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MODELLING AND SIMULATION OF SPARK IGNITION ENGINES
Rohit M , Rohit K
CHAPTER 1
Introduction:-
The term spark-ignition engine refers to internal combustion engines, usually petrol engines,
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where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug.
This is in contrast to compression-ignition engines, typically diesel engines, where the heat
generated from compression is enough to initiate the combustion process, without needing
any external spark.
Over the last two decades there has been a dramatic evolution in engine control systems
which are largely driven by government regulations, customer‟s demand for fuel efficient
vehicles and minimum safety and reliability standards that are independent of age,
environment and varying fuel properties. All of these requirements create challenging
control problems for two reasons:
 It is increasingly important to achieve control over the behavior and meet
performance objectives over the life of the vehicle. This requires the development of
high performance and robust controllers.
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The performance objectives are often conflicting, or at best interrelated. One way to
meet their requirement is to introduce additional design parameters via innovative
mechanical configurations. The design parameters, control variables in the system
terminology, provide additional degrees of freedom to optimize the performance of
the engine over its wide range of operation. The EFI i.e., electronic fuel injection,
DBW (drive by wire technology), variable cam timing (VCT) are examples of
recently introduced systems that affects overall performance of the vehicle, all these
are added each time the designers need to meet additional engine performance
requirement without compromising on the existing benchmarks.
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1.1 Role of control systems in automobile engineering
A control system is a device, or set of devices, that manages, commands, directs or regulates
the behavior of other device(s) or system(s). There are two common classes of control
systems, open loop control systems and closed loop control systems. In open loop control
systems output is generated based on inputs. In closed loop control systems output is taken
into consideration and corrections are made based on feedback. A closed loop system is also
called a feedback control system.
In the case of linear feedback systems, a control loop, including sensors, control algorithms
and actuators, is arranged in such a fashion as to try to regulate a variable at a set
point or reference value. Open-loop control systems do not make use of feedback, and run
only in pre-arranged ways.
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A proportional-integral-derivative controller (PID controller) is a control loop feedback
mechanism (controller) widely used in control systems. A PID controller calculates an
"error" value as the difference between a measured process variable and a desired setpoint.
The controller attempts to minimize the error in outputs by adjusting the process control
inputs.
Control
System
Knock control
Directly
Manipulate
controlled
d Variable
variable
Knock sensor Ignition
output
timing
Sensor
Air-fuel
ratio
Wheel
limit
Exhaust
oxygen
content
slip Wheel speed
Actuator
Piezo-electric Ignition
accelerometer control coil
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Fuel injection
system
Anti-lock
braking
system
Indirectly
controlled
variable
Knock
Titanium
Quality of based electro
injection
chemical
fuel
Brake time Magnetic
pressure
reluctance
Fuel
injector
ABS
solenoid
valve
Table 1.1 Control systems in automobiles
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Figure 1.1 Engine Control unit block diagram
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Measured
variable
Intake manifold
absolute pressure
Direct/indirect
measurement
Indirect
measurement of
engine load or mass
air-flow intake
Sensor
technology.
Wheatstone bridge
arrangement
Sensor
mounting
location
Within intake
manifold
Throttle position
Direct
measurement
Potentiometer
Accelerator pedal
Knock
Direct
measurement
Piezoelectric
accelerometer
type.
Cylinder block or
head
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Mass airflow
Temperature
Engine speed and
crankshft reference
position
Direct and indirect
measurement of fuel
injector basic pulse
width
Direct
measurement at
various locations
Direct
measurement
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Various
forms
including „flap‟
type diaphragm
Within air intake
Thermistor
or
thermocouple
depending
on
temperature range
Intake
air,
outside
air,
catalytic
converter, engine
coolant,
hydraulic oil
Magnetic
reluctance or Hall
effect device
Flywheel on end
of
engine
crankshaft
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Table 1.2 Engine management sensors
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Figure 1.2 Engine control Unit
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CHAPTER 2
Preliminaries and Literature Survey:-
The purpose of this chapter is to introduce the reader to control issues in a typical SI (spark
ignition) engine. In section 2.1, the performance expectations from an automotive engine are
put forward. The role played by control engineering in meeting those expectations is
explained. In section 2.2, the important control problems in engines such as Air-Fuel ratio
control, Ignition control and the control of torque are explained.
