The effects of adding long-chain ethers in n-heptane counterflow diffusion flames on the formation characteristics of soot precursors

doi:10.11949/0438-1157.20221399

Abstract

Abstract:

Biomass-derived long-chain oxygenated fuels have good soot emission reduction properties and are promising diesel additives. In this work, the effects of 25% tripropylene glycol methyl ether (TPGME) and 25% polyoxymethylene dimethyl ether (PODE) additions on the soot precursor formation characteristics in n-heptane counterflow diffusion flames were experimentally and numerically analysed. The mole fractions of C₁—C₄ hydrocarbons in counterflow diffusion flames were measured by gas chromatography (GC). The experiments showed that the additions of TPGME and PODE suppressed the formation of ethylene and acetylene. The numerical simulations were performed through a reaction kinetic mechanism combined with the decoupling strategy, which could well capture the experimental observations. The simulations showed that the temperature differences in the key combustion zone were not more than 50 K, indicating that the oxygenated additives had little effects on the flame temperature. The dilution effect and thermal effect reduced the concentration of acetylene and ethylene, while chemical effect was beneficial to the formation of acetylene and ethylene. The rate of production (ROP) and reaction pathway analyses illustrated that unsaturated hydrocarbons were mainly generated via hydrogen abstraction and β-scission of n-heptane, and neither of the two additives had a remarkable impact on the pathways. Due to the presence of oxygen atoms, the carbon atoms on TPGME and PODE molecules trended to be converted into aldehydes and carbon monoxide (CO) instead of unsaturated hydrocarbons. Ultimately, the dilution effect and thermal effect played dominant roles in reducing the soot precursor emissions of n-heptane flame.

Key words: oxygenated additives, soot precursors, counterflow flame, bio-oil, kinetic mechanism

摘要：

生物质基长链含氧燃料具有良好的碳烟减排特性，是富有前景的柴油添加剂。通过实验和数值模拟分析了25%三丙二醇单甲醚(TPGME)和25%聚甲氧基二甲醚(PODE)添加对正庚烷对冲扩散火焰中碳烟前体生成特性的影响。通过气相色谱(GC)测量了对冲扩散火焰中C₁~C₄烃类的摩尔分数，实验结果表明TPGME和PODE的添加减少了乙烯和乙炔的形成。通过反应动力学机理结合解耦方法实现了燃烧动力学过程模拟，能够很好匹配实验结果。模拟结果表明核心燃烧区域的温差不超过50 K，说明含氧添加剂对火焰温度影响较小；稀释效应和热效应降低了乙炔、乙烯的浓度，而化学效应则有利于乙烯和乙炔的生成。生产率(ROP)和反应路径计算表明不饱和烃主要由正庚烷的氢提取和β-断键反应生成，两种添加剂均不会对该路径产生实质性影响。由于氧原子的存在，TPGME和PODE分子中碳原子极易转化为醛和一氧化碳(CO)而非不饱和烃。最终，稀释效应和热效应是降低正庚烷火焰中碳烟前体排放的关键因素。

关键词: 含氧添加剂, 碳烟前体, 对冲火焰, 生物油, 动力学机理

CLC Number:

TK 6

Jiajing BAO, Hongfei BIE, Ziwei WANG, Rui XIAO, Dong LIU, Shiliang WU. The effects of adding long-chain ethers in n-heptane counterflow diffusion flames on the formation characteristics of soot precursors[J]. CIESC Journal, 2023, 74(4): 1680-1692.

包嘉靖, 别洪飞, 王子威, 肖睿, 刘冬, 吴石亮. 正庚烷对冲扩散火焰中添加长链醚类对碳烟前体生成特性的影响[J]. 化工学报, 2023, 74(4): 1680-1692.

Figures/Tables 12

Fig.1 The molecular structure of n-heptane, PODE (n=3—5), and TPGME

Fig.2 Schematic diagram of the counterflow diffusion flame experiment system[31]

Table 1 The counterflow diffusion flame experiment setups

项目	正庚烷	正庚烷+ 25%TPGME	正庚烷+ 25%PODE
燃料端
燃料/(ml/min)	0.30	0.30	0.30
N₂/(L/min)	0.30	0.30	0.30
氧化剂端
O₂/(L/min)	0.16	0.16	0.16
N₂/(L/min)	0.34	0.34	0.34
屏蔽气
N₂/(L/min)	4.0	4.0	4.0

