S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
SIMULATION INVESTIGATION OF IN-CYLINDER
PRESSURE CHARACTERISTIC OF PORT INJECTION
COMPRESSED NATURAL GAS ENGINE MODEL
S. SEMIN
Department of Marine Engineering,
Institute of Technology Sepuluh Nopember, Surabaya, Indonesia
URL: http://www.its.ac.id
Email:[email protected], [email protected]
ABDUL RAHIM ISMAIL, ROSLI ABU BAKAR, ISMAIL ALI
Automotive Excellent Center, Faculty of Mechanical Engineering,
University Malaysia Pahang, 25000 Kuantan, Pahang, Malaysia
URL: http://www.ump.edu.my
Abstract: In-cylinder pressure performance profile of port injection compressed natural gas (CNG) engine has
been investigated using computational model simulation in this paper. In this research, the computational model
and simulation of engine model is using GT-POWER software. The engine is running in variations engine
speeds from 500 until 4000 rpm. The engine research is designed focuses in investigation the correlation of
characteristic in-cylinder pressure performance profile. The output data is collected from the results plots in post
processing. The results of the engine are shown the characters of pressure versus crank angle and in-cylinder
pressure versus engine speed of CNG engine is lower than base diesel engine.
Keywords: CNG engine, computational model, in-cylinder pressure, simulation
temperature and high pressure in-cylinder air. Since
the air temperature and pressure are in the gas fuel’s
ignition point, spark ignition of portions of the
already-mixed fuel and after air a delay period of a
few crank angle degrees. The cylinder pressure
increases as combustion of the gas fuel-air mixture
occurs. The major problem in port injection CNG
engine combustion chamber design is achieving
sufficiently rapid mixing between the injected gas
fuel and the air in the cylinder to complete
combustion in the appropriate crank angle interval
close to top-center [Bakar et al., 2007b; Czerwinski et
al., 1999; Heywood, 1998; Hollnagel et al., 1999;
Kowalewicz, 1984; Sera et al., 2003).
Cylinder pressure changes with crank angle as a result
of cylinder volume change, combustion, heat transfer
to chamber walls, flow into and out of crevice regions
and leakage. The effect of volume change on the
pressure can readily be accounted for combustion rate
information from accurate pressure data provided of
model. Cylinder pressure versus crank angle data over
the compression and expansion strokes of the engine
operating cycle can be used to obtain quantitative
information on the progress of combustion (Eriksson,
1. INTRODUCTION
The computational model of CNG engine has been
developed in this research (Bakar et al., 2007a). This
research is focuses in-cylinder pressure performance
of single cylinder four stroke port injection CNG
engine converted from direct injection diesel engine.
The aim is to give an insight into the CNG engine incylinder gas flow pressure performance using GTPOWER simulation model, how the engine model
developed and the components interact. To determine
port injection CNG engine pressure performance incylinder the engine is the essence of modeling at
small intervals time. Appropriate summation of these
gas conditions over an engine cycle then leads to an
estimate in-cylinder engine pressure performance.
In the port injection CNG engine, fuel is injected by
the gas fuel injection system via intake port trans
valve into the engine cylinder toward the end of the
compression stroke, just before the desired start of
combustion (Cho et al., 2007; Czerwinski et al.,
1999). The gas fuel, usually injected at high velocity
as one or more jets through small orifices or nozzles
in injector tip. The gas fuel mixes with high
IJSSST Vol. 9 No. 5, December 2008
1
ISSN 1473-804x Online, 1473-8031 Print
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
connected to the engine with EngCylConn part made
from the predefined object which available in the
template library. While EngCylConn parts have no
user defined attributes, the global cylinder number for
cylinder is assigned by the port number where the
EngCylConn connection is attached to the engine.
Cylinder are connected to intake and exhaust ports
with Valve*Conn connections. Many Valve*Conn
connection templates are available to define different
types of valve and their characteristics.
To develop of single-cylinder four-stroke port
injection CNG engine model using GT-POWER
software is step by step, the first step is open all of the
selected diesel engine components to measure the
engine components part size. To create the GTPOWER model, select window and then tile with
template library from the menu. This will place the
GT-POWER template library on the left hand side of
the screen. The template library contains all of the
available templates that can be used in GT-POWER.
