So do the fuels used by jet engines. That is why the space shuttle doesn't use jet engines. The oxygen is built right into the fuel. I don't design piping anymore. That was the job I was doing before I came to my new job.
Engines do have piping of sorts though that deliver the fuel to the combuster.
The combuster in the engine is where the fuel is burned to make the energy needed to make the engine go. Designing a new plane is the work of many people. All of these need to work together. Using a wind tunnel to test the aerodynamic performance of the airplane helps greatly. It's not always possible to predict with a computer how an aircraft will perform.