International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
CFD Studies of Combustion in DI Diesel
Engine at Different Injection Timing and
Ethanol Addition
1
Maheboob Pasha, 2Yeshwanthray ashtagi, 3Rahul G Panchal
1.
Student M.Tech Department of Thermal Power Engineering, V.T.U. PG Centre RO, Gulbarga, India
Assistant Professor Department of Thermal Power Engineering, V.T.U. PG Centre RO, Gulbarga, India
3. Assistant Professor Department of Mechanical Engineering Al Ameen COE and MS Pune Maharashtra,
India.
2.
ABSTRACT
In recent years, due to increasing demand for fuel
economy and tightening legislation for emissions,
there has been growing requirement to develop more
efficient and cleaner engines in a shorter time scale.
Computational Fluid Dynamics, as a rapid and cost
effective tool, is being increasingly used in different
stages of engine design and optimization. By using
CFD tools effectively it is easy to predict and
analyse various details that are technically difficult
like in cylinder process of diesel combustion,
temperature & pressure distribution and emissions
etc. prior to experimental tests to reduce the number
of investigated parameters as well as time and thus
costs. Here in our approach we have used Species
Transport Model of ANSYS FLUENT14.5 to find the
complex phenomenon of in cylinder process of
combustion, temperature and pressure distribution,
CO2 and NOX emissions etc. The process is carried
out at different injection timing of the Diesel liquid,
the cases considered are 1. Injection at 2 degree
after TDC, 2. Injection at 5 Degree bTDC, 3.
Injection at 10 Degree bTDC. Once we get an
optimized value of Injection than 10 % of ethanol is
added in order to increase the efficiency of the
combustion and thus still reduce the NOx emissions.
Keywords- Diesel combustion FLUENT 14.5, NOx,
CFD, CO2 emission, Combustion modelling, k-ε
model, Ethanol.
1. INTRODUCTION-The Internal Combustion
(IC) engines play an important role in the fields of
transportation of goods and passengers, agricultural
and industry. They develop power by consuming
precious fossil fuels and cause pollution. Among
different types of engines, the direct-injection (DI)
diesel engine exhibits the best fuel economy along
with lowest engine-out emissions. Efforts have been
put to improve exhaust emissions and fuel economy
continuously. The complex task of improving IC
engines, which have reached a higher degree of
sophistication, can be achieved by combination of
advanced experiments and computational studies.
Modern methods of experimental investigations are
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being developed to provide more insight. The
modelling of combustion engine processes is useful
to carry out extensive parametric studies, rather than
hardware development and Experimentation.
Depending on the various possible applications,
different types of models for engine combustion
processes have been developed. Rapid Increase in
pollution levels, increase of fuel prices, and
depletion of hydrocarbon reserves of the world have
forced the engineers to look for appropriate
technology and alternative fuels to provide to the
ever-increasing demands of energy.[1]
II.COMPUTATIONAL PROCEDURE
The combustion simulation of CI engine was
developed using fluent software (ANSYS 14.5
package) and the various equations of the multidimensional model were solved by the software
automatically. The main inputs include engine speed,
injection details, bore, stroke, connecting rod length,
initial pressure and temperature. The program
concerning the simulation model predicts the
cylinder pressure, cylinder temperature, heat release
rate, emission etc. The results including graphs and
various contours (temperature, pressure etc) were
generated by fluent software as outputs to the
program for given inputs.[2],[3].
III.MODEL DEFINITION AND MESHING
A 2D cylinder geometry with centrally located
injector was considered .The mesh was created using
GAMBIT 2.4.6.The engine geometry details and
specification details are given below. Mesh
generation plays an important role in obtaining
accurate results. A quadrilateral mesh was created
uniformly throughout the area and analysed using
FLUENT, ANSYS 14.5 package. The complete
meshed geometry contains 821098 Elements and
145400 nodes. Fig.1 shows the meshed geometry.
Connecting rod length
: 10.35 inch
Bore
:130mm
Stroke
:158mm
Crank radius
:55 mm
Crank shaft speed
:1500 rpm
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International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
Fig.1 Meshed geometry of cylinder
The above Figure1 shows Meshed geometry of
cylinder in 2D cylinder geometry.
