Week 10 - Simulating Combustion of Natural Gas.

 

COMBUSTION:

Burning in a high temperature exothermic redox chemical reaction between a fuel and an oxidant usually atmospheric oxygen, that produces oxidized often gaseous products in a mixture termed as smoke. combustion does not always result in fire because a flame is only visible when substances undergoing combustion vapourised but when it does a flame is a characteristic indictor of the reaction while the activation energy must be overcome to indicate combustion the heat from a flame may provide enugh energy to make reaction self sustaining. combustion is often a complicated sequence of elementry radical reaction. 

Solid fules such as wood and coal first undergoes endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them combustion is often hot enough that incandescent light in the form of either glowing or a flame is produced.

combustion of an organic fuel in air is always exothermic because the double bond in o2 is much weaker than other double bonds or pairs of single bonds and therefore the formation of the dtronger bonds in the combustion produce CO2 and H2O result in the relase of energy.

stoichiometric combustion of a hydrocarbon in oxygen:

chemical equation of stoichiometric combustion of hydrocarbon in oxygen is:

for example the stoichiometric burning of proprane in oxygen is:

CHEMICAL KINETICS:

chemical kinetics also known as reaction kinetics is the branch of physical chemistry that is concerned with understanding the rate of chemical reaction. it is to be constrasted with thermodynamics which deals with the direction in which a process occcur but in itself tells nothing aboiy its rate.

chemical kinetics includes investigations of how experimental condition influence the speed of a chemical reaction and yield information about the reaction mechanicm and transtion states as well as the construction of mathematical models that also can describe the characyeristics of a chemical reaction.

 

CHEMICAL REACTION MODEL:

chemical reacation model transport physical knowledge into a mathematical formulation that can be utilized in computational simulation of practical in chemical engineering. computer simulation provides the flexiblity to study chemical processes under a wide range of conditions modelling a chemical reaction involves solving conservation equation describing convection, diffusion,and raction source for each component species.

 REACTION RATE MODELS:

1 laminar finate rate model

2 eddy dissipation model

MASS FRACTION:

A mass fraction can also be expresed with a denominator of 100 as a percentage by mass it is one way of expressing the composition of a mixture in a dimensionless size, model fraction and volume fraction are others. when the prevalence of intrest are those of individual chemocal reaction elements rather than of component or other substance the term mass fraction can also refer to the ratio of mass of an element to the total mass of a sample. in these contexts an alternative terms is a mass per cent composition the mass fraction of an element in a compound can be calculated from the compound empirical formula or its chemical formula.

NITROGEN OXIDE EMISSION:

Nitrogen dioxide is an irritant gas which at high concentration causes inflammation of the airways when nitrogen is released during fuel combustion it combines with oxygen atoms to create nitric oxide (No). this further combines with oxygen to create nitrogen dioxide(NO2). nitric oxide is not considered to be hazzardous to healthat typical ambient concentration but nitrogeen dioxide can be. nitrogen dioxide and nitric oxide are referred together as oxides of nitrogen(N0x) .

 

SOOT FORMATIONS:

Soot forms when hydrocarbon fuels such as oil , natural gas, and wood are burned. soot particles form when gaseous molecules are heated to high temperature, and they dont easily turn back into gaseous molecules the way water droplets do when they are heated. soot as an airbone contaminant in the enviroment has many different sources, all of which are result of same form of pyrolisis. they include soot from coal burning internal combustion engines power plant boilers, etc. these exterior source also contribute to the indoor enviroment sources such as smoking of plant matter,cooking oil,and defective furnances.

 

 

 

geometry:

splitting the body:

after that copying it in 2D model 2D geometry:

MESH:

MESH SETTING:

NAME SELECTION:

AXIS

FUEL INLET:

AIR INLET:

WALLS:

OUTLETS:

GENERAL SETTING:

VISCOUS MODEL AND SPECIES:

AIR INLET:

FUEL INLET:

RESULT AND OBSERVATION:

LINE PROBES

RESIDUAL:

temperature contour and mass fraction chart:

CO2 contour and mass fraction chart:

H2O contour and mass fraction chart:

CH4 contour and mass fraction chart:

N2 contour and mass fraction chart:

O2 contour and mass fraction chart:

NOX emission  contour and mass fraction chart:

soot formation:

 

FOR 10% WATER ADDITION:

RESIDUAL:

temperature contour and mass fraction chart:

CO2 contour and mass fraction chart:

H2O contour and mass fraction chart:

CH4 contour and mass fraction chart:

N2 contour and mass fraction chart:

O2 contour and mass fraction chart:

NOX emission  contour and mass fraction chart:

soot formation:

 

FOR 20% WATER ADDITION:

RESIDUAL:

 

temperature contour and mass fraction chart:

 

CO2 contour and mass fraction chart:

 

H2O contour and mass fraction chart:

 

CH4 contour and mass fraction chart:

 

 

N2 contour and mass fraction chart:

 

 

O2 contour and mass fraction chart:

 

 

NOX emission  contour and mass fraction chart:

 

 

soot formation:

 

FOR 30% WATER ADDITION:

RESIDUAL:

 

 

temperature contour and mass fraction chart:

 

 

 

CO2 contour and mass fraction chart:

 

 

 

H2O contour and mass fraction chart:

 

 

 

CH4 contour and mass fraction chart:

 

 

 

 

N2 contour and mass fraction chart:

 

 

 

 

O2 contour and mass fraction chart:

 

 

 

 

NOX emission  contour and mass fraction chart:

 

 

 

 

soot formation:

 

 CONCLUSION:

percentage of water% addition	ratio of methane and water mixed	mass fraction of NOx emmision	mass fraction of soot formations
10	0.9:0.1	2.756e-04	3.69e-02
20	0.8:0.2	1.639e-04	2.85e-02
30	0.7:0.3	8.567e-05	1.216e-02

 

* we can conclude that NOx emission and soot formations reduced as there is an increase in  the addition of water

*and the efficiency of combustion reduced as there is reduction incomplete combustion.