Industrial energy management Reciprocating engines

1

Industrial energy management

Reciprocating engines

Jun.-Prof. Benoît Fond, G-10/R-119

[email protected]

mailto:[email protected]

2

Combustion devices

• In steam power plant, heat is supplied to the water from an external

source (coal, gas, nuclear fuel) via a heat exchanger (boiler) – no direct

contact.

• Working fluid is external to combustion

• Closed working fluid cycle – The fluid recirculates

• In gas turbines and reciprocating engines, chemical heat release takes

place within the working fluid.

• Internal combustion engines

• Open cycle – Air is drawn from the atmosphere and combustion products are

exhausted to the atmosphere.

Open and closed cycle / Internal and External Combustion

3

Layout

1. Basics of reciprocating engines

1. Classification

2. The Spark Ignition Engine

3. The Compression Ignition Engines

4. Fuels

5. Efficiency analysis

6. Power control

7. Emissions

2. Development strategies for reciprocating engines

1. Current challenges

2. Exhaust after treatment

3. Strategies for Spark Ignition Engines

4. Strategies for Compression Ignition Engines

4

Reciprocating engine (or Piston Engine)

Combustion chamber with a flexible wall

(piston), resulting in variable volume.

Gas pressure leads to boundary work,

which is converted to technical work

(for example by a crank mechanism)

Time response of the combustion :

• Continuously (steam motor, Gas turbine)

• Intermittently (Otto / Diesel engine)


https://en.wikipedia.org/wiki/File:4StrokeEngine_Ortho_3D.gif

5


1860 J.J.E. Lenoir: first reciprocating gas engine, th = 2-3% - No mixture

compression

1862 Beau de Rochas, patented the four stroke engine but did not build it

1878 Nikolaus Otto: four stroke gas engine with mixture compression,

th = 12%, Pe = 3 hp

1897 Rudolf Diesel: first engine with air compression and self ignition,

th = 26%

Today : 44% in Diesel cars, 38% in gasoline cars, max 53% in 2-

stroke marine diesel engines

A bit of history

6

Reciprocating Engines

IC Engine as powertrain : More than 100 years of development

Development driven by :

• Production Cost

• Fuel economy

• Environment concern

• Energy supply / policy

• Fun / Customer Satisfaction

Significance of IC Engine development

7

Basics of IC engines

The nature of the gas exchange:

• 4-stroke: piston movement is alternately used for work output or gas

exchange (intake, compression, expansion, exhaust stroke)

• 2-stroke: gas exchange is realized by scavenging the exhaust gas by

the fresh load (compression, expansion stroke)

8

IC Engines

Four – stroke Cycle

9

IC Engines

Four Stroke Engine

Terminology

Source: http://what-when-how.com/energy-engineering/reciprocating-engines-diesel-and-gas-energy-engineering/

10

IC Engines

Two Stroke Cycle

The exhaust gases are scavenged by the

fresh load

Compact, no moving part.

High power density

Lubrication oil is entrained and burned in

mixture -> Pollutants

https://commons.wikimedia.org/wiki/File:Two-Stroke_Engine.gif

11


Pressure level at the intake:

• Naturally aspirated engine: suction from the ambient

• Supercharged engine: increased the fresh air density using a

compressor or an exhaust turbocharger (specific power increase)

Time of the fuel input:

• Air is compressed (Diesel, „stratified GDI“)

• Mixture is compressed (Otto)

Nature of the power control:

“Quantity” of mixture (throttle) controlled (Otto)

“Quality” i.e. stoichiometry of mixture controlled (Diesel, „stratified GDI“)

12


Nature of Ignition:

Extraneous ignition (Otto): external energy supply (spark

plug)

Self ignition (Diesel): injection of the fuel in compressed

hot air

Nature of the engine cooling:

Air or water cooling

Nature of the piston motion:

Reciprocating and rotary piston (“Wankel”) engine

Nature of the Cylinder configuration:

In-line, V, W, H, opposed cylinder engine.

