Study on cetane number dependence of. with a controlled temperature profile

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3 August 2012 (5E06) The 34th International Symposium on Combustion Study on cetane number dependence of diesel surrogates/air weak flames in a micro flow reactor with a

1 3 August 2012 (5E06) The 34th International Symposium on Combustion Study on cetane number dependence of diesel surrogates/air weak flames in a micro flow reactor with a controlled temperature profile Satoshi Suzuki*, Mikito Hori, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa and Kaoru Maruta Institute of Fluid Science, Tohoku University

2 Background For modeling chemical kinetics of a fuel, experimental data are obtained by, shock tube RCM flow reactor Targeted fuels are extended to large hydrocarbons Diesel fuels (C10-16): Low vapor pressure Difficult to form homogeneous mixture gas Only a few data were reported for low vapor pressure fuels 3/Aug/2012 Institute of Fluid Science, Tohoku University 2

3 Micro flow reactor with a controlled temperature profile T w Wall temperature profile 1300 K 400 K Flame Quartz tube x Fuel/Air Laminar flow Constant pressure External heat Investigate combustion phenomena in simple conditions Controlled steady temperature Observe oxidation process at wide temp. range ( K) d<quenching diameter 3/Aug/2012 Institute of Fluid Science, Tohoku University 3

4 Previous works: weak flame (flame in low inlet velocity) T w 1300 K Wall temperature profile 400 K Flame Quartz tube x Fuel/Air Cool flame Blue flame Hot flame External heat K n-heptane/air, 1 atm Yamamoto et al., PCI 33 Gas-phase temperature wall temperature Weak flames exist at specific temperatures Fuel oxidation process can be observed in weak flames 3/Aug/2012 Institute of Fluid Science, Tohoku University 4

5 Diesel surrogates and Cetane number (CN) n-cetane (C 16 H 34 ) CN Cetane number 100 Ignitibility of diesel fuel n-decane (C 10 H 22 ) 76 High ignitibility n-heptane (C 7 H 16 ) 53 iso-cetane (C 16 H 34 ) 15 AMN : a-methylnaphthalene 0 (C 11 H 10 ) How the flames in our reactor respond to Cetane number? 3/Aug/2012 Institute of Fluid Science, Tohoku University 5

6 Objectives Investigate oxidation process of diesel surrogate Weak flame response to Cetane number Gas analysis for clarifying flame structure 3/Aug/2012 Institute of Fluid Science, Tohoku University 6

7 Experimental setup T w 1300 K Fuel/Air K Test section Flame x Quartz tube d = 1-2 mm Flat flame for heating H 2 /air External heat source: H 2 /air burner Inlet temperature: K depending on applied fuels Flame images were taken by CH-filtered digital still camera 3/Aug/2012 Institute of Fluid Science, Tohoku University 7

8 Computational method Computational code: PREMIX based 1D steady code 1 Gas-phase energy equation K K dt 1 d dt A dt A A 4λNu M& λ A + ρ Y kvkc pk + ωk hk Wk ( T ) 0 2 w Tg = dx c dx dx c k = 1 dx c & k = 1 c d p p p p Chemical kinetics models C8-16 n-alkane 2 (2115 species 8157 reactions) Heat transfer to the wall iso-cetane 3 (1114 species 4469 reactions) developed by LLNL n-heptane 4 ( 561 species 2539 reactions) substituted aromatic 5 (158 species 1049 reactions) developed by Pitsch et al. * Estimated values are used for missing species in n-alkane and iso-cetane models due to lack of their transport database Conditions Same as the experiments; inlet velocity 3.0 cm/s, equivalence ratio 1, pressure 1 atm [1] K. Maruta, T. Kataoka, N.I. Kim, S. Minaev and R. Fursenko, Proc. Combust. Inst. 30 (2005) [2] C. K. Westbrook, W. J. Pitz, O. Herbinet, H. J. Curran, E. J. Silke, Combust. Flame. 156 (2009) [3] M. A. Oehlschlaeger, J. Steinberg, C. K. Westbrook, W. J. Pitz, Combust. Flame. 156 (2009) [4] H.J. Curran, P. Gaffuri, W.J. Pitz, C.K. Westbrook, Combust. Flame 114 (1-2) (1998) [5] K. Narayanaswamy, G. Blanquart, H. Pitsch, Combust. Flame. 157 (2010) /Aug/2012 Institute of Fluid Science, Tohoku University 8

9 Weak flames response to Cetane number Comparison of weak flame images of diesel surrogates 3/Aug/2012 Institute of Fluid Science, Tohoku University

10 Weak flames of the various CN fuels n-cetane CN 100 n-decane CN 76 n-heptane CN 53 iso-cetane CN 15 AMN CN 0 Flow direction Wall temperature [K] Cool flame Around 800 K In higher CN fuels Hot flame: CN : K CN 0: over 1200 K Higher CN fuels react at lower temperature u = 3.0 cm/s φ = 1 P = 1 atm Exposure time : 2 minutes 3/Aug/2012 Institute of Fluid Science, Tohoku University 10