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2.1 Performance expectations and role of control engineering in engines
The main job of an automotive engine is to develop power as demanded by the driver. As a
byproduct of power, engines also produce harmful gasses-the most significant being
partially or unburnt fuel which leads to carbon monoxide production. Also automobile users
expect their vehicles to be fuel efficient. In order to deliver performance on all three fronts
i.e., Produce power, produce less emissions and be fuel efficient, engines are equipped with
a control unit. The purpose of the engine control unit is to continually choose the engine
inputs (air fuel ratio, spark timing) so that the engine outputs (torque, emissions and fuel
efficiency) meet targets.
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2.2 Important Control Problems:-
1. Air- Fuel Ratio(AFR):
Air–fuel ratio is the mass ratio of air to fuel present in
an internal combustion engine. If exactly enough air is provided to completely burn
all of the fuel, the ratio is known as the stoichiometric mixture. For precise AFR
calculations, the oxygen content of combustion air should be specified because of
possible dilution by ambient water vapor or enrichment by oxygen additions. The air
fuel ratio is an important measure for anti-pollution and performance-tuning
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reasons. The lower the air fuel ratio, the "richer" the mixture.
In theory a stoichiometric mixture has just enough air to completely burn the
available fuel. In practice this is never quite achieved, due primarily to the very
short time available in an internal combustion engine for each combustion cycle.
Most of the combustion process completes in approximately 4–5 milliseconds at an
engine speed of 6,000 rpm. (100 revolutions per second; 10 milliseconds per
revolution). This is the time that elapses from when the spark is fired until the
burning of the fuel-air mix is essentially complete.
A stoichiometric mixture unfortunately burns very hot and can damage engine
components if the engine is placed under rated load at this fuel–air mixture. Due to
the high temperatures at this mixture, detonation of the fuel-air occurs shortly after
maximum cylinder pressure is reached under high load. Detonation can cause
serious engine damage as the uncontrolled burning of the fuel air mixture can create
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very high pressures in the cylinder. As a consequence, stoichiometric mixtures are
only used under light load conditions. For acceleration and high load conditions, a
richer mixture (lower air-fuel ratio) is used to produce cooler combustion products
and thereby prevent detonation and overheating of the cylinder head.
In order to improve fuel economy, engines are equipped with sensors to measure the
amount of un-burnt fuel in the exhaust and to measure the oxygen content in the
inlet air. Depending on these values and a few other parameters like driver input,
load etc., the controller system has to control the amount of fuel that is mixed with
inlet air. The controller system also has to ensure that while cold starting the engine,
more amount of air has to be mixed with inlet air to produce a rich mixture. These
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are some of the control problems that are associated with air fuel control.
2
Ignition control: Ignition timing, in a spark ignition, internal combustion (IC)
engine , is the process of setting the angle relative to piston position and
crankshaft angular velocity that a spark will occur in the combustion chamber near
the end of the compression stroke. The need for advancing the timing of the spark is
because fuel does not completely burn the instant the spark fires, the combustion
gasses take a period of time to expand, and the angular or rotational speed of the
engine can lengthen or shorten the time frame in which the burning and expansion
should occur. In a vast majority of cases, the angle will be described as a certain
angle advanced before top dead center (BTDC). Advancing the spark BTDC means
that the spark is energized prior to the point where the combustion chamber reaches
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its clearance volume, the purpose of the power stroke in the engine is to push the
piston downwards and produce mechanical output. Sparks occurring after top dead
center (ATDC) are usually counter-productive (producing wasted spark, backfire, engine knock etc.) unless there is need for a supplemental or continuing spark
prior to the exhaust stroke.
For other engine inputs held constant, the brake torque produced changes the spark
advance or spark timing. At a particular value of spark advance, the brake torque
maximizes, this value is called as “Maximum brake torque” timing MBT. The MBT
value varies with engine speed and load. At MBT the fuel efficiency also peaks
because same amount of air and fuel produce maximum work. However, it may not
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be possible to operate the engine always at MBT setting. This is because the
tendencies of knocking and NOx production also peak at MBT.