https://upload.wikimedia.org/wikipedia/commons/f/fc/Wankel_Cycle_anim_en.gif

13

IC Engines

Spark Ignition Engines

Fuel and Air mix to form a combustible mixture

The mixture is compressed and then ignited near

top-dead center

Described by the Otto cycle

Constant-Volume Heat Addition


14

Spark ignition engine propagation

-15 CAD BTDC -13 CAD BTDC -10 CAD BTDC -8 CAD BTDC

0 CAD BTDC-5 CAD BTDC +5 CAD BTDC

Aleiferis et al. (2013)

Fuel 109,256-278

Spark happens

at -35 CAD

BTDC

15

IC Engines

Spark Ignition Engine Efficiency

Typical rv is 9, with theoretical

efficiency of 58 %.

True efficiency is 30-38%, but trend is

correct.

Limited rv to prevent pre ignition and

knock

No more lead additive -> Other design

improvements

0 5 10 150

0.1

0.2

0.3

0.4

0.5

0.6

0.7

compression ratio

effi

cien

cy

16

IC Engines

p

V

pmax

pu

Vk,OT (V +V ),h k UT

OO

ICIO

OC

hVimepdVpW

zVimepn2

1P hi

rie PPP

W work per cycle

imep indicated mean

effective pressure

n engine speed

z number of cylinders

Pe effective power (friction)

Pi internal power

Pr engine friction

V volume

Vh displaced volume

17

IC Engines

Intake stroke Compression stroke - self ignition

Compression Ignition Engine

18

IC Engines

Working stroke Exhaust stroke


19

IC Engines

Compression Ignition Engine - Constant Pressure Heat addition

Fuel injection – Spray – Droplet – Vaporisation – Combustion

Significant time to burn fuel


High-speed color imaging of a flame-wall interaction event, captured using Photron SA5 at 20,000 frames per second. Diesel was injected using a single-hole injector. Courtesy the of Advanced Combustion Diagnostics Laboratory, University of new South Wales

20

IC Engines

Typical Diesel Engine –

rv~12-30


21

IC engines

Ideal engine :

• High compression ratio

• Constant volume heat addition

-> Slow Diesel Engines (Marine)

Efficiency <50 % (with turbocharging)

MAN G95ME, 110,000 hp

22

Fuels

Otto Fuels – Light compounds –high volatility (low boiling point), high

Autoignition temperature to prevent knock

Reference fuels

Octane rating - Blend of n-heptane and iso-octane which gives same

knock tendency

n-heptane C7H16: octane number 0

paraffins: single linear

iso-Octane C8H18: octane number 100

isoparaffins: branched chain,

H – C – C – C – C – C – H

H CH3 H CH3 H

H CH3 H H H

H – C – C – C – C – C –C – C – H

H H H H H H H

H H H H H H H

23

Fuels

Diesel fuel – Middle range compounds - Low volatility (high boiling point)

Low Auto-ignition temperature – Large chains

Cetane number – Blend which has same ignition delay

24

Fuels

Diesel fuel – Middle range compounds - Low volatility (high boiling point)

Low Auto-ignition temperature – Large chains

Replaced by heptamethyl nonane

Cetane number – Blend which has same ignition delay

25

Fuels

Property Gasoline Diesel

Research Octane Number 95.4

Cetane number 52

Lower Heating value (MJ/kg) 43.5 43.1

Density (kg/L @ 15°C) 0.738 0.833

Initial boiling point (°C) 28 168

Final boiling point (°C) 198.5 348

Normal paraffins, % vol. 10.8

Iso-Paraffins, % vol. 43.4

Total paraffins, % vol. 54.2 43

Naphtenes, % vol. 2.9 29

Olefins, % vol. 8.6

Aromatics, % vol. 33.6 27

Average Formula C6.64H12.11 C15.4H32.4

Some properties of a

typical gasoline and

Diesel in Europe

Source:

Kalghatgi et al., SAE

Tech. Paper 2005-

01-0239 (2005)

• Paraffins (alkanes) –

Saturated

• Olefins (alkenes) – at

least one double bond

• Naphtenes – Cyclo-

saturated

• Aromatics – Benzene

rings

26

Alternative fuels

Biofuels

1st Generation, from plants grown especially for fuel production (canola,

soya corn, sugar beets, grain)