Table 2 The physicochemical properties of n-heptane， TPGME， and PODE［7,33］

项目	正庚烷	TPGME	PODE₃	PODE₄	PODE₅
化学式	C₇H₁₆	C₁₀H₂₂O₄	C₅H₁₂O₄	C₆H₁₄O₅	C₇H₁₆O₆
分子量/(g/mol)	100.2	206.3	136.1	166.2	196.2
密度(20℃)/(g/cm³)	0.68	0.97	1.02	1.06	1.10
黏度(20℃)/(mm²/s)	0.59	5.50	1.03	1.65	2.04
低位发热量/(MJ/kg)	44.6	28.1	19.1	18.4	17.8
汽化潜热/(kJ/kg)	318	210	—	—	—
沸点/℃	98	243	156	202	242
十六烷值	56	81	78	90	100
含氧量/%(质量)	0	31.0	47.1	48.2	49.0

Table 3 The locations used for the analysis of reaction kinetics

反应物	距离/mm	正庚烷转化率/%
正庚烷	0.90	30.0
25%TPGME	0.85	29.1
25%PODE	0.85	29.9

Fig.3 Mole fractions of CH4, C2H6, and C3H8 in different counterflow diffusion flame conditions

Fig.4 Mole fractions of C2H2, C2H4, C3H6, i-C4H8, and n-C4H8 in different counterflow diffusion flame conditions

Fig.5 The simulated temperature (a) and temperature difference profiles (b) for n-C7H16, 25%TPGME, 25%FTPGME, 25%PODE, and 25%FPODE flames

Fig.6 The variations of peak mole fraction and the rate of productions for C2H2 [(a),(b)], C2H4 [(c),(d)], and C3H6 [(e),(f)] in n-C7H16, 25%TPGME, 25%FTPGME, 25%PODE and 25%FPODE flames

