Ignition kernel development studies relevant to lean-burn natural-gas engines

In lean-burn premixed natural-gas engines, ignition and combustion can be accelerated by burning a small fraction of the mixture in a pre-chamber. High pressure generated in the pre-chamber results in the discharge of burned products into the main chamber. This creates multiple ignition kernels along the surface of the resulting jet. In this work, lean-burn characteristics of methane under the high pressure and high temperature conditions of a hot-jet ignited combustion chamber are investigated numerically by initializing a kernel of specified composition, temperature and size in a lean premixed gas, and following the development of the flame. In the case of hot-jet ignition the kernel temperature is limited by the temperature of the hot products. The influence of variations in ignition energy, affected by both temperature and size, and equivalence ratio, on the flame development is studied in an initially quiescent gas. It is shown that as long as the available ignition energy is greater than a minimum, the duration in which a steady flame speed is achieved is a strong function of kernel temperature; it is not a function of kernel size.