Numerical Study on the Ignition and Flame Structures of Premixed n-Heptane/Methanol under Engine-Relevant Conditions

  • SUN Ting ,
  • ZHAO Wanhui ,
  • WANG Tao ,
  • WEI Haiqiao ,
  • ZHOU Lei
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  • 1. State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China 
    2. College of Aeronautical Engineering, Civil Aviation University of China, Tianjin 300300, China
    3. National Industry-Education Platform of Energy Storage, Tianjin University, Tianjin 300350, China

Online published: 2025-10-29

Supported by

The work is supported by the National Natural Science Foundation of China (Grant No. U2233201 and No. 52206187), and the Significant Science and Technology Projects of Ningbo (No. 2024Z250).

Copyright

Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2025

Abstract

The autoignition process of methanol/n-heptane dual-fuel (DF) premixtures is studied in a simplified inflow-outflow configuration using numerical simulations under engine-like conditions. Variations in the initial gas temperatures, inlet velocities, and methanol substitution ratio (MSR) on the low-temperature combustion (LTC) and high-temperature combustion (HTC) of DF mixtures are investigated. The LTC is initiated at the locations close to the inlet. A propagating hot flame front is observed after the formation of the HTC. Both the LTC and HTC are delayed at a high value of the MSR. The negative temperature coefficients (NTC) characteristics are insignificant when the MSR reaches 54% due to the decreased LTC at a low concentration of n-heptane. The ignition delay times (IDTs) for the DF mixtures are prolonged with the increase in the MSR due to the competition of OH between n-heptane and methanol. OH is consumed by the reaction pathway CH3OH+OH=CH2OH+H2O, which inhibits the autoignition of fuel/air mixtures and delays the second-stage ignition of n-heptane. Meanwhile, the longer residence time causes a longer distance between the HTC region and the inlet. Finally, the ignition Damkӧhler number (Daign) defined as the ratio of the residence time to the IDT is introduced to reveal the stabilization process of the DF mixtures. The values of the Daign are all lower than unity at different inlet velocities and MSR, indicating that diffusion plays a critical role for LTC. However, larger values of Daign are observed for the HTC indicating that autoignition dominates the oxidization process.

Cite this article

SUN Ting , ZHAO Wanhui , WANG Tao , WEI Haiqiao , ZHOU Lei . Numerical Study on the Ignition and Flame Structures of Premixed n-Heptane/Methanol under Engine-Relevant Conditions[J]. Journal of Thermal Science, 2025 , 34(6) : 2140 -2153 . DOI: 10.1007/s11630-025-2177-3