Fig.7 Reaction pathways of n-heptane in different flame conditions

Fig.8 Reaction pathways of TPGME in 25%TPGME flame

Fig.9 Reaction pathways of PODE in 25%PODE flame

References 50

1	Viswanathan V K, Thomai P. Performance and emission characteristics analysis of Elaeocarpus Ganitrus biodiesel blend using CI engine[J]. Fuel, 2021, 288: 119611.
2	Wu S, Kang D, Xiao R, et al. Autoignition characteristics of bio-based fuels, farnesane and TPGME, in comparison with fuels of similar cetane rating[J]. Proceedings of the Combustion Institute, 2021, 38(4): 5585-5595.
3	Khalife E, Tabatabaei M, Demirbas A, et al. Impacts of additives on performance and emission characteristics of diesel engines during steady state operation[J]. Progress in Energy and Combustion Science, 2017, 59: 32-78.
4	Bhurat S, Pandey S, Chintala V, et al. Effect of novel fuel vaporiser technology on engine characteristics of partially premixed charge compression ignition (PCCI) engine with toroidal combustion chamber[J]. Fuel, 2022, 315: 123197.
5	Agarwal A K, Singh A P, Kumar V. Particulate characteristics of low-temperature combustion (PCCI and RCCI) strategies in single cylinder research engine for developing sustainable and cleaner transportation solution[J]. Environmental Pollution, 2021, 284: 117375.
6	Telli G D, Zulian G Y, Lanzanova T D M, et al. An experimental study of performance, combustion and emissions characteristics of an ethanol HCCI engine using water injection[J]. Applied Thermal Engineering, 2022, 204: 118003.
7	Wu S, Bao J, Wang Z, et al. The regulated emissions and PAH emissions of bio-based long-chain ethers in a diesel engine[J]. Fuel Processing Technology, 2021, 214: 106724.
8	Wu S, Kang D, Liu Y, et al. The oxidation of C₂—C₄ diols and diol/TPGME blends in a motored engine[J]. Fuel, 2019, 257: 116093.
9	Wu S, Kang D, Zhang H, et al. The oxidation characteristics of furan derivatives and binary TPGME blends under engine relevant conditions[J]. Proceedings of the Combustion Institute, 2019, 37(4): 4635-4643.
10	Zhang H, Kaczmarek D, Rudolph C, et al. Dimethyl ether (DME) and dimethoxymethane (DMM) as reaction enhancers for methane: combining flame experiments with model-assisted exploration of a polygeneration process[J]. Combustion and Flame, 2022, 237: 111863.
11	Liang D, Ren K, Wu Z, et al. Combustion characteristics of oxygenated slurry droplets of nano-Al/EtOH and nano-Al/TPGME blends[J]. Energy, 2021, 220: 119693.
12	Sun W, Liu Z, Zhang Y, et al. Comparing the pyrolysis kinetics of dimethoxymethane and 1, 2-dimethoxyethane: an experimental and kinetic modeling study[J]. Combustion and Flame, 2021, 226: 260-273.
13	Bora A P, Gupta D P, Durbha K S. Sewage sludge to bio-fuel: a review on the sustainable approach of transforming sewage waste to alternative fuel[J]. Fuel, 2020, 259: 116262.
14	Bae C, Kim J. Alternative fuels for internal combustion engines[J]. Proceedings of the Combustion Institute, 2017, 36(3): 3389-3413.
15	Burke U, Pitz W J, Curran H J. Experimental and kinetic modeling study of the shock tube ignition of a large oxygenated fuel: tri-propylene glycol mono-methyl ether[J]. Combustion and Flame, 2015, 162(7): 2916-2927.
16	Li N, Sun W, Liu S, et al. A comprehensive experimental and kinetic modeling study of dimethoxymethane combustion[J]. Combustion and Flame, 2021, 233: 111583.
17	Sun W, Wang G, Li S, et al. Speciation and the laminar burning velocities of poly(oxymethylene) dimethyl ether 3 (POMDME₃) flames: an experimental and modeling study[J]. Proceedings of the Combustion Institute, 2017, 36(1): 1269-1278.
18	Westbrook C K, Pitz W J, Curran H J. Chemical kinetic modeling study of the effects of oxygenated hydrocarbons on soot emissions from diesel engines[J]. The Journal of Physical Chemistry A, 2006, 110(21): 6912-6922.
19	Burke U, Shahla R, Dagaut P, et al. Species measurements of the particulate matter reducing additive tri-propylene glycol monomethyl ether[J]. Proceedings of the Combustion Institute, 2019, 37(1): 1257-1264.
20	Jacobs S, Döntgen M, Alquaity A B S, et al. Detailed kinetic modeling of dimethoxymethane (Part Ⅱ): Experimental and theoretical study of the kinetics and reaction mechanism[J]. Combustion and Flame, 2019, 205: 522-533.
21	Kopp W A, Kröger L C, Döntgen M, et al. Detailed kinetic modeling of dimethoxymethane (Part Ⅰ): Ab initio thermochemistry and kinetics predictions for key reactions[J]. Combustion and Flame, 2018, 189: 433-442.
22	de Ras K, Kusenberg M, Vanhove G, et al. A detailed experimental and kinetic modeling study on pyrolysis and oxidation of oxymethylene ether-2 (OME-2)[J]. Combustion and Flame, 2022, 238: 111914.
23	Gao Z, Hu E, Xu Z, et al. Low to intermediate temperature oxidation studies of dimethoxymethane/n-heptane blends in a jet-stirred reactor[J]. Combustion and Flame, 2019, 207: 20-35.
24	Natarajan M, Frame E A, Naegeli D W, et al. Oxygenates for advanced petroleum-based diesel fuels (Part 1): Screening and selection methodology for the oxygenates [J]. SAE Transactions, 2001, 110: 2221-2245.