The usual practice is to carry out extensive laboratory testing on the engine
prototype in order to find out values of spark advance (as function of engine speed
and load) that produce best torque while avoiding knocking and excessive NOx
production. The spark advance values, called “nominal spark timings”, are stored in
the engine control unit. A feed forward scheme is then devised to produce nominal
spark advance by sensing engine speed and load (usually inferred from intake
manifold pressure). To ensure that the engine does not knock in actual working, a
feedback scheme is deployed. It involves placing a knock sensor (typically a
vibration sensor) and causing an offset (retardation) in spark advance in case the
engine knocks.
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3. Torque Control: The controller design challenges for torque control are threefold.
First, the system contains a pure delay, which must be incorporated in the design.
Second, many parameters such as air fuel ratio, engine speed, mass air flow rate,
spark and exhaust gas recirculation affect the engine torque produced. Third, the
controller must accommodate a large range of engine operating conditions. With airfuel ratio and spark timing values always dictated by the considerations of emissions
and fuel efficiency, air flow rate is the only input left to control. The controller must
choose the air flow rate such that the driver's torque demand is met. Recognizing
what the driver wants the engine to do, is crucial in any engine control problem. In
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order to obtain a quick torque response, sometimes a multivariable strategy is used
that involves controlling the spark advance and the throttle. When the driver's torque
demand increases, the spark timing is advanced to that corresponding to MBT value
from the nominal value. This causes immediate increase in the torque produced.
The throttle is also actuated so that air flow rate increases. As the air flow rate nears
the desired value, spark timing is gradually retarded to its nominal value.
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CHAPTER 3
Modeling Parameters and Engine Modeling:The engine model has been constructed using MATLAB®/SIMULINK.
Simulink, developed by math works, is a data flow graphical programming language tool for
modeling, simulating and analyzing multi domain dynamic systems. Its primary interface is
a graphical block diagramming tool and a customizable set of block libraries. It offers tight
integration with the rest of the MATLAB® environment and can either drive MATLAB® or
be scripted from it. Simulink is widely used in control theory and digital signal
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processing for multi domain simulation and Model-Based Design (MBD).
Mathematical modeling of a system is a way of describing the entire system in terms of
mathematical concept and language. A mathematical model may help the user to explain the
functioning of the system and their by help in predicting the behavior of the system. In
general, mathematical models may include logical models, as far as logic is taken as a part
of mathematics.
This paper demonstrates Simulink capabilities to model an internal combustion engine from
the throttle to the crankshaft output. The ensuing sections (listed below) analyze the key
elements of the engine model that were identified after thorough research in Ford motors,
USA.
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1) Throttle
2) Intake manifold
3) Mass flow rate
4) Compression stroke
5) Torque generation and acceleration
3.1 Throttle:In SI engine, the throttle is a valve that directly regulates the amount of air entering the
engine, indirectly controlling the charge (fuel + air) burned on each cycle due to the fuel-
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injector or carburetor maintaining a relatively constant fuel/air ratio. In automobiles the
control used by the driver to regulate power is sometimes called as the throttle pedal or
accelerator. An engine's power can be increased or decreased by the restriction of inlet air.
The term throttle has come to refer, informally and incorrectly, to any mechanism by which
the power or speed of an engine is regulated.
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Figure 3.1 Throttle valve
When the driver presses the accelerator pedal, opening the throttle passage to allow more air
into the intake manifold. Usually an airflow sensor measures this change in flow of air by
measuring change in pressure and communicates to the ECU. The ECU then increases the
amount of fuel being sent to the fuel injectors in order to obtain the desired air-fuel ratio.
Often a Throttle Position Sensor (TPS) is connected to the shaft of the throttle plate to
provide the ECU with information on whether the throttle is in the idle position, Wide Open
Throttle (WOT) position, or somewhere in between these extremes.
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The first element of the model is the throttle body. The control input is the angle of the
throttle plate. The rate at which the model introduces air into the intake manifold, mai can be
expressed as the product of two functions - one, an empirical function of the throttle plate
angle only; and the other, a function of the atmospheric Pamb and manifold pressures, Pm. In
cases of lower manifold pressure, the flow rate through the throttle body is only a function
of the throttle angle as given in the formula below. This model accounts for the low pressure
behavior with a switching condition in the compressibility equations shown below.
