Inhibition Effect and Kinetic Study of Novec-1230 on the Ammonia-Doped Methane Flames

The synchronization among the central electrode ignition control system, high-speed schlieren imaging system and pressure data acquisition system inside a constant volume combustion chamber (CVCC) should be accurately controlled in the study of the laminar burning velocity of fuel by spherical expansion flame method in a CVCC. In this paper, the digital delay pulse generator and the high-speed data acquisition card are used to control the synchronization among the abovementioned three systems with the control error in 30 μs, and then the schlieren image of the flame front and the pressure inside a CVCC are captured successfully. These lay a solid foundation for the measurement of laminar burning velocity by constant pressure method (CPM) and constant volume method (CVM).

Formulating a quaternary gasoline surrogate (MTRF-87) using laminar burning velocity measurements

Landfill gas (LFG) produced from depletion of biological waste has the potential to become one of the main energy resources in the future. In this study, laminar burning velocity (ul), Markstein length, and flammability limits of different compositions of landfill gas (LFG) are measured using the Schlieren flame front visualization method in an 11 liter constant volume combustion chamber. Three common compositions of LFG with carbon dioxide (CO2) volumetric fraction of fuel ranging from 0.3 to 0.5 are examined. Pressure was changed from atmospheric pressure to 5 bar with an increment of 2 bar. The effects of equivalence ratio, pressure, and CO2 content of fuel on laminar burning velocity are investigated, and rich and lean burn limits of different compositions of fuel are obtained. Numerical investigation is also performed using the CHEMKIN package via GRI3.0 and UBC2.1 chemical kinetic mechanisms. The results indicate that increasing the pressure reduces laminar burning velocity, whereas it increases the...

Measurements of laminar burning velocities and Markstein lengths for methanol–air–nitrogen mixtures at elevated pressures and temperatures

<div class="section abstract"><div class="htmlview paragraph">Co-Optimization of Fuels and Engines initiative (Co-Optima) of the U.S Department of Energy started investigations on several candidates of biofuels and blends for internal combustion engines. At this stage, only a few biomass-derived fuel blendstocks (including ethanol) for advanced spark-ignition engines have been selected using enhanced screening criteria, which included boiling point, toxicity, research octane number, octane sensitivity, and economical distribution system, etc. Ethanol, of which this paper is focused on, is also an important fuel because of its high-octane number which in turn promotes advance ignition timing and higher thermal efficiencies in reciprocating engines. Measurements of laminar burning velocity (LBV) is a key metric to understand fuel performance and applicability in engines. Furthermore, in order to quantify more complicated, and practical, burning regimes such as turbulent combustion much of the underlying theory requires knowledge of LBV. While there exist many studies for ethanol LBV under atmospheric conditions, there are only few studies on combustion characteristics at high pressures that are relevant to engines. Here measurements of ethanol LBVs at two initial pressures of 2 atm and 10 atm and two initial temperatures of 373 K and 428 K are presented. Equivalence ratio was varied in a wide range from 0.7 to 1.5 to examine the effects on laminar burning velocity. It has been noticed that a cellular structure formed during combustion at 10 atm with synthetic air. To restrain occurrence a cellular flame during combustion, a mixture of helium and nitrogen in synthetic air was employed. The results presented are also compared with the predictions of some of the available detailed kinetic mechanisms as part of their validation process and found to be in good agreement with simulations. Current effort provides a comprehensive investigation of ethanol LBVs which can be used in the development of detailed and reduced kinetic mechanisms in the future.</div></div>

Experimental measurements of laminar burning velocity are presented for mixture temperatures above the autoignition temperature of premixed n-heptane + air mixtures using an externally heated mesoscale diverging channel method. Direct measurements of laminar burning velocity are carried out at 1 atm of pressure for an unburnt mixture temperature range (350–600 K) with the mixture equivalence ratio varying from ϕ = 0.6 to 1.5. Nonlinear power-law correlation is proposed to delineate the effect of change in the mixture temperature on the burning velocity variation at various equivalence ratios. A minimum value for the temperature exponent is observed for stoichiometric n-heptane + air mixtures. The maximum value of laminar burning velocity is measured for ϕ ≈ 1.1 at all mixture temperatures. The reported data sets are compared with the available experimental results and the predictions of various detailed kinetic models, i.e., LLNL V3.1 (2011), JetSurF 2.0 (2010), and Poli Mi (2014). Good agreement of the present data is observed with the predictions of the LLNL V3.1 reaction mechanism at all unburnt mixture temperatures. The predictions of other kinetic models show slight under-prediction at higher mixture temperatures. Sensitivity analysis using the LLNL V3.1 mechanism is reported to highlight the contribution of key reactions enhancing/reducing the laminar burning velocity at 470 and 600 K mixture temperatures. With an increase in the mixture temperature from 470 to 600 K, the influence of the chain branching reaction (H + O₂ ↔ O + OH) on laminar burning velocity increases nearly 63.5%. Formation of a vinyloxy radical (CH₂CHO) from the oxidation of a vinyl radical (C₂H₃) enhances the burning velocity at a 470 K temperature. Oxidation of C₂H₃ (at 600 K) becomes crucial in governing engine knocking in low-temperature oxidation of n-heptane. It is deduced from the reaction pathway diagram that the production of a highly reactive compound, C₂H₂, at 600 K plays a significant role and governs the overall reaction rate of the mixture.

