The invention relates to an injection device (10) for atomizing a liquid into droplets using a gas, comprising a hollow tubular body (12) having a longitudinal direction (X). An inner wall (13) defines a first region, referred to as contact region (Z1), and a second region (Z2). The body (12) has an inner cross-section that varies continuously or constantly over the entire length thereof except at the junction between the first and second regions, where the inner wall (13) of the body includes at least one cavity (201) which increases the size of the inner cross-section of the body, said at least one cavity extending over a predefined length in the longitudinal direction.