GT-Suite Users International Conference Frankfurt a.m., October 22 nd 2012

Transcription

1 GT-Suite Users International Conference Frankfurt a.m., October 22 nd 2012 Computational Analysis of Internal and External EGR Strategies combined with Miller Cycle Concept for a Two Stage Turbocharged Medium Speed Marine Diesel Engine F. Millo, M. Gianoglio Bernardi (Politecnico di Torino - Italy) D. Delneri (Wärtsilä)

2 Presentation Overview Introduction Model set-up and validation Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

3 Presentation Overview Introduction Model set-up and validation Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

4 Introduction Marine exhaust NOx emission limits IMO Tier 1 1 January % IMO Tier 2 1 January 2011 IMO Tier 3 1 January 2016 The IMO has developed the Annex VI of MARPOL 73/78, which represents the first set of regulations on the marine exhaust emissions. The Annex VI sets limits on Nitrogen Oxides, Sulphur Oxides and Volatile Organic Compounds. IMO Tier 3 NOx limit corresponds to 80% reduction from today IMO Tier 1 level.

5 Introduction Emission Control Areas (ECA s)

6 Introduction NOx emission reduction technologies potentials Although different combustion and aftertreatment technologies could be combined in order to reach the IMO Tier 3 NOx emissions target, the aim of this work is the analysis of the potential of internal and external Exhaust Gas Recirculation strategies combined with Miller cycle concept and dual stage turbocharging.

7 Introduction Miller cycle concept and two stage turbocharging One possible strategy to approach IMO Tier 3 limits and decrease NOx emissions is the combustion process cooling that can be achieved using a Miller cycle. The Miller cycle is an operating cycle for ICE which is essentially characterized by an effective compression stroke shorter than the expansion stroke. One possible way to reduce the compression ratio in the Miller cycle is the Early Intake Valve Closing (EIVC) strategy Diesel cycle

8 Introduction Miller cycle concept and two stage turbocharging One possible strategy to approach IMO Tier 3 limits and decrease NOx emissions is the combustion process cooling that can be achieved using a Miller cycle The Miller cycle is an operating cycle for ICE which is essentially characterized by an effective compression stroke shorter than the expansion stroke. One possible way to reduce the compression ratio in the Miller cycle is the Early Intake Valve Closing (EIVC) strategy In cylinder charge expansion Diesel cycle Miller cycle EIVC Higher boost pressure level

9 Introduction Miller cycle concept and two stage turbocharging However, to achieve the high boost pressure level needed for the Miller cycle, a 2 stage turbocharging system is mandatory. Nevertheless, although two stages turbocharging, combined with extreme Miller timings may allow up to 50 % NOx reduction compared to a conventional architecture, further NOx emissions reductions are necessary to meet the IMO Tier 3 limits. One possible solution could be the combination of this combustion cooling strategy with the external Exhaust Gas Recirculation (EGR).

10 Presentation Overview Introduction Model set-up and validation Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

11 Model set-up and validation Main design features of test engine Bore 200 mm Stroke 280 mm Compression Ratio 16 Speed 1000 rpm Maximum Power 200 kw/cylinder BMEP 27.3 bar (load 100%) From real engine To 1D GT-Power model

12 Model set-up and validation GT-Power model characteristics Combustion model: predictive combustion model DI-Jet. NOx emissions estimation based on the Extended Zeldovich Mechanism coupled with Multi Zones combustion model. Engine Load: 100%. Imposed outlet EGR temperature: 100 C.

13 Model set-up and validation Steady state engine model validation Model validation has been performed over 2 steady state operating points: Speed [rpm] Load [%] Miller [deg] Standard intake valve lift profile: EIVC of 33 CA (Miller 33) EIVC of 83 CA (Miller 83) Standard exhaust valve lift profile: Overlap: 60 CA symmetric Miller 33 Miller 83 Scavenging period Valve overlap

