Motores CI reciprocantes - Combustion

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Combustion• Detonacion

• Pre-ignicion•

Teoria Pobre



Detonation andPreignition



Objectivos de esta Seccion

• Entender la importancia de detectar

con anticipacion la detonacion y pre-

ignicion

•Enlistar las causas de la detonaciony pre-ignicion

• Entender como eliminar detonacion

and pre-ignicion



Ka KnockKnock

Ka Knock

Knock

Knock

Ka Ping

Bang Bang

Knock

WAUKESHA



Early damage on piston crown edge is common.



Advanced damage



Aluminum deposits

on the cylinder wall



Damage in the ring groove area



Total piston seizure





Aluminum deposits

from the piston



DetonationAuto Ignition of the End Gas

The End Gas is the air fuel mixture inside the

combustion chamber that is ahead

of the normal flame front.



Cylinder Wall

Direction Of

Flame Travel



Flame Front Propagation



Detonation

Normal

TDC TDC



Detonations pinging

sound is caused bypressure waves forcing

the cylinder walls tovibrate



OCTANE NUMBER

A FUEL STABILITY RATING

A MEASURE OF A FUEL’S ABILITY TORESIST DETONATION

NO LONGER USED BYWAUKESHA



WAUKESHA

KNOCK INDEXValues

•

Pure Methane 100• Digester 125

• Landfill 140

• Processed Natural Gas 90

• Propane 34



WKI Number

Btu

When a fuel’s Btu rises the Waukesha

Knock Index Number drops





Detonation affects an

engine’s potential power output

Why?



Effect Of Operating Conditions

On Detonation

• Spark Timing• Compression Ratio

• Inlet Fuel / Air Temperature

• Coolant Temperature

• Waukesha Knock Index® Number

• Engine Speed

• Exhaust Back Pressure

•

Atmospheric Humidity• Combustion Chamber Deposits

• Fuel Air Ratio

• Engine Load



60° 50° 40° 30° 20° 10°

Degrees before TDC

P r e s s u

r e

Ignition Timing



Compression Ratio

Detonation

tendencies increase

with the rising

compression ratio

11:1

10.5:1

10:1

9.4:1

8.2:1

8:1

7:1

Final compression

gas temperatureincreases



A .060” (1.52 mm) depositcan raise the compression

by 1/4 of a ratioDeposits



Pressure Higher combustion

chamber pressurestend to increase

detonation tendencies



Increased

temperature of the

combustion chamber

can increase detonation

tendencies

HEAT

•

Jacket Water • Air Induction



Hot generator

air discharge

Air intake



Engine Speed

W K I R e q

u i r e m e n t

140

130

120

110

100

90

80Low High



Effect of Back Pressure

on Detonation

Combustion

Temperature Compression

Temperature



…decreases

detonation

tendencies

Rising intake air

humidity…



Air/Fuel RatioRich Lean

Temp

16.09:1

Exhaust



WKI Number Requirements

E n g i n e

L o a d Heat

Pressure

LOW

HIGH

HIGH



Engine design factors

can influence an engine’s tendency to detonate

• Spark plug location• Combustion chamber shape

• Piston head shape

• Cylinder head size



Detonation Summary

Detonation Promoters Detonation Reducers

Higher Cylinder Temps Lower Cylinder Temps

Lower WKI ® Fuels Higher WKI® Fuels

More Advanced Timing Less Advanced TimingHigher Compression Ratio Lower Compression Ratio

Higher Inlet Pressure Lower Inlet Pressure

Higher Coolant Temp Lower Coolant Temp

Lower Engine Speeds Higher Engine Speeds

Lower Humidity Higher Humidity

Higher Engine Load Lower Engine Load

Stoichiometric A/F ratio Lean or Rich A/F ratio



PreignitionIgnition before the timed spark



Preignition Promoters

• Incandescent cylinder deposits

• Spark plug with incorrect heat

range

• Burning valve

• Overheated piston crown





Detonation - Preignition

Preignition - Detonation



Lean CombustionTheory



OOxygen

- 20.9% of atmosphere- Naturally found as 2

atoms

- Chemical designation: O2

Nitrogen

- 78% of atmosphere- An inert gas- Naturally found as 2

atoms

- Chemical designation: N2

Major Components in the Atmosphere(98.9%)

