid

The Burner in Fenix+ 3 is characterized by the following thermal parameters, which are calculated from the material properties and the Burner area:

  • specific power (kW/m²);
  • maximum power (kW), – the power equal to the product of the specific power by the area of the horizontal part of the Burner. If the Flame Spread to Side Surfaces option is enabled, the side surfaces are not taken into account when calculating the maximum power.

Burner properties{width=40%}

Specific power is defined as the product of the inferior calorific value, specific mass burnup rate and combustion efficiency, which characterize the material of the object on which the Fire Source element is plated. These material properties are set on the Flammable Properties tab in the Substances and Materials Editor.

Substances and Materials Editor

In the properties of the Fire Source element, it is also possible to set the times of the beginning and end of its operation (combustion).

When simulating, a fire will appear at the time specified in the fire settings and will spread from the central point of the Burner at a speed equal to the linear flame spread rate specified in the Substances and Materials Editor for the material from which the object is made, on which the Fire Source element is placed.

If the linear flame spread rate is specified equal to zero, the Burner will flare up entirely at the same time. This is the default speed in the Substances and Materials Editor for liquid fuels.

The FDS input file for a Burner flaring up with a finite speed will have a code similar to the following:

&SURF ID=‘1’ FYI=‘Ochag pozhara 1’ HRRPUA=180.792 COLOR=‘RED’/

&VENT XB= -1.5, 0, 1.5, 3.25, 0.5, 0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ= -0.625, 2.375, 0.5 CTRL_ID=‘2’/

&CTRL ID=‘2’ FUNCTION_TYPE=‘CUSTOM’ INPUT_ID(1:1)=‘CLOCK’ RAMP_ID=‘3’ LATCH=.False./

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=29 F=-1/

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=31 F=1/

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=599 F=1/

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=601 F=-1/

Here, the HRRPUA parameter of the SURF group is responsible for the specific power of the Burner, the SPREAD_RATE parameter of the VENT group – for the linear spread rate, and XYZ is the initial combustion point lying in the plane of the VENT element and located in the center of the computational mesh face closest to the VENT element’s geometric center.

Location of the combustion start point on the VENT{width=60%}

The parameters of the CTRL and RAMP groups are responsible for controlling the start and end times of combustion, which in this case correspond to the 30th and 600th seconds.

If the Burner flares up entirely at the same time, the SPREAD_RATE and XYZ parameters will be absent in the VENT group.

Additional features

In the Fire Simulation Parameters window, it is possible to specify additional settings for the Burner:

  1. Reduce the burnup rate by half;

  2. Spread of flame to the side surfaces.

Fire simulation parameters{width=80%}

  1. Reduce the burnup rate by half

The ability to reduce the burnup rate by half will work if automatic fire-fighting systems (AFFS) are made according to the standards.

For a project of the Civil Building type, information about the AFFS is specified in the Building properties.

Building properties

For a project of the Production Facility type, information about AFFS is specified for the Room in the Room Schedule window.

Room Schedule menu

Moreover, the AFFS corresponding to the standards must be specified, of course, if available.

Specification of an automatic fire-fighting system

A twofold decrease in the burnup rate will be reflected in the Burner description in the FDS file as a halving of the HRRPUA parameter of the SURF group.

  1. Spread of flame to the side surfaces.

It should be borne in mind that the element dimensions can change when the input file for FDS is generated, since any object in FDS must have dimensions that are multiples of the mesh cell size. The Fire Source in the FDS file is represented using VENT. The VENT object has a rectangular shape and occupies an integer number of computational mesh faces. The element on which the Burner is located is represented in the FDS file using OBST objects that occupy an integer number of cells.

The object dimensions in FDS depend on the original dimensions of the script elements, as well as on the mesh cell size. As a result, after the transformation of script elements into FDS objects, the Burner and the object on which it is located may or may not have common boundaries.

The side surfaces of the Burner, as well as its horizontal surface, are represented using VENT, and appear only on those side faces of OBST, where the horizontal VENT border coincides with the border of OBST, on which it “lies”.

Let us look at a Fire Source lying on a Solid of non-rectangular shape.

Fire Source on non-rectangular Solid in Fenix+ 3{width=40%}

Below is how such a script would be presented in FDS. The Burner side faces appeared only where the horizontal VENT boundary coincides with the OBST boundary.

Fire Source on non-rectangular Solid in FDS{width=50%}

The Burner side face also will not appear in the place where another object, for example, a wall, adjoins the object on which the Burner is located.

Fire source with side surfaces and wall

The side surfaces do not flare up simultaneously with the upper surface of the Burner. The figure below shows a developed view of the Burner, when the flame can spread to the side surfaces.

Developed view of the Burner with side faces{width=60%}

Let us denote the linear flame spread rate through V.

Initially, the flame spreads from the center of the upper face (point C) in all directions. After time a/2/V, the flame will reach points B1 and B2. At this moment, according to the model laid down in Fenix+ 3, combustion of two corresponding side faces from points B1 and B2 will begin. Similarly, after time b/2/V, the flame will reach points A1 and A2. At this moment, combustion of two corresponding side faces from points A1 and A2 will begin.