25	González D M A, Piel W, Asmus T, et al. Oxygenates screening for advanced petroleum-based diesel fuels (Part 2): The effect of oxygenate blending compounds on exhaust emissions [J]. SAE Transactions, 2001, 110: 2246-2255.
26	Huang H, Li Z, Teng W, et al. Influence of n-butanol-diesel-PODE_3-4 fuels coupled pilot injection strategy on combustion and emission characteristics of diesel engine[J]. Fuel, 2019, 236: 313-324.
27	Huang H, Teng W, Li Z, et al. Improvement of emission characteristics and maximum pressure rise rate of diesel engines fueled with n-butanol/PODE_3-4/diesel blends at high injection pressure[J]. Energy Conversion and Management, 2017, 152: 45-56.
28	Liu H, Wang X, Wu Y, et al. Effect of diesel/PODE/ethanol blends on combustion and emissions of a heavy duty diesel engine[J]. Fuel, 2019, 257: 116064.
29	Dumitrescu C E, Mueller C J, Kurtz E. Investigation of a tripropylene-glycol monomethyl ether and diesel blend for soot-free combustion in an optical direct-injection diesel engine[J]. Applied Thermal Engineering, 2016, 101: 639-646.
30	Zhao X, Xu L, Chen C, et al. Experimental and numerical study on sooting transition process in iso-octane counterflow diffusion flames: diagnostics and combustion chemistry[J]. Journal of the Energy Institute, 2021, 98: 282-293.
31	Zhao R, Liu D. Chemical effects of carbon dioxide in ethylene, ethanol and DME counter-flow diffusion flames: an experimental reference for the fictitious CO₂ flame[J]. Journal of the Energy Institute, 2022, 100: 245-258.
32	Carbone F, Gomez A. The structure of toluene-doped counterflow gaseous diffusion flames[J]. Combustion and Flame, 2012, 159(10): 3040-3055.
33	Aydoğan B. Combustion characteristics, performance and emissions of an acetone/n-heptane fuelled homogenous charge compression ignition (HCCI) engine[J]. Fuel, 2020, 275: 117840.
34	Burke U, Metcalfe W K, Burke S M, et al. A detailed chemical kinetic modeling, ignition delay time and jet-stirred reactor study of methanol oxidation[J]. Combustion and Flame, 2016, 165: 125-136.
35	Zellner R. S.W. Benson: Thermochemical Kinetics, 2nd Ed. John Wiley & Sons, New York-London-Sydney-Toronto 1976.320 Seiten, Preis: £ 16.-, $ 27.-[J]. Berichte Der Bunsengesellschaft Für Physikalische Chemie, 1977, 81(9): 877-878.
36	Zhang K, Banyon C, Bugler J, et al. An updated experimental and kinetic modeling study of n-heptane oxidation[J]. Combustion and Flame, 2016, 172: 116-135.
37	Li Y, Zhou C-W, Somers K P, et al. The oxidation of 2-butene: a high pressure ignition delay, kinetic modeling study and reactivity comparison with isobutene and 1-butene[J]. Proceedings of the Combustion Institute, 2017, 36(1): 403-411.
38	Burke S M, Burke U, Mc Donagh R, et al. An experimental and modeling study of propene oxidation (Part 2): Ignition delay time and flame speed measurements[J]. Combustion and Flame, 2015, 162(2): 296-314.
39	Kéromnès A, Metcalfe W K, Heufer K A, et al. An experimental and detailed chemical kinetic modeling study of hydrogen and syngas mixture oxidation at elevated pressures[J]. Combustion and Flame, 2013, 160(6): 995-1011.
40	Burke S M, Metcalfe W, Herbinet O, et al. An experimental and modeling study of propene oxidation (Part 1): Speciation measurements in jet-stirred and flow reactors[J]. Combustion and Flame, 2014, 161(11): 2765-2784.
41	Pan W, Liu D. Effects of hydrogen additions on premixed rich flames of four butanol isomers[J]. International Journal of Hydrogen Energy, 2017, 42(6): 3833-3841.
42	Du D X, Axelbaum R L, Law C K. The influence of carbon dioxide and oxygen as additives on soot formation in diffusion flames[J]. Symposium (International) on Combustion, 1991, 23(1): 1501-1507.
43	Lutz A E, Kee R J, Grcar J F, et al. OPPDIF: a Fortran program for computing opposed-flow diffusion flames [R]. Livermore, CA (United States): Sandia National Lab (SNL-CA), 1997.
44	Valencia-López A M, Bustamante F, Loukou A, et al. Effect of benzene doping on soot precursors formation in non-premixed flames of producer gas (PG)[J]. Combustion and Flame, 2019, 207: 265-280.
45	Xu L, Wang Y, Liu D. Effects of oxygenated biofuel additives on soot formation: a comprehensive review of laboratory-scale studies[J]. Fuel, 2022, 313: 122635.
46	Sun W, Tao T, Zhang R, et al. Elucidating the flame chemistry of monoglyme via experimental and modeling approaches[J]. Combustion and Flame, 2018, 191: 298-308.
47	Zhang Y, Li Y, Liu P, et al. Investigation on the chemical effects of dimethyl ether and ethanol additions on PAH formation in laminar premixed ethylene flames[J]. Fuel, 2019, 256: 115809.
48	Frenklach M, Warnatz J. Detailed modeling of PAH profiles in a sooting low-pressure acetylene flame[J]. Combustion Science and Technology, 1987, 51(4/5/6): 265-283.
49	Tan Y R, Salamanca M, Pascazio L, et al. The effect of poly(oxymethylene) dimethyl ethers (PODE₃) on soot formation in ethylene/PODE₃ laminar coflow diffusion flames[J]. Fuel, 2021, 283: 118769.
50	Meng X, Hu E, Yoo K H, et al. Experimental and numerical study on autoignition characteristics of the polyoxymethylene dimethyl ether/diesel blends[J]. Energy & Fuels, 2019, 33(3): 2538-2546.