• Biodiesel, fatty acid methyl esters (FAME), only standardised biofuel

(0.88 kg/L, LHV 37.1 MJ/kg, CN 48-67)

• Bioethanol – from crop fermentation, used blended with gasoline (up to

10 % - improves octane rating)

2nd Generation, from biomass (straw, wood) in Biomass-to-Liquid (e.g. via

Fischer-Tropsch process) – not using feedstock – CN as high as 80

Autogas (LPG)

Propane/Butane blend. RON ~90-110 HHV~28.7 MJ/kg

27

Engine efficiency

• Air cycle efficiency, e.g. Otto

Assumptions

• Fluid is air – Perfect gas, (no changes in Cp, Cv)

• Adiabatic and reversible compression and expansion

• Constant volume heat additions (instantaneous combustion)

• Constant volume heat rejection (instantaneous pressure drop, no work

required to exchange fluid)

• No mass losses

28

Indicated Cycle

• Real gas effects (power stroke) – Thermophysical properties of

evolving mixture of C,CO,CO2,H,OH,H2,H2O,N,NO,NO2,N2,O

• Strongly dependent on Φ – 31 % drop in efficiency at Φ = 1

• Time losses

• Heat losses

• Exhaust blowdown losses

• Indicated efficiency – Efficiency

of Real cycle ηI

• Combustion efficiency, ηC

For 4 strokes engines

p

V

pmax

pu


OO

ICIO

OC

Vd: displaced volume

mf : fuel mass flow rate

Q: fuel heating value

N: rotational speed

29

Brake power

Measured at the flywheel

Pb = bmepVdN

2Prony brakeSource : The New Students Reference work

Include mechanical losses (friction, pumping losses)

Limited by Piston speed Pb = bmepApnVp

4

Specific Power (per unit Area)

Pb

Apn= bmep

Vp

4

Vd = nApS

Specific Power (per displaced volume)

Pb

Vd= bmep

Vp

4S

Vp: piston speed

Ap : piston area

n: number of cylinder

S: stroke ma: air mass flow rate

N:rotational speed F/A: fuel air ratio

30

Air rate and volumetric efficiency

If no pressure drop,

Viscous pressure drop across valve

Sonic velocity at high piston speed

Residual gases (if pe>pi)


31

Design considerations

Volumetric efficiency – Number of valves, Valve timing …

Indicated efficiency – Compression ratio, ceramic coating

Mechanical efficiency – Lower piston speed (smaller Stroke-to-bore ratio),

Ring materials

Inlet density – No throttling (GDI, Diesel), Supercharging/Turbocharging +

Intercooling, Fuel LHV

Two stroke engines

32

Supercharging and Turbocharging

Increases inlet density

Turbo lag, Knock Source : auto.howstuffworks.com

33

Power control

p

V

pu

Vk,OT (V +V)h+k, UT

OO

ICIO

OC

High load: high amount of fuel

Low load: low amount of fuel

Low gas exchange losses

p

V

pu

Vk,OT

OOIO

High load: high inlet density

Low load: low inlet density via

throttling

High gas exchange losses

at low load conditions

IC

OC

Diesel engine Otto engine

(V +V)h+k, UT

34

Emissions

1940s – First smogs in Los Angeles

1953 – Haggen-Smit, Smog caused by reaction of

NOx, UHC and sunlight

1960s – US starts emission standards followed by

Japan and Europe

1970s – TEL ban, use of catalytic converters

CO2: Combustion product - Greenhouse effect

CO: Produced in zones of rich mixture, toxic odorless gas, forms a chemical bond

with hemoglobin of the blood, affects the oxygen supply

HxCy: Produced in zones of too rich/lean mixture, different chemical compounds

depending on the fuel composition, carcinogen

NOx: Is mainly formed at high temperatures because of the rapid energy

conversion (less time for equilibrium condition), very toxic

Soot: Produced in zones of rich mixture, carbon in combination with accumulated

toxic HC (aromatics)

SO2: Caused by the sulfur in the fuel, in combination with water sulfurous acid is

produced known as acid rain, Therefore low sulfur and sulfur free fuel has been

adopted at the EU

LA, 1943 (UCLA archives)

35

Exhaust after treatment, 3-way catalytic converter

Co

nve

rsio

n r

ate

[%

]

Air/fuel ratio [-]

Emissions

Requires tight control on

equivalence ratio

36

Otto Engine fuel metering

Fuel and air mixed in

intake manifold.