Some of these templates those that will be needed in
the project need to be copied into the project before
they can be used to create objects and parts. For the
purpose of this model, click on the icons listed and
drag them from the template library into the project
library. Some of these are templates and some are
objects that have already been defined and included in
the GT-POWER template library. Then, the engine
components size data input to the GT-POWER library
of the all engine components data. All of the
parameters in the model will be listed automatically in
the case setup and each one must be defined for first
case of the simulation. Diesel engine convert to port
injection CNG engine model is shown in Figure 1.
and Andersson, 2002; Klein et al., 2002). Suitable
methods of analysis which yield the rate of release of
the fuel’s chemical energy, or rate of the burning will
be described in the paper. The objective of this
research is to investigate the correlation of pressure
characteristic in-cylinder of port injection CNG
engine model simulation compare with base diesel
engine based on engine speeds.
2. MATERIALS AND METHODS
The specification of engine for this research is
presented in the Table 1.
Table 1: Specification of the engine
Engine Parameter
Diesel Engine
CNG Engine
Bore (mm)
Stroke (mm)
Displacement (cc)
Compression ratio
Ignition system
Fuel system
Fuel
86.0
70.0
407.0
20.28
Compression
Direct Injection
Diesel
86.0
70.0
407.0
14.5
Spark
Port Injection
CNG
In the diesel engine and port injection CNG engine
model development using GT-POWER, a typical
engine is modeled using EngCylinder and
EngineCrankTrain
component
objects
and
Valve*Conn and EngCylConn connection objects.
EngCylinder and EngineCranktrain are used to define
the basic geometry and characteristics of engine. Both
objects further refer to several reference objects for
more detailed modeling information on such attributes
as combustion and heat transfer. Cylinder must be
Figure 1: Port injection CNG engine model using GT-POWER software
exhaust environment. Components 1 to 10 are intake
system, components 11 to 12 are engine, and
components 13 to 18 are exhaust system.
In the GT-POWER, characterization of in-cylinder
pressure performance are pressure versus crank angle,
P-V diagram, IMEP, pump MEP, maximum pressure,
crank angle of maximum pressure, maximum rate of
In the Figure 1, 1 is intake environment, 2 is
intake pipe1, 3 is air cleaner, 4 is intake pipe2, 5 is
throttle, 6 is intake pipe3, 7 is intake runner, 8 is fuel
injector, 9 is intake port, 10 is intake valve, 11 is
engine cylinder, 12 is engine crank train, 13 is
exhaust valve, 14 is exhaust port, 15 is exhaust
runner, 16 is muffler, 17 is exhaust pipe and 18 is
IJSSST Vol. 9 No. 5, December 2008
2
ISSN 1473-804x Online, 1473-8031 Print
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
pressure rise, maximum temperature, average intake
pressure and average exhaust pressure. The solver of
GT-POWER determines the main performance of an
engine simulation based on engine speed mode in the
EngineCrankTrain object in this research. Speed
mode is the most commonly used mode of engine
simulation, especially for steady states cases (Gamma
Technologies, 2003). In the research imposes the
engine speed as either constant or by a dependency
reference object. This method typically provides
steady-state results very quickly because the speed of
the engine is imposed from the start of the simulation,
thus eliminating the relatively long period of time that
a loaded engine requires for the crankshaft speed to
reach steady-state.
The idealized P-V diagram used to determine the
cylinder pressure (Gamma Technologies, 2003). The
area of this curve must match the specified indicated
output at the engine operating condition. The
transition point in the figure marks the transition
between the combustion and expansion segments of
the power stroke. The slope is defined by the
following equation:
⎛V ⎞
P = Pmax ⎜ TDC ⎟
⎝ V ⎠
Inter sec t
ipmep =
(1)
∫ PdV
Vdisp
In the simulation investigation using GT-POWER, the
results of the engine performance are viewed from
GT-Post plot and casesRLT. The GT-Post plots
results are in-cylinder pressure versus crank angle and
P-V diagram in every cases engine speed. GT-Post
plots results shown in Figure 2 – Figure 5. The GTPost casesRLT results are shows the pressure
performance versus engine speed cases. The GT-Post
casesRLT in-cylinder pressure results are IMEP,
pumping MEP, intersection pumping integral,
maximum pressure, average intake pressure and
average exhaust
pressure. GT-Post casesRLT incylinder pressure are shown in Figure 6 – Figure 11.
