The purpose of this study is to investigate the characteristics of soot particles in C

2

H

4

/CO

2

/O

2

/N

2

combustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO

2

/O

2

/N

2

mixture

the key species C

2

H

2

C

3

H

3

responsible for formation of first aromatic ring

the typical aromatics and 4-ring aromatics total production rate all decrease greatly. In addition

with CO

2

mole fraction from 0.2 to 0.5 in the mixture

the soot particle number density

volume fraction

surface area density

which are three most important parameters to soot particle property

are suppressed obviously. Furthermore

the increasing content of CO

2

in the oxidizer influences mostly H

OH radical concentrations by two reactions: CO+OH=CO

2

H and H+O

2

=O+OH

and the production rate of H

OH from the two reactions declined

which revealed that CO

2

in mixture has an inhibiting effect on soot particle generation.