  Mixing of two fluids can lead to the formation of a precipitate. If one of
the fluids is injected into a confined space filled with the other, a created
precipitate disrupts the flow locally and forms complex spatiotemporal
patterns. The relevance of controlling these patterns has been highlighted in
the engineering and geological contexts. Here, we show that such injection
patterns can be controlled consistently by injection rate and obstacles. Our
experimental results revealed filament patterns for high injection and low
reaction rates, and the injection rate can control the number of active
filaments. Furthermore, appropriately spaced obstacles in the cells can
straighten the motion of the advancing tip of the filament. A mathematical
model based on a moving boundary adopting the effect of precipitation
reproduced the phase diagram and the straight motion of filaments in structured
cells. Our study clarifies the impact of the nonlinear permeability response on
the precipitate density and that of the obstacles in the surrounding medium on
the motion of the injected fluid with precipitation.