Figure 2 shows in-cylinder pressure of port injection
CNG engine simulation investigation results. The
results are shown, that increasing engine speed will be
decrease pressure maximum in-cylinder for all engine
speed operation from 1000 – 4000 rpm. Figure 3
shows that, the highest in-cylinder pressure maximum
in combustion process is 71.44 bar in the lowest
engine speed in 1000 rpm and the lowest in-cylinder
pressure maximum in combustion pressure is in 4000
rpm engine speed in 21.05 bar, because in this case
the combustion is in rapidly so the combustion
process is not excellent and unburned fuel is highest,
this phenomenon will be decrease the in-cylinder
(3)
−180
pmep =
∫ PdV
180
Vdisp
IJSSST Vol. 9 No. 5, December 2008
(5)
3. RESULTS AND DISCUSSION
(2)
where, P is instantaneous cylinder pressure between
top dead center (TDC) and the transition point, Pmax
is maximum cylinder pressure or pressure at TDC,
VTDC is cylinder volume at TDC, V is instantaneous
cylinder volume between TDC and the transition
point, m is slope of P-V curve after TDC, PIVC is
cylinder pressure at IVC, Rc is cylinder compression
ratio, γ is specific heat ratio and Pcomb is pressure rise
due to combustion.
If the P is instantaneous cylinder pressure (bar) and
Vdisp is cylinder displacement volume (m3), the
indicated mean effective pressure (imep), pumping
mean effective pressure (pmep) and intersection
pumping integral (ipmep) in-cylinder engine is
formulated in equation (3), (4) and (5).
imep =
Vdisp
The average intake pressure in the cylinder is pressure
from the first subvolume upstream of the cylinder,
typically the last subvolume of the component
representing the intake port. The upstream component
is attached to the valve that has the most flow rate
into the cylinder when comparing the mass flow rate
of all valves attached to the cylinder. The value
reported in this research should be identical to the
RLT variable for average pressure in the component
adjacent to the cylinder.
Average exhaust pressure in the cylinder is pressure
from the first subvolume downstream of the cylinder,
typically the first subvolume of the component
representing the exhaust port. The downstream
component is attached to the valve that has the most
flow rate out from the cylinder when comparing the
mass flow rate of all valves attached to the cylinder.
The value reported should be identical to the RLT
variable for average pressure in the component
adjacent to the cylinder.
m
Pmax = PIVC Rcγ + Pcomb
∫ PdV
Inter sec t
(4)
3
ISSN 1473-804x Online, 1473-8031 Print
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
engine pressure. In the operating condition in 1000
rpm engine speed, the combustion process is most
excellent than the other condition, in the engine speed
condition is not higher and not lower for the
combustion of port injection CNG engine spark
ignition. Burned gas fuel rate in 1000 rpm is most
excellent than the other engine speed and the effect is
can be product higher pressure.
Figure 3 shows in-cylinder pressure versus crank
angle of diesel engine. The lowest in-cylinder
pressure maximum in combustion pressure is in 4000
rpm engine speed and the nominal is 72.82 bar,
because in this case the combustion is in rapidly so
the combustion process is not excellent and unburned
fuel is highest, this phenomenon will be decrease the
in-cylinder engine pressure. The highest pressure
maximum in combustion process is 84.0 bar, when
the engine is operated in 1500 rpm engine speed. In
this operating condition, the combustion process is
most excellent than the other condition, in the engine
speed condition is not higher and not lower for the
combustion of compression ignition engine. Burned
fuel rate in 1500 rpm is most excellent and product
the higher pressure. In-cylinder pressure profile of
compression ignition engine is higher than the port
injection CNG engine. This is caused the compression
ratio of port injection CNG engine is lower than
compression ignition engine, where the compression
ratio of compression ignition engine is 20.28:1 and
compression ration of port injection CNG engine is
reduced to 14.5:1. Both of the engines the pressure in
compression ignition is higher than the pressure in
expansion strokes for exhaust gas from combustion
and for air intake needed to combustion.