ṁai = f(θ) g (Pm)
= mass flow rate into manifold (g/s) where,
f(θ) =2.821 – 0.05231θ +0.10299θ2-0.00063θ3
θ= throttle angle (deg)
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g(Pm) =
Pm≤ Pamb/2
[2√(PmPamb - Pm2)/2]
Pamb/2≤ Pm ≤ Pamb
[-2√(PmPamb – Pamb2)/2]
Pamb≤ Pm ≤ 2Pamb
-1
69
Pm ≥ 2Pamb
Where,
Pm = Manifold pressure (bar)
Pamb= Atmospheric pressure (bar)
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a. Intake Manifold:-
In automotive engineering, an inlet manifold or intake manifold is the part of an engine that
supplies the fuel/air mixture to the cylinders. The primary function of the intake manifold is
to evenly distribute the combustion mixture (or just air) to each intake port in the cylinder
head(s). Even distribution is important to optimize the efficiency and performance of the
engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors and other
components of the engine. Due to the downward movement of the pistons and the restriction
caused by the throttle valve, in a reciprocating spark ignition piston engine, a
partial vaccum (lower than atmospheric) exists in the intake manifold. This manifold
vaccum can be substantial, and can be used as a source of automobile ancillary power to
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drive auxiliary systems such as : power assisted brakes, emission control devices, cruise
control, ignition advance, windshield wipers, power windows, ventilation system valves, etc.
The design and orientation of the intake manifold is a major factor in the volumetric
efficiency of an engine. Abrupt contour changes provoke pressure drops, resulting in less air
entering the combustion chamber; high-performance manifolds have smooth contours and
gradual transitions between adjacent segments. Modern intake manifolds usually
employ runners, individual tubes extending to each intake port on the cylinder head which
emanate from a central volume or "plenum" beneath the carburetor.
The simulation models the intake manifold as a differential equation for the manifold
pressure. The difference in the incoming and outgoing mass flow rates represents the net rate
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of change of air mass with respect to time. This quantity, according to the ideal gas law, is
proportional to the time derivative of the manifold pressure, 𝑃m.
Ṗm =RT (ṁai−ṁao)/ Vm
Where,
R= Specific gas constant, (287 J/kg-K)
T= Temperature (K),
Vm= Manifold volume (m3),
𝑚̇ai= Mass flow rate of air out of the manifold (g/s)
𝑃̇m= Rate of change of manifold pressure (bar/s),
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The mass rate, 𝑚̇ai is a function of the manifold pressure and the engine speed.
3.3 Intake Mass Flow Rate:A mass air flow sensor (MAF) is used to find out the mass flow rate of air entering a fuelinjected internal combustion engine.
The air mass information is necessary for the engine control unit (ECU) to balance and
deliver the correct fuel mass to the engine. Air changes its density as it expands and
contracts with temperature and pressure. In automotive applications, air density varies with
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the ambient temperature, altitude and the use of forced induction, which means that mass
flow sensors are more appropriate than volumetric flow sensors for determining the quantity
of intake air in each piston stroke.
The mass flow rate of air that the model pumps into the cylinders from the manifold is
described by an empirically derived equation. This mass rate is a function of the manifold
pressure and the engine speed.
ṁai = −0.366 + 0.08979NP − 0.0337NPm + 0.0001N2Pm
Where,
N=Engine angular speed (rad/s),
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Pm=Manifold pressure (bar).
To determine the total air charge pumped into the cylinders, the simulation integrates the
mass flow rate from the intake manifold and samples it at the end of each intake stroke
event. This determines the total air mass that is present in each cylinder after the intake
stroke and before compression.
b. Compression Stroke:The compression stroke is the second of the four strokes in an IC engine. In this stage, the
mixture is compressed to the top of the cylinder by the piston until it is either ignited by a
spark plug causing an explosion and forcing the piston downwards.
