Advanced Internal Combustion Engine

Dr. Bahram Bahri

Department of Mechanical Engineering

Islamic Azad University, Shahreza Branch, Iran

Bahri@iaush.ac.ir

In the name of God

Reference Books:

2

1. An Introduction to Thermodynamic Cycle Simulations for Internal Combustion Engines by JERALD A. CATON

2. Internal Combustion Engines Applied Thermo-sciences by Colin R. Ferguson and Allan T. Kirkpatrick

3. Internal Combustion Engines by John B. Heywood

4. Modeling and control of engines and drivelines by Eriksson

Shift from traditional ICE

towards alternatives

Use alternative and

sustainable fuels

LTC is a promising concept

Introduction

3

Globalization and the rise in mobility

Exhaust gas emissions and air pollution

Uncertainty in conventional fuel price

More stringent environmental regulations

Advanced combustion engine operating mode

4

• Homogenous Charge Compression Ignition (HCCI) همگن مخلوط تراکمی اشتعال موتورهای

• Premixed Charge Compression Ignition (PCCI) پیش آمیخته مخلوط تراکمی احتراق موتورهای

• Reactivity-controlled Compression Ignition (RCCI) کنترل شده واکنش پذیری با تراکمی-اشتعال های موتور

Low Temperature Combustion (LTC) موتورهای با احتراق دما پایین

HCCI engines HCCI = Homogeneous Charge Compression Ignition

Homogeneous mixture auto-ignites by compression due to increased pressure and temperature.

Homogeneous air-fuel mixture auto-ignites at many locations. 3

Combustion happens without any external device.

5

RCCI and PCCI engines

6

Graphical summary of SI, CI, and LTC Modes 6 Diesel (CI) combustion

Soot – –

–

–

Controlled heat release (mixing) Controlled combustion timing

Wide load range

High efficiency

(relative to Sl)

NO and PM

5

4

– x

emissions 3

2

1 NOX Spark ignition (SI) combustion

– Controlled heat release

(flame propagation)

Controlled combustion timing

Wide load range

Three-way catalyst

Low efficiency

(relative to diesel)

0 1000 1400 1800 2200 2600 3000

Temperature [K] – –

–

– – –

–

–

–

High efficiency (high CR, no throttle)

Low NOx and PM emissions Operation range?

Combustion timing control?

Fuel?

HCCI

Equiv

ale

nce r

atio,

φ

LTC

CI

SI

7

Operating Map of LTC

8

SI Combustion Process

3

9

3. When the flame has propagated through the chamber it is extinguished (quenched) at the cylinder walls.

1. The combustion is ignited by a spark at the spark plug that gives a small flame kernel.

2. The flame kernel increases in size and develops into a turbulent flame that propagates through the homogeneous air and fuel mixture in the combustion chamber.

CI Combustion Process

3

10

1. The fuel spray mixes with warm air and there is a delay from the start of injection to when the combustion reactions start.

2. This occurs when the temperature is high enough and when there is oxygen available for the fuel to react with.

3. Diesel engines thus operate with stratified charge since the fuel is injected directly into the cylinder and does not have time to mix before the combustion.

Classification of Internal Combustion Engine

Engine Cycle

1. •

Four Stroke Cycle Four strokes to complete the thermodynamic cycle :

Intake process - one stroke (fresh mixture inducted in, work done by piston to

induct mixture)

Compression process - one stroke (mixture compressed almost adiabatically,

work done by piston on mixture; process Pv = constant)

Combustion and expansion - one stroke mixture is ignited and burned through

flame propagation in SI engine and the high pressure gases then expand

producing work. In CI engine, ignition occurs after fuel injetion and a delay

period, mixture is burned, and high pressure gases expand producing work

output.

