Overview
Applications:
 Heating appliances
 Bunsen burners
 Burner for glass product manufacturing
Importance of studying laminar premixed
flames:
 Some burners use this type of flames as shown by examples
above.
 Prerequisite to the study of turbulent premixed flames. Both
have the same physical processes and many turbulent flame
theories are based on underlying laminar flame structure.
PHYSICAL DESCRIPTION
Physical characteristics
 Figure 1 shows typical flame temperature profile,
mole fraction of reactants, R, and volumetric heat
release, . Q
 Velocity of reactants entering the flame, u = flame
propagation velocity, SL
 Products heated  product density (b) < reactant
density (u). Continuity requires that burned gas
velicity, b >= unburned gas vel., u
u SL A = u u A = b b A
(1)
 For a typical hydrocarbon-air flame at Patm, u/b  7 
considerable acceleration of the gas flow across the
flame (b to u).
Fig. 1 Laminar flame structure, temperature and heat rate profiles
based on experiments of Friedman and Burke
A flame consists of 2 zones:
 Preheat zone, where little heat is released
 Reaction zone, where the bulk of chemical
energy is released
Reaction zone consists of 2 regions:
 Thin region (less than a millimeter), where
reactions are very fast
 Wide region (several millimeters), where
reactions are slow
 In thin region (fast reaction zone), destruction of the
fuel molecules and creation of many intermediate
species occur. This region is dominated by bimolecular
reactions to produce CO.
 Wide zone (slow reaction zone) is dominated by radical
recombination reactions and final burnout of CO via CO
+ OH  CO2 +H
Flame colours in fast-reaction zone:
 If air > stoichiometric proportions, excited CH radicals
result in blue radiation.
 If air < stoichiometric proportions, the zone appears
blue-green as a result of radiation from excited C2.
 In both flame regions, OH radicals contribute to
the visible radiation, and to a lesser degree due to
reaction CO + O  CO2 + h.
 If the flame is fuel-rich (much less air), soot will
form, with its consequent blackbody continuum
radiation. Although soot radiation has its maximum
intensity in the infrared (recall Wien’s law for
blackbody radiation), the spectral sensitivity of the
human eye causes us to see a bright yellow (near
white) to dull orange emission, depending on the
flame temperature
Figure 2. Spectrum of flame colours
Typical Laboratory Premixed Flames
 The typical Bunsen-burner flame is a dual flame:
a fuel rich premixed inner flame surrounded by a
diffusion flame. Figure 3 illustrates a Bunsen burner.
 The diffusion flame results when CO and OH from the
rich inner flame encounter the ambient air.
 The shape of the flame is determined by the combined
effects of the velocity profile and heat losses to the tube
wall.
For the flame to remain stationary,
SL = normal component of u = u sin
Figure 3b illustrates vector diagram.
Fig. 3
(2)
a Bunsen burner schematic
b Laminar flame speed equals normal component of unburned gas velocity
Example 1. A premixed laminar flame is stabilized in
a one-dimensional gas flow where the vertical velocity
of the unburned mixture, u, varies linearly with the
horizontal coordinate, x, as shown in the lower half of
Fig. 6. Determine the flame shape and the distribution
of the local angle of the flame surface from vertical.
Assume the flame speed SL is independent of position
and equal to 0.4 m/s (constant), a nominal value for a
stoichiometric methane-air flame.
 Solution
 From Fig. 7, we see that the local angle, , which the
flame sheet makes with a vertical plane is (Eqn. 2)
 = arc sin (SL/u), where, from Fig. 6,
u (mm/s) = 800 + (1200 – 800)/20 x (mm) (known).
u (mm/s) = 800 + 20x.
So,
 = arc sin (400/(800 + 20x (mm))
and has values ranging from 30o at x = 0 to19.5o at x = 20
mm, as shown in the top part of Fig. 6.
 To calculate the flame position, we first obtain an
expression for the local slope of the flame sheet
(dz/dx) in the x-z plane, and then integrate this
expression with respect to x find z(x). From Fig. 7, we
see that:
becomes
1/ 2
 ,which, for u=A + Bx,
dz  A  Bx 
 
