Combined fuel and oxidizer metering jets, systems, and methods for simultaneously metering fuel and oxidizer

Combined fuel and oxidizer metering jet arrangement is disclosed. The arrangement can be selected to simultaneously meter the flow rate of a liquid and/or LG fuel and an oxidizer for delivery to a single or multi-fuel burner. This allows a single type of fuel delivery conduit and mixing tube to be optimized for a variety of fuels without dynamic user modulation of oxidizer flow rates. Features of various embodiments include enhancements to modify the fuel-oxidizer inflow character such as velocity and/or vector as well as modify the fuel-oxidizer ratio through use of spacers for repositioning (as opposed to replacement) of the metering jet relative to a mixing tube.