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Compression serves to increase the proportion of energy which can be extracted from the air
fuel mixture and should be limited for a given application. Too high a compression can
cause detonation, which is undesirable compared with a smooth, controlled burn. Too low a
compression may result in the fuel/air mixture still burning when the piston reaches the
BDC, the exhaust valve opens.
The compression ratio of an internal-combustion engine or external combustion engine is a
value that represents the ratio of the volume of its combustion chamber from its largest
capacity to its smallest capacity. It is a fundamental specification for many common
combustion engines.
In a reciprocating engine, it is the ratio between the volume of the cylinder and combustion
chamber when the piston is at the bottom of its stroke, and the volume of the combustion
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chamber when the piston is at the top of its stroke. A high compression ratio is desirable
because it allows an engine to extract more mechanical energy from a given mass of air-fuel
mixture due to its higher thermal efficiency. This occurs because internal combustion
engines are heat engines, and higher efficiency is created because higher compression ratios
permit the same combustion temperature to be reached with less fuel, while giving a longer
expansion cycle, creating more mechanical power output and lowering the exhaust
temperature. It may be more helpful to think of it as an "expansion ratio", since more
expansion reduces the temperature of the exhaust gases, and therefore the energy wasted to
the atmosphere. Higher compression ratios will however make gasoline engines subject
to engine knocking if lower octane-rated fuel is used, also known as detonation. This can
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reduce efficiency or damage the engine if knock sensors are not present to retard the timing.
In an inline four-cylinder four-stroke engine, 180° of crankshaft revolution separate the
ignition of each successive cylinder. This results in each cylinder firing on every other crank
revolution. In this model, the intake, compression, combustion, and exhaust strokes occur
simultaneously (at any given time, one cylinder is in each phase). To account for
compression, the combustion of each intake charge is delayed by 180° of crank rotation
from the end of the intake stroke.
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Figure 3.2 Engine Model
c. Torque Generated by the engine and Acceleration:-
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Torque, moment or moment of force, is the tendency of a force to rotate an object about
an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque is a twist to an object.
Mathematically, torque is defined as the cross product of the distance vector and
the force vector, which tends to produce rotation.
The final element of the simulation involves simulating the torque developed by the engine.
An empirical relationship dependent upon the mass of the air charge, the air/fuel mixture
ratio, the spark advance, and the engine speed is used for the torque computation.
TORQUEeng = -181.3 + 379.36 ma + 21.91 (A/F) - 0.85(A/F)2 + 0.26 σ - 0.0028 σ2 + 0.027
N -0.000107 N2 + 0.00048 N σ + 2.55 σ ma - 0.05 σ2 ma
Where,
Ma = Mass of air in the cylinder for combustion (g)
A/F = Air to Fuel ratio
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σ= Spark advance
TORQUEeng= Torque produced by the engine (Nm)
The engine torque less the net torque results in acceleration
JṄ = TORQUE eng –TORQUEload
J = Engine rotational moment of inertia
Ṅ = Engine acceleration(rad/sec2)
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CHAPTER 4
SIMULINK MODELLING:4.1 Throttle and manifold:-
The throttle and intake manifold subsystems are shown in Figure. The throttle valve behaves
in a nonlinear manner and is modeled as a subsystem with three inputs. The individual
equations are implemented using function blocks. These provide a convenient way to
describe a nonlinear equation of several variables. A Switch block determines whether the
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flow is sonic by comparing the pressure ratio to its switch threshold, which is set at one half.
In the sonic regime, the flow rate is a function of the throttle position only. The direction of
flow is from the higher to lower pressure, as determined by the Sign block.
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4.1.1 Throttle
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Figure 4.1 Throttle model
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4.1.2 Throttle flow Vs valve angle and pressure
Throttle Angle ,
theta (deg )
f(theta )
1
2.821 - 0.05231 *u + 0.10299 *u*u - 0.00063 *u*u*u
2
Manifold Pressure ,
Pm (bar )
g(pratio )
min pratio
2*sqrt(u - u*u)
1
3
1.0
Atmospheric Pressure ,
Pa (bar )
Sonic Flow
Throttle
Flow , mdot
(g/s)
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flow direction
Throttle Flow
Figure 4.2 Throttle flow model
4.1.3 Intake manifold vaccum.
If the engine is operating under light or no load and low throttle, there is high manifold
vaccum. As the throttle is opened, the engine speed increases rapidly. The engine speed is
limited only by the amount of fuel/air mixture that is available in the manifold. Under full
throttle and light load the manifold pressure increases.