  1
dx  S L 


2
2 1/ 2
  u  x   SL 
dz
 tan   

2
dx
SL


2
Integrating the above with A/SL = 2 and B/SL =
0.05 yields
 dz 

2
0.5  x
z(x)     dx  (x  80x  1200)   1 
dx 
 40 
0
x
-10 ln[(x2+80x+1200)1/2+(x+40)]
-203+10 ln(203+40)
 The flame position z(x) is plotted in upper half of
Fig. 8.6.
Fig. 5 a) Adiabatic flat flame burner
b) Non-adiabatic flat flame burner
Fig. 6 Flow velocity, flame position, and angle from vertical of
line tangent to flame
Fig. 7 Definition of flame geometry for Example 1
SIMPLIFIED ANALYSIS
Turns (2000) proposes simplified laminar flame speed
and thickness on one-dimensional flame.
Assumptions used:
1- One-dimensional, constant-area, steady flow. Onedimensional flat flame is shown in Figure5.
2-Kinetic and potential energies, viscous shear work,
and thermal radiation are all neglected.
3-The small pressure difference across the flame is
neglected; thus, pressure is constant.
4- The diffusion of heat and mass are governed by
Fourier's and Fick's laws respectively (laminar flow).
5- Binary diffusion is assumed.
 The Lewis number, Le, which expresses the ratio of thermal
diffusivity, , to mass diffusivity, D, i.e., is unity,

k
Le  
D C p D
k

u C p
 The Cp mixture ≠ f(temperature, composition). This is
equivalent to assuming that individual species specific heats
are all equal and constant.
 Fuel and oxidizer form products in a single-step exothermic
reaction. Reaction is
1 kg fuel +  kg oxidiser  ( + 1)kg products
 The oxidizer is present in stoichiometric or excess proportions;
thus fuel is completely consumed at the flame.
 For this simplified system, SL and  found are
1/ 2
(8.20)

m 
S L   2   1 F 
u 


 and
 2 u 
 




1
m
 F 
 
 or
2
 
SL
(21)
where is m  volumetric mass rate of fuel and  is
thermal diffusivity. Temperature profile is assumed linear
from Tu to Tb over the small distance, as shown in Fig. 9.
F
Fig. 9 Assumed temperature profile for laminar premixed flame analysis
FACTORS INFLUENCING FLAME SPEED (SL) AND
FLAME THICKNESS ()
1. Temperature (Tu and Tb)
 Temperature dependencies of SL and  can be inferred
from Eqns 20 and 21. Explicit dependencies is
proposed by Turns as follows

(27)
k (T )
0.75
1
 T Tu P
u C p (T )
 where  is thermal diffusivity,
 Tu is unburned gas temperature,
,
 Tb is burned gas temperature.
T  0.5 Tb  Tu 

n Tu

F  .
mF / u
P
 Tb n P n 1Tu exp( E A /( RuTb )
(28)
where the exponent n is the overall reaction order,
Ru = universal gas constant (J/kmol-K), EA = activation
energy (J/kmol)
 Combining above scalings yields and applying Eqs. 20
and 21
  EA  ( n 2) / 2
0.375
n / 2
TuTb
exp 
 SL  T
(29)
P
 2 RuTb 

T
0.375
Tb
n/2
 EA   n / 2
exp 
P
 2 RuTb 
(30)
 For hydrocarbons, n  2 and EA  1.67.108 J/kmol (40
kcal/gmol).
 Eqn 29 predicts SL to increase by factor of 3.64 when Tu
is increased from 300 to 600K.
 Table 8.1 shows comparisons of SL and 
 The empirical SL correlation of Andrews and Bradley
[19] for stoichiometric methane-air flames,
SL (cm/s) = 10 + 3.71.10-4[Tu (K)]2
(31)
which is shown in Fig. 8.13, along with data from
several experimenters.
 Using Eqn. 31, an increase in Tu from 300 K to 600 K
results in SL increasing by a factor of 3.3, which
compares quite favourably with our estimate of 3.64
(Table 8.1).
Fig. 13 Effect of gas temp. on laminar flame
speeds of stoichiometric methane-air mixture at 1
atm, various lines are data from various
investigators
 Table 8.1 Estimate of effects of Tu and Tb on SL and 
using Eq 29 and 30
Case
Tu (K)
Tb (K)
SL/SL,A
/A
A (ref)
300
2,000
1
1
B
600
2,300
3.64
0.65
C
300
1,700
0.46
1.95
 Case A: reference
 Case C: Tb changes due to heat transfer or changing
equivalent ratio, either lean or rich.
 Case B: Tu changes due to preheating fuel
Pressure (P)
 From Eq. 29, if, again, n  2, SL  f (P).
 Experimental measurements generally show a negative
dependence of pressure. Andrews and Bradley [19]
found that
SL (cm/s) = 43[P (atm)]-0.5
(32)
fits their data for P > 5 atm for methane-air flames
(Fig. 14).
Fig. 14 Effect of pressure on laminar flame speeds of
stoichiometric methane-air mixture for Tu=16-27oC
Equivalent Ratio ()
 Except for very rich mixtures, the primary effect of 
on SL for similar fuels is a result of how this
parameter affects flame temperatures; thus, we
would expect S L,max at a slightly rich mixture and fall
off on either side as shown in Fig. 8.15 for behaviour
of methane.
 Flame thickness () shows the inverse trend, having a
minimum near stoichiometric (Fig. 16).
Fuel Type
 Fig. 8.17 shows SL for C1-C6 paraffins (single bonds),
olefins (double bonds), and acetylenes (triple bonds).
Also shown is H2. SL of C3H8 is used as a reference.
 Roughly speaking the C3-C6 hydrocarbons all follow
the same trend as a function of flame temperature.
C2H4 and C2H2‘ SL > the C3-C6 group, while CH4’SL
lies somewhat below.
Fig. 15 Effect of equivalence ratio on the laminar flame speed of
methane-air mixture at atmospheric pressure
Fig. 16 Flame thickness for laminar methane-air flames at
atmospheric pressure
Fig. 17 Relative flame speeds for c1-c6 hydrocarbon fuel