O

NN



Water

- Concentration depends onhumidity and temperature

- Chemical designation: H20

Carbon Dioxide- Makes up 0.034% of

atmosphere- By-product of combustion- Major contributor to

greenhouse effect- Chemical designation: CO2

Trace Compounds in the Atmosphere

O

H

H

O

OC



Ozone - Bluish, pungent gas- Formed by ultraviolet light

- Formed in upper atmosphere- By-product of photochemical- Chemical designation: O3

Regulated Compounds in the

Atmosphere

O O

O

R l d G F d i h



CH H

OC

Hydrocarbons:- Methane not included as toxic- Pollutant emitted by engines- Fuel in photochemical smog

- Chemical designation: NMHC

Carbon Monoxide:- Colorless and odorless

- Extremely toxic- Believed to promotephotochemical smog

- Chemical designation: CO

Regulated Gases Found in the

Atmosphere

H H

(Methane)



ONitric Oxide

- emitted by the engine- Oxidizes quickly to nitrogen

dioxide- Chemical designation: NO

Nitrogen dioxide

- The catalyst in photochemicalsmog

- Yellowish brown in color (Haze)- Chemical designation: NO2

Regulated Gases Found in theAtmosphere

N

ON

O



Regulated Gases Found in

the Atmosphere

Formaldehyde

- Higher levels produced in GLengines (0.2-0.3 GL, 0.05 GSI g/BHP-hr)

- Considered toxic and restricted by

government agencies- Chemical designation: CH2O

OO

H

C



Toxic Gas Which May Be Regulated

OS

OSulfur Dioxide

- Occurs in combustion when gascontains H

2S

- Heavy, pungent, colorless gas- Can form sulfuric acid- Chemical designation: SO2



Two Types of Smog:

Particulate Smog (Cold wet days)Photo-chemical Smog (Hot dry days)



NO O(Nitric Oxide)(Atomic Oxygen)

NO2(NitrogenDioxide)

Ultra-violetlight

NO2

O

NO



OO

O

Formation of Ozone

(Atomic Oxygen)

(Oxygen)

OO

O (Ozone)



NO2

NO

O

O2

O3OzoneMain

ToxicantPhotochemic

al Smog

HC

HCO

HCNO2



Stoichiometric Combustion

Chemically Ideal Combustion

CH4 + 202 + 2N2 CO2 + 2H20 + 2N2Combustion



OO

OON

N

N

NC

H

HH

H

CH

HH

H

OO

O

O

Stoichiometric Combustion



OO

NN

N

NC

H

C

O

Stoichiometric Exhaust

OO

H

H

O

H

HO

H H

OH



OO

OO

N

N

N

NC

H

HH

H

O

O

Rich Combustion

CH

HH

H

C H

HH

H



NN

N

N

HO

Rich Exhaust

H

H

O

H

HO

H

H

OH

CH

HH

H

OC

OC

Cooler Flame



OO

OON

N

N

NC

H

HH

H OO

O

O

OO

Lean Combustion



OO

N N

NC

Lean Exhaust

H

O

H

HO

H

ON

OOO

OO

Cooler Flame

NOx Production



NOx ProductionTemperature vs. Oxygen

MaxNOx

oF

EXHAUST O2

oC

807

670

642

615

587

559

53214 15 16 17 18 19 20

1000

1050

1100

1150

1200

1250

1300

0

1

2

3

4

5

AIR / FUEL RATIO

02 %

EXHAUST TEMP

Emissions



EmissionsNOx, CO, & HC

CO

HC

NOX

% CO & NOX

AIR /FUEL RATIO

%HC

GL Emissions vs Ignition Timing



GL Emissions vs. Ignition Timing

NOX

CO

NMHC

G/BHP/HR

IGNITION TIMING (BTDC)

GL O ti Wi d



GL Operating Window

Too

rich

AFR

Toolean

AFR

Timing Advance

Timing Retard

•

HighCombustionTemperature

• Detonation

• Power Loss

• Misfire

• Elevated emissions

• Detonation

• Elevated BSFC

Emissions



EmissionsNOx, CO, & HC

NOX

HCCO

%HC%CO &NOX

AIR / FUEL RATIO



Emission Levels

Series II VHPAFR NOx NMHC CO

Best Power (G/GSI engine out)

8.5 0.35 32

Best

Economy(G/GSI engine out)

22 0.25 1.5

Catalyst(G/GSI exhaust out)

0.15 0.15 0.6

GL(G/GSI engine out)

1.5 1 2.65

Grams /BHP-hr





Date post:	08-Aug-2018
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Motores CI reciprocantes - Combustion

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