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Procedia Engineering 00 (2017)000–000
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Procedia Engineering 206 (2017) 305–311
International Conference on Industrial Engineering, ICIE 2017
International Conference on Industrial Engineering, ICIE 2017
The Numerical Study of Compressed-Air Atomizer for SparkThe Numerical Study
of Compressed-Air
ignited
Jet Fuel EngineAtomizer for Sparkignited Jet Fuel Engine
M.D. Garipov*, R.F. Zinnatullin, V.A. Shayakhmetov
M.D. Garipov*, R.F. Zinnatullin, V.A. Shayakhmetov
Ufa State Aviation Technical University (USATU), 12, Karl Marx st., Ufa, 450008, Russia
Ufa State Aviation Technical University (USATU), 12, Karl Marx st., Ufa, 450008, Russia
Abstract
Abstract
There is increasing interest in the aircraft engine with spark ignition, which is capable of working using jet and diesel fuel. The
reason
that the engines
spark
ignition
have
a lower
specific weight
diesel
engines.using
The working
process
of The
the
There isisincreasing
interestwith
in the
aircraft
engine
with
spark ignition,
which isunlike
capable
of working
jet and diesel
fuel.
spark
ignition
engine
which
can
operate
on
heavy
fuels
at
the
compression
ratio
of
a
base
engine
was
described
in
our
previous
reason is that the engines with spark ignition have a lower specific weight unlike diesel engines. The working process of the
works.
The operating
cycle of
this
engineonis heavy
implemented
use of a compressed-air
(CAA)
in combination
with a
spark ignition
engine which
can
operate
fuels at by
thethe
compression
ratio of a baseatomizer
engine was
described
in our previous
spray-guided
concept.cycle
An ignition
systemishas
a traditionalbydesign
parameters
characteristic
gasoline engines.
works.
The operating
of this engine
implemented
the useand
of adischarge
compressed-air
atomizer
(CAA) inofcombination
with a
This
paper presents
zero-dimensional
model
of theand
processes
occurring
in acharacteristic
CAA. The model
verification
is
spray-guided
concept.a An
ignition systemmathematical
has a traditional
design
discharge
parameters
of gasoline
engines.
presented.
This paper presents a zero-dimensional mathematical model of the processes occurring in a CAA. The model verification is
©
2017 The Authors. Published by Elsevier B.V.
presented.
© 2017 The Authors.
Published by
Ltd. committee of the International Conference on Industrial Engineering.
Peer-review
under responsibility
of Elsevier
the scientific
©
2017 The Authors.
Published by
Elsevier
B.V. committee of the International Conference on Industrial Engineering
Peer-review
under stratified-charge
responsibility
ofengines;
the scientific
Keywords:
multifuel
compressed-air
atomizer;
fuel; spark ignition
engine; spray-guided
Peer-review under responsibility of the scientific committee
of thejetInternational
Conference
on Industrialconcept.
Engineering.
Keywords: multifuel stratified-charge engines; compressed-air atomizer; jet fuel; spark ignition engine; spray-guided concept.
Nomenclature
Nomenclature
САА compressed-air atomizer
САА compressed-air atomizer
1. Introduction
1. Introduction
The studies, related to the development of engines that can run on different fuels, were always of interest. In
recent
thisrelated
interesttois the
related
to "SingleofFuel
Forward"
USdifferent
Department
Defense.
According
to this
Theyears
studies,
development
engines
that policy
can runofon
fuels,ofwere
always
of interest.
In
policy,
it is recommended
use diesel
fuel and
jet Forward"
fuel as thepolicy
fuels for
the Department
US Army (jp-5,
jp8) [1,2].
recent years
this interest istorelated
to "Single
Fuel
of US
of Defense.
According to this
policy, it is recommended to use diesel fuel and jet fuel as the fuels for the US Army (jp-5, jp8) [1,2].
* Corresponding author. Tel.: +7-987-251-4594;
E-mail address:author.
garipov.md@net.ugatu.su
* Corresponding
Tel.: +7-987-251-4594;
E-mail address: garipov.md@net.ugatu.su
1877-7058 © 2017 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the scientific committee of the International Conference on Industrial Engineering .
1877-7058 © 2017 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the scientific committee of the International Conference on Industrial Engineering .
1877-7058 © 2017 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the scientific committee of the International Conference on Industrial Engineering.
10.1016/j.proeng.2017.10.478
306
2
M.D. Garipov et al. / Procedia Engineering 206 (2017) 305–311
M.D. Garipov et al. / Procedia Engineering 00 (2017) 000–000
Existing multifuel engines have certain shortcomings. The main drawback of the traditional multi-fuel diesel
engines is a high specific weight due to the need to use very high compression ratio (17 to 24) [1]. The main
disadvantage of multi-fuel engines with spark ignition is a high fuel consumption at high loads when low-octane
fuels are used, which is explained by the need of low compression ratio application (around 7.4) [3].
