POLITECNICO DI TORINO - ENERGY DEPARTMENT
Federico Millo, Luciano Rolando
1st GTI Italian User Conference
March 18th , 2013 – Turin
Analysis of knocking phenomena in a high performance
engine
POLITECNICO DI TORINO - ENERGY DEPARTMENT
OUTLINE
2
• Introduction
• Experimental setup
• Results & discussion
• Conclusions
POLITECNICO DI TORINO - ENERGY DEPARTMENT
130 g/km CO2
Fleet standards 2015
Proposed fleet standards 2020 95 g/km CO2
Introduction
The main downsizing driver: CO2 reduction targets
130 g/km by 2015 95 g/km by 2020
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Technologies for improving fuel economy of gasoline engines:
– Downsizing + Turbocharging
– Gasoline Direct Injection (GDI)
– Variable Valve Actuation (VVA)
– Electrification and Hybridization
– …..
Introduction
POLITECNICO DI TORINO - ENERGY DEPARTMENT
B
ME
P
Specific Brake Power [kW/dm3]
Introduction
BMEP vs. Specific Brake Power European Gasoline Engines 2009
Source: Indagine sui principali parametri prestazionali nei motori ad accensione comandata autoveicolistici di attuale produzione,
P. Paniccia, BSc Thesis, Politecnico di Torino, 2010
25 bar bmep
100 kW/ltr
POLITECNICO DI TORINO - ENERGY DEPARTMENT
The use of GDI in turbocharged engines allows a reduction of the octane request, thus permitting to increase
compression ratio, boost level, spark timing: significant performance improvements can thus be achieved, allowing
an effective engine downsizing.
However the low end torque of a turbocharged engine is usually limited by compressor surge.
The use of GDI, combined with VVT, allows a cylinder “scavenging” effect, with significant improvements in the
low-end torque performance.
SURGE
CHOKING
OVERSPEED
Introduction
Scavenging
(Source: Andriesse et al. The New 1.8 ltr DI Turbo-Jet Gasoline Engine from FPT,17. Aachener Kolloquium Fahrzeug und Motorentechnik, 2008)
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Introduction
Knock
However, although the achievement of high boost levels at low engine speed definitely improves
engine low end torque performance, the likelihood of engine knock increases dramatically.
Furthermore, the risk of pre-ignition or mega knock, with pressure peaks reaching or exceeding 200
bars, is also significantly increased, due to the high power density.
Therefore, reliable knock predictive models are necessary to support the design and calibration
activities of new turbocharged high performance engines.
0
50
100
150
200
250
330 360 390
Mega knock: Immediate effects
causing damages to spark plug,
rings, piston.
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Introduction
• Increase in the complexity of calibration of GDI turbocharged engines • Increase in the number of calibration parameters:
• Lambda
• Boost level
• Spark Advance
• Intake Valve Opening
• Exhaust Valve Opening
• Traditional “one parameter at a time” calibration approach unsuitable
• Interactions between calibration and design parameters choices (eg. between boost and compression ratio)
• Possibilities offered by the continuous development of CAE tools to carry out the system optimization on a “virtual test bench”
POLITECNICO DI TORINO - ENERGY DEPARTMENT
OUTLINE
9
• Introduction
• Experimental setup
• Results & discussion
• Conclusions
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Experimental Setup Engine: FIAT T-Jet family
10
Racing Engine N° of cylinder 4 – In line Displacement 1368 cm3 Bore 72 mm Stroke 84 mm Injection System PFI Turbocharger FGT - Garrett GT 1446 Pistons Forged Compression Ratio 9.4 Max Nominal Torque 270 Nm@3000 RPM Max Nominal Power 180 CV@ 5750 RPM
Production Engine N° of cylinder 4 – In line Displacement 1368 cm3 Bore 72 mm Stroke 84 mm Injection System PFI Turbocharger IHI RHF3 Pistons Forged Compression Ratio 9.8 Max Nominal Torque 230 Nm@3000 RPM Max Nominal Power 150 CV@ 5750 RPM
POLITECNICO DI TORINO - ENERGY DEPARTMENT
4 Sensorized Spark Plugs: Kistler 6115
Accelerometer: Bosch 0261231148
Additional Sensors: • 4 Thermocouples (k-series) in the intake runners,
• 1 Lambda sensor mounted downstream of the turbine
• Turbocharger speed
Experimental Setup
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Test Matrix
12
• Engine Speed: 2500 - 3000 - 3500 - 4000 - 5000 - 6000 [rpm]
• Relative A/F Ratio: 0.7 – 0.8 – 0.9 [-]
• Boost Pressure: 2000 – 2200 – 2400 [mbar]
For each operating conditions 3 different spark advance settings were tested :
• Knock Limited Spark Advance (KLSA),
• KLSA +2,
• KLSA -2
For each op.cond. and spark timing 200 consecutive engine cycles were acquired
0
0.5
1
1.5
2
2.5
3
1012141618202224
0 2 4 6 8 10 12 14 16
ID/I
Dm
[-]
BM
EP [
bar
]
Spark Advance [°]
Spark Advance
2000 3000 4000 5000 6000 2000
2200
2400
0.7
0.8
0.9
Rela
tive A
/F [-]
Engine Speed [RPM]
Boost Pressure [mbar]
Norm
Knock
intensity
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Test Matrix
13
Additional tests were carried out evaluating the effects of:
• Different Gasoline:
Racing Gasoline
Composition [% m/m] Carbon: 83.72 % Hydrogen: 13% Oxygen: 3.28%
Lower Heating Value [MJ/kg] 41.41
Octan Number [R.O.N.] 102
Density [kg/m3] 758.4
Unleaded Gasoline
Composition [% m/m] Carbon: 86.45 % Hydrogen: 13.55%
Lower Heating Value [MJ/kg] 44.47
Octan Number [R.O.N.] 95.7
Density [kg/m3] 724.6
• Temperature of the intake manifold downstream of intercooler:
• T1 = 44° C
• T2 = 55° C
POLITECNICO DI TORINO - ENERGY DEPARTMENT
OUTLINE
14
• Introduction
• Experimental setup
• Results & discussion
• Conclusions
POLITECNICO DI TORINO - ENERGY DEPARTMENT
• Knocking phenomena were analyzed by means of the Three Pressures Analysis (TPA).