References

[1] Kaario O.T., Karimkashi S., Bhattacharya A., et al., A comparative study on methanol and n-dodecane spray flames using Large-Eddy simulation. Combustion and Flame, 2024, 260: 113277.
[2] Wu Y., Panigrahy S., Sahu A.B., et al., Understanding the antagonistic effect of methanol as a component in surrogate fuel models: A case study of methanol/n-heptane mixtures. Combustion and Flame, 2021, 226: 229–242.
[3] Li L., Hu M., Qu W., et al., Shock tube and kinetic study on auto-ignition characteristics of methanol/n-heptane mixtures at high temperature. Energy, 2021, 233: 121152.
[4] Zhang X., Yuan C., Zhou L., et al., Effects of initial temperature on ignition and flame propagation of dual-fuel mixture in mixing layer. Combustion and Flame, 2021, 225: 468–484.
[5] Zhen X., Wang Y., An overview of methanol as an internal combustion engine fuel. Renewable and Sustainable Energy Reviews, 2015, 52: 477–493.
[6] Liu K., Chen C., Su M., et al., Experimental study of the macroscopic characteristics of methanol low-pressure injection spray. International Journal of Energy Research, 2022, 46(15): 23259–23272.
[7] Karimkashi S., Gadalla M., Kannan J., et al., Large-eddy simulation of diesel pilot spray ignition in lean methane-air and methanol-air mixtures at different ambient temperatures. International Journal of Engine Research, 2023, 24(3): 965–981.
[8] Zhao W., Zhou L., Qi J., et al., The influence of intermediate species on the combustion process of n-dodecane flame. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2019, 234: 334–348.
[9] Zhu J., Wang S., Raza M., et al., Autoignition behavior of methanol/diesel mixtures: Experiments and kinetic modeling. Combustion and Flame, 2021, 228: 1–12.
[10] Xu S., Zhong S., Hadadpour A., et al., Large-eddy simulation of the injection timing effects on the dual-fuel spray flame. Fuel, 2022, 310: 122445.
[11] Cui Y., Liu H., Wen M., et al., Optical diagnostics and chemical kinetic analysis on the dual-fuel combustion of methanol and high reactivity fuels. Fuel, 2022, 312: 122949.
[12] Wang B., Yao A., Yao C., et al., In-depth comparison between pure diesel and diesel methanol dual fuel combustion mode. Applied Energy, 2020, 278: 115664.
[13] Wang Q., Wei L., Pan W., et al., Investigation of operating range in a methanol fumigated diesel engine. Fuel, 2015, 140: 164–170.
[14] Ahmad Z., Kaario O., Qiang C., et al., Effect of negative valve overlap in a heavy-duty methanol-diesel dual-fuel engine: a pathway to improve efficiency. Fuel, 2022, 317: 123522.
[15] Wang Y., Xiao G., Li B., et al., Study on the performance of diesel-methanol diffusion combustion with dual-direct injection system on a high-speed light-duty engine. Fuel, 2022, 317: 123414.
[16] Chen Z., Zhao P., Zhang H., et al., An optical study on the cross-spray characteristics and combustion flames of automobile engine fueled with diesel/methanol under various injection timings. Energy, 2024, 290: 130286.
[17] Zhao W., Shi H., Sun T., et al., A numerical study on the ignition and flame propagation for locally stratified methanol/n-heptane dual-fuel mixtures. Combustion Science and Technology, 2023, 197(7): 1248–1271.
[18] Chen G., Yu W., Jiang X., et al., Experimental and modeling study on the influences of methanol on premixed fuel-rich n-heptane flames. Fuel, 2013, 103: 467–472.
[19] Liu S., Sun T., Zhou L., et al., A new skeletal kinetic model for methanol/n-heptane dual fuels under engine-like conditions. Energy, 2023, 263: 125648.
[20] Wang Z., Zhao H., Yan C., et al., Methanol oxidation up to 100 atm in a supercritical pressure jet-stirred reactor. Proceedings of the Combustion Institute, 2023, 39(1): 445–453.
[21] Li Z., Wang Y., Wang Y., et al., Effects of fuel injection timings and methanol split ratio in M/D/M strategy on a diesel/methanol dual-fuel direct injection engine. Fuel, 2022, 325: 124970.
[22] Zhou L., Zhao W., Luo K.H., et al., Spray-turbulence-chemistry interactions under diesel engine-like conditions. Progress in Energy and Combustion Science, 2021, 86: 100939.
[23] Musculus M.P.B, Miles P.C, Pickett L.M., Conceptual models for partially premixed low-temperature diesel combustion. Progress in Energy and Combustion Science, 2013, 39(2–3): 246–283.
[24] Deiterding R., High-resolution numerical simulation and analysis of mach reflection structures in detonation waves in low-pressure H2-O2-Ar mixtures: a summary of results obtained with the adaptive mesh refinement framework AMROC. Journal of Combustion, 2011, 2011: 738969.
[25] Kee R.J, Rupley F.M, Miller J.A., Chemkin-II: a Fortran chemical kinetics package for the analysis of gas-phase chemical kinetics. Sandia National Laboratories, Livermore, Calif, USA, 1989.
[26] Zhong L., Zhang X., Zhou L., et al., Direct numerical simulation of flame propagation and deflagration to detonation transition in confined space with different perforated plate positions. Combustion Science and Technology, 2021, 193(16): 2907–2934.
[27] Zhou Y., Zhang X., Zhong L., et al., Effects of fluctuations in concentration on detonation propagation. Physics of Fluids, 2022, 34: 076101.
[28] Zhao W., Sun T., Liu S., et al., Ignition and stabilization of laminar premixed n-heptane/air flames under engine-like conditions. Fuel, 2023, 344: 128035.
[29] Bhattacharjee S., Haworth D.C., Simulations of transient n-heptane and n-dodecane spray flames under engine-relevant conditions using a transported PDF method. Combustion and Flame, 2013, 160(10): 2083–2102.
[30] Pei Y., Hawkes E.R., Bolla M., et al., An analysis of the structure of an n-dodecane spray flame using TPDF modelling. Combustion and Flame, 2016, 168: 420–435.
[31] Li H., Interaction of end-gas autoignition and cold wall in closed chamber. Combustion and Flame, 2024, 259: 113158.
[32] Zhou L., Zhao W., Wei H., Large eddy simulation on the flame structure for split injections of n-dodecane at different temperatures and densities. Combustion Science and Technology, 2018, 190(12): 2224–2244.
[33] Faghih M., Li H., Gou X., et al., On laminar premixed flame propagating into autoigniting mixtures under engine-relevant conditions. Proceedings of the Combustion Institute, 2019, 37(4): 4673–4680.
[34] Ji W., Zhao P., He T., et al., On the controlling mechanism of the upper turnover states in the NTC regime. Combustion and Flame, 2016, 164: 294–302.
[35] Schulz O., Noiray N., Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure. Combustion and Flame, 2019, 205: 253–268.
[36] Gong X., Ren Z., Flame speed scaling in autoignition-assisted freely propagating n-heptane/air flames. Proceedings of the Combustion Institute, 2021, 38(2): 2153–2161.
[37] Gong X., Xie Q., Zhou H., et al., Structure and propagation speed of autoignition-assisted flames of jet fuels. Combustion and Flame, 2022, 236: 111822.
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