Diesel engines, equipped with a turbocompressor unit with a combustion chamber upstream of the turbine, comprising a by-pass duct enabling direct and permanent passage between the outlet of the compressor of the turbocompressor unit and said combustion chamber, comprise in addition, for the starting of the turbocompressor unit, a starting device comprising pressure difference generating means. These means are positioned in the by-pass duct in the midst of the air-flow between the compressor and the turbine and arranged to create a flow in the direction of the turbine of the turbocompressor unit. The pressure difference generating means may be constituted by a blower driven by an electric motor, or by an injector supplied with air under pressure and generating a flow by the effect of induction.