skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures

Abstract

The ignition delay times of mixtures containing 35% n-heptane and 65% toluene by liquid volume at room temperature (i.e., 28% n-heptane/72% toluene by mole fraction) were determined in a high-pressure shock tube in the temperature range 620{<=} T{<=}1180 K at pressures of about 10, 30, and 50 bar and equivalence ratios, {phi}, of 0.3 and 1.0. The equation {tau}/{mu}s=9.8 x 10{sup -3} exp (15,680 K/T)(p/bar){sup -0.883} represents the data for {phi}=0.3 in the temperature range between 980 and 1200 K. At lower temperatures no ignition was found at 10 bar within the maximum test time of 15 ms, whereas for 50 bar, a reduced activation energy was observed. A pressure coefficient of -1.06 was found for the data with {phi}=1.0. No common equation for the data at {phi}=1.0 could be found analogous to that for {phi}=0.3 because the ignition delay times show no Arrhenius-like behavior. A comparison with ignition delay times of n-heptane/air and toluene/air for {phi}=1.0 and 30 bar shows that the values of the mixture of the two components are between the values of the single substances. Furthermore, the results confirm the negative temperature coefficient behavior found for the mixtures at 30 and 50 bar, similar to n-heptane/air.more » A comparison for the other pressure and equivalence ratio values of this study was not possible because of the lack of data for pure toluene. These experimental data have been used in the development of a chemical kinetics model for toluene/n-heptane mixtures as described in a companion paper. (author)« less

Authors:
; ; ; ; ;  [1];  [2]
  1. IVG, Universitaet Duisburg-Essen, D-47048 Duisburg (Germany)
  2. Shell Global Solutions, P.O. Box 1, Chester CH1 3SH (United Kingdom)
Publication Date:
OSTI Identifier:
20880638
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 149; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; HEPTANE; TOLUENE; PRESSURE RANGE MEGA PA 10-100; AIR; MIXTURES; EXPERIMENTAL DATA; AUTOIGNITION; TEMPERATURE RANGE 0400-1000 K; TEMPERATURE RANGE 1000-4000 K; SHOCK TUBES; TEMPERATURE DEPENDENCE; PRESSURE DEPENDENCE; ACTIVATION ENERGY; COMBUSTION KINETICS; PRESSURE RANGE MEGA PA 01-10

