Post on 21-Jan-2016
description
Combustion• Detonacion• Pre-ignicion• Teoria Pobre
Detonation and Detonation and PreignitionPreignition
Objectivos de esta Seccion
• Entender la importancia de detectar con anticipacion la detonacion y pre-ignicion
• Enlistar las causas de la detonacion y pre-ignicion
• Entender como eliminar detonacion and pre-ignicion
Ka KnockKnock
Ka Knock
Knock
Knock
Ka Ping
Bang Bang
Knock
WAUKESHAWAUKESHA
Early damage on piston crown edge is common.
Advanced damage
Aluminum depositson the cylinder wall
Damage in the ring groove area
Total piston seizure
Aluminum depositsfrom 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 OfFlame Travel
Flame Front Propagation
DetonationDetonation
NormalNormal
TDC TDC
Detonations pinging sound is caused by
pressure waves forcing the cylinder walls to
vibrate
OCTANE NUMBER
A FUEL STABILITY RATING
A MEASURE OF A FUEL’S ABILITY TO RESIST DETONATION
NO LONGER USED BY WAUKESHA
WAUKESHA KNOCK INDEX
Values • 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 anengine’s potential power
output
Why?
Effect Of Operating ConditionsOn 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
Pre
ssu
reP
ress
ure
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 temperature increases
A .060” (1.52 mm) deposit can raise the compression by 1/4 of a ratio
DepositsDeposits
Pressure Higher combustionchamber pressurestend to increasedetonation tendencies
Increased temperature of the combustion chambercan increase detonation tendencies
HEAT
• Jacket Water • Air Induction
Hot generator air discharge
Air intake
Engine Speed
WK
I R
equ
irem
ent
140
130
120
110
100
90
80Low High
Effect of Back Pressureon Detonation
CombustionTemperature
CompressionTemperature
…decreases detonation tendencies
Rising intake air humidity…
Air/Fuel RatioRich Lean
Temp
16.09:1
Exhaust
WKI Number Requirements
Eng
ine
Load
HeatHeatPressurePressure
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 SummaryDetonation Promoters Detonation Reducers
Higher Cylinder Temps Lower Cylinder TempsLower WKI® Fuels Higher WKI® FuelsMore Advanced Timing Less Advanced TimingHigher Compression Ratio Lower Compression RatioHigher Inlet Pressure Lower Inlet PressureHigher Coolant Temp Lower Coolant TempLower Engine Speeds Higher Engine SpeedsLower Humidity Higher HumidityHigher Engine Load Lower Engine LoadStoichiometric 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 Combustion Theory
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 on humidity 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
OH
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
OO
O
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 promote
photochemical 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 photochemical
smog- Yellowish brown in color (Haze)- Chemical designation: NO2
Regulated Gases Found in the Atmosphere
N
ON
O
Regulated Gases Found in the Atmosphere
Formaldehyde
- Higher levels produced in GL engines (0.2-0.3 GL, 0.05 GSI g/BHP-hr)
- Considered toxic and restricted by government agencies
- Chemical designation: CH2O
OO
HC
Toxic Gas Which May Be Regulated
OS
O
Sulfur Dioxide
- Occurs in combustion when gas contains H2S- 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(Nitrogen Dioxide)
Ultra-violet light
NO2
O
NO
OO
O
Formation of Ozone
(Atomic Oxygen)
(Oxygen)
O O
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
OONN
NN
CH
HH
H
CH
HH
H
OO
OO
Stoichiometric Combustion
OO
NN
NN
C
H
C
O
Stoichiometric Exhaust
OOH
H
OH
HO
H H
OH
OO
OONN
NNC
H
HH
H
OO
Rich Combustion
CH
HH
H
CH
HH
H
NN
NN
HO
Rich Exhaust
H
H
OH
HO
HH
OH
CH
HH
H
OC
OC
Cooler Flame
OO
OONN
NN
CH
HH
H OO
OO
OO
Lean Combustion
OO N NN
C
Lean Exhaust
H
OH
HO
HO
NOOO
OO
Cooler Flame
NOx ProductionTemperature vs. Oxygen
Max NOx
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
EmissionsNOx, CO, & HC
CO
HC
NOX
% CO & NOX
AIR /FUEL RATIO
%HC
GL Emissions vs. Ignition Timing
NOX
CO
NMHC
G/BHP/HR
IGNITION TIMING (BTDC)
GL Operating Window
Too rich
AFR
Too lean
AFR
Timing Advance
Timing Retard
• High CombustionTemperature
• Detonation
• Power Loss
• Misfire
• Elevated emissions• Detonation
• Elevated BSFC
EmissionsNOx, CO, & HC
NOX
HCCO
%HC%CO & NOX
AIR / FUEL RATIO
Emission LevelsSeries II VHP
AFR 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