Experimental observations on the influence of hydrogen atoms diffusion on laminar and turbulent premixed burning velocities

Measurements of the laminar and turbulent burning velocity of premixed hydrogen–air, n-hexane–air and n-octane–air flames were made and compared to corresponding measurements of deuterium–air, n-hexane-d14–air and n-octane-d18–air flames performed at identical initial conditions. Experiments were conducted in a constant volume, optically accessed vessel, at elevated initial pressure and temperature of 0.5 MPa and 360 K, for a range of equivalence ratios. Burn rate data was determined via schlieren imaging of flames. It was found that the isotope effect accounted for an average reduction of 20% in the laminar burn rate of alkanes. Similarly, deuterium was measured to burn around 30% slower than hydrogen at the range of equivalence ratios explored. The isotope effect on burn rate was significantly reduced under turbulence. The difference between the turbulent burn rates of the deuterated alkanes and their normal alkane counterparts were measured to be approximately 10%. The difference between the turbulent burn rates of deuterium and hydrogen was even smaller. Nonetheless, the laminar burn rate ranking was maintained under turbulence for all fuels and conditions explored, thus suggesting a degree of influence of radical transport and chemistry under turbulent burning

Turbulent burning rates of gasoline components, Part 2-Effect of carbon number

Experimental measurements of turbulent and laminar burning velocities have been made for premixed hydrocarbon–air flames of straight chain molecules of increasing carbon number (from n-pentane to n-octane). Measurements were performed at 0.5 MPa, 360 K and rms turbulent velocities of 2 and 6 m/s, for a range of equivalence ratios. The laminar burning velocities were used to interpret the turbulent data, but were also found to be broadly in line with those of previous workers. At lean conditions the turbulent burning velocity was measured to be similar between the four alkanes studied. However, at rich conditions there were notable differences between the turbulent burn rates of the fuels. The equivalence ratio of the mixtures at which the maximum burning velocities occurred in the turbulent flames was richer than that under laminar conditions. The equivalence ratio of the peak turbulent burning velocity was found to be a function of the carbon number of the fuel and the turbulent intensity and became gradually fuel rich with increases in each of these values

Turbulent premixed flames: experimental studies over the last decades

International audienc

Chemistry of NOx decomposition at flame temperatures

Detailed N/O kinetic sub-mechanism (for species containing only nitrogen and/or oxygen atoms) was updated on the basis of a literature survey of new experimental data for pertinent reactions. It was shown that without any adjustment of the rate constants the proposed N/O kinetic mechanism provides at least satisfactory agreement with different sets of experimental data on NOx decomposition. Burning velocities of pure N2O were measured at a pressure of 5 atm for further validation of the mechanism. It was found that the mechanism substantially underpredicts these data by a factor of approximately two. Possible reasons for this disagreement are suggested

Chemistry of NOx decomposition at flame temperatures

Detailed N/O kinetic sub-mechanism (for species containing only nitrogen and/or oxygen atoms) was updated on the basis of a literature survey of new experimental data for pertinent reactions. It was shown that without any adjustment of the rate constants the proposed N/O kinetic mechanism provides at least satisfactory agreement with different sets of experimental data on NOx decomposition. Burning velocities of pure N2O were measured at a pressure of 5 atm for further validation of the mechanism. It was found that the mechanism substantially underpredicts these data by a factor of approximately two. Possible reasons for this disagreement are suggested

Laminar burning velocities of three C3H6O isomers at atmospheric pressure

Laminar flames of three C3H6O isomers (propylene oxide, propionaldehyde and acetone), representative of cyclic ether, aldehyde and ketone species important as intermediates in oxygenated fuel combustion, have been studied experimentally and computationally. Most of these flames exhibited a non-linear dependency of flame speed upon stretch rate and two complementary independent techniques were adopted to provide the most reliable burning velocity data. Significant differences in burning velocity were noted for the three isomers: propylene oxide + air mixtures burned fastest, then propionaldehyde + air, with acetone + air flames being the slowest; the latter also required stronger ignition sources. Numerical modelling of these flames was based on the Konnov mechanism, enhanced with reactions specific to these oxygenated fuels. The chemical kinetics mechanism predicted flame velocities in qualitative rather than quantitative agreement with the measurements. Sensitivity analysis suggested that the calculated flame speeds had only a weak dependency upon parent fuel-specific reactions rates; however, consideration of possible break-up routes of the primary fuels has allowed identification of intermediate compounds, the chemistry of which requires a better definition

KNOCK CHARACTERISTICS ANALYSIS OF A SUPERCHARGED SPARK IGNITION ENGINE USING THREE GRADES OF FUELS

The power output of a spark ignition engine could be improved by boosting the intake pressure and compression ratio; however the applications of these are limited by knock in engines. This study examined the knocking behaviours of three commercially available fuels for spark ignition engines operated at engine intake pressures of 1.6 and 2.0 bar. The pressure data for the fuels tested were grouped into three: the fast cycle, medium cycle and slow cycles. Knock intensities from the pressure data were processed with Fast Fourier Transform (FFT) and band pass filtering techniques. The results showed that the knocking cycles occurred only in the fast and medium cycles. These results supported the view that auto-ignition of end-gases was due to compression from the high speed propagating flames. FTiR spectrums showed that the presence of aromatics was responsible for the better anti-knock quality exhibited by E5 and ULG 98 over PRF 95. Keywords: End gas, Fuel, FTiR , Knock, Spark Ignition Engine, Supercharging, Pressure