In the FDS file, the VENT parameter group corresponds to the side faces as well as to the upper face of the Burner. The linear rate (SPREAD_RATE) on the side faces is the same as on the upper, and the start points (XYZ) correspond to the coordinates of points A1, A2, B1 and B2. The times of the combustion beginning at these points are delayed in relation to the combustion beginning at point C by the values justified above.

In the FDS input file, a Burner with side faces will be represented as follows:

General settings

“Zdanie 1” – “Tverdoe telo 1”

&OBST XB= -1.75, -0.5, 2.25, 3.5, 0, 0.5 RGB=191,191,191/ Ochag pozhara 1

&SURF ID=‘1’ FYI=‘Ochag pozhara 1’ HRRPUA=180.792 COLOR=‘RED’/

Upper face

&VENT XB=-1.75,-0.5,2.25,3.5,0.5,0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ= -1.125,2.875,0.5 CTRL_ID=‘2’/

&CTRL ID=‘2’ FUNCTION_TYPE=‘CUSTOM’ INPUT_ID(1:1)=‘CLOCK’ RAMP_ID=‘3’ LATCH=.False./

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=-1 F=-1/

&RAMP ID=‘3’ FYI=‘Ochag pozhara 1’ T=1 F=1/

One pair of side faces

(Let us recall that if another object adjoins the solid on which the Burner is located on one side, there can be only one side face. Also, there may not be both side faces if foreign objects adjoin the Burner on both sides)

&VENT XB=-1.75,-1.75,2.25,3.5,0,0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ=-1.75,2.875,0.25 CTRL_ID=‘4’/

&VENT XB=-0.5,-0.5,2.25,3.5,0,0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ=-0.5,2.875,0.25 CTRL_ID=‘4’/

&CTRL ID=‘4’ FUNCTION_TYPE=‘CUSTOM’ INPUT_ID(1:1)=‘CLOCK’ RAMP_ID=‘5’ LATCH=.False./

&RAMP ID=‘5’ FYI=‘Ochag pozhara 1 side X ramp’ T=35.4 F=-1/

&RAMP ID=‘5’ FYI=‘Ochag pozhara 1 side X ramp’ T=37.4 F=1/

In fact, side VENTs will appear at 36.4 s.

Second pair of side faces

&VENT XB=-1.75,-0.5,2.25,2.25,0,0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ=-1.125,2.25,0.25 CTRL_ID=‘6’/

&VENT XB=-1.75,-0.5,3.5,3.5,0,0.5 SURF_ID=‘1’ SPREAD_RATE=0.0154 XYZ=-1.125,3.5,0.25 CTRL_ID=‘6’/

&CTRL ID=‘6’ FUNCTION_TYPE=‘CUSTOM’ INPUT_ID(1:1)=‘CLOCK’ RAMP_ID=‘7’ LATCH=.False./

&RAMP ID=‘7’ FYI=‘Ochag pozhara 1 side Y ramp’ T=41 F=-1/

&RAMP ID=‘7’ FYI=‘Ochag pozhara 1 side Y ramp’ T=43 F=1/

On Fire property

The On Fire property is available for the Fenix+ 3 script elements that have the Material property, if the material is combustible.

Wall element with activated On Fire property{width=70%}

Activation of the On Fire property will result in the element being covered with a surface (SURF group) during simulation with a specific combustion power (HRRPUA parameter) equal to the combustion power of the selected material.

&MATL ID=‘1’ FYI=‘Derevo + oblicovka’ CONDUCTIVITY=1 DENSITY=1000 HEAT_OF_COMBUSTION=14400 SPECIFIC_HEAT=1/

&SURF ID=‘2’ HRRPUA=180.792 THICKNESS=0.2 RGB=193,191,180 MATL_ID=‘1’/

&OBST XB=0.75,0.75,1,1.25,0,3 SURF_ID=‘2’/

The element will be engulfed in flames immediately and completely.

Instant engulfing of the element in flames{width=70%}

This method of creating a Burner can be used in cases where it is not required to simulate a gradual flare-up. That is, in cases where the element is engulfed in flame very quickly, and also when the simulation results until the element is completely burnt up are not interesting. The second case is typical when measuring the heat flux falling on a building during a fire in an adjacent building.

Flame extinction when oxygen burns out and temperature drops

Burnout of oxygen and lowering the temperature in the room with the Burner leads to the flame extinction. The FDS system allows to choose a method for simulating such attenuation: more coarse, but less computationally expensive, or more realistic, but slower in computation.

By default, Fenix+ 3 uses a faster method, and the SUPPRESSION = .False parameter is added to the COMB parameter group in the FDS file.

&COMB SUPPRESSION=.False./

To select a more accurate simulation method, select the Flame Extinguishing checkbox in the Fire Simulation Parameters.

Flame suppression in the gaseous phase{width=70%}

In this case, the SUPPRESSION parameter will not be mentioned in the FDS file in the COMB parameter group. By default, it is true, which is equivalent to the line

&COMB SUPPRESSION=.True./