• The TPA represents a simulation based methodology to analyze experimental data and to
determine quantities that are difficult or impossible to measure directly, such as:
• Apparent burn rate
• Residual fraction
• Trapping ratio
• Valve mass flow profiles
• Focuses on a cylinder, cuts-off rest of system
• Replacing it by measured port pressures
• Input exp. cylinder pressure to get comb. rate
• Valid only for steady state operating points
• Single cylinder model (typically)
• Provides as output combustion and knock metrics such as, for instance:
• Crank angle at knock onset
• Unburned mass fraction at knock onset, etc.
Three Pressure Analysis (TPA)
15
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Band pass filtered
pressure MAPO
Maximum
Amplitude
Pressure
Oscillation
Knock metrics
In cylinder pressure
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Chun, Heywood, SAE-890156 Borg, Alkidas, SAE-2008-01-1088
Unburned Mass % at Knock Onset
MA
PO
(a
tm)
Unburned Mass Fraction
at Knock Onset
MA
PO
(b
ar)
MA
PO
(b
ar)
Unburned Mass Fraction
at Knock Onset
No correlation was initially found between
knock intensity and unburned mass fraction at
knock onset, in good agreement with
literature data.
Lack of correlation could be due to incorrect
knock metrics ?
Chun, Heywood, SAE-890156 Borg, Alkidas, SAE-2008-01-1088
Knock metrics: why use also engine
block vibration signal ?
POLITECNICO DI TORINO - ENERGY DEPARTMENT
fm,n [kHz] f1.0 f2.0 f0.1 f3.0 f4.0
theoretical 8.1 13.5 16.9 18.6 23.5
Knock free
Test results
Incipient
Knock
Light Knock
Heavy
Knock
Medium-
Heavy
Knock
Knock free Incipient
Knock
Light Knock
Medium
Knock
Heavy
Knock
Knock metrics: why use also engine block vibration signal ?
In cylinder pressure frequency spectra
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Knock intensity: block vibration vs. in-cylinder pressure correlation
19
Engine Speed: 2500 RPM
Engine Speed: 5000 RPM
Engine Speed: 3500 RPM
Pboost = 2.2 [bar] - λ = 0.8 [-] – S.A: 4°
After a proper tuning of the bandpass filtering frequencies, a good correlation between block vibration based and in cylinder pressure based knock intensity measurements was found.
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Chun, Heywood, SAE-890156
Unburned Mass % at Knock Onset
MA
PO
(a
tm)
Borg, Alkidas, SAE-2008-01-1088
Unburned Mass Fraction
at Knock Onset
MA
PO
(b
ar)
MA
PO
(b
ar)
Unburned Mass
Fraction at Knock Onset
Knock intensity vs. unburned mass fraction at knock onset
Engine Speed 2500 RPM Engine Speed 5000 RPM
A good correlation between knock intensity and unburned mass fraction at knock onset was also found, differently from data previously reported in literature.
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Test Results – Statistics – Knock intensity thresholds
21
Knock Free - S.A. = 0
Incipient Knock - S.A. = 2
Light Knock - S.A. = 4
Knock threshold
Knock threshold
Knock threshold Knock threshold
Knock threshold
Knock threshold
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Different models available in literature (Douaud&Eyzat, Franzke, Worret) have been included in the EngCylKnock object They are generally based on the assumption that end gas autoignition will occur when the condition ∫ dt/ = 1 will be reached (where t is the elapsed time from the start of end-gas compression and τ is the induction time)
- Mass fraction burned
- Induction time integral
- Mass fraction burned
- Induction time integral
Knocking cycle
Knock prediction: phenomenological models
Douaud & Eyzat
- MaMass fraction burned - MaMass fraction burned
Knock Free
cycle
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Knock prediction: phenomenological models
Very good correlation between
prediction of crank angle at knock
onset based on Douaud&Eyzat
model and experimental values was
found.
POLITECNICO DI TORINO - ENERGY DEPARTMENT
Conclusions & Future Work
24
• After a proper tuning of the knock intensity metrics and of the knock
prediction models, a good correlation could be found between experimental
measurements and simulation results, both in terms of knock intensity ad in
terms of knock onset prediction.
• Further investigations will be carried out in order to evaluate the effects of:
• internal EGR
• different fuel properties (e.g. E85)
• mixture inhomogeneity
POLITECNICO DI TORINO - ENERGY DEPARTMENT
The valuable support provided to the research activity by Centro Ricerche
Fiat, Fiat Powertrain Technologies Racing, Kistler Italy and Gamma
Technologies is gratefully acknowledged.
The authors would also like to thank in particular mr. Fabrizio Mirandola
(formerly at FPT racing) for his precious and constant support during the
experimental activities.
AKNOWLEDGMENTS