It is reasonable to create a multifuel engine that combines the fuel efficiency of diesel and a low specific weight
of an engine with spark ignition. This was managed to perform in the framework of the operating cycle of multifuel
stratified-charge engines [4-10]. A long-duration spark discharge was used in these processes for different fuel
ignition.
But the ignition in a multifuel stratified-charge engine is desirable to produce by the ignition system, which has a
structure and discharge parameters characteristic of engines with spark ignition. Despite the fact that such an
ignition was managed to implement in practice (Orbital combustion process is one example of it [11]) to perform the
not-knocking combustion it is necessary to reduce the compression ratio relative to the engine variant running on
gasoline
The processes of mixing and combustion for a multifuel stratified-charge engine that would solve this problem is
being developed on the department of internal combustion engine in Ufa State Aviation Technical University. The
operating cycle of this engine is implemented by the use of compressed-air atomizer (CAA) in combination with a
spray-guided concept. Diesel fuel, jet fuel, low octane gasoline, and wet ethanol are considered as the fuels which
the engine with developed processes should consume. The possibility of ignition and combustion of heavy fuels
without detonation was confirmed experimentally in our previous studies [12,13]. However, the issues relating to the
processes in the CAA were covered poorly. This paper presents the mathematical model of these processes.
2. Injection system description
Fig. 1a demonstrates the scheme of CAA design. Fuel with a small amount of air enters the CAA working
chamber 2, where a preliminary stage of mixing takes place: heating, breaking, mixing and partial vaporization of
fuel. The swept volume of CAA makes about 2.5% of an engine swept volume. The CAA piston 1 is driven by an
engine crankshaft. When the pressure is sufficient to overcome a nozzle needle spring force, the injection of a fuelair jet 5 takes place into an engine combustion chamber where a fuel-air mixture is finally formed. The CAA is
equipped with the necessary devices for fuel metering. An ignition system has a traditional design and discharge
parameters characteristic of gasoline engines.
3. Mathematical model
The conditions of a CAA working chamber are such that the pressure at the end of compression substantially
exceeds the critical values of the components included in fuels for automotive internal combustion engines. The
volume fractions of a liquid phase and a vapour phase have similar values. Under such conditions, a vapour phase
must be considered as a real solution not as an ideal gas mixture (fuel and air). The liquid phase should also be
considered as a real air-fuel solution.
Two extreme states of coexisting phases were taken as a basis:
1. The model of thermodynamic equilibrium of heterogeneous systems.
2. There is no heat and mass transfer between phases. The pressures in the phases are equal, there is no slipping
of phases.
One of the main areas of vapor-liquid equilibrium mathematical modeling at high pressures is the application of
uniform state equations to describe the properties of coexisting equilibrium phases [10,15]. The use of a state
equation gives the opportunity to address these challenges on the basis fugacity (f) equality provisions of each
mixture component in coexisting phases [15]:
Garipov
al. / Procedia
Engineering
206 (2017)
305–311
M.D.M.D.
Garipov
et al.et/ Procedia
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00 (2017)
000–000
T (1) T (2) ... T ( m ) ,
 (1)
(2)
( m)
 p  p  ... p ,
 (1)
(2)
(m)
i 1,..., N
 fi  fi  ... fi , 
3073
(1)
where m is the number of phases; N is the number of components.
Fig. 1. (a) the design scheme for the implementation of the proposed operating cycle: 1 - CAA piston; 2 - the working chamber of CAA; 3 - a
spark plug; 4 – valve of the engine; 5 – the air-fuel jet; 6 - CAA belt drive; 7- nozzle; (b) model injection system.
During the modeling of heat and mass transfer absence case the temperature of a liquid phase remains constant
and fugacities are not calculated.
This paper uses a state equation for oils and natural gases proposed by A.I. Brusilovsky, based on a cubic
equation of a generalized form state [14]. It has a higher modeling accuracy of heavy hydrocarbon PVT-properties
than Peng-Robinson equation for heavy hydrocarbons starting from n-С9Н20, and oil and gas mixtures at high
pressures (up to 100 MPa). The equation of a state applied to a multi-component system has the following form
[14]:
z
pV
N
RT  nk
(2)
k 1
here nk is the number of moles of k component; z – compressibility factor.
The initial system of equations for the processes of two-phase mixture compression and discharge in the CAA
working chamber 2 (fig. 1b) excluding the heat exchange with the environment is the following one:
d
0
 dt   m dV    m ( wn)dF 
F
 V

