Sheet 1 -Flame

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Mech. Power Eng. Dept

1- What are the condit

2- Define the lower an

the limits.

3- What are the differ

speed?

4- Discuss which flam

- Port injection ga

- Diesel engines

- Flame from a su

- Fire in a buildin

- Bunsen burner

- Candle

5- What are the reaso

quenching distance.

6- Employ correlation

gasoline-air mixture

a. At referenc

b. At condition

18.38 atm

c. At same con

recirculatio

7- A laminar premixed

mm nozzle. The Pro

through a pressure

connecting pipe. W

assume the temper

connecting pipe and

flame velocity is 44

.

Tutorial Sheet

Combustion Fundam

Third year mechanic

ions for the ignition of a fuel gas to occur?

higher flammability limits and what are the fac

nt types of flames and what is the main factor a

of the following is considered premixed or diff

soline engines

rface of a gasoline tank

s of flame quenching and what are the factors a

f Metghalchi and Keck to compare laminar flam

s with φ = 0.8 for 3 cases:

conditions of T = 298 K and P = 1 atm

s typical of a spark ignition engine operating at

ditions as (b) but with 15 percent (by mass) exh

flame is required to be formed using Propane as

ane gas is supplied from a 200 bar pressure bot

egulator. The bottle is connected to the nozzle

at should be the regulator pressure in mm H2O.

ture of the gas remains constant at 300 K throu

the flame half cone angle is 20 degree. The pro

m/s

entals

al Power, 2011

tors affecting

f fecting their

sion.

ffecting flame

e speed of

= 685 K and P =

ust gas

a fuel from a 3

tle of 200 litres

y a 2 inches

You may

h the

ane laminar



8- A full propane cylinder from a stove leaks contents of 1.02 lb (0.464 kg) into a 12’ x

14’ x 8’ (3.66 m x 4.27 m x 2.44 m) room at 20 ºC and 1 atm. After a long time, the

fuel gas and the room air are well mixed. Is mixture in room flammable?

9- A premixed propane-air mixture emerges from a round nozzle with a uniform

velocity of 75 cm/s. The laminar flame speed of propane-air mixture is 35 cm/s. The

flame is lit at the nozzle exit. What is the cone angle of this flame?

10- A methanol-air combustible mixture forms a combustible laminar premixed flame.

The air supply orifice diameter is adjusted to provide a stoichiometric mixture. What

happen if the air orifice diameter has been reduced to 80% and 40% of its original

diameter. What will you notice on the flame? ( Assume the methanol is supplied

through a pressure regulator that keeps a constant flow of methanol through the

burner nozzle)

11- A stoichiometric methane air flame has a laminar burning velocity of 0.33 m/s and a

temperature of 2200K. The reactants are initially at 300 K and 1 bar. Find the

velocity of the combustion products relative to the flame front and the pressure

change across the flame. Assume complete combustion and no dissociation.

12- A premixed laminar flame is stabilized in a one dimensional gas flow where the

vertical velocity of the unburned mixture varies linearly with the horizontal distance

according to the following equation:

Vu=0.8+0.02x [m/s], for 0 < x < 20 mm

Determine the flame shape and the distribution of the local angle of the flame

surface from the vertical. Assume flame speed is independent of position and equal

to 0.4 m/s.

13- Estimate the laminar flame speed of a stoichiometric propane-air mixture using the

simplified-theory. Use the global one step reaction mechanism to estimate the

mean reaction rate as follows:

14- The laminar burning velocity of a stoichiometric mixture of propane-air at 1 bar and

298 K is 0.4 m/s. Estimate the average reaction rate and the reaction zone

thickness. Consider the thermal conductivity of the mixture is 0.026 W/mK at 298 K

and increases at T0.5

. Assume an appropriate average mixture temperature and

ignition temperature. Calculate also the flame quench distance.



Simplified laminar flame mo

Metghalchi and Keck Correl

( )( )

( )122.016.0

18.018.2

2

2,

,

,

−+−=

−−=−+=

=

φ β

φ γ φ φ

γ

M M ref L

ref ref u

uref L L

B BS

P

P

T

T SS

5.0

)(

)(

−

−

= uoig

ig f

L T T

T T

V ρ

ω α

Formulae Sheet and Useful Data

del

tion

( )1.21−

β

dilY







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Sheet 1 -Flame