IV. GOVERNING EQUATIONS AND
MODEL
There are mainly three equations we solve in
computational fluid dynamics problem. They are
Continuity equation, Momentum equation (Navier
Stokes equation) and Energy equation. The flow of
most fluids may be analyzed mathematically by the
use of two equations. The first, often referred to as
the Continuity Equation, requires that the mass of
fluid entering a fixed control volume either leaves
that volume or accumulates within it. It is thus a
"mass balance" requirement posed in mathematical
form, and is a scalar equation. The other governing
equation is the Momentum Equation, or NavierStokes Equation, and may be thought of a
“momentum balance" The Navier-Stokes equations
are vector equations, meaning that there is a separate
equation for each of the coordinate directions
(usually three).The basic approach of in-cylinder
diesel combustion models are typically compressible
turbulent flow. Apart from the complexity of
turbulent model, the high pressure spray and
resulting spray penetration , evaporation, and
involvement of multiphase , multi-component nature
only increases its complexity. Even then the nature
of fluid is still governed by the basic equations
including
continuity
(mass
conservation),
momentum (Navier-Stokes equation), energy and
turbulence (k-ε model) equations. Of the three
combustion
modelling
(thermodynamic,
multidimensional and phenomenological modelling)
the software use multidimensional modelling, i.e.
CFD modelling
V. COMBUSTION SIMULATION
In engine environments, the combustible
mixture is subject to a turbulent flow and, once
mixed, undergoes subsequent elementary reactions
which convert the fuel vapour to complete and
incomplete combustion products with the
accompanying release heat. So, in diesel engine
simulations, combustion modelling mainly deals
with two processes: first, low-temperature
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chemistry, which leads to auto ignition and produces
intermediate species, and second, these intermediate
species trigger high-temperature reactions that
contribute the main heat release, as well as further
complete and incomplete combustion products.
Another important task for combustion models is to
properly account for the significance of the effect of
turbulence on the combustion processes. The
combustion of diesel fuel was considered which is
simulated using FLUENT, ANSYS 14.5 package. A
single cylinder, single zone, multi-dimensional
model was considered in analysis process. The
mixture material, diesel-air, properties were copied
from the Fluent material database for combustion.
Using species transport model of fluent the analysis
is done. While using this model conservation
equation for chemical species, ANSYS FLUENT
predicts the local mass fraction of each species
through the solution of convection diffusion
equation for the ith species.[4].
VI .METHODOLOGY&BOUNDARY
CONDITIONS
After modelling the geometry, for analysis viscous
standard k-e model is enabled for considering eddy
dissipation. Since geometry is subjected to motion of
piston, dynamic meshing is enabled subjected to
suitable boundary condition for piston, cylinder,
walls etc. Combustion in a diesel engine involves the
transient injection of finely atomized liquid fuel into
the air at high temperature and pressure. The fuel
injection parameters like location of the injector, size
of the injector, injection temperature and pressure,
mass flow rate etc are having significant effect in
diesel combustion modelling. The injection
parameters and specifications are given below
1
X-Position
0.0197 inch
2
Y-Position
0.00984 inch
3
Z-Position
6.98 inch
4
Diameter
0.01 inch
5
Temperature
341K
6
Injection Type
Solid Cone
7
8
9
10
11
12
Velocity
Magnitude
Cone Angle
Total Flow Rate
Particle Type
Starting Crank Angle
Starting Crank Angle
468 m/s
8 Degree.
0.00807 Kg/Sec
Droplet.
722 Degree.
744 Degree
VII. RESULTS AND DISCUSSIONS
The below section shows the results of the cases
considered in this project.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
CASE 1: INJECTION OF FUEL AT 0 DEGREE
BEFORE TDC.