2
2
 d  (u  w )dV   (u  w )( wn)dF 
  p ( wn)dF


m
mm
m
mm
 dt V
2
2
F
F
(3)
M.D. Garipov et al. / Procedia Engineering 206 (2017) 305–311
M.D. Garipov et al. / Procedia Engineering 00 (2017) 000–000
308
4
where umm is the specific enthalpy of two-phase mixture (J/kg); V– two-phase mixture volume (m3); w– two-phase
mixture velocity (m/s); ρm– two-phase mixture density (kg/m3); F – the surface area of a considered volume of a
two-phase mixture (m2); n– normal to a surface; index l means the belonging to a liquid phase, the index v – to a
vapour phase, the index m – to two-phase mixture.
The additional equations required for the system of equations (3) closure are presented below. For a singlecomponent system the equation of state describes the properties of both vapour and liquid phases on the saturation
line. For a multi-component system the equation of state is a thermodynamic model of the equilibrium vapour and
liquid phases separately [14]. PVT dependency for a two-phase mixture can be obtained from the condition of
pressure equality in the phases and the phase volume additivity:
p

N

RTv  Tl N
 zl  nkl  zv  nkv 
V
 Tv k 1 k 1 
(4)
The enthalpy of a multi-phase system is additive:
H
Hl  Hv
m
(5)
With PVT dependence of each phase one can determine their molar enthalpy according to the expression [14]:
h  hT0 
p

p0

v



 v  T  T   dp

 p 
(6)
where hT0 – the enthalpy in an ideal gas state.
In order to calculate molar enthalpies in an ideal gas state we use NASA polynomial dependences, which are
given in [16, 17]:
In order to calculate the fugacity of the mixture component fi the following equation is applied [14]:

n RT
1  p 
1 
ln fi  


dV  ln i





RT
n
V
V
V
 i T ,V , n j , j  i


(7)
The flowing of two-phase mixture in the channels 1, 2 of nozzle on Fig. 1b is described in the approximation of a
homogeneous model. There are the following assumptions at the basis of its design: both phases are in mechanical
equilibrium (pressures and phase velocities are equal); phases are distributed uniformly, one in another. In order to
calculate the mass flow rate with considering of losses let's use the discharge coefficient Cd:
Gm  Cd Gt
(8)
where Gt is the theoretical discharge.
At a critical mode of flow the calculation of two-phase mixture sound speed is required. Let's assume that in the
process of a sound wave propagation, the phase transition in its front does not have time to occur. At the same time,
we believe that the velocities and the pressures of phases are equal. Let's put down Laplace equation in the
following form:
2  P 
a  -vmm


