Heptane ignition temperature

Auto-ignition temperature 204° C Heptane spontaneously combusts above 204°C. 

Heptane is a seven-carbon alkane and has a boiling point of 98°C, a flash point of 25°F, a flammable range of 1.05 to 6.7%, and an ignition temperature of 433°F. The stracture and molecular formula is shown in Figure 5.30. 

Four important tests which are used to characterize an engine fuel are the spontaneous ignition temperature (SIT), flash point, fire point, and smoke point. These tests are standardized, and specialized fuels have specific requirements as defined by these tests. The SIT is dependent on the composition of the fuel and the conditions of the walls of the cylinder. Diesel fuels require low SIT with short delay times of the order of 1-2 ms. The SIT of heptane (CN = 60) is 330°C, whereas benzene with CN = —10 has a SIT of 420°C. 

Mellor, 1941, Vol. 2, 292 1956, Vol. 2, Suppl. 1, 380 1943, Vol. 11, 26 Liquid chlorine at —34°C explodes with white phosphorus, and a solution in heptane at 0°C ignites red phosphorus. Boron, active carbon, silicon and phosphorus all ignite in contact with gaseous chlorine at ambient temperature. Arsenic incandesces on contact with liquid chlorine at —34°C, and the powder ignites when sprinkled into the gas at ambient temperature. Tellurium must be warmed slightly before incandescence occurs. 

Fig. 6. 21. Ignition delays as a function of compressed gas temperature for the normal alkanes, n-butane to n-heptane, i-octane (2,2,4-trimethylpentane) and toluene in stoichiometric proportions in air. The results were obtained in a rapid compression machine at a compressed gas density of 128 mol m (0.65-0.75 MPa). Ignition in the ntc and lower temperature range was not observed under these experimental conditions [50].

Although the ability to cope with complex mixtures of fuels may be some way off, dealing with alkane mixtures is certainly within our grasp. However, there appears to be one key aspect that requires clarification. From the evidence in Section 6.4, it is clear that the longer chain n-alkanes, such as n-heptane, can undergo spontaneous ignition at very low-temperatures. This is in marked contrast to the lower reactivity of the shorter n-alkane chains such as n-butane, or of highly branched isomers... 

Fig. 7.10. Comparison of ignition delay-times measured in a rapid compression machine (points) with Shell model predictions (lines) [71]. Fuels are all RON 90 with different sensitivities PRF, primary reference fuel, 10% n-heptane, 90% isooctane, MON = 90 TRF toluene reference fuel, 30% heptane, 70% toluene MON = 77.9 2-methyl-2-hexene, MON = 78.9. Compression ratio 9.6, 0.9 stoichiometric mixtures, wall temperatures 373 K. (a) Effect of temperature at end of compression charge density 3.20 x 10" mol cm . (b) Effect of charge density end of compression temperature 690 K. (Note all end of compression temperatures are averages over whole charge.) From [71].

K. Fieweger, U. Pfahl and G. Adomeit, Self Ignition of n-Heptane/Iso-Octane Mixtures and n-Decane with Air under Engine Conditions Temperature, 20th International Symposium on Shock Waves (Passedena, 1995). 

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