2. CO2 Emission
The mass fraction of CO2 was generated by the
simulating software and was found to be near 0.0800
at the end of expansion. (fig.6)
Fig.2. Contours of Start of Fuel Injection
Fig- 6: Variation of CO2 V/S flow time
3. NOx Emission
The mass fraction of NOx was generated by the
simulating software and was found to be near 0.0160
at the end of expansion. (fig.7)
Fig.3. Contours of Start of combustion
The above figure shows variation contours of start of
fuel injection & contours of start of combustion for
2D cylinder.
1. Cylinder pressure and Cylinder temperature
The modelled cylinder pressure data is
shown in fig.4. From the graph the peak pressure
generated by the software was approximately equal
to 20 bar which is in agreement with the theoretical
value. Also the maximum cycle temperature
obtained was near 2400K (Fig.5). The static pressure
and static temperature contours at the end of
expansion was also generated by the software
(shown in fig.4. and fig.5).
Fig-7 Variation of NOx V/S flow time.
Case 2: Injection 5 Degree before TDC
The Results for Injection of Diesel Liquid 5 Degree
before TDC are shown below
Fig- 4: Variation of Pressure (Pa) V/S flow time.
Fig-5: Variation of temperature V/S flow time.
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Fig-8: contours Start of combustion
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International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
Fig-9: contours End of combustion
1. Cylinder pressure and Cylinder temperature
The peak pressure generated by the software was
approximately equal to 19bar which is in agreement
with the theoretical value. Also the maximum cycle
temperature obtained was near 2400K (Fig.11). The
static pressure and static temperature contours at the
end of expansion was also generated by the software
(shown in fig.10. and fig.11). [7]
Fig- 12: Variation of CO2 V/S flow time
3. NOx Emission
The mass fraction of NOx was generated by the
simulating software and was found to be near 0.0140
at the end of expansion
Fig-13 Variation of NOx V/S flow time.
CASE 3: Injection of Diesel-Liquid 10 Degree before TDC
In the Third Case the Injection was performed 10
Degree before TDC and the Results are Shown in
the Coming Slides
Fig10- : Variation of Pressure V/S flow time.
Fig-14: contours Start of combustion
Fig- 11: Variation of Temperature V/S Flow time
2. CO2 Emission
The mass fraction of CO2 was generated by the
simulating software and was found to be near 0.0800
at the end of expansion
Fig-15: contours end of combustion
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International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
1. Cylinder pressure and Cylinder temperature
The modelled cylinder pressure data is
shown in fig.16. From the graph the peak pressure
approximately equal to 19 bar which is in agreement
with the theoretical value. Also the maximum cycle
temperature obtained was near 2400K (Fig.17). The
static pressure and static temperature contours at the
end of expansion was also generated by the software
(shown in fig.16. and fig.17).
Fig-19: Variation of NOx V/S flow time.
Case 4: Addition of Ethanol, to diesel liquid.
1. In the case 4 we have used the injection timing as
per our previous analysis results in which we found
that the injection with 10 degree before TDC is
giving better results.
Fig-16: Variation of Pressure V/S flow time.
2. In this case we will add 10% of ethanol to further
reduce the NOx emission
Fig-17: Variation of Temperature V/S flow time.
Fig-20: contours start of combustion
2. CO2 Emission
The mass fraction of CO2 was generated by the
simulating software and was found to be near 0.0750
at the end of expansion
Fig-21: contours End of combustion
Fig- 18: Variation of CO2 V/S flow time
3. NOx Emission
The mass fraction of NOx was generated by the
simulating software and was found to be near 0.0120
at the end of expansion
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1.CO2 Emission
The mass fraction of CO2 was generated by the
simulating software and was found to be near 0.1400
at the end of expansion
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International Journal of Engineering Trends and Technology (IJETT) – Volume 34 Number 4- April 2016
Fig- 22: Variation of CO2 V/S flow time
2.NOx Emission
The mass fraction of NOx was generated by the
simulating software and was found to be near 0.0110
at the end of expansion
reduced before TDC better combustion takes place
and NOx Reduces, so from our analysis we found
that the ANSYS Fluent 14.5 was helpful in giving
good results for the combustion modelling. The
addition of Ethanol has been added only upto 10%
and it has been found that the addition of ethanol has
reduced further the NOx emission. So in future if
India implemented ethanol blending with diesel and
petrol the blending ratio of 10% of ethanol will be
consider to be more effective than the neat diesel in
every aspect. It has also been considered according
to the production, demand and supply of the ethanol
in India.