 vmm  s
(9)
M.D. Garipov et al. / Procedia Engineering 206 (2017) 305–311
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309
5
Using the condition of phase volume additivity and expressing a specific volume through the molar volume we
obtain the expression for a sound speed in two-phase multi-component environment:
a
vm 2
 X i M i (1  L)  vv   L  vl 
i 1
 p  s
 p  s
1
N
(10)
where Xi - mole fraction of a component in two-phase mixture; Mi - the molar mass of a mixture component; L - the
mole fraction of a liquid phase.
With PVT-dependence one can calculate the partial derivatives in the expression for sound speed concerning each
of the phases according to the known thermodynamic identities.
4. Mathematic model verification
Russian aviation kerosene TS-1 (analogue of Jet A-1 / JP-8) was used in the experiment as a fuel. According to
[18-21], the chemical composition of the model mixture proposed for JP-8, consists mainly of n-dodecane. In this
paper, in order to simplify the simulation the main component only of the model mix was used - n-dodecane. The air
was replaced by nitrogen
The equation of state was created for the temperatures up to 200 °C. But the temperatures in a CAA working
chamber may be higher. In the studied case we are interested in the area up to the maximum temperature at which a
two-phase state of a nitrogen-carbon-hydrogen mixture still exists. It corresponds to hydrocarbon critical
temperature. Accordingly, describing the two-phase equilibrium the value of this temperature is extremely different
from the range of state equation application studied by Brusilovsky A.I. Therefore, in order to estimate the error of
property description in the field of two-phase mixture existence the state along the isotherm will be used in this
work corresponding to hydrocarbon critical temperature.
The graphs of compressibility factor Z - the reduced pressure (Pr=P/Pci) and reduced temperature (Tr=T/Tci),
created according to experimental Р-V-Т data are shown in [15]. The difference between the calculated properties of
nitrogen according to the used equation of state and data [15] is within the error of experimental data.
Fig. 2 shows the dependence designed according to the experimental data from [15] and the compressibility factor
calculations of various hydrocarbons at a critical temperature, which were obtained according to used equation of
states. At Pr =15 the maximum difference of calculated data and the data taken from [15] in a studied pressure range
does not exceed 13.5%. This value of the reduced pressure corresponds to the absolute pressure value which is equal
to P = 36,7 MPa - for n-octane, P = 27 MPa - for n-dodecane and P = 25,5 MPa - for n-tridecane. At the pressures
Pr below 10 the difference is within the experimental data error of [15].
Fig. 2. The dependence of the compressibility factor on the reduced pressure at Tr = 1:1 - the data of [15]; 2 - calculation for n-octane; 3 calculation for n-dodecane; 4 - calculation for n-tridecane.
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During the experiments an injection is carried out in the environment with the conditions close to the standard
ambient temperature and pressure. The mass fraction of a fuel in a CAA work chamber makes 0.8, which
corresponds to an engine operation at full load. During the experiment a cycle-by-cycle variation of pressure curves
were observed. Fig. 3 shows the pressure change in the CAA working chamber as points from a CAA crank angle
for five cycles. These points describe the dispersion of the experimental data.
Fig. 3 also shows the results of described above simulations concerning two extreme cases of the coexistence
phases. It can be seen that the model based on the assumption of heat and mass transfer absence showed more
adequate results as compared to experiments.
Fig. 3. The pressure (p, MPa) in the CAA working chamber depending on a crank angle: 1 - the model based on the assumption of heat and mass
transfer absence; 2 - thermodynamic equilibrium model; 3 - experimental data.
5. Conclusion
After the experimental and theoretical pressure curves comparison in the CAA working chamber, it can be
concluded that the model based on the assumption of heat and mass transfer absence between the mixture phases
gives closer experimental results.
The results of this work are planned to be used as the boundary conditions during 3D modeling of the processes
in an engine combustion chamber.
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