Exhaust process - one stroke (the burned gases are purged out by opening the

exhaust valve and moving the piston from BDC to TDC)

–

–

–

–

11

Four stroke Spark Ignition (SI) Engine

Stroke 1: Fuel-air mixture introduced into cylinder through intake valve

Fuel-air mixture compressed

Combustion (roughly constant volume) occurs and

product gases expand doing work

Stroke Stroke

2: 3:

Stroke 4: Product gases pushed out of the cylinder through the

exhaust

FUEL

valve

A Ignition I

R

Combustion

Products

Intake Stroke

Power Stroke

Compression Stroke

Exhaust Stroke

Fuel/Air

Mixture

12

Four-Stroke SI Engine Cylinder Pressure

Exhaust gas residual

IVO - intake valve opens, IVC – intake valve closes EVO – exhaust valve opens, EVC – exhaust valve closes Xb – burned gas mole fraction

13

10-40 40-60 CAD

Four stroke Compression Ignition (CI) Engine

Stroke Stroke

Stroke

1: 2:

3:

Air is introduced into cylinder through intake valve Air is compressed

Combustion (roughly constant pressure) occurs and

product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the

exhaust valve

A Fuel Injector

I

R

ustion

Intake Stroke

Compression Stroke

Power Stroke

Exhaust Stroke

Comb

Produ

cts

Air

14

Four-Stroke CI Engine Cylinder Pressure

SOI – start of injection EOI – end of injection

SOC – start of combustion

EOC – end of combustion

ignition delay Δ𝜃i,d

Fuel mass flow rate

Fuel mass burn rate

15

20 CAD

Classification of Internal Combustion Engine

16

Compression ignition (CI) combustion is initiated by the start of injection (SOI) and is characterized by three phases; o ignition delay, o premixed combustion, o mixing controlled combustion. 1. When the diesel fuel is injected it must be transformed from a cold liquid to

a vapor and be heated so that it can autoignite. 2. This time from the start of injection to start of combustion is called the

ignition delay Δ𝜃i,d. 3. When this vapor–fuel mixture is at or above the autoignition temperature it

will ignite and combust and this phase is called the premixed combustion phase.

4. Then the fuel in the main body of the spray will mix with the air and burn during the mixing controlled combustion phase. In the CI engine, the fuel follows a path from a fuel rich spray with 𝜆 ≪ 1 to a global lean mixture where there are sufficient amounts of air to oxidize the fuel.

Four stroke Compression Ignition (CI) Engine

Stroke Stroke

Stroke

1: 2:

3:

Air is introduced into cylinder through intake valve Air is compressed

Combustion (roughly constant pressure) occurs and

product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the

exhaust valve

A Fuel Injector

I

R

ustion

Intake Stroke

Compression Stroke

Power Stroke

Exhaust Stroke

Comb

Produ

cts

Air

17

Classification of Internal Combustion Engine

Fuel

•

•

•

•

•

•

•

Used

Gasoline

Diesel Oil of Fuel Oil

Gas, Natural Gas, Methane

LPG

Alcohol – Ethyl, Methyl

Dual Fuel

Gasohol

18

Classification of Internal Combustion Engine

Application

•

•

•

•

•

•

Automobile,

Locomotive

Stationary

Marine

Aircraft

Truck, Bus

Small Portable, Chain Saw, Model Airplane

19

I C Engine’s Components Cylinder head

Air cleaner Breather cap

Rocker arm Choke

Valve spring

Valve guide Throttle

Pushrod

Intake manifold Sparkplug

Exhaust manifold Combustion chamber

Tappet

Piston rings Dipstick Piston

Cam Wrist pin

Camshaft Cylinder block Water jacket Connecting rod

Oil gallery to piston Wet liner Oil gallery to head

Connecting rod bearing Crankcase

Crankpin

Crankshaft Main bearing

Oil pan or sump

CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE 20

Oil pickup Crank sprocket Oil pump

Crankshaft Timing belt

tensor

Timing belt Connecting rod

Piston

Exhaust valve Cam sprocket

Intake valve

Rocker arm

Camshaft Carburetor

Air cleaner

21

Engine Temperature Profiles

What two purposes does

engine lubrication serve?

