In the present paper new results on the combustion of n-octane obtained by molecular beam mass spectrometry in a flat flame are presented. Corresponding experiments on i-octane have been reported [1] and comparisons to that compound are made to explore the different ignition and combustion behaviour of n-and i-octane.
The reactants, 1.9% n-C8Hjs, 24% O2, and 74% N2, were introduced into a porous cooled (60ยฐC) burner with a diameter of 60 ram. At the burning pressure, 9.3 kPa, the velocity of the cold gas mixture was 0.44 ms-1. A quartz cone with an apex angle of 60* and an orifice of 50/~m was used for gas sampling. To reduce wall reactions the cone tip was treated with 5% HF. The mass spectrometer was a quadrupole (Balzers QMG511) with an electron impact ion source and is described elsewhere . Due to fragmentation of molecules in the ion source, more than one species may contribute to a certain mass peak. To reduce this effect and still have a strong signal intensity an electron energy of 20 eV was used in the experiments. N2 was measured at mass number (= M) 14 at an electron energy of 70 eV. The temperature of the undisturbed flame was measured with a Pt 30% Rh/Pt 6% Rh thermocouple of 0.1 mm wire thickness. To prevent catalytic reactions the wires were coated with YtC13/BeO [3] and the emission was corrected for in a procedure based on Kaskan's relation .