H2's SL,max is many times > that of C3H8. Several
factors combine to give H2 its high flame speed:
i. the thermal diffusivity () of pure H2 is many times
> the hydrocarbon fuels;
ii. the mass diffusivity (D) of H2 likewise is much >
the hydrocarbons;
iii. the reaction kinetics for H2 are very rapid since the
relatively slow CO CO2 step that is a major factor
in hydrocarbon combustion is absent.
 Law [20] presents a
compilation of laminar
flame-speed data for
various pure fuels and
mixtures shown in Table
2.
Table 2 SL for various 
pure fuels burning in air
for  = 1.0 and at 1 atm
Fuel
SL (cm/s)
CH4
40
C2H2
136
C2H4
67
C2H6
43
C3H8
44
H2
210
FLAME SPEED CORRELATIONS FOR SELECTED
FUELS
 Metghalchi and Keck [11] experimentally determined
SL for various fuel-air mixtures over a range of
temperatures and pressures typical of conditions
associated with reciprocating internal combustion
engines and gas turbine combustors.
 Eqn 8.33 similar to Eqn. 8.29 is proposed
SL = SL,ref  T   P   (1 – 2.1Ydil)
(8.33)
 u  

 Tu ,ref   Pref 
for Tu  350 K.
 The subscript ref refers to reference conditions defined
by
Tu,ref = 298 K, Pref = 1 atm and
SL,ref = BM + B2( - M)2 (for reference conditions)
where the constants BM, B2, and M depend on fuel
type and are given in Table 3.
 Exponents of T and P,  and  are functions of ,
expressed as
 = 2.18 - 0.8( - 1) (for non-reference conditions)
 = -0. 16 + 0.22( - 1) (for non-reference conditions)
 The term Ydil is the mass fraction of diluent present in
the air-fuel mixture in Eqn. 8.33 to account for any
recirculated combustion products. This is a common
technique used to control NOx in many combustion
systems
Table 8.3 Values for BM, B2, and M used in Eqn 8.33 
[11]
Fuel
M
BM (cm/s)
B2 (cm/s)
Methanol
1.11
36.92
-140.51
Propane
1.08
34.22
-138.65
Iso octane 1.13
26.32
-84.72
RMFD-303 1.13
27.58
-78.54
Example 8.3
Compare the laminar flame speeds of gasoline-air
mixtures with  = 0.8 for the following three cases:
i. At ref conditions of T = 298 K and P = 1 atm
ii. At conditions typical of a spark-ignition engine
operating at wide-open throttle: T = 685 K and P =
18.38 atm.
iii. Same as condition ii above, but with 15 percent (by
mass) exhaust-gas recirculation
Solution
 RMFD-303 research fuel has a controlled composition
simulating typical gasolines. The flame speed at 298 K
and 1 atm is given by
 SL,ref = BM + B2( - M)2
 From Table 8.3,
 BM = 27.58 cm/s, B2 = -78.38cm/s, M = 1. 13.
 SL,ref = 27.58 - 78.34(6.8 - 1.13)2 = 19.05 cm/s
 To find the flame speed at Tu and P other than the
reference state, we employ Eqn. 33