Carburetor

Venturi effect to deliver fuel

Utilises charge cooling

Port Fuel injection

Mass flow sensor

Solenoid valve control fuel

mass flow

Tighter control on Φ

(combined with lambda

sensors)

Source :

https://en.wikipedia.org/wiki/

Carburetor

37

SI Engine Performance

Source : J. Heywood, Internal

Combustion Engine fundamentals,

McGraw-Hill

Gross indicated, Brake and Friction

Power and effective mean

pressure

Indicated and brake fuel

consumption, mechanical efficiency

Full throttle 3.8 L SI Engine (Compression ratio 8.6)

38

Diesel Engine performance

Gross indicated, brake power (Pi,

Pb) and effective mean pressure

(imep,bmep), and indicated and

brake specific fuel consumption

Full throttle 8.4 L Direct Ignition

Diesel Engine (Compression ratio 16)

Source : J. Heywood, Internal

Combustion Engine fundamentals,

McGraw-Hill

39

Traditional comparison of Otto and Diesel power train

systems

Otto (manifold injection)

• high power density

• simple exhaust after treatment

• (3-way catalytic converter)

• lower noise level

Diesel

• lower fuel consumption

• high torque

• easy application for turbo

charging

• low raw emissions (HC,

CO, CO2), but high amount

of particles & NOx

Otto and Diesel Engines

40

Challenges on vehicle development

Consumption

improvement

Internal methods (combustion chamber,

injection system, process improvement ..)

Improvement of the power train

(gear box, differential gear..)

Vehicle specific improvements

(weight, rolling drag, air drag ..)

Emission reduction

In addition: exhaust after treatment

(3-way catalytic converter, oxidation

catalytic converter, NOx storage catalytic

converter, filter systems ..)

Internal methods (combustion chamber,

injection system, process improvement ..)

41

Goal conflict • The desire of the customer (air condition, diagnostic

systems, electronic assisting systems ..)

• The need for higher passive safety (airbags, deformable

zones, crash stability ..)

Consequences Increasing vehicle weight

More energy consumers in the car

Increasing fuel consumption & emissions

More powerful engines


42

weight empty:

Individual measures to save 1l / 100km in fuel consumption

(Basis: 2,0 L Gasoline(Otto) / Diesel-engine; VW Golf)

Fuel consumption

NEDC [l/100km]


Otto Diesel

Fuel consumption

NEDC (l/100 km)

7,28 6,28 5,64 4,64

Empty weight 1424 860 kg ~ 40% 1445 820 kg ~ 43%

Air drag x Area 0,68 0,15 kg ~ 78% 0,68 0 kg ~ 100%

Friction coefficient 0,0100 0,0003 kg ~

66%

0,0108 0,0003 kg ~

97%

43

Stage Year CO HC+NOx HC NOx PM PM

g/km #/km

DIE

SE

L

Euro 1 1992 2.72 0.97 - 0.14 -

Euro 2 1996 1 0.7 - - 0.08 -

Euro 3 2000 0.64 0.56 - 0.50 0.05 -

Euro 4 2005 0.50 0.3 - 0.25 0.025 -

Euro 5 2009 0.50 0.23 0.18 0.005 6.0 1011

Euro 6 2014 0.50 0.17 0.08 0.005 6.0 1011

GA

SO

LIN

E

Euro 1 1992 2.72 0.97 -

Euro 2 1997 2.2 0.5 -

Euro 3 2000 2.3 0.20 0.15 - -

Euro 4 2005 1.0 0.10 0.08 -

Euro 5 2009 1.0 0.06 0.005*

Euro 6 2015 1.0 0.10 0.06 0.005* 6.0 1011*

European Emission standards

*GDI Engines only

44

State-of-the-art:

