Aiming at probing the direct interaction between unsaturated hydrocarbons and NO

x

in hydrazine rocket propellant

the auto-ignition process of ethylene(C

2

H

4

)and N

2

O mixtures was studied experimentally and theoretically. The ignition delay time of stoichiometric C

2

H

4

/N

2

O/O

2

/Ar with bl

ending ratios of N

2

O/(N

2

O+O

2

)=0%

50%

80% and 100% was measured in the reflected shock conditions covering pressure range of 0.12-1.01 MPa and temperature range of 1 214-1 817 K in a shock tube. Experimental results show that compared to O

2

the reactivity of C

2

H

4

is significantly decreased by N

2

O

resulting in longer ignition delay time

and this inhibition effect increases with the concentration of N

2

O

meaning that the ignition delay presents a non-linear dependence on N

2

O addition. Simulation results reveal that only Aramco-Z model shows a reasonable agreement with the measurements. Direct interaction between N

2

O and C

2

H

4

appears to be not favorable. Longer ignition delay time caused by the addition of N

2

O is due mainly to the reduction in the reaction rate of C

2

H

3

+O

2

and the concentration of free radical pool.