Method for injecting a fuel-air mixture into a combustion chamber

A method for injecting a fuel/air mixture into a combustion chamber, the mixture comprising liquid fuel, gaseous fuel, and purge air injected through a fuel lance having a lance tip, two ducts for receiving the fuels, and a duct for receiving the purge air, with the ducts being formed by a central, inner tube and middle and outer tubes arranged concentrically with respect to the inner tube, the method comprising:

• routing the liquid fuel to the lance tip through the central, inner tube;
• flowing the purge air between the central, inner tube and the middle tube to an injection location proximate the lance tip, with the purge air and liquid fuel being injected into the combustion chamber, the purge air being injected substantially about an axis and surrounding the liquid fuel so that the liquid fuel is shielded from the gaseous fuel by the purge air;
• injecting the liquid fuel at the injection location in a direction that is oriented slightly radially outward and onto the purge air;
• injecting the gaseous fuel in a direction that is oriented slightly radially inward and onto the purge air.