Combustor arrangement having arranged in an upstream to downstream flow sequence a radial swirler, pre-chamber with a convergent portion and a combustion chamber

A combustor for a gas turbine engine, the combustor comprising:

• a central axis about which are arranged in an upstream to downstream flow sequence
• a radial swirler,
• a pre-chamber partly defined by a wall and
• a combustion chamber,
• wherein the radial swirler comprises a base plate having an annular array of vanes and fuel injectors arranged to deliver an air/fuel mixture radially inwardly and tangentially to an inlet of the pre-chamber to create a vortex that flows through the pre-chamber to an outlet of the pre-chamber and then into the combustion chamber,
• wherein a fuel comprises a mixture having a hydrogen gas content, wherein the hydrogen gas content is at least 5% by volume of the fuel,
• wherein the base plate comprises a pilot surface which faces the pre-chamber and bounds an upstream axial extent of the pre-chamber,
• wherein the pre-chamber has a portion which is convergent in a downstream direction and is configured to accelerate the air/fuel mixture to a velocity effective to prevent flashback of a flame from the combustion chamber into the radial swirler, and
• wherein the pre-chamber has an inlet area and an outlet area and a ratio of the inlet area to the outlet area is between 1.45 and 1.70.