[1]	Runtao WANG, Zejun LUO, Chu WANG, Xifeng ZHU. Synergistic effect during catalytic co-pyrolysis of bio-oil distillation residue and waste plastic [J]. CIESC Journal, 2022, 73(11): 5088-5097.
[2]	YAN Beibei, WANG Jian, LIU Bin, CHEN Guanyi, CHENG Zhanjun. Research progress of bio-oil metal hydrothermal in-situ hydrogenation technology [J]. CIESC Journal, 2021, 72(4): 1783-1795.
[3]	Yaojun YANG, Rui DIAO, Chu WANG, Xifeng ZHU. Catalytic effect of different metal oxides on pyrolysis behaviors of heavy bio-oil: a comparative study [J]. CIESC Journal, 2021, 72(11): 5820-5830.
[4]	Yan SUN, Xiaowen SHEN, Xiwei XU, Enchen JIANG, Xuecong LIU. Coupled chemical looping and catalytic reforming to produce syngas from pyrolysis bio-oil [J]. CIESC Journal, 2021, 72(11): 5607-5619.
[5]	Wei DENG,Chunho LAM,Zhe XIONG,Xuepeng WANG,Jun XU,Long JIANG,Sheng SU,Yi WANG,Song HU,Jun XIANG. Research progress in electrocatalytic hydrogenation upgrading of bio-oil [J]. CIESC Journal, 2021, 72(10): 4987-5001.
[6]	Yinhai SU,Shuping ZHANG,Lingqin LIU,Yuanquan XIONG. Synergetic production of phenols and syngas from the catalytic pyrolysis of cellulose on activated carbon [J]. CIESC Journal, 2021, 72(10): 5206-5217.
[7]	Shanhong MA, Feng YE, Yanhong WANG, Xuemei LANG, Shuanshi FAN, Gang LI. Permeation properties and regeneration of a ZSM-5 zeolite membrane for bio-oil dehydration [J]. CIESC Journal, 2020, 71(7): 3345-3353.
[8]	Zejun LUO, Yonghua HU, Yusong WANG, Xiefei ZHU, Xifeng ZHU. Physicochemical properties and pyrolysis characteristics of heavy bio-oil [J]. CIESC Journal, 2019, 70(8): 3196-3201.
[9]	Laizhi SUN, Lei CHEN, Baofeng ZHAO, Shuangxia YANG, Xinping XIE, Fanjun MENG, Hongyu SI. Experiment research on catalytic fast pyrolysis of biomass into bio-oils over Mo/ZSM-5 catalyst [J]. CIESC Journal, 2019, 70(8): 3160-3166.
[10]	Yongchen ZHU, Xiaohua LI, Xiaolei ZHANG, Chao HU, Wenbin DONG, Jingfeng CHENG, Shanshan SHAO. Study on regeneration of La modified multistage pore HZSM-5 by NTP and catalytic upgrading of bio-oil [J]. CIESC Journal, 2019, 70(5): 1795-1803.
[11]	ZHANG Jizong, CHANG Houchun, CHANG Jianmin, LONG Jinxing, LI Xuehui. Effect of bio-oil on properties of bio-oil starch adhesive [J]. CIESC Journal, 2018, 69(S1): 123-128.
[12]	ZHANG Jizong, CHANG Houchun, CHANG Jianmin, LONG Jinxing, LI Xuehui. Curing characteristics of bio-oil starch adhesive [J]. CIESC Journal, 2018, 69(12): 5309-5315.
[13]	CHEN Yongxing, WEI Qifeng, REN Xiulian. Analysis of hydrothermal liquefaction of algae residue with n-propylamine solution [J]. CIESC Journal, 2017, 68(9): 3592-3599.
[14]	HU Yanjun, MA Wenchao, WU Yanan, CHEN Jiang. Characterization on PAHs distributions in pyrolysis bio-oil from different wastewater sewage sludge [J]. CIESC Journal, 2016, 67(7): 3016-3022.
[15]	ZHANG Jixiang, WANG Dong, JIANG Baohui, WEI Yaodong. Hydrothermal liquefaction of kitchen waste for bio-oil production [J]. CIESC Journal, 2016, 67(4): 1475-1482.