REFERENCES
[1]
Gavudhama Karunanidhi et.al “CFD Studies of Combustion
in Diesel Engine” (IJERA)
Vol. 3, Issue 4, Jul-Aug 2013,
Suresh Patil.G.L et.al. Fuel Injector’s Stratergies Of Hcci
Engine. VOL. 3,
ISSUE 1, JANUARY -FEBRUARY 2013
[3] Vijayendra et.al.InCylinder Combustion Analysis of DI
Diesel Using Experimental and CFD Approach Volume 14
Number 5 – Aug 2014
[2]
[4]
Y Ren, Z-H Huang,et.al“Combustion and emission
characteristics of a direct-injection diesel engine fuelled
with diesel–ethanol blends”2008
[5]
G. Li and S.M. Sapsfordas et.al “Direct-inject (DI) diesel
engine combustion with the newly implemented Ricardo
Two-Zone Flamelet (RTZF) combustion model” (2010)
[6]
Saeed Baghdar Hosseini,et.al“The Experimental and
Simulations Effect of Air Swirler on Pollutants from
Biodiesel combustion” Published: May 05, 2013
[7]
F.E.Corcione,M.Costa,et.al Multidimensional Modeling of
the Combustion Process in a Diesel EngineEquipped with a
Fully Flexible Common Rail Injection System
R Thundil Karuppa et.alEffect of Swirl in a Constant Speed
DI Diesel Engine using Computational Fluid Dynamics, Vol.
4 (4) – December 2012
Umakant et.al’CFD Modeling and Experimental Validation
of Combustion in Direct Ignition Engine, Volume 1, No
3, 2010, ISSN 09764259
Weiji Wang et.al.CFD Investigation into Diesel PCCI
Combustion with Optimized Fuel Injection 18 March 2011
Sangjin Hong, Dennis et.al Modeling of Diesel Combustion
and NO Emissions Based on a Modified Eddy Dissipation
Concept Combustion Science and Technology · June 2008
S Gavudhama karunanidhi.et.al CFD Studies of Split
Injection on the Combustion and Emission Characteristics in
DI Diesel EngineInt. Journal of Engineering Research and
Applications Vol. 4, Issue 7(Version 1), July 2014
PatilPradipkailas et.al “Study of Combustion in Di Diesel
Engine for Different Compression Ratios Using
Experimental and CFD Approach” Volume: 03 Special
Issue: 08 | NCAME-2014 | June-2014,
Fig-23: Variation of NOx V/S flow time.
VIII Comparison of Results with Base Data and
Different Injection Timings
Case
No
Injection
Timings
0
Max
P(bar+)
Max
T(k)
CO2
NOx
Base
Case
Case 1
0 b TDC
200 * 10 ^5
2500
0.0754
---
00 b TDC
200 * 10 ^5
2500
0.0160
Case 2
50 b TDC
190 * 10 ^5
2400
0.076
0
0.078
0
0.0140
[9]
190* 10 ^5
160* 10 ^5
2400
1800
k
0.0780
0.0140
0.0110
[10]
Case 3
Case 4
0
10 b TDC
100b TDC
0.140
0
Table-1 Comparison of Results with Base Data
and Different Injection Timings.
[11]
[12]
IX.CONCLUSION
The model was created using Gambit, and the
combustion phenomenon was analysed using Fluent
Ansys 14.5.Based on the present investigation the
following conclusions have been drawn.
From the above Results we can conclude that the
Maximum Reduction in NOx occurs when the fuel is
injected at least 10 degree before TDC. NOx reduces
when the peak temperature reduces. Maximum
Pressure i.e. 200*10^5 is obtained in the case of
injection at 0 Degree before TDC, this high pressure
may be harmful since it may cause High Stresses
inside the cylinder. From many experimental works
it has been found that as the Injection timing is
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[8]
[13]
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