– minimize friction

– dissipate heat

•

22

23

Engine Geometry

Brake = gross indicated + pumping + friction

=net indicated + friction

Components of piston engine

Piston moves between Top Dead Center (TDC) and Bottom Compression Ratio = rc = ratio of BDC/TDC volumes

Stroke = L = travel distance from BDC to TDC

Bore = B = cylinder diameter

Dead Center (BDC).

cylinders Vd = Displacement = (BDC-TDC) volume .#

B2 = L /4 . # cylinders

Basic Equations

P = T.N P [kW] = T [Nm].N [rpm].1.047 E-04

BMEP = P.(rev/cyc) ./ VdN BMEP [kPa] = P [kW].(2 for 4-stroke) E03

. m.fuel

/ Vd [l]. N [rev/s]

BSFC = BSFC =

/ P [g/hr] / P [kW] mfuel

mfuel = fuel mass flow rate [g/hr]

P = (Brake) Power [kW]

T = (Brake) Torque [Nm] = Work = W

B. MEP = Brake mean effective pressure

BSFC = Brake specific fuel consumption

24

CEFRC1-1 2014

Engine Power

Indicated power of IC engine at a given sp.eed mair is proportional to the air mass flow rate,

. P = f . mair N. LHV . (F/A) / nr

f = fuel conversion efficiency LHV = fuel lower heating value F/A fuel-air ratio mf/mair

nr = number of power strokes / crank rotation =2 for 4-stroke

Efficiency estimates:

SI: 270 <bsfc < 450 g/kW-hr

Diesel: 200 < bsfc < 359 g/kW-hr

f = 1/46 MJ/kg / 200 g/kW-hr = 40-50% 500 MW GE/Siemens combined cycle gas turbine

natural gas power plant ~ 60% efficient

SGT5-8000H ~530MW 25

26

27

Power and Torque versus Engine Speed

There is a maximum in the brake power

versus engine speed called the rated

brake power (RBP).

At higher speeds brake power decreases as

friction power becomes significant compared

to the indicated power

There is a maximum in the torque versus speed called maximum brake torque (MBT) brake torque drops off:

• at lower speeds do to heat losses

• at higher speeds it becomes more difficult to

ingest a full charge of air.

Rated brake power

1 kW = 1.341 hp

Max brake torque

28

29

1. The indicated mean effective pressure (imep) is the net work per unit displacement volume done by the gas during compression and expansion. The name originates from the use of an ‘‘indicator’’ card used to plot measured pressure versus volume. The pressure in the cylinder initially increases during the expansion stroke due to the heat addition from the fuel, and then decreases due to the increase in cylinder volume.

2. The brake mean effective pressure (bmep) is the external shaft work per unit volume done by the engine. The name originates from the ‘‘brake’’ dynamometer used to measure the torque produced by the rotating shaft. Typical values of measured bmep for naturally aspirated automobile engines depend on the load, with maximum values of about 10 bar, and greater values of about 20 bar for turbo or supercharged engines.

30

31

Typical 1998 Passenger Car Engine Characteristics

Vehicle Engine

type

Displ .

(L)

Max Power

(HP@rpm)

Max Torque

(lb-ft@rpm)

BMEP at

Max BT (bar)

BMEP at

Rated BP (bar)

Mazda

Protégé LX

L4 1.839 6000@122 4000@117 10.8 9.9

Honda

Accord EX

L4 2.254 5700@150 4900@152 11.4 10.4

Mazda

Millenia S

L4

Turbo

2.255 5300@210 3500@210 15.9 15.7

BMW

328i

L6 2.793 5300@190 3950@206 12.6 11.5

Ferrari

F355 GTS

V8 3.496 8250@375 6000@268 13.1 11.6

Ferrari

456 GT

V12 5.474 6250@436 4500@398 12.4 11.4

Lamborghini

Diablo VT

V12 5.707 7000@492 5200@427 12.7 11.0

32

Indicated Mean Effective Pressure (IMEP)

imep is a fictitious constant pressure that would produce the same work per cycle if it acted on the piston during the power stroke.

imep does not depend on engine

imep is a better parameter than torque to compare engines for design and output because it is independent of engine speed, N, and engine size, Vd.