 Tu   P 
 SL(Tu, P) = SL,ref

 

 Tu ,ref   Pref 

 

where
 = 2.18-0.8(-1) = 2.34
 = -0.16+0.22(-1) = - 0.204
Thus,
SL(685 K, 18.38 atm) =
19.05 (685/298)2.34(18.38/1)-0.204 =73.8cm/s
With dilution by exhaust-gas recirculation, the flame
speed is reduced by factor (1-2.1 Ydil):
SL(685 K, 18.38 atm, 15%EGR) =
73.8cm/s[1-2.1(0.15)]= 50.6 cm/s
QUENCHING, FLAMMABILITY, AND
IGNITION
 Previously  steady propagation of premixed
laminar flames
 Now  transient process: quenching and ignition.
Attention to quenching distance, flammability
limits, and minimum ignition energies with heat
losses controlling the phenomena.
1. Quenching by a Cold Wall
 Flames extinguish upon entering a sufficiently small
passageway. If the passageway is not too small, the
flame will propagate through it. The critical diameter of
a circular tube where a flame extinguishes rather than
propagates, is referred to as the quenching distance.
 Experimental quenching distances are determined by
observing whether a flame stabilised above a tube does
or does not flashback for a particular tube diameter
when the reactant flow is rapidly shut off.
 Quenching distances are also determined using highaspect-ratio rectangular-slot burners. In this case, the
quenching distance between the long sides, i.e., the slit
width.
 Tube-based quenching distances are somewhat larger
(20-50 percent) than slit-based ones [21]
Ignition and Quenching Criteria
Williams [22] provides 2 rules-of-thumb governing
ignition and flame extinction.
 Criterion 1 -Ignition will only occur if enough energy
is added to heat a slab thickness steadily propagating
laminar flame to the adiabatic flame temperature.
 Criterion 2 -The rate of liberation of heat by chemical
reactions inside the slab must approximately balance
the rate of heat loss from the slab by thermal
conduction. This is applicable to the problem of flame
quenching by a cold wall.
Fig. 18 Schematic of flame quenching between two parallel wall
Simplified Quenching Analysis.
 Consider a flame that has just entered a slot
formed by two plane-parallel plates as shown in
Fig. 8.18. Applying Williams’ second criterion: heat
produced by reaction = heat conduction to the
walls, i.e.,
QV  Qcond ,tot

(8.34)

Qis volumetric heat release rate
Q  mF hc
(8.35)
where mF is volumetric mass rate of fuel,
hc is heat of combustion
 Thickness of the slab of gas analysed = .
Find quenching distance, d.
Solution
dT

Qcond  kA
in gas  wall
(36)
dx
 A = 2L, where L is slot width ( paper) and 2
accounts for contact on both sides (left and
right). dT
is difficult to approximate. A
dx
dT =
reasonable lower bound of
Tb  Tw  (37)
dx
d /b
where b = 2, assuming a linear distribution of T
from the centerline plane at Tb to the wall at Tw.
In general b > 2.
 Quenching occurs from Tb to Tw.
 Combining Eqns 8.35-8.37,

Tb  Tw
(mF hc )( dL))  k (2 L)
d /b
 or
2kb Tb  Tw 
2
d 

mF hc
(38a)
(38b)
 Assuming Tw = Tu, using Eqn 8.20 (about SL), and relating
 . hc  (  1)c p (Tb  Tu )
, Eqn 8.38b becomes
d = 2b /SL
(39a)
 Relating Eqn 8.21 (about ), Eqn 8.39a becomes

d = 2b 
 Because b  2, value d is always > . Values of d for fuels are
shown Table 8.4.

