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DNV GL © 2017
Ungraded
Thursday, April 6, 2017 SAFER, SMARTER, GREENERDNV GL © 2017
Howard Levinsky
Thursday, April 6, 2017
Ungraded
OIL & GAS
An accurate ‘octane number’ for LNG as a transportation fuel
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Sander Gersen, Martijn van Essen, Gerco van Dijk and Howard Levinsky
DNV GL Oil&Gas and University of Groningen, the Netherlands
DNV GL © 2017
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Thursday, April 6, 2017
Acknowledgement
We thank the TKI program of the Dutch government for financial support. We gratefully
acknowledge the participants in this project for their contributions: Shell and ENGIE for financial
support and their input regarding LNG in developing the algorithms, and Wärtsilä and FPT
Industrial for providing data, engine platforms and invaluable advice regarding engine operation.
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DNV GL © 2017
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Thursday, April 6, 2017
LNG as a transportation fuel; Why is composition important?
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DNV GL © 2017
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Thursday, April 6, 2017
LNG as a transportation fuel
LNG growing as transportation fuel
Lower emissions (no sulfur, low NOx, no soot) attractive marine fuel
+ Very low noise emissions: also attractive as truck fuel
Relatively low CO2 emissions compared to other fossil fuels
Abundant supply internationally
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DNV GL © 2017
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Thursday, April 6, 2017
LNG has significant quality variations
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LNG composition varies around the world.
Composition also changes with time due to ‘boil-off’ of lighter components
(N2, CH4)
But the variation in composition is less important than the resulting
variations in properties.
Market for traditional liquid fuels
(gasoline, diesel, HFO, etc.) has
already decided how to characterize
the fitness for purpose for the end
user:
- octane number, cetane number, etc.
Does not yet exist for LNG
DNV GL © 2017
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Thursday, April 6, 2017
The quality of commercially available LNG varies significantly across the globe
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35.0 37.0 39.0 41.0 43.0 45.0
Australia – NWS
Australia – Darwin
Algeria – Skikda
Algeria – Bethioua
Algeria – Arzew
Brunei
Egypt – Idku
Egypt – Damietta
Equatorial Guinea
Indonesia - Arun
Indonesia – Badak
Indonesia –…
Libya
Malaysia
Nigeria
Norway
Oman
Peru
Qatar
Russia – Sakhalin
Trinidad
USA - Alaska
Yemen
Lower calorific value, MJ/m3(n)
17% variation32 point variation in
Methane number
DNV GL © 2017
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Thursday, April 6, 2017
LNG and its compositional variations
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Variations bring differences in things like heating value, but also in knock resistance of
fuel…knock can (seriously) compromise engine performance
Essential for optimum engine performance to match fuel with engines
Need to characterized the knock resistance accurately
DNV GL © 2017
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Thursday, April 6, 2017
Benefits for industry
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Accurate knock prediction benefits:
– allows engine manufacturers to size and tune engines for a given range of LNG compositions
more precisely
– lowers CAPEX and OPEX for engine owner, and improves engine availability and safety
– Fuel suppliers can manage LNG quality more precisely to meet market demands, by
assuring that no LNGs are excluded from the market or overtreated without cause.
Better prediction will thus help the adoption of LNG as a cost-effective, clean and reliable
transportation fuel.
Dedicated knock algorithm for a specific engine type allows incorporation in a control system
to maximize knock-free engine performance for a wide range of fuel compositions.
DNV GL © 2017
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Thursday, April 6, 2017
TKI LNG project
1. Characterize the knock resistance of LNG fuels for three engines, a spark-ignited lean-burn
CHP engine, a dual-fuel engine used in the maritime sector and a stoichiometric truck engine.
2. Quantify possible differences in response to variations in LNG composition.
3. Use results in international discussions regarding standardization, but also for benefit of
individual parties to assess the risk of engine knock for their own engine/fuel combinations.