Fig. 2:
In-cylinder pressure profile of CNG engine
Fig. 3:
In-cylinder pressure profile of diesel engine
Fig. 4:
In-cylinder pressure profile of CNG engine
Fig. 5:
In-cylinder pressure profile of diesel engine
Figure 4 shows the P-V diagram in combustion
process of port injection CNG engine. In the CNG
engine, increasing the in-cylinder pressure will be
decrease the in-cylinder volume and the decreasing
IJSSST Vol. 9 No. 5, December 2008
the in-cylinder pressure will be increase the incylinder volume. P-V diagram results are shown that
increasing engine speed will be decrease pressure incylinder. From the Figure 4 shows that, the lowest
4
ISSN 1473-804x Online, 1473-8031 Print
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
pressure of P-V diagram in combustion pressure is in
4000 rpm engine speed, because in this case the
combustion is in rapidly so the combustion process is
not excellent and unburned gas fuel is highest, this
phenomenon will be decrease the in-cylinder engine
pressure of P-V diagram. The highest pressure of P-V
diagram in combustion process is if the engine
operated in 1000 rpm engine speed, the combustion
process is most excellent than the other. Burned gas
fuel rate in 1000 rpm is most excellent and the effect
is product the highest pressure and power.
Figure 5 shows the P-V diagram in combustion
process of diesel engine. The results are shown that
increasing engine speed until 1500 rpm will be
increase pressure in-cylinder and increasing engine
speed more than 1500 rpm will be decrease pressure
in-cylinder. The lowest pressure of P-V diagram in
combustion pressure is in 4000 rpm engine speed,
because in this case the combustion is in rapidly so
the combustion process is not excellent and unburned
fuel is highest, this phenomenon will be decrease the
in-cylinder engine pressure of P-V diagram. The
highest pressure of P-V diagram in combustion
process is in 1500 rpm engine speed, the combustion
process is most excellent than the other. Burned fuel
rate in 1500 rpm is most excellent than the other.
-0.1
Pumping MEP (Bar)
-0.2
-0.3
-0.4
-0.5
-0.6
CNG Engine
-0.7
Diesel Engine
-0.8
1000
1500
2000
2500
3000
3500
4000
Engine Speed (rpm)
Figure 7: Pumping MEP
Pumping MEP performance of CNG engine compare
with base diesel engine is shown in Figure 7. The
highest pumping MEP for CNG engine is -0.285 bar
in 1000 rpm engine speed and minimum is -0.72 bar
in 4000 rpm engine speed. For the base diesel engine
the highest pumping MEP is -0.275 bar in 1000 rpm
engine speed and minimum is -.0.74 bar in 4000 rpm
engine speed. Pumping MEP in CNG engine is higher
than diesel engine. The pumping MEP in CNG engine
is increase because the reducing of compression ratio
and substitution of diesel fuel to natural gas fuel for
CNG engine will be increase the pumping MEP.
Intersect. Pumping Integr. (Bar) .
Cylinder IMEP (Bar)
8.0
7.0
6.0
5.0
4.0
3.0
CNG Engine
Diesel Engine
2.0
1000
1500
2000
2500
3000
3500
-0.15
-0.25
-0.35
-0.45
CNG Engine
Diesel Engine
-0.55
4000
1000
Engine Speed (rpm)
1500
2000
2500
3000
3500
4000
Engine Speed (rpm)
Figure 6: Cylinder IMEP
Figure 8: Intersection pumping integral
Figure 6 shows the in-cylinder indicated mean
effective pressure performance versus engine speed
profile of CNG engine compare with base diesel
engine. The highest IMEP of CNG engine is 6.35 bar
in 2000 rpm engine speed and minimum is 2.93 bar in
4000 rpm engine speed. For the base diesel engine the
highest IMEP is 7.52 bar in 3000 rpm engine speed
and minimum is 6.30 bar in 4000 rpm engine speed.
The IMEP in CNG engine is decrease because the
reducing of compression ratio and substitution of
diesel fuel to natural gas fuel for CNG engine from
base diesel engine will be reduce IMEP.
IJSSST Vol. 9 No. 5, December 2008
-0.05
Figure 8 shows that, the highest intersection pumping
integral for CNG engine is -0.166 bar in 1000 rpm
engine speed and minimum is -0.423 bar in 4000 rpm
engine speed. Diesel engine highest intersection
pumping intergral is -0.201 bar in 1000 rpm and
minimum is -.0.51 bar in 4000 rpm engine speed.
Intersection pumping integral of CNG engine is
higher than diesel engine, reducing of compression
ratio and substitution of diesel fuel to natural gas fuel
for CNG engine will be increase the intersection
pumping integral.
5
ISSN 1473-804x Online, 1473-8031 Print
Average Exhaust Pressure (Bar) .
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
Maximum Pressure (Bar)
.