11 Heat release rate (HRR) of the various CN fuels Heat relea ase rate [kw W/cm3] Wall temperature [K] n-cetane n-decane n-heptane iso-cetane AMN 0.04 n-decane 0.03 CN 76 n-cetane n-heptane 0.02 CN 100 CN u = 3.0 cm/s iso-cetane AMN φ = 1 CN 15 CN 0 P = 1 atm Location [cm] HRR peaks corresponds to the flame luminescence zones Sharp peaks in higher temp. range: Hot flames 3/Aug/2012 Institute of Fluid Science, Tohoku University 11

12 Heat release rate (HRR) of the various CN fuels Heat relea ase rate [kw W/cm3] Wall temperature [K] u = 3.0 cm/s φ = 1 n-cetane iso-cetane n-cetane n-decane AMN CN 100 CN 76 CN 15 CN 0 P = 1 atm n-decane n-heptane CN 53 n-heptane iso-cetane AMN Location [cm] Small peaks in low temp. range: Cool flames Found in CN Qualitative agreement to Experiments 3/Aug/2012 Institute of Fluid Science, Tohoku University 12

13 Relationship of flame temperature and Cetane number Cetane number Cool flame 100 Experimental data Model predictions Hot flame Wall temperature [K] Comparison of temperature difference Hot flame: Within 30 K Cool flame:models predict 100 K lower Further studies for low temperature reaction are required 3/Aug/2012 Institute of Fluid Science, Tohoku University 13

14 Relationship of flame temperature and Cetane number Cetane number Cool flame 100 Experimental data Model prediction Hot flame Wall temperature [K] Increasing CN, wall temperature decrease Higher CN, higher ignitability Flame appearance in our reactor agree with Cetane rating 3/Aug/2012 Institute of Fluid Science, Tohoku University 14

15 Flame structure of n-cetane and iso-cetane Gas analysis for CH 2 O 3/Aug/2012 Institute of Fluid Science, Tohoku University

16 Gas analysis method T w Wall temperature profile T max Gas chromatography (SHIMADZU GC-14B) Detector (TCD) Column(Porapak T 50/80) 400K Flame Quartz tube x Fuel/Air Extracting gas from tube exit, then analyzed by GC Target species: CH 2 O = Typical product in cool flame Comparative validation with n-heptane whose cool flame is confirmed in a lot of studies 3/Aug/2012 Institute of Fluid Science, Tohoku University 16

17 CH 2 O profiles of n-heptane Flow direction Cool flame n-heptane (C7H16) GC outp put signal [arbitrary units] Experiments Mole fra action [-] Mole fractio on [%] Wall temperature [K] HRR peak of cool flame Computation Wall temperature [K] CH 2 O is produced in cool flame 3/Aug/2012 Institute of Fluid Science, Tohoku University 17

18 CH 2 O profiles of n-cetane and n-heptane Flow direction Cool flame n-cetane (C16H34) GC outp put signal [arbitrary units] Experiments n-cetane n-heptane Mole fr raction [-] Mole fracti ion [%] n-heptane Computation n-cetane Wall temperature [K] Wall temperature [K] CH 2 O is produced in cool flame CH 2 O profiles of n-cetane are similar to n-heptane 3/Aug/2012 Institute of Fluid Science, Tohoku University 18

19 CH 2 O profiles of iso-cetane and n-heptane iso-cetane (C16H34) GC ou utput signa al [arbitrar ry units] Experiment n-heptane iso-cetane Mole fraction [-] Mole frac ction [%] Computation n-heptane iso-cetane Wall temperature [K] Wall temperature [K] Comparison to n-heptane Experiment Computation CH 2 O begin to produce at 200 K higher 50 K higher Amount of CH 2 O peak 50 % 80% Numerical model overestimated CH 2 O production 3/Aug/2012 Institute of Fluid Science, Tohoku University 19

20 Blended fuel of n-cetane and iso-cetane Cetane number variation Pure fuels with specific CN Blended fuels of two fuels Pure n-cetane (CN 100) Blended fuel (CN 76) Pure iso-cetane (CN 15) Increasing CN Cool flames become stronger Hot flames shift to low temperature 3/Aug/2012 Institute of Fluid Science, Tohoku University 20

21 Summary Ignition and combustion characteristics of a gaseous diesel surrogates/air mixture were examined by micro flow reactor with a controlled temperature profile. Experimental data of low vapor pressure fuels are obtained in wide temperature range by the reactor Cool flames are observed in high Cetane number fuels in atmospheric pressure The weak flame trends corresponds to Cetane rating Model predictions agree well with experimental data except iso-cetane case 3/Aug/2012 Institute of Fluid Science, Tohoku University 21

22 Acknowledgement S.S. was supported by, The Combustion Institute office s travel award and IFS Graduate Student Overseas Presentation Award This study was partially supported by, 3/Aug/2012 Institute of Fluid Science, Tohoku University

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