Injection device conformed for atomising a liquid into droplets by means of a gas, comprising a hollow tubular body extending in a longitudinal direction and an internal wall of which defines a first so-called contact zone and a second zone located downstream of the first zone with respect to a direction of circulation of the liquid and of the gas inside the body, the latter having: - at least two inlet openings (16, 17) emerging in said first zone, for injecting a liquid inside the first zone, said openings each having an axis oriented so that flows of liquid coming from said openings converge on a longitudinal line extending inside the body, - an inlet opening emerging in said first zone, for injecting an atomisation gas inside the first zone, - at least one outlet orifice located downstream of the first and second zones for discharging the atomised liquid out of the body, characterised in that the body has an internal cross section varying continuously or constantly over the entire length thereof and the internal wall of the body is provided, between the first and the second zone, with at least one baffle (26 i, 126 1, 226 1, 226' 1, 226" 1, 326 1, 426 i, 526 i, 626 1) conformed so that, in each plane perpendicular to the longitudinal direction of the body containing said baffle, the latter reduces an internal cross section of the body over the entire periphery of the internal wall, and in that the internal wall is provided with a single baffle (626 1) extending in particular over a length, in the longitudinal direction, at least equal to a maximum internal dimension of the body measured perpendicularly to the longitudinal direction, said baffle (626 1) having an irregular profile in the longitudinal direction of the body, or in that said internal wall is provided with a plurality of separate baffles (26 i, 126 1, 226 1, 226' 1, 226" 1, 326 1, 426 i, 526 i) and a plurality of adjacent baffles (426 i) having heights, measured perpendicularly to the longitudinal direction of the body, that are non-zero and different. - at least two inlet openings (16, 17) emerging in said first zone, for injecting a liquid inside the first zone, said openings each having an axis oriented so that flows of liquid coming from said openings converge on a longitudinal line extending inside the body, - an inlet opening emerging in said first zone, for injecting an atomisation gas inside the first zone, - at least one outlet orifice located downstream of the first and second zones for discharging the atomised liquid out of the body, characterised in that the body has an internal cross section varying continuously or constantly over the entire length thereof and the internal wall of the body is provided, between the first and the second zone, with at least one baffle (26 i, 126 1, 226 1, 226' 1, 226" 1, 326 1, 426 i, 526 i, 626 1) conformed so that, in each plane perpendicular to the longitudinal direction of the body containing said baffle, the latter reduces an internal cross section of the body over the entire periphery of the internal wall, and in that the internal wall is provided with a single baffle (626 1) extending in particular over a length, in the longitudinal direction, at least equal to a maximum internal dimension of the body measured perpendicularly to the longitudinal direction, said baffle (626 1) having an irregular profile in the longitudinal direction of the body, or in that said internal wall is provided with a plurality of separate baffles (26 i, 126 1, 226 1, 226' 1, 226" 1, 326 1, 426 i, 526 i) and a plurality of adjacent baffles (426 i) having heights, measured perpendicularly to the longitudinal direction of the body, that are non-zero and different. in that the internal wall is provided with a single baffle (626 1) extending in particular over a length, in the longitudinal direction, at least equal to a maximum internal dimension of the body measured perpendicularly to the longitudinal direction, said baffle (626 1) having an irregular profile in the longitudinal direction of the body, or in that said internal wall is provided with a plurality of separate baffles (26 i, 126 1, 226 1, 226' 1, 226" 1, 326 1, 426 i, 526 i) and a plurality of adjacent baffles (426 i) having heights, measured perpendicularly to the longitudinal direction of the body, that are non-zero and different.