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DNV GL © 2017
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Thursday, April 6, 2017
Engine types selected for this study
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CHP
E2876LE302
MAN
Marine
W34DF
Wärtsilä
Truck
FPT Cursor 9
Combustion system -mono-gas
-open chamber
-lean burn
-spark ignited
-dual fuel
-pilot injection
-ultra lean burn
- mono-gas
- open chamber
- stoichiometric burn
- spark ignited
Rated power 200kW
(6 cylinders)
3MW
(6 cylinders)
280 kW
(6 cylinders, in line)
CR 11 12 12
rpm 1500 750 600-2400
Bore*Stroke 128*166 340*400 117*135
Air factor 1.55 2 1
Intake manifold
pressure
2.07 3.5 -
BMEP 13 bar 22 bar 24 bar
DNV GL © 2017
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Thursday, April 6, 2017
Recalling engine knock
Normal combustion vs. knocking combustion
Normal combustion end gas is consumed by propagating
flame front
t combustion < t autoignition
End gas
Unburned mixture
Burned mixture
Spark plug
Far end of combustion chamber
autoignition reactions in end gas
DNV GL © 2017
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Thursday, April 6, 2017
Recalling engine knock
Knock is autoignition of end gas
competition between propagating flame front and autoignition reactions in end gas
Impacted by changes in fuel composition
autoignition chemistry, burn rate and heat capacity
Normal combustion vs. knocking combustion
Knocking combustion end gas spontaneously ignites
t autoignition < t combustion
End gas
Unburned mixture
Spark plug
Far end of combustion chamber
autoignition reactions in end gas
autoignition
Burned mixture
DNV GL © 2017
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Thursday, April 6, 2017
Engine Knock model
DNV GL approach: understanding and describing
(changes) in end-gas autoignition process with varying fuel
gas composition
– based on combustion properties rather than purely on
empirical methods
– calculate end-gas autoignition during burn cycle with
varying conditions rank fuels for knock
– Incorporates changes in:
– autoignition chemistry (>2000 reactions/300 species)
– Burn rate (computed SL), and
– thermophysical properties (heat capacity)
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DNV GL © 2017
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Thursday, April 6, 2017
Ignition chemistry: verify/alter using RCM autoignition studies
Rapid Compression Machine
- test and optimize chemical mechanism used in knock model
- revealing ‘rules’ on autoignition behavior
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50
Pre
ssure
(b
ar)
Time (ms)
Measured and computed RCM pressure traces
Measurement
Simulation
Mechanical compression
Autoignition delay time
Compressionend pressure
Autoignition event
Pure fuelsCH4, C2H6, n-C4H10, i-C4H10 and H2
Binary mixtures of CH4 with...
...C2H6, C3H8, n-C4H10, i-C4H10, n-C5H12, i-C5H12, neo-C5H12, H2, CO, N2 and CO2
Ternary mixtures of CH4
with......H2 and CO
Pipeline fuels Dutch natural gas
The building blocks of the model are supported by a stringent testing program, verified with experimental data
DNV GL © 2017
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Thursday, April 6, 2017
Verify model predictions: phasing and knock measurements (KLST) in CHP engine
Make - type MAN - E2876LE302
Rated powerRated speed
208 kW1500 rpm
Bore x strokeC.R.
128 x 166 mm11 : 1
Configuration
6 cyl. in-line, turbocharged-intercooled
Combustion spark ignition, open chamber, lean-burn
Gas composition
- on-stream adjustment- flow-independent- verification w. gas chromatography
Source gas streams
- max. 6- calibrated for Dutch natural gas/CH4, C3H8, H2, CO, CO2, N2, but other
fuels possible
- flow range 150 to 400 m3s/h
p/stream
engine blending station
DNV GL © 2017
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Thursday, April 6, 2017
How well can the traditional tools predict engine knock? (SAE Int. J. Fuels Lubr. 9(1):2016)
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For same MN, cannot distinguish KLST of ±2°CA, constant KLST spread ~14-15 points
Spread is far outside the experimental uncertainty
DNV GL © 2017
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Thursday, April 6, 2017
Sharper scalpel: DNV GL method (SAE Int. J. Fuels Lubr. 9(1):2016)
Simulate burn cycle, under conditions w/wo knock, verify
using engine measurements.
Use methane/propane scale to rank gases for knock
(Propane Knock Index, PKI) and convert to 0-100 MN scale.
Easy-to-use computational algorithm (digital product)
Compare with measurements in engine
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Set to 90% burn by increasing initial temperature in simulations for test fuel and compute propane equivalent under same conditions.
0
20
40
60
80
100
120
5 7 9 11 13 15 17 19
Pre
ssu
re, b
ar
Crank angle timing, ms
Measured
Simulation (non-knocking)
Simulation (knocking)
Autoignitiondelay time
Fixed referencetiming
DNV GL © 2017
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Thursday, April 6, 2017
Results: KLST vs. PKI Methane Number (SAE Int. J. Fuels Lubr. 9(1):2016)
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Results are within experimental uncertainty, much better
characterization of impact of fuel composition on knock.
