The straining of premixed turbulent flames

Modeling and calculation of turbulent lifted diffusion flames

“…5 and 11 or the strain rate s. The quenching value tlq is determined from laminar diffusion flamelet calculations [13][14][15] or from experiments [10]. The form of the pdfs P(12) are a lognormal distribution for the scalar dissipation [5] and a quasi Gaussian pdf for the strain rate [16]. The latter is written as…”

On The Transition from Deflagration to Detonation

“…Even more significant is the magnitude of the fluctuating strain rate w' = u' /,\ = 2.5 X 10 4 s-l! This is a factor of fifty larger than the characteristic strain Sui i, = 500 s-1 needed for extinction by stretching and several times the maximum strain experimentally observed [6] to be required to quench flames in turbulent flows. It is these simple estimates that lead us to the conclusion that a highly unusual regime of combustion exists in the high-speed flame propagation just prior to transition to detonation.…”

The railplug: Development of a new ignitor for internal combustion engines. Final report

“…We believe that this is because the railplug-ignited flame enters the fully developed phase of combustion earlier (at 30 oBTDC), when the turbulence intensity, u', is higher. Because flame strain typically scales with ( u ' )~'~ (e.g., Herweg and Maly, 1992;Abdel-Gayed et al, 1989), the flame is strained harder with earlier ignition, thereby slowing down the main phase of the combustion process of this very weak mixture. Railplug operation with retarded timing (by -15 CAo) to achieve the same LPP and imep as for the wide gap spark plug does not exhibit this trend because this weak flame enters the fully developed phase of combustion later in crank angle degrees.…”