Laminar burning velocities of premixed nitromethane/air flames: An experimental and kinetic modeling study

Abstract

Due to its high lubricity, nitromethane is a fuel regularly used in model engine or more generally in race engine. The objective of this study is to improve our knowledge and understanding of the combustion of nitromethane for better evaluating its potential as fuel for automotive spark-ignition engines. To achieve this goal, unstretched laminar burning velocities of nitromethane-air mixtures were measured using spherical propagation methodology at 423 K over a pressure range from 0.5 to 3 bar and equivalence ratios from 0.5 to 1.3. The data indicated a typical adverse effect of pressure on laminar burning velocities. Based on the work done by Zhang et al., Proc. Combust. Inst., 33 (2011) 407-414, a modified detailed kinetic model including 88 species and 701 reactions was proposed. Comparisons between experimental and simulated un-stretched laminar flame speed were made and showed good agreement. The new kinetic mechanism was also used to successfully simulate published experiments and rationalize the unusual occurrence of maximum flame speed in the fuellean region.

Fuel performances in Spark-Ignition (SI) engines: Impact of flame stretch

“…Nevertheless, SL 0 cannot be considered as the speed of an expanding flame since expanding flames are subject to flame stretch, which is a compound of strain rate and flame curvature [11]. The flame stretch can be defined as the relative growth rate of the flame surface A [12]: (1) Initially presented in the work of Karlovitz et al [13] and Markstein [14], flame stretch is usually linearly linked [15] to the laminar flame speed Sb as below, with Lb the Markstein length and Sb 0 the unstretched laminar flame speed: (2) In some recent studies, a more realistic nonlinear relationship between flame speed and flame stretch has been used [16 18]: (3) Under certain assumptions the unstretched laminar flame speed, Sb 0 is directly related to SL 0 by using the expansion ratio , where b and u are respectively the burnt and fresh gas densities: (4) In equations (2) and (3), the Markstein length Lb is a key parameter because it represents the flame stretch sensitivity of an air-fuel mixture. It is a function of the Zeldovich number, the flame thickness and particularly of the Lewis number Le (i.e.…”

Insights into nitromethane combustion from detailed kinetic modeling – Pyrolysis experiments in jet-stirred and flow reactors

“…In Figure 20, laminar flame speeds of a CH3NO2/air flame at 423 K are compared against the model predictions for initial pressures of 1, 2, and 3 bar. The measurements (symbols) were performed by Brequigny et al [28] for propagating spherical flames. To determine the equivalence ratio, they used the equation CH3NO2 + 0.75(O2 + 3.76 N2) ⇋ CO2 + 1.5 H2O + 3.32 N2 (Equation (1)).…”

“…were not available in literature. Nauclér et al [27] performed ignition delay time experiments of CH3NO2/O2/N2 in a shock tube and used two mechanisms from literature [28,29] to compare against their experimental data and mechanism predictions. Similarly, Brackmann et al [30] measured the burning velocity of CH3NO2/O2 diluted with CO2 and the concentrations of NO, CO and CH2O in two CH3NO2 flames (experimental condition shown in Table 1).…”

“…Similarly, Brackmann et al [30] measured the burning velocity of CH3NO2/O2 diluted with CO2 and the concentrations of NO, CO and CH2O in two CH3NO2 flames (experimental condition shown in Table 1). They used the same two mechanisms [28,29] as Nauclér et al and compared model predictions and measurements. It was concluded in both studies that none of the mechanisms is able to accurately predict the experimental data [27,30].…”

Experimental assessment of various methods of determination of laminar flame speed in experiments with expanding spherical flames with positive Markstein lengths

“…These observations are beneficial for the LC Eq. (6) when compared to alternative expressions, especially as the sub-range B 2 is sufficiently wide (flame radii are varied from 9 to 16 mm) and is characterized by sufficiently large R f (the ignition perturbations were claimed to be weak when flame radii were larger than 6.5 mm [34,35,71,72], 7 mm [50,61], or 8 mm [59]). If each run is processed independently, then, the LC Eq.…”