TY - JOUR

T1 - Spark ignition transitions in premixed turbulent combustion

AU - Shy, Shenqyang (Steven)

N1 - Publisher Copyright:