Citation Formats

Herzler, J., Fikri, M., Hitzbleck, K., Starke, R., Schulz, C., Roth, P., and Kalghatgi, G.T. Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures. United States: N. p., 2007. Web. doi:10.1016/J.COMBUSTFLAME.2006.12.015.
Herzler, J., Fikri, M., Hitzbleck, K., Starke, R., Schulz, C., Roth, P., & Kalghatgi, G.T. Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures. United States. doi:10.1016/J.COMBUSTFLAME.2006.12.015.
Herzler, J., Fikri, M., Hitzbleck, K., Starke, R., Schulz, C., Roth, P., and Kalghatgi, G.T. Sun . "Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures". United States. doi:10.1016/J.COMBUSTFLAME.2006.12.015.
@article{osti_20880638,
title = {Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures},
author = {Herzler, J. and Fikri, M. and Hitzbleck, K. and Starke, R. and Schulz, C. and Roth, P. and Kalghatgi, G.T.},
abstractNote = {The ignition delay times of mixtures containing 35% n-heptane and 65% toluene by liquid volume at room temperature (i.e., 28% n-heptane/72% toluene by mole fraction) were determined in a high-pressure shock tube in the temperature range 620{<=} T{<=}1180 K at pressures of about 10, 30, and 50 bar and equivalence ratios, {phi}, of 0.3 and 1.0. The equation {tau}/{mu}s=9.8 x 10{sup -3} exp (15,680 K/T)(p/bar){sup -0.883} represents the data for {phi}=0.3 in the temperature range between 980 and 1200 K. At lower temperatures no ignition was found at 10 bar within the maximum test time of 15 ms, whereas for 50 bar, a reduced activation energy was observed. A pressure coefficient of -1.06 was found for the data with {phi}=1.0. No common equation for the data at {phi}=1.0 could be found analogous to that for {phi}=0.3 because the ignition delay times show no Arrhenius-like behavior. A comparison with ignition delay times of n-heptane/air and toluene/air for {phi}=1.0 and 30 bar shows that the values of the mixture of the two components are between the values of the single substances. Furthermore, the results confirm the negative temperature coefficient behavior found for the mixtures at 30 and 50 bar, similar to n-heptane/air. A comparison for the other pressure and equivalence ratio values of this study was not possible because of the lack of data for pure toluene. These experimental data have been used in the development of a chemical kinetics model for toluene/n-heptane mixtures as described in a companion paper. (author)},
doi = {10.1016/J.COMBUSTFLAME.2006.12.015},
journal = {Combustion and Flame},
number = 1-2,
volume = 149,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • Toluene is often used as a fluorescent tracer for fuel concentration measurements, but without considering whether it affects the auto-ignition properties of the base fuel. We investigate the auto-ignition of pure toluene and its influence on the auto-ignition of n-heptane and iso-octane/air mixtures under engine-relevant conditions at typical tracer concentrations. Ignition delay times {tau}{sub ign} were measured behind reflected shock waves in mixtures with air at {phi}=1.0 and 0.5 at p=40 bar, over a temperature range of T=700-1200 K and compared to numerical results using two different mechanisms. Based on the models, information is derived about the relative influence ofmore » toluene on {tau}{sub ign} on the base fuels as function of temperature. For typical toluene tracer concentrations {<=}10%, the ignition delay time {tau}{sub ign} changes by less than 10% in the relevant pressure and temperature range. (author)« less
  • The rate of soot formation during the pyrolysis and oxidation of rich mixtures of toluene and benzene, and the pyrolysis of toluene/n-heptane mixtures has been determined using a reflected shock technique over the temperature range of 1500-1950K and for pressures between 2.6 and 3.6 x 10/sup 5/ Pa. A laser beam attenuation technique was used to determine soot concentrations using helium-neon lasers at 632.8 and 1152.0 nm. The test gas mixtures were diluted with at least 98 mol% argon and for the pyrolysis experiments the hydrocarbon concentration did not exceed 0.35 mol m/sup -3/. The oxidation experiments employed fuel richmore » mixtures with equivalence ratios between 6 and 11. Rates of soot formation and soot yields exhibited an Arrhenius dependence and could be expressed by a correlation equation in a form which is also suitable for the prediction of soot limits.« less
  • Ignition times were determined in high-pressure shock-tube experiments for various stoichiometric mixtures of two multicomponent model fuels in air for the validation of ignition delay simulations based on chemical kinetic models. The fuel blends were n-heptane (18%)/isooctane (62%)/ethanol (20%) by liquid volume (14.5%/44.5%/41% by mole fraction) and n-heptane (20%)/toluene (45%)/isooctane (25%)/diisobutylene (10%) by liquid volume (17.5%/55%/19.5%/8.0% by mole fraction). These fuels have octane numbers comparable to a standard European gasoline of 95 RON and 85 MON. The experimental conditions cover temperatures from 690 to 1200 K and pressures at 10, 30, and 50 bar. The obtained ignition time data aremore » scaled with respect to pressure and compared to previous results reported in the literature. (author)« less
  • Iso-cetane (2,2,4,4,6,8,8-heptamethylnonane, C{sub 16}H{sub 34}) is a highly branched alkane reference compound for determining cetane ratings. It is also a candidate branched alkane representative in surrogate mixtures for diesel and jet fuels. Here new experiments and kinetic modeling results are presented for the autoignition of iso-cetane at elevated temperatures and pressures relevant to combustion in internal combustion engines. Ignition delay time measurements were made in reflected shock experiments in a heated shock tube for {phi} = 0.5, 1.0, and 1.5 iso-cetane/air mixtures at temperatures ranging from 879 to 1347 K and pressures from 8 to 47 atm. Ignition delay timesmore » were measured using electronically excited OH emission, monitored through the shock tube end wall, and piezoelectric pressure transducer measurements, made at side wall locations. A new kinetic mechanism for the description of the oxidation of iso-cetane is presented that is developed based on a previous mechanism for iso-octane. Computed results from the mechanism are found in good agreement with the experimental measurements. To our knowledge, the ignition time measurements for iso-cetane presented here are the first of their kind. (author)« less
  • The phase behavior of methane, ethane, and propane in n-heptane and toluene solvents has been studied for a range of temperatures from 0 to -100/sup 0/F and pressures from 100 to 1600 psia. Gas chromatographic retention data were used to calculate the vapor-liquid equilibrium constants. It was necessary to modify a chromatographic technique in order to accurately determine the phase behavior of methane. The K-values found in this experimental work are plotted and tabulated. A favorable comparison was found between this experimental work and other published data. (28 refs.)