14 Model set-up and validation Steady state engine model validation Speed [rpm] Load [%] Miller [deg]

15 Presentation Overview Introduction Model set-up Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

16 Dual stage turbocharging and Miller cycle analysis Simulation Matrix 6 IVC timings: 33 CA (Miller 33) 50 CA (Miller 50) 70 CA (Miller 70) 80 CA (Miller 80) 90 CA (Miller 90) 100 CA (Miller 100) 5 scavenging period durations: 60 CA (Overlap 60) 45 CA (Overlap 45) 30 CA (Overlap 30) 15 CA (Overlap 15) 0 CA (Overlap 0) 2 scavenging period variation strategies: asymmetric overlap (A) symmetric overlap (S) Miller Timing [ CA] Overlap [ CA] 60 A/S A/S A/S A/S A/S A/S 45 A/S A/S A/S A/S A/S A/S 30 A/S A/S A/S A/S A/S A/S 15 A/S A/S A/S A/S A/S A/S 0 A/S A/S A/S A/S A/S A/S

17 Dual stage turbocharging and Miller cycle analysis

18 Dual stage turbocharging and Miller cycle analysis The best solution in order to reduce NOx emissions without excessive penalties in term of fuel consumption seems to be the adoption of an early intake valve closure of 90 (Miller 90) coupled with a symmetric overlap of 30.

19 Presentation Overview Introduction Model set-up Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

20 External EGR analysis Different external EGR architectures 1 Solution #1: Intermediate connection 2 Solution #2: EGR Blower 3 Solution #3: EGR Turbocharger 4 Solution #4: Backpressure driven EGR

21 External EGR analysis

22 External EGR analysis Even if system # 4 shows the best NOx-bsfc trade-off, it leads to significant increasesofthehpturbineinlettemperature,thatsuggeststhechoiceofegr system #3 (i.e. EGR turbocharger), which using a 20% EGR rate can achieve comparable NOx reductions (about 90% lower than IMO Tier 1 values) with still acceptable fuel consumption penalties (about 3%).

23 Presentation Overview Introduction Model set-up Dual stage turbocharging and Miller cycle analysis External EGR analysis Conclusions

24 Conclusions Different internal and external EGR strategies, combined with extreme Miller cycles, were analyzed by means of numerical simulation. Extreme Miller cycles, with EIVC (up to 100 crank angle degrees before BDC), combined with 2 stage turbocharging were firstly evaluated and the best solution, in order to reduce NOx emissions without excessive BSFC penalties, was found to be the adoption of a 90 EIVC coupled with a symmetric overlap of 30, whichalloweda 35% NOx abatement and BSFC values comparable with the reference solution. Afterwards, several different complex EGR routes were evaluated in combination with the two-stage turbocharged, 90 EIVC Miller, for the preliminary assessment of their NOx emissions abatement potentialities. Although all the tested external EGR systems were capable to reduce NOx emissions down to approximately 10% of the reference Miller 33 value when using the highest EGR rate(20%),the use of an EGR turbocharger allowed maintaining components thermal loads under control, with still acceptable fuel consumption penalties (about 3%). In conclusion, the achievement of IMO Tier 3 NOx emissions levels was proved to be feasible, although further experimental investigation will be needed to confirm the numerical simulation results.

25 GT-Suite Users International Conference Frankfurt a.m., October 22 nd 2012 Computational Analysis of Internal and External EGR Strategies combined with Miller Cycle Concept for a Two Stage Turbocharged Medium Speed Marine Diesel Engine F. Millo, M. Gianoglio Bernardi (Politecnico di Torino - Italy) D. Delneri (Wärtsilä)

26 Further discussions Working principle of the low-pressure loop Miller 33 Symmetric overlap The pumping loop analysis does not show any remarkable difference between symmetric overlap 60 and symmetric overlap 0. The pumping work is positive (i.e. transferred from cylinder gases to the piston) for both cases, since the pressure level during the exhaust stroke is lower than the pressure level during the intake stroke.

27 Further discussions Working principle of the low-pressure loop Miller 100 Symmetric overlap The pumping work becomes negative (i.e. transferred from the piston to cylinder gases) since the pressure level during the exhaust stroke is higher than the pressure level during the intake stroke. This induces the fuel consumption worsening. Thanks to the overlap reduction from 60 to 0 CA degrees, the exhaust stroke pressure level decreases under boost pressure level, achieving a positive pumping work with some benefits in term of fuel economy.