If the engine is operating under heavy load at wide throttle openings (such as accelerating
from a stop or pulling the car up a hill) then engine speed is limited by the load and minimal
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vacuum will be created. Engine speed is low but the butterfly valve is fully open. Since the
pistons are descending more slowly than under no load, the pressure differences are less
marked and parasitic drag in the induction system is negligible. The engine pulls air into the
cylinders at the full ambient pressure.
2
Manifold Pressure ,
Pm (bar )
1
s
0.41328
1
mdot Input
(g/s)
RT /Vm
f(u)
1
Pumping
mdot to
Cylinder
(g/s)
p0 = 0.543 bar
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2
N (rad /sec)
Vaccum in Intake manifold
Figure 4.3 Intake manifold vaccum model
4.2 Torque generated
The maximum attainable power Pe of an internal combustion engine is a function of the
engine angular velocity ωe. This power can be determined by a third order polynomial.
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If we use ωm to indicate the angular velocity, measured in rad/sec2, at which the engine
power reaches the maximum value Pm measured in Watt. The for spark ignited engines
P1 = Pm/ωm
P2 = Pm / ωm2
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P3= - Pm/ ωm2
Using the above equation the torque can be found as
Torque = Power/ ωe
The engine torque model which incorporates all of the mentioned models i.e., Throttle angle,
air flow through manifold, air mass flow rate etc is shown in the figure 4.4
On mentioning the input values the performance of the engine can be determined.
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Figure 4.4 Torque model
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CHAPTER 5
SIMULATION AND RESULTS:-
The above models which are created in simulink environment are simulated and the engine
performance is checked.
5.1 Case 1- Varying load and throttle angle:-
The initial engine RPM is set at 2000RPM and the final RPM is set at 4000 RPM with
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variable load varying from 20 to25 Nm.
The input values given to the engine are the load which depends on the type of terrain and
the number of people sitting in the vehicle. The second input is the amount of throttle input
the driver is giving.
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load
Throttle
angle
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Figure 5.1
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Load Vs Time
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Case 1 Output:
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Figure 5.2: Engine speed corresponding to load in figure 5.1
As the engine was initially set at 2000 RPM, the engine continues to operate at 2000RPM
till time t=500 millisecond. At time t=500 ms the load on the engine decreases from 20 Nm
to 25 Nm, this causes an increase in engine speed, the engine control unit senses the
decrease in load and takes necessary control action to maintain 2000RPM, the control action
includes changing the throttle angle. It can be inferred from the graph that the control time
of the system is less than 100 ms. At t=1000ms the throttle angle θ is wide open. The
corresponding effect on the engine speed can be seen in figure 5.2 at t=1000 ms, the engine
goes from 2000RPM to 4000RPM. Further the disturbance in the engine speed at 2000ms is
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due to the increase in load of torque (from wheels) from 20 Nm to 25Nm, when the load is
increased by 5Nm the corresponding speed decrease can be observed at t=2000ms.
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Figure 5.3 Acceleration corresponding to figure 5.1
Under normal operating conditions ie., constant load and constant throttle angle position the
acceleration of the engine is 0. But when the load decreases by 5Nm the engine accelerates
causing an increase in RPM, the ECU quickly decelerates the engine to maintain 2000RPM.
The deceleration of the engine can be observed at t=500ms. At time t=1000ms the engine
accelerates as the throttle angle is wide open and the engine accelerates from 2000RPM to
4000RPM after the engine reaches 4000RPM the acceleration becomes zero to prevent
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further increase in speed. The deceleration at t=2000ms is due to the increase in load by
5kN. This 5kN load tries to decelerate the engine. The ECU take necessary control action
and the engine is brought back to acceleration is brought back to zero thereafter.
5.2 Case 2:- Engine performance under constant throttle angle and varying load
The throttle angle is maintained constant to check the performance of engines against
varying load conditions. The load varies from 25 Nm to 20Nm. However the throttle angle is
maintained near constant.