33

pdv

4-stroke (Otto) cycle

“Suck, squeeze, bang, blow” 1. Intake: piston moves from TDC to BDC with the intake valve open,

drawing in fresh reactants

2. Compression:

180 BDC

180 BDC pdv Win, gross pdv

3 valves are closed and piston moves from BDC to TDC,

Combustion is initiated near TDC

3. Expansion:

(net = gross + pumping)

Win,net high pressure forces piston

from TDC to BDC, transferring work

to crankshaft

4. Exhaust: 2

exhaust valve opens and piston moves from BDC to TDC pushing out exhaust

1,4 Pumping loop – An additional

rotation of the crankshaft used to: - exhaust combustion products

- induct fresh charge

1 4

TDC BDC Four-stroke diesel pressure-volume

diagram at full load

pdv

34

Four stroke Spark Ignition (SI) Engine Pressure and Volume Curve

35

1. Figure shows the cylinder pressure as a function of cylinder volume for the base case conditions.

2. The start and end of combustion are denoted, as are the valve events.

3. For this part load condition, the “pumping loop” represents work done to the cylinder gases during the gas exchange.

4. The area of the compression‐expansion loop” is proportional to the gross indicated work done by the gases.

Four stroke Spark Ignition (SI) Engine Combustion

36

1. Engine operating conditions, like speed and load, influence these processes.

2. Higher engine loads shorten the combustion duration which is due to: less residual gases, higher gas velocity (turbulence), and higher temperature.

3. The motoring pressure is nearly symmetrical about TDC (0°aTDC) with a maximum pressure of about 720 kPa.

4. The firing pressure has a maximum of 1904 kPa at 16.0°aTDC.

Cylinder gas temperature increases rapidly during the combustion period and reaches a maximum of 2393 K at 27.8°aTDC.

Four stroke Spark Ignition (SI) Engine Combustion Duration

37

1. For most of the work reported here, the combustion duration is based on 0–100% fuel burned. Other definitions of the combustion duration exist. One popular definition is 10–90% fuel burned. This is a particularly useful definition for use with experimental work.

2. Since the start of combustion is gradual, detecting the exact 0% point is difficult if not impossible. The 10% point is much easier to detect from experimental data.

Four stroke Spark Ignition (SI) Engine Cylinder Temperature

38

1. Figure shows the cylinder pressure and the average gas temperature as functions of crank angle for the complete four strokes (720°CA) for the base case conditions.

2. At exhaust valve open (EVO), both the pressure and temperature change slope as the mass flow out adds to the expansion decrease of pressure and temperature.

3. At intake valve open (IVO), a further decrease occurs for both the pressure and temperature. After exhaust valve close (EVC), the temperature increases slightly during the portion of flow that is from the intake manifold back into the cylinder

Thermodynamics review - First law

During an interaction between a system and its surroundings, the

amount amount

of energy gained by the system must be exactly equal to the of energy lost by the surroundings

Engine System Surroundings

Gained (input) (J) Lost (output) (J)

- Work

+Heat Lost

(Cylinder wall,

Exhaust gas )

Friction

Gained (J) Intake flow

Lost (J) Energy of fuel combustion

=

syste

m

(

39

tend

W

Qdt m

Constant volume combustion - HCCI:

T tbegin tend

Tburn Isentropic

expansion During constant volume combustion process:

tbegin - tend 0 1100K

800K

Shaft Motored tbegin Isentropic

compression end TDC

t Q f QLHV

R mf QLHV

Tburn Tunburn

Pd 0

t

begin

( 1)

40

Heat Engine Cycles

41

The Otto cycle (𝛾 = 1.40, 𝑟 = 8) 1 to 2 isentropic compression 2 to 3 constant volume heat addition 3 to 4 isentropic expansion 4 to 1 constant volume heat rejection

The Otto cycle

42

Heat Engine Cycles

43

The Diesel cycle (𝛾 = 1.30, 𝑟 = 20) 1 to 2 isentropic compression 2 to 3 constant pressure heat addition 3 to 4 isentropic expansion 4 to 1 constant volume heat rejection

Ideal cycles

Diesel Otto

T T 3 3

2 2

4 4

s s

1-2 Isentropic compression

2-3 Constant pressure heat addition

3-4 Isentropic expansion

4-1 Constant volume heat rejection

1-2 Isentropic compression

2-3 Constant volume heat addition

3-4 Isentropic expansion

4-1 Constant volume heat rejection

1

1

44

Heat Engine Cycles

45

LIMITED PRESSURE CYCLE

The limited pressure cycle (𝛾 = 1.30, 𝑟 = 15).