The invention concerns a burner, particularly an auxiliary burner in a motor vehicle and most especially a burner to rapidly heat up a three way catalytic converter of an internal combustion engine of a motor vehicle, with a fuel supply mechanism to deliver fuel to the burner, an air supply mechanism to deliver air to the burner, as well as with an open-loop or closed-loop control mechanism to set a desired fuel-air-ratio in the burner. The invention additionally concerns a procedure to operate such a burner. Provision is made, that the open-loop or closed-loop mechanism adjusts the fuel mass delivered from the fuel supply mechanism to the burner to the air mass delivered from the air supply mechanism to the burner.