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Figure 5.4 Case 2 Input load Vs time
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Case 2 Output :
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Figure 5.5 Engine Speed Corresponding to figure 5.4
As long as the load is constant the engine holds a constant RPM of 2000RPM. At t=500 ms
the engine RPM increases to 2077RPM as the load is decreased by 5Nm. The ECU takes
necessary control action to keep the RPM constant at 2000RPM. At t= 1500 ms as the load
increases by 5 Nm the engine RPM decreases as there is no throttle angle increase to offset
the decrease in RPM.
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Figure 5.6 Engine acceleration corresponding to figure 5.4
The acceleration is zero initially as the load on the engine and the throttle angle is kept
constant. At 500 ms when the load on the engine decreases by 5Nm the acceleration
suddenly increases which causes an increase in engine speed, but the ECU changes the
control inputs, it decreases amount of fuel supply to decrease to engine set speed. The
variations in the engine acceleration is due to the increase of 5Nm in the load.
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5.3 Case 3:- Engine performance keeping constant load and varying throttle angles
In this case the load on the engine is kept constant load and the throttle angle is varied from
minimum to maximum value. The speed and acceleration of the engine is then examined
under constant load conditions.
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Figure 5.7 Throttle angle Vs time
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Output :
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Figure 5.8 Engine speed corresponding to figure 5.7
As the graph shows there is no change in engine speed from t=0 sec to t= 1000ms, this
behavior of the engine is because both the load and the throttle angle are constant. At
t=1000ms as the throttle angle increases the speed of the engine increases to 4000RPM and
remains constant thereafter.
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Figure 5.9 Acceleration corresponding to figure 5.7
Since acceleration depends on the throttle angle and the load on the engine. The acceleration
remains constant as long as the load and the throttle angle remain constant. The sudden
increase in acceleration at time t= 1000 ms is due to the increase in the throttle angle. As the
throttle angle becomes constant at time t=1300ms the acceleration value also becomes zero
at time t=1300 ms.
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5.4 Conclusion
The above graphs show the performance of the engine under varying conditions, based on
the above conditions the engine control unit can be tuned or modeled. The ECU can be
programmed to sense the increase in load and take necessary control action such as
increasing the throttle angle and increasing the mass flow rate.
In addition to controlling the throttle angle and mass flow rate, a lot more parameters such as
cam timing, turbocharger speed, intercooler performance, cooling system performance,
stratified injection charge etc can be monitored and controlled by the ECU. How ever since
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these technologies are relatively new, the complete understanding of its working and
optimizing them will take some time.
By simulating the load torques that act on the engine due to various factors like gradient,
aerodynamic drag, passenger load, friction between tire and road etc., the actual
performance of the engine under road conditions can be estimated.
The costs associated in modeling and simulating an engine is computer is far less than the
cost involved in building prototypes and checking the engine performance using engine test
rigs. The cost involved in implementing this project in an industry is very minimal, this is
because this project involves a computer with MATLAB® software, a printer to document
the performance and some skilled designers.
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REFERENCES:Published paper references:1. Joint Air-fuel ratio and torque regulation using secondary cylinder air flow actuator,
A.G Stefanopoulou, J. A. Cook, J. W. Grizzle
2. Virtual Diesel engine in simulink, Pavel Kucera, Vachav Pistek, Number 2, Volume
VIII, July 2013
3. Modelling and control of advanced technology engines, Anna stefanopoulou
4. Fuzzy logic controller for speed control of an IC engine using MATLAB®/simulink,
Namitha sona, Shantharama rai, IJRTE, Volume 2, Issue 2, May 2013
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Text Book references:-
1. Vehicle Dynamics applications, Reza N Jazar
2. Internal Combution Engines, R.K Rajput
3. Mastering MATLAB®, Duane C. hanselman, Bruce L. Little Field, Pearson
Education, 2008
Web Site References:1. http://en.wikipedia.org/wiki/Inlet_manifold
2. http://www.howstuffworks.com/car-driving-safety/safety-regulatorydevices/electronic-throttle-control-systems.htm
3. http://en.wikipedia.org/wiki/Mass_flow_rate
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