Environmental Engineering Reference
In-Depth Information
Table 1 Fuel properties (Panchasara et al.
2009b
)
Property
Diesel
Biodiesel
VO
Glycerol
Molecular weight (kg/k mol)
142.2
291.5
277.9
92.1
C (kg/m
3
)
Density at 25
°
834.0
880.0
925.0
1,260.0
C (mm
2
/s)
Viscosity at 25
°
3.88
5.61
53.74
740.0
Surface tension at 25
°
C (m N/m)
28.2
31.1
30.1
62.5
LHV (MJ/m
3
)
37,198
33,442
34,225
20,400
Specific heat (J/kg K)
1,750
2,000
2,269
2,430
Latent heat of evaporation (kJ/kg)
250
200
-
662
Boiling point (
°
C)
195
372
338
380
290
-
-
-
Auto-ignition temperature (
°
C)
315
445
370
-
comparison with diesel, glycerol has kinematic viscosity approximately 200 times
greater and over twice the surface tension. Glycerol also has higher enthalpy of
vaporization and higher vaporization and auto-ignition temperatures than diesel.
Thus, signi
flame must be recirculated to the liquid to
ensure proper glycerol vaporization before combustion. In summary, glycerol is
extremely dif
cant thermal energy from the
fl
cult to breakup into droplets to form a spray and the resulting
glycerol droplets are rather dif
cult to vaporize and combust. For these reasons,
existing combustion systems cannot utilize glycerol as fuel.
In this research, we will show that with proper fuel injector and combustor designs,
it is possible to cleanly combust all of the fuels listed in Table
1
, without any upstream
processing and/or hardware modi
cations. The study challenges the traditional
approach to combustor design, which relies on upstream fuel processing to ensure
strict fuel property speci
cations. Instead, the study illustrates that fuels with widely
different physical and chemical properties can be utilized, cleanly, in a combustion
system speci
flexibility. Wide-spread application of
this latter combustor design strategy can result in signi
cally designed to achieve fuel
fl
ts in the
emerging markets for the alternative fuels. The impetus of this study is to engineer
innovative liquid combustion systems to handle conventional and alternative fuels
while reducing harmful environmental impact from various emissions. We will focus
on continuous
cant economic bene
flow combustion systems, thereby precluding reciprocating systems
such as diesel engines from the scope of the present study.
fl
2 Liquid Fuel Combustion
Figure
1
illustrates a typical liquid fuel combustion system, denoted as lean direct
injection or LDI combustion. The liquid fuel is injected directly into the strongly
swirling
flow of combustion air. A fuel injector is used to atomize the liquid, i.e.,
disintegrate the fuel into droplets in a turbulent spray. Numerous fuel injector
designs are available with many based on twin-
fl
uid atomization, whereby a gas
(usually air, denoted as atomizing air) is used to create the fuel spray by the transfer
fl
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