A passive infrared suppression (IRS) device is an important and integral part of the modern naval/cargo ships, fighter jets, and helicopters to cool down the hot exhaust gas to suppress the infrared (IR) signatures. A modified IRS device has been proposed by putting inward/outward guides. The air entrainment and temperature ratios of the new type IRS device have been investigated by solving transport equations (continuity, momentum, energy, and turbulence) using the finite volume solver in ansys fluent. The Reynolds number (Ren), guide lengths (Lg/Dn), the inclination angle of guides (θg), overlap-height (Hov/Dn), and outlet temperature ratio (Tout/T∞) have been varied in the range of 1.5 × 10–1.5 × 106, 0–0.326, 0–75 deg, −0.326–0.018, and 1.243–2.576, respectively. It has been observed that the dimensional air entrainment increases with the Reynolds number and inlet temperature. The guide length alters the flow inside the IRS device and affects the entrainment ratio. We observed that, at the optimal value of guide length (Lg/Dn = 0.163) and inclination angle (θg = 15 deg), the IRS device entrains the maximum air, and attains a minimum temperature at the outlet. The mass suction and the outlet temperature of two different types of IRS devices have also been compared to choose the best one for the practical engineering application. An empirical correlation equation for air entrainment has been developed using nonlinear regression analysis.