Simulating Combustion of Natural Gas using Ansys Fluent

Description:

Combustion, a chemical reaction between substances, usually including oxygen, and usually accompanied by the generation of heat and light in the form of flame. The rate or speed at which the reactants combine is high, in part because of the nature of the chemical reaction itself and in part because more energy is generated than can escape into the surrounding medium, with the result that the temperature of the reactants is raised to accelerate the reaction even more.

In general terms, combustion is one of the most important of chemical reactions and may be considered a culminating step in the oxidation of certain kinds of substances. Though oxidation was once considered to be simply the combination of oxygen with any compound or element, the meaning of the word has been expanded to include any reaction in which atoms lose electrons, thereby becoming oxidized. As has been pointed out, in any oxidation process the oxidizer takes electrons from the oxidizable substance, thereby itself becoming reduced (gaining electrons). Any substance at all can be an oxidizing agent. But these definitions, clear enough when applied to the atomic structure to explain chemical reactions, are not as clearly applicable to combustion, which remains, generally speaking, a type of chemical reaction involving oxygen as the oxidizing agent but complicated by the fact that the process includes other kinds of reactions as well and by the fact that it proceeds at an unusually fast pace. Furthermore, most flames have a section in their structure in which, instead of oxidations, reduction reactions occur. Nevertheless, the main event in combustion is often the combining of combustible material with oxygen.

Geometry:

Mesh

Mesh size 1mm

No of elements 17121

Named selection

Axis

Fuel-inlet

Air-inlet

Wall

Setup and solution

Solver: Pressure-based/steatdy-state/Axisymmetric

Model: 

Species model

Boundary conditions

Air inlet at 300K

Fuel-inlet

NOx model

Soot model

Number of iterations 1500

Line probes

 

For 0%H2O

 

Temperature across the combustor

 

Mass-fraction of CH4

 

Mass-fraction of H2O

 

Mass-fraction of CO2

 

Mass-fraction of O2

 

Mass-fraction of N2

 

NOx emission

 

Soot formation

 

Part 2

5% water addition

 

Temperature

 

Mass-fraction of CH4

 

Mass-fraction of H2O

 

Mass-fraction of CO2

 

Mass-fraction of O2

 

Mass-fraction of N2

 

NOx emission

 

Soot formation

 

15% water addition

 

Temperature

 

Mass-fraction of CH4

 

Mass-fraction of H2O

 

Mass-fraction of CO2

 

Mass-fraction of O2

 

Mass-fraction of N2

 

NOx emission

 

Stool formation

 

30% water addition

Temperature

 

Mass-fraction of CH4

 

Mass-fraction of H2O

 

Mass-fraction of CO2

 

Mass-fraction of O2

 

Mass-fraction of N2

 

NOx emission

 

Soot formation

 

Tabulation:

Percentage of water	CH4:h2o	Mass-fraction of NOx	Soot formation
5	0.95:0.12	0.000064	0.0151
15	0.85:0.15	0.000059	0.0114
30	0.7:0.3	0.000048	0.01

Conclusions:

NOx emission and soot formation reduced as the water level is increased.

But the efficiency of the engine reduces as the water level increases there will be incomplete combustion.

We can observe that as the water level increases in fuel, CH4 level reduced