Page 354 - Advanced thermodynamics for engineers

15.5 CONCLUDING REMARKS 343

Concentration, y 1 HO O 2
2

x = L
Distance along flame, x

L

O 2

H 2
d Potential
core
Mixing zone
Flame
Section A Section B
Section C

y y
y O O
O
y y
d/2 d/2 HO d/2 HO
y y y
H H H
Concentration 1 Concentration 1 Concentration 1
FIGURE 15.12
Combustion of a jet of hydrogen in an oxygen atmosphere.

more detail in Chapter 16. Gas turbine combustion chambers work in a similar way, with a spray of fuel
entraining primary air to initiate the combustion, and subsequent entrainment of secondary air to
complete the process: these are discussed briefly in Chapter 17.

15.5 CONCLUDING REMARKS
The physical phenomena which affect combustion have been introduced. It has been shown that
premixed combustible mixtures exhibit a characteristic combustion velocity called the laminar flame
speed. This is related to the mixture strength and temperature of the reactants, but is too slow for most
engineering applications and must be enhanced by turbulence to achieve levels appropriate for power
plant.
Diffusion flames which occur in heterogeneous mixtures have been described, and it has been
shown that these rely on the mixing of the fuel and oxidant to achieve combustion of the mixture.
Chapters 16 and 17 explain how these basic phenomena are harnessed in engines, and show how
flame speeds can be enhanced by combustion chamber design, and how entrainment of air can be
brought about in heterogeneous combustion systems.