The Effect of Minor Components on the Ignition of Lean Mixtures of Methane in Air

  • Miss Yii Leng Chan, Centre for Petroleum, Fuels and Energy, The University of Western Australia, Australia
  • Dr John Bromly, Centre for Advanced Energy Science and Engineering, Curtin University of Technology, Australia
  • Prof Alexander Konnov, Department of Mechanical Engineering, Vrije Universiteit Brussel, Belgium
  • Prof Dongke Zhang, The University of Western Australia, Australia

    • It is known that the low concentrations of higher hydrocarbons usually present in natural gas can substantially alter its ignition properties (autoignition temperature and ignition delay) compared to those of pure methane/air mixtures. This is the case even when the level of these higher hydrocarbons is so low as to not greatly affect other combustion properties. Likewise, low concentrations of NOx can have a similar effect. This has implications for the ignition properties of natural gas. Similarly, the presence of NOx in the combustion air may affect the ignition characteristics of either methane or natural gas.

    In this study, low levels (in the order of a few percents v/v) of ethane, propane and butane were added individually to pure methane to determine the effect on its ignitability in a flow reactor at essentially atmospheric pressure. In each case, various concentrations (up to 400 ppm v/v) of nitric oxide were added in order to study the effect of higher hydrocarbons and NO in combination.

    It was found that the presence of the higher hydrocarbons significantly reduced the ignition temperature compared to that of pure methane under comparable conditions. The NO addition had the same effect, though in terms of concentration, the NO was a much more potent promoter than the hydrocarbons, the effect of a few parts per million having an equivalent effect to percent level of hydrocarbons. At higher levels the NO dominates the ignition process to the extent that the influence of the higher hydrocarbons becomes negligible.