TABLE D-2 Matrix Summary of Propulsion Taxonomy

Cyclea

Operation

Pressurization

Energy release

Propulsion

1

Isothermal-isothermal

1

Continuous

1

Mechanical

1

Oxidation (combustion)

1

Propeller

2

Isothermal-isovolume

2

Intermittent

2

Self-pressurized

 

2

Turbofan

3

Isothermal-isobaric

 

 

3

Both

2

Electrochemical (fuel cell)

3

Turbofan and afterburner

4

Isovolume-isothermal

 

 

 

 

 

 

5

Isovolume-isovolume

 

 

 

 

3

Photochemical (photosynthesis)

4

Turbojet

6

Isovolume-isobaric

 

 

 

 

 

5

Ramjet

7

Isobaric-isothermal

 

 

 

 

4

Photoelectric (solar cell)

6

Rocket

8

Isobaric-isovolume

 

 

 

 

 

7

Turbojet and afterburner

9

Isobaric-isobaric

 

 

 

 

5

Photodirect (laser/electromagnetic heating)

 

10

Fuel cell

 

 

 

 

 

8

Pulse-jet (pulse detonation engine)

aCycle name describes methods of heat absorption and heat rejection, respectively.

Selecting one item from the first column and one from the second column defines, in an elemental way, a family of 20 power plants. However, the continuous isothermal and isovolume cycles can be immediately ruled out as physically impossible because in the steady state the fluid is forced to move uphill against the total pressure gradient. This leaves 12 potential power plants (10 intermittent and 2 continuous: isobaric-isobaric and fuel cell). The next column of the taxonomy is pressurization:

Pressurization

1

Mechanical

2

Self-pressurized

3

Both

These three entries create a total of 36 options (30 intermittent and 6 continuous). Consider next energy release processes from fuel. The terms in parentheses are common names for the processes.

Energy Release

1

Oxidation (combustion)

2

Electrochemical (fuel cell)

3

Photochemical (photosynthesis)

4

Photoelectric (solar cell)

5

Photodirect (laser/electromagnetic heating)

Etc.

Recombination of excited molecular and atomic states, free radicals, and antimatter recombination are included in the term “etc.” but are not further considered because of the problems of storing the fuels. Nuclear energy release is excluded because of the weight of shielding material and radioactive hazards. With this exclusion, we now have five more options, which creates a total of 180 possible devices. Photochemical, photoelectric, and photodirect systems arguably possess a low energy density and in all likelihood will only find niche applications. Setting aside low-power-density processes reduces the number of options to 72 (60 intermittent and 12 continuous).

Propulsion mechanism is the next area for consideration.

Propulsion

1

Propeller

2

Turbofan

3

Turbofan + afterburner

4

Turbojet

5

Ramjet

6

Rocket

7

Turbojet + afterburner

8

Pulse-jet (pulse detonation engine)

These eight items provide one intermittent propulsion option and seven continuous propulsion options, one of which (the propeller) can also be used with intermittent cycles. This results in 204 options (2 × 60 + 7 × 12), which is quite a large number.

COMMENTS

Both the constant temperature and constant volume heat absorption (or combustion) cycles are usually intermittent (pulsed). Intermittent processes have the potential to operate at higher temperatures and reasonable wall temperatures because the wall can be cooled during the part of the cycle when no heat is applied. However, in practice some of this heat is lost and reduces efficiency. Further, while intermittent cycles have a high efficiency per pulse, the average efficiency is lower because power is available only part of the time.

The fuel cell could require a precompression of fuel depending on the fuel storage mechanism. The fuel cell has the



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