There are two types of fuel nozzles – simplex and duplex. With simplex fuel nozzles, you have two different nozzles, primary and secondary. Each nozzle has a single orifice. Simplex nozzles are typically set up as either all primary or in a ratio of 7 to 7 or 10 to 4 primary to secondary. The configuration depends on the engine model and the configuration status of the engine. Upon startup, fuel is distributed to the primary nozzles only.
With duplex nozzles, fuel is introduced in a similar way as with a simple nozzle system in two stages with primary spray upon startup and secondary kicking in as the engine spools up. The difference is that in a duplex nozzle system, all of the nozzles are identical. Each one has two passages and two concentric ports in the tip that spray fuel. The primary and secondary are, in effect, within each nozzle.
The principal difficulty of radiation heat transfer calculations in a supersonic nozzle is a significant variation of the medium temperature and density along the nozzle axis. In contrast to combustion chamber conditions, the temperature of condensed phase particles in the nozzle is several tens or even hundreds of degrees greater than the temperature of gas, and it is different for particles of various sizes. For this reason, a proper calculation of the plunger radiation heat transfer in a supersonic nozzle is impossible without two-phase flow calculations.
Calculation of concentration and temperature fields of two-phase combustion products in a supersonic nozzle is a complicated physical and mathematical problem due to the substantial velocity and temperature nonequilibrium of the condensed phase. Strictly speaking, one should take into account the influence of particles on the gas flow field, as well as break up and coagulation of delivery valve particles. Both break up and agglomeration of alumina melt particles appear to be important at separate regions of the nozzle flow. The latter makes the problem especially complicated.