Not only for alkanes, but also for renewable components,
H2, CO and CO2
DNV GL © 2017
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Thursday, April 6, 2017
Other engine platforms?
The analysis of the physics and chemistry
related to engine knock shows that the
different platforms can be grouped based on
combustion behavior
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Dual fuel engine
Spark ignited engine
Autoignition calculations (P=120bar, =2)
Crossing lines indicates that ranking of fuels can depend on engine conditions
DNV GL © 2017
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Thursday, April 6, 2017
Properties Dual-Fuel engine
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CHP
E2876LE302
MAN
Marine
W34DF
Wärtsilä
Truck
FPT Cursor 9
Combustion system -mono-gas
-open chamber
-lean burn
-spark ignited
-dual fuel
-pilot injection
-ultra lean burn
- mono-gas
- open chamber
- stoichiometric burn
- spark ignited
Rated power 200kW
(6 cylinders)
3MW
(6 cylinders)
280 kW
(6 cylinders, in line)
CR 11 12 12
rpm 1500 750 600-2400
Bore*Stroke 128*166 340*400 117*135
Air factor 1.55 2 1
Intake manifold
pressure
2.07 3.5 -
BMEP 13 bar 22 bar 24 bar
DNV GL © 2017
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Thursday, April 6, 2017
Modeling burn rates: variable ignition timing for diesel pilot
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Determination of ignition timing:
Autoignition Diesel at 167 CA
for basis LNG (derived from
measured heat release profile)
Temperature and pressure at 167
CA is 788K and 58bar
Simulation of LNG + 10%
propane at 167 CA ignition
Peak pressure too high and too
early
Simulation of LNG + 10%
propane at 788 K
Heat capacity of LNG/air
mixture impacts ignition
timing and phasing
DNV GL © 2017
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Thursday, April 6, 2017
Differences in knock behavior between engine types
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PKI MN is roughly 6 points higher for the dual-fuel engine at 14.5% ethane in methane than for the spark-ignited engine
Maximum difference in methane number found between the spark-ignited and diesel-pilot engine for these LNG composition is 4.5 MN points
DNV GL © 2017
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Thursday, April 6, 2017
Can we neglect pentanes?
Simulate compositions with varying fractions of pentane
isomers in spark-ignited engine.
1% n-pentane decreases MN by 20 points
0.15% pentane (as seen in some GIIGNL data) gives
difference of 2.5 MN points…too large to neglect.
Therefore, included in the algorithm.
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DNV GL © 2017
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Thursday, April 6, 2017
Outlook 2017
Significant differences in ranked knock resistance between spark-ignited and diesel-pilot engines;
both lean burn. What about different stoichiometry? Examine stoichiometric truck engine.
Truck engine (FPT Cursor 9) :
– Truck engine tests with a different fuel compositions (phasing and knock experiments)
– Modeling Truck engine
– Development dedicated PKI MN algorithm truck engine
Compare the results for the different engine platforms for a wide variety of LNG compositions, to
quantify the possible differences in ranking of fuel compositions.
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DNV GL © 2017
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Thursday, April 6, 2017
Conclusions
More accurate characterization of knock resistance: based on changes in physics and chemistry.
within the experimental uncertainty, including the effects of renewable fuels.
Dual-fuel engine gives a different ranking from the spark-ignited engine.
caused by impact different regimes of temperature and pressure on physics and chemistry.
Expect different stoichiometry (truck engine) will also respond differently.
‘simply’ using one method to characterize knock may not be enough.
Results can serve as input for international discussions on standardization, but can also be used to
assess the risk of engine knock for individual engine/fuel combinations.
Propane-based scale allows testing (new) engines using methane-propane mixtures, rather than
complex fuel compositions.
The algorithm(s) can be used for feed-forward fuel-adaptive engine control to optimize engine
performance for a wide range of fuel compositions.
Together with Shell demonstrated 6% improved fuel efficiency in spark-ignited engine
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DNV GL © 2017
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Thursday, April 6, 2017
SAFER, SMARTER, GREENER
www.dnvgl.com
A ‘correct’ octane number for LNG
Technical background of the TKI project
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Howard Levinsky
+31-50-7009739