Abstract: An apparatus comprising a chamber enclosing a flow path of a first fluid and having a second inlet arranged downstream of the first inlet for receiving a second fluid. The apparatus further comprises a vertically adjustable throttle body an end portion comprising three parts, the first part being upstream of the second part, the third part being downstream of the second part, wherein, in an operating position, the second inlet is upstream of the third part of the throttle body and downstream of the first inlet and wherein the first part and the third part of the end portion are adapted to achieve a higher flow rate than the second part.