90
75
60
45
CNG Engine
30
Diesel Engine
15
1.016
CNG Engine
Diesel Engine
1.014
1.012
1.010
1.008
1.006
1.004
1.002
1.000
1000
1000
1500
2000
2500
3000
3500
1500
4000
Engine Speed (rpm)
2000 2500 3000
Engine Speed (rpm)
3500
4000
Figure 11: Average exhaust pressure
Figure 9: Maximum Pressure
Maximum pressure performance of CNG engine
compare with base diesel engine is shown in Figure 9.
The highest maximum pressure for CNG engine is
lower than the base diesel engine. It caused
compression ratio of CNG engine is lower than the
base diesel engine and the combustion of diesel fuel is
produced highest power than the natural gas fuel.
Average exhaust pressure of CNG engine compare
with base diesel engine is shown in Figure 11. The
average exhaust pressure in-cylinder of CNG engine
is lower than base diesel engine, because the natural
gas fuel for CNG engine is design in 14.5 bar and
diesel engine is operate in 20.28 bar. The combustion
of diesel fuel in engine is produce higher power and
pressure than engine fueled using natural gas fuel.
Avr. Intake Pressure (Bar)
1.002
4. CONCLUSSION
1.000
The simulation investigation results are shown that
the highest in-cylinder pressure of CNG engine is
produced in the 1000 rpm engine speed mode
compared with the other engine speed. The lowest incylinder pressure and temperature is produced in the
4000 rpm engine speed mode compared with the other
engine speed. The investigation result is shown that
the in-cylinder engine pressure as a function of crank
angle degree for the different engine speed. Base on
the engine speed, the pressure performance
characteristics in-cylinder of CNG engine is lower
than the base diesel engine.
0.998
0.995
CNG Engine
Diesel Engine
0.993
1000
1500
2000
2500
3000
3500
4000
Engine Speed (rpm)
Figure 10: Average intake pressure
Average intake pressure of CNG engine compare with
base diesel engine is shown in Figure 10. The average
intake pressure in-cylinder of CNG engine is higher
than diesel engine, because the natural gas fuel for
CNG is injected via intake port, the effect is increase
the average intake pressure in CNG engine.
IJSSST Vol. 9 No. 5, December 2008
REFERENCES
Bakar, R.A., Semin., Ismail, A.R., Ali, I (2007a)
Computational Modeling of Compressed Natural Gas
as an Alternative Fuel for Diesel Engines, Proceeding
2nd ANGVA Conference, November 27-29, Bangkok,
Thailand.
Bakar, R.A., Semin., Ismail, A.R (2007b) The
Internal
Combustion
Engine
Diversification
Technology And Fuel Research for the Future: A
Review, Proceeding AEESEAP Regional Symposium,
Kuala Lumpur, Malaysia, pp: 57-62.
Cho, H. M., He, Bang-Quan (2007) Spark Ignition
Natural Gas Engines—A review, Energy Conversion
and Management 48, pp. 608–618.
6
ISSN 1473-804x Online, 1473-8031 Print
S SEMIN et al: IN-CYLINDER PRESSURE CHARACTERISTIC . .
Czerwinski J., Comte P., Janach.W., Zuber P (1999)
Sequential Multipoint Trans-Valve-Injection for
Natural Gas Engines, SAE Paper, 1999-01-0565.
Eriksson, L., Andersson, I (2002) An analytic model
for cylinder pressure in a four-stroke SI engine, SAE
Paper, 2002-01-0371.
Gamma Technologies (2003) GT-POWER user
manual, Gamma Technologies, Inc.
Heywood, J.B (1998) Internal Combustion Engine
Fundamentals, McGraw-Hill, Singapore.
Hollnagel, C., Borges, L.H., Muraro, W (1999)
Combustion Development of the Mercedes-Benz
MY1999 CNG-Engine M366LAG, SAE Paper, 199901-3519.
Klein, M., Eriksson., Nilsson (2002) Compression
estimation from simulated and measured cylinder
pressure, SAE Paper, 2002-01-0843.
Kowalewicz, A (1984) Combustion System of HighSpeed
Piston
I.C.
Engines,
Wydawnictwa
Komunikacji i Lacznosci, Warszawa.
Sera, M.A., Bakar, R.A., Leong, S (2003) CNG
Engine Performance Improvement Strategy through
Advanced Intake System, SAE Paper, 2003-01-1937.
IJSSST Vol. 9 No. 5, December 2008
7
ISSN 1473-804x Online, 1473-8031 Print