Co-optima fuels combustion: A comprehensive experimental investigation of prenol isomers

A new adiabatic burner allowing the measurement of burning velocities at high pressure with the heat flux method has been developed. Experimental measurements of laminar burning velocities of methane and n-pentane were performed for pressures up to 6 atm at 298 K and at atmospheric pressure for temperatures from 298 to 398 K. Equivalence ratios varied from 0.6 to 1.9. The results for methane flames are in good agreement with the only results of literature obtained above atmospheric pressure using the heat flux method; those for n-pentane are to our knowledge the first application of this method to a flame of a liquid fuel above atmospheric pressure. Based on these measurements, empirical correlations of the variation of the measured laminar flame velocities with pressure and temperature have been proposed for methane and n-pentane. In the case of methane, these correlations lead to a satisfactory prediction of literature measurements made using constant volume bombs.

<div class="section abstract"><div class="htmlview paragraph">Laminar burning velocity (LBV) measurements are reported for promising high-performance fuels selected as drop-in transportation fuels to automotive grade gasoline as part of the United States Department of Energy’s Co-Optimization of Fuels and Engines Initiative (Co-Optima). LBV measurements were conducted for ethanol, methyl acetate, and 2-methylfuran with synthetic air (79.0 % N<sub>2</sub> and 21.0 % O<sub>2</sub> by volume) within a constant-volume spherical combustion rig. Mixture initial temperature was fixed at 428±4 K, with the corresponding initial pressure of 1.00±0.02 atm. Current LBV of ethanol is in good agreement with literature data. LBV of ethanol and 2-methylfuran showed similar values over the range of equivalence ratios, while methyl acetate exhibited an LBV significantly lower over the range of tested equivalence ratios. The maximum laminar burning velocity occurred at slightly richer equivalence ratio from the stoichiometric value for all fuels tested. LBV data were compared to simulations by chemical kinetic mechanisms. The predicted LBVs of ethanol and methyl acetate were in reasonable agreement with data, however, those for 2-methlyfuran were slightly under-predicted. Current data will serve as valuable validation targets for future chemical kinetic mechanisms for Co-Optima fuels.</div></div>

Measurement of laminar burning velocities of methanol–air mixtures at elevated temperatures

The present work reports the measurement of the laminar burning velocity of liquefied petroleum gas (LPG)–air mixtures at high temperatures using the planar flame propagation mode appearing in the preheated mesoscale diverging channel. The experiments were carried out for a range of equivalence ratios, 0.7 ≤ Φ ≤ 1.3. The present data for LPG–air mixtures are reported for a temperature range of 370–650 K in comparison to maximum mixture temperatures of 400 K reported in the literature. Experimental studies complimented with computational studies for conditions similar to present experiments confirm that the effect of heat loss from flame to channel walls on burning velocity is minimal and measured burning velocities are nearly equal to adiabatic burning velocity. The stabilized flame is nearly flat in both transverse and depth directions. The power law form of correlations from present experiments help in understanding the variation of laminar burning velocity with mixture temperatures and equivalence rati...

Measurement of laminar burning velocity of high performance alternative aviation fuels

An experiment is described for the direct measurement of laminar burning velocity within an opticallyaccessed cylindrical combustion chamber. The laminar burning velocity was determined directly as thedifference between the flame propagation speed and the unburned gas velocity immediately ahead of theflame front. Particle Image Velocimetry (Ply) has been applied to measure the unburned gas velocity field.The local flame speed and flame front position were determined from a pair of ionisation probes inconjunction with the simultaneous NV measurement. The laminar burning velocity of propane-air mixtures initially at atmospheric condition for different equivalence ratios ranging from 0.7 - 1 .4 are presented. Closeagreement with other measurements and predicted results was found. Keywords: Particle Image Velocimetry, flame, flame speed, laminar burning velocity, unburned gasvelocity 1 . INTRODUCTION Laminar burning velocity is one of the most important characteristics for analysing and predicting thecombustion process. Andrews and Bradley 1

Measurements of the laminar burning velocity of hydrogen–air premixed flames

Measurement of laminar burning velocities of methane-air mixtures simultaneously at elevated pressures and elevated temperatures