TY - JOUR
T1 - Three-stage auto-ignition of n-heptane and methyl-cyclohexane mixtures at lean conditions in a flat piston rapid compression machine
AU - AlRamadan, Abdullah
AU - Houidi, Moez Ben
AU - Sotton, Julien
AU - Bellenoue, Marc
AU - Johansson, Bengt
AU - Sarathy, Mani
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The experimental work was supported by the French research agency (Association Nationale de la Recherche et de la Technologie ANRT), Renault S.A., and PPRIME Institute during the Ph.D. thesis of M. Ben Houidi (CIFRE N:384/2010). The simulation work was supported by King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) with funds given to the Clean Combustion Research Center. We acknowledge funding from the KAUST Clean Fuels Consortium and its member companies.
PY - 2020/7/28
Y1 - 2020/7/28
N2 - One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture.
AB - One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture.
UR - http://hdl.handle.net/10754/664482
UR - https://linkinghub.elsevier.com/retrieve/pii/S1540748920300869
U2 - 10.1016/j.proci.2020.05.038
DO - 10.1016/j.proci.2020.05.038
M3 - Article
SN - 1540-7489
JO - Proceedings of the Combustion Institute
JF - Proceedings of the Combustion Institute
ER -