Experimental Investigation on Laminar Burning Velocities and Markstein Lengths of Premixed Methane–n-Heptane–Air Mixtures

Abstract

Laminar burning velocities and Markstein lengths of premixed methane−n-heptane−air mixtures were experimentally investigated at an initial pressure of 0.1 MPa, initial temperatures of 358, 393, and 428 K, and equivalence ratios of 0.7−1.5. The methane content in the methane−n-heptane mixtures ranges from 0 to 1. The experiments were conducted in a combustion chamber with central ignition. In the present study, the difference between the linear and nonlinear extrapolation methods was analyzed quantitatively for methane−n-heptane−air flames. Comparisons of the laminar burning velocities of methane−air and n-heptane−air flames were conducted, respectively, between the present and other studies. Subsequently, effects of the initial temperature and methane content on the laminar burning velocity and flame instability of methane−n-heptane−air mixtures were analyzed. Then, the critical methane content at which the laminar burning velocity and flame instability of methane−n-heptane−air flames start to change relatively significantly was explored. The results show that the laminar burning velocities of methane−air and n-heptane−air flames measured in the present study are in good agreement with the data available in the literature. Laminar burning velocities and flame instabilities of methane−n-heptane−air flames seem to be less sensitive to the methane content when the methane content is below 0.75. The change in the initial temperature tends to diminish the difference in the laminar burning velocity between methane−air and n-heptane−air flames and only has weak effects on the flame instability of methane−n-heptane−air mixtures. According to variations of the laminar burning velocities and Markstein lengths of methane−n-heptane−air flames with the methane content, the value of 0.75 can be treated preliminarily as the critical methane content.

Development and Validation of 3D-CFD Injection and Combustion Models for Dual Fuel Combustion in Diesel Ignited Large Gas Engines

“…Unlike the ignition delay calculations, the results for the laminar flame speed of the fuel mixture exhibit linear behavior with respect the fuel mixture fraction. Recent experimental studies carried out by Li [44] support this assumption. The laminar flame speed for n-heptane was tabulated with the LLNL-v3 mechanism and that of methane was tabulated using the GRI 3.0 mechanism for natural gas.…”

“…Furthermore, the validation of the measurements of laminar flame speeds is shown. Figure 7 compares the full scale mechanism and the reduced mechanism, whereas Figure 8 provides the results of the reduced mechanism in relation to the experimental data found in [44]. As the laminar flame speed might also be the subject of tabulation in future research, this underlines the fact that the same mechanism can tabulate dual fuel ignition delay as well as laminar flame speed.…”

“…An accurate description of the laminar flame speed is necessary to depict the heat release rate coming from flame front propagation. Once again, the laminar flame speed depends on the two fuels involved in the combustion process; with n-heptane methane mixtures, it was able to be shown experimentally [44] and numerically [41,45].…”

“…Comparison of laminar flame speed calculations for dual fuel mixtures. The reduced dual fuel mechanism is compared to the experimental data found in[44].…”

Development of a simplified n-heptane/methane model for high-pressure direct-injection natural gas marine engines

“…It is because that a part of CH3 for the 334-step mechanism is oxidized to form CH2 species, while for the 35-step mechanism, CH2O is the only oxidation species. Comparisons between the calculated and experimental laminar flame speeds [46][47][48][49][50][51][52][53][54][55][56][57] of the n-heptane/air and methane/air mixtures at 1 bar are shown in Figs. 6 and 7, respectively.…”