Ignition delay of syngas is an important factor that affects stable operation of combustor and adding diluents to syngas can reduce NO

x

emission. This paper used H

2

O

CO

2

and N

2

as diluents and calculated ignition delay of syngas in temperature range of 900-1400 K and at pressures of 10 and 30 atm respectively. In high temperature range

comparing with N

2

dilution

adding H

2

O and CO

2

can significantly inhibit autoignition of syngas because they have higher collision efficiencies in reaction H+O

2

(+M)=HO

2

(+M). As for low temperature conditions

adding H

2

O can increase reactivity of syngas

especially under high pressure

because of its high collision efficiency in reaction H

2

O

2

(+M)=2OH (+M). Comparing with different dilution rates shows that for syngas and operating conditions in this paper

adding N

2

mainly influences temperature rising process of syngas combustion

thus inhibiting reactivity of syngas. In addition

this paper calculated ignition delay of syngas at different equivalence ratios (

φ

=0.5

1.0).

Higher equivalence ratio (

φ

≤1) means that less air (especially N

2

) needs to be heated

thus promoting ignition of syngas.