• 4-valve-technology: good volumetric

efficiency

• Central spark plug location: short flame

path

• 3-way catalytic converter and =1-concept:

good emissions values in stationary

operation

• Simple injection system with a high

development status

Conventional Otto engine with MPI

Development strategies

45

Optimization possibilities for the Otto engine

• Controlled intake manifold

• Supercharging & „downsizing“

• Exhaust gas recirculation

• Cylinder shut-off

• Optimization of injection and ignition

• Lean-mix engine

• Variable valve control (timing and lift)

• Gasoline direct injection (GDI)


46

Variable valve control

Indicator diagram schematically for:

throttling early inlet closing late inlet closing

V

pu


OO

IC

IO

OC

p

V

pu


ICIO

OC

OO

p

Variable valve timing

47

Operation mode of „Valvetronic“ von BMW:

1...Inlet valve

2...Camshaft

3…Eccentric shaft

4...Lever

5…servo motor

1

5

4

3

2

Variable valve lift

48

Stratified Charge concept

Gasoline Direct Injection - GDI

High load – Premixed Low load – Lean stratified

49

Gasoline Direct Injection

Potentials of gasoline direct injection (GDI)

• Higher effective and geometric compression ratio, because of internal

mixture vaporization cooling (minor knocking affinity at high loads)

• No wall wetting in the manifold

» improves the emission level at cold start and warm up conditions

» Improves the transient behaviour

• Reduction of throttling-, heat- and exhaust gas losses by using the

stratified operation

Potential in improving the fuel economy is about 15-20 %

50

Gasoline Direct Injection

Disadvantages of the gasoline direct injection engine

• Short time for mixture formation

• High amount of parameters, complex development of the operation and

combustion processes

• Stable operation over a wide range of the engine map demands a great deal on

the injection system and the electronics for controlling (EGR, injection,

ignition..)

• Wall wetting at the cylinder and the piston

• High amount HC-, Soot- und NOx- raw emissions

• 3-way exhaust catalytic converter not usable at stratified operation

• Special requirements on fuel and lubricant

• Increased energy demand (high pressure injection system, ignition system)

• Engine noise, costs

51

State-of-the-art:

• High pressure injection system (CR or unit-

injection)

• Exhaust gas turbo charger

• Exhaust gas recirculation

• Low fuel consumption

Diesel DI engine


52

Diesel engine emissions

Soot are formed in fuel

rich regions and then

oxidised

NOx are formed in hot

near stochiometric zones

53

Exhaust gas recirculation

EGR decreases peak

temperature by diluting

with inert gases

Compromise between

low peak temperature

and completeness of the

reactions

54

Difficulties realizing a Diesel engine with less emissions:Conflictive relation between NOX- / soot formation and consumption

Partic

les

[g/k

m]

NOx + HC / NOx [g/km]

0,3 / 0,25

0,025

0,05

0,08

0,19

0,56 / 0,50 0,9 / -- 0,97 / --

EURO II

EURO I Basis EURO I: 2,27(1992)

CO [g/km]

EURO IV: 0,50(2005)

EURO II: 1,00(1996)

EURO III: 0,64(2000)

Soot filter

DeNOx - Kat

DI technology4 valve technology-improvement

Development strategy Diesel Engine

55

Engine downsizing

Higher inlet density via turbocharging and supercharging

Smaller swept volume means :

• Less heat losses

• Less friction

• Less mass moved

Technologies :

• Waste gate (high rpm)

• Variable geometry

56

Main components of a conventional SI engine (VW, 1,4l)

Oil pump

Oil filter

Fly wheel

Cylinder head

Inlet valve

Valve spring

Cam shaft

Intake manifold

Piston

Bucket tappet

Combustion chamber

Connecting rod

Mass balance weight

Crank shaft

Exhaust manifold

Water pump

Injection valve

Construction

Date post:	18-Mar-2022
Category:	Documents
Upload:	others
View:	4 times
Download:	0 times

Industrial energy management Reciprocating engines

Documents