An accurate octane number for LNG as a transportation fuel

Transcription

1 OIL & GAS An accurate octane number for LNG as a transportation fuel Sander Gersen, Martijn van Essen, Gerco van Dijk and Howard Levinsky DNV GL Oil&Gas and University of Groningen, the Netherlands Howard Levinsky 1 SAFER, SMARTER, GREENER

2 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. 2

3 LNG as a transportation fuel; Why is composition important? 3

4 LNG as a transportation fuel LNG growing as transportation fuel Lower emissions (no sulfur, low NO x, no soot) attractive marine fuel + Very low noise emissions: also attractive as truck fuel Relatively low CO 2 emissions compared to other fossil fuels Abundant supply internationally 4

5 LNG has significant quality variations LNG composition varies around the world. Composition also changes with time due to boil-off of lighter components (N 2, CH 4 ) 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 5

6 The quality of commercially available LNG varies significantly across the globe Yemen USA - Alaska Trinidad Russia Sakhalin Qatar Peru Oman Norway Nigeria Malaysia Libya Indonesia Indonesia Badak Indonesia - Arun Equatorial Guinea Egypt Damietta Egypt Idku Brunei Algeria Arzew Algeria Bethioua Algeria Skikda Australia Darwin Australia NWS point variation in Methane number Lower calorific value, MJ/m 3 (n) 17% variation 6

7 LNG and its compositional variations 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 7

8 Benefits for industry 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. 8

9 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. 9

10 Engine types selected for this study 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 rpm Bore*Stroke 128* * *135 Air factor Intake manifold pressure BMEP 13 bar 22 bar 24 bar 10

11 Recalling engine knock Spark plug Normal combustion vs. knocking combustion End gas Burned mixture Unburned mixture Far end of combustion chamber autoignition reactions in end gas Normal combustion end gas is consumed by propagating flame front t combustion < t autoignition

12 Recalling engine knock Spark plug Normal combustion vs. knocking combustion End gas Burned mixture Unburned mixture Far end of combustion chamber autoignition autoignition reactions in end gas Knocking combustion end gas spontaneously ignites t autoignition < t combustion 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

13 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) 13

14 Pressure (bar) 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 Measured and computed RCM pressure traces Measurement Simulation Compression end pressure Autoignition event Mechanical compression Autoignition delay time Pure fuels Binary mixtures of CH 4 with... Ternary mixtures of CH 4 with... Pipeline fuels CH 4, C 2 H 6, n-c 4 H 10, i-c 4 H 10 and H 2...C 2 H 6, C 3 H 8, n-c 4 H 10, i-c 4 H 10, n- C 5 H 12, i-c 5 H 12, neo-c 5 H 12, H 2, CO, N 2 and CO 2...H 2 and CO Dutch natural gas Time (ms) The building blocks of the model are supported by a stringent testing program, verified with experimental data

15 Verify model predictions: phasing and knock measurements (KLST) in CHP engine engine blending station Make - type MAN - E2876LE302 Rated power Rated speed Bore x stroke C.R. Configurati on 208 kw 1500 rpm 128 x 166 mm 11 : 1 6 cyl. in-line, turbochargedintercooled Combustion spark ignition, open chamber, lean-burn Gas composition Source gas streams - on-stream adjustment - flow-independent - verification w. gas chromatography - max. 6 - calibrated for Dutch natural gas/ch 4, C 3 H 8, H 2, CO, CO 2, N 2, but other fuels possible - flow range 150 to 400 m 3 s/h p/stream

16 How well can the traditional tools predict engine knock? (SAE Int. J. Fuels Lubr. 9(1):2016) For same MN, cannot distinguish KLST of ±2 CA, constant KLST spread ~14-15 points Spread is far outside the experimental uncertainty 16

17 Pressure, bar 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 Measured Simulation (non-knocking) Use methane/propane scale to rank gases for knock (Propane Knock Index, PKI) and convert to MN scale. Easy-to-use computational algorithm (digital product) Simulation (knocking) Compare with measurements in engine 40 Autoignition delay time 20 Fixed reference timing Crank angle timing, ms Set to 90% burn by increasing initial temperature in simulations for test fuel and compute propane equivalent under same conditions. 17

18 Results: KLST vs. PKI Methane Number (SAE Int. J. Fuels Lubr. 9(1):2016) Results are within experimental uncertainty, much better characterization of impact of fuel composition on knock. Not only for alkanes, but also for renewable components, H 2, CO and CO 2 18

19 Other engine platforms? Dual fuel engine The analysis of the physics and chemistry related to engine knock shows that the different platforms can be grouped based on combustion behavior Spark ignited engine Autoignition calculations (P=120bar, =2) Crossing lines indicates that ranking of fuels can depend on engine conditions 19

20 Modeling results Dual-Fuel engine (Marine engine) 20

21 Properties Dual-Fuel engine 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 rpm Bore*Stroke 128* * *135 Air factor Intake manifold pressure BMEP 13 bar 22 bar 24 bar 21

22 Modeling burn rates: variable ignition timing for diesel pilot 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 22

23 Differences in knock behavior between engine types Maximum difference in methane number found between the spark-ignited and diesel-pilot engine for these LNG composition is 4.5 MN points PKI MN is roughly 6 points higher for the dual-fuel engine at 14.5% ethane in methane than for the spark-ignited engine 23

24 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. 24

25 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. 25

26 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 26

27 A correct octane number for LNG Technical background of the TKI project Howard Levinsky SAFER, SMARTER, GREENER 27