Table 8.4 Flammability limits, quenching distances 
and minimum ignition energies
Flammability limit
min
max
Quenching distance, d
Stoich-mass For =1
Absolute
air-fuel ratio
min, mm
C 2H 2
0.19

13.3
2.3
-
CO
0.34
6.76
2.46
-
-
C10H22
0.36
3.92
15.0
2.1
-
C 2H 6
0.50
2.72
16.0
2.3
1.8
C2H4
0.41
> 6.1
14.8
1.3
-
H2
0.14
2.54
34.5
0.64
0.61
CH4
0.46
1.64
17.2
2.5
2.0
CH3OH
0.48
4.08
6.46
1.8
1.5
C8H18
0.51
4.25
15.1
-
-
C 3H 8
0.51
2.83
15.6
2.0
1.8
Fuel
Minimum ignition energy
For =1 (10-5 J)
Absolute
minimum (10-5 J)
C 2H 2
3
-
CO
-
-
C10H22
-
-
C 2H 6
42
24
C 2H 4
9.6
-
H2
2.0
1.8
CH4
33
29
CH3OH
21.5
14
C8H18
-
-
C 3H 8
30.5
26
Example 8.4.
 Consider the design of a laminar-flow, adiabatic,
flat-flame burner consisting of a square
arrangement of thin-walled tubes as illustrated in
the sketch below.
 Fuel-air mixture flows through both the tubes and
the interstices between the tubes.
 It is desired operate the burner with a
stoichiometric methane-air mixture exiting the
tubes at 300 K and 5 atm


Determine the mixture mass flowrate per unit
cross-sectional area at the design condition.
Estimate the maximum tube diameter allowed
so that flashback will be prevented.
Solution
 To establish a flat flame, the mean flow velocity must equal the
laminar flame at the design temperature and pressure. From Fig.
14,
 SL (300K, 5atm) = 43/P (atm) = 43/5 = 19.2cm/s.
 The mass flux, ,
ism
 m = m / A
= uu = uSL
 Assuming an ideal-gas mixture, where
 MWmix = CH4MWCH4 + (1 - CH4)MWair

= 0.095(16.04) + 0.905(28.85)

= 27.6 kg/kmol =5.61kg/m3
 (Stoichimetric mass ratio air/ methane = 17.2, see Table 4)
 Thus, the mass flux is = uSL = 5.61(0.192)= 1.08 kg/(s.m2)
m
 We assume that if the tube diameter < the quench
distance (d), with some factor-of-safety applied, the
burner will operate without danger of flashback.
 Thus, we need to find the quench distance at the
design conditions.
 Fig. 16 shows that dslit 1.7 mm. Since dslit = dtube –
(20-50%), use dslit outright (our case) with factor of
safety 20-50%. Data in Fig 8.16 is for slit, design is of
tube.
 Correction for 5 atm:
 Eqn. 39a, d  /SL
 Eqn 27,   T1.75/P
 2 S L ,1
P1 S L ,1

d2 =
d1
 d1
1 S L,2
P2 S L,2
 d(5atm) =1.7mm. 1 atm 43 cm / s
5 atm 19.2 cm / s
 ddesign  0.76 mm
 Check whether d=0.76 mm gives laminar flow (Red <
2300).
u ddesign SL 5.61(0.00076)(0.192)
Red 

 51.5
6

15.89.10
 Flow is still laminar
2. Flammability Limits
 A flame will propagate only within a range of
mixture the so-called lower and upper limits of
flammability. The limit is the leanest mixture ( <
1), while the upper limit represents the richest
mixture ( > 1).  = (A/F)stoich /(A/F)actual by mass or
by mole
 Flammability limits are frequently quoted as %fuel
by volume in the mixture, or as a % of the
stoichiometric fuel requirement, i.e., ( x 100%).
Table 8.4 shows flammability limits of some fuels
 Flammability limits for a number of fuel-air mixtures
at atmospheric pressure is obtained from experiments
employing "tube method".
 In this method, it is ascertained whether or not a flame
initiated at the bottom of a vertical tube
(approximately 50-mm diameter by 1.2-m long)
propagates the length of the tube.
 A mixture that sustains the flame is said to be
flammable. By adjusting the mixture strength, the
flammability limit can be ascertained.
 Although flammability limits are physicochemical properties of the fuel-air mixture,
experimental flammability limits are related to
losses from the system, in addition to the mixture
properties, and, hence, generally apparatus
dependent [31].
Example 8.5.
 A full C3H8 cylinder from a camp stove leaks its
contents of 1.02 lb (0.464 kg) in 12' x 14' x 8' (3.66 m x
4.27 m x 2.44 m) room at 20oC and 1 atm. After a long
time fuel gas and room air are well mixed. Is the
mixture in the room flammable?
Solution
 From Table 8.4, we see that C3H8-air mixtures are
flammable for 0.51 <  < 2.83. Our problem, thus, is to
determine  of the mixture filling the room. Partial
pressure of C3H8 by assuming ideal-gas behaviour
PF 
mF  Ru / MWF  T
Vroom
0.464(8315/44.094)(20  273)

3.66(4.27)(2.44)
= 672.3 Pa
 Propane mole fraction =
 F = PF/P = 672.3/101,325 = 0.00664
 and
 air = 1 - F = 0.99336
 The air-fuel ratio of the mixture in the room is
 (A/F)act =
 air MWair
0.99336 (28.85)

 97.88
 fuel MW fuel 0.00664 (44.094)
 From the definition of  and the value of (A/F)stoich
from Table 8.4 (i.e. 15.6 by mass ratio), we have
 = (A/F)stoich /(A/F)act = 15.6/97.88 = 0.159
 Since  = 0.159 < lower limit (= 0. 51), the mixture in
the room is not capable of supporting a flame.
Comment
 Although our calculations show that in the fully
mixed state the mixture is not flammable, it is quite
possible that, during the transient leaking process, a
flammable mixture can exist somewhere within the
room.
 C3H8 is heavier than air and would tend to
accumulate near the floor until it is mixed by bulk
motion and molecular diffusion.
 In environments employing flammable gases,
monitors should be located at both low and high
positions to detect leakage of heavy and light fuels,
respectively.
3. Ignition
 Most of ignition uses electrical spark (pemantik
listrik). Another means is using pilot ignition (flame
from very low-flow fuel).
Simplified Ignition Analysis
 Consider Williams’ second criterion, applied to a
spherical volume of gas, which represents the
incipient propagating flame created by a point spark.
Using the criterion:
 Find a critical gas-volume radius, Rcrit, below which
flame will not propagate
 Find minimum ignition energy, Eign, to heat critical
gas volume from initial state to flame temperature
(Tu to Tb).
Critical radius, Rcrit, and Eign

(8.40)
QV  Qconduction
(propagation)
2
 mFhc 4 R 3crit / 3   k 4 Rcrit

dT
dr
(8.41)
Rcrit
where is mass flowrate/volume
 Heat transfer process is shown in Figure 8.20
Tb  Tu 
dT



(8.42)
dr
R
Rcrit
crit
 Substitution Eqn 8.42 to 8.41 results in
 .
Rcrit
3k Tb  Tu 

mFhc
(8.43)
 Rcrit is therefore determined by the flame propagation
 If R < Rcrit, it would require exothermic heat > hc
 Substituting from Eqn 8.20 into Eqn 8.43 will give


(8.44)
Rcrit  6
 6/2 
SL


Ignition is aimed to increase fluid from Tu to Tb at 
the onset of combustion to replace hc (ignition)
 E  m c T T
(8.45)
ign
crit p

b
u

where Eign is minimum ignition energy
 Substitution mcrit=b.4Rcrit3/3 and b using gas
ideal formulae to Eqn 8.45 results in

Eign
 c p  Tb  Tu    
 61, 6 P  
 
 Rb  Tb   S L 
3
(8.47)
 where Rb = Ru/MWb and Ru = gas constant
4. Dependencies on Pressure, Temperature
and Composition
 Using Eqn 8.27 and 8.29 on Eqn 8.47 demonstrates
effect of pressure to be
Eign  P-2
(8.48)
(see comparison with experimental result in Fig 8.21)
 Eqn 8.47 implies that in general, Tu Eign (see
Table 8.5).
 Eign vs %fuel gives U-shaped plot (Figures 8.22 and
8.23). This figure indicates that Eign is minimum as
a mixture composition is stoichiometric or near it.
 If the mixture gets leaner at au richer, Eign
increases first gradually and then abruptly. %fuel
at Eign =  to be ignited are flammability limits
Figure 8.22. Effect of %fuel on Eign
Figure 8.22. Effect of %fuel on Eign
Figure 8.23. Effect of methane composition on Eign
Table 8.5 Temperature influence
on spark-ignition energy
Fuel
n-heptane
Iso-octane
n-pentane
Initial temp (K)
298
373
444
298
373
444
243
253
Eign (mJ)
14.5
6.7
3.2
27.0
11.0
4.8
45.0
14.5
Fuel
n-heptane
Initial temp (K)
298
Eign (mJ)
7.8
propane
373
444
233
4.2
2.3
11.7
243
253
298
331
9.7
8.4
5.5
4.2
356
373
477
3.6
3.5
1.4
References:
 Turns, Stephen R., An Introduction to Combustion, Concepts
and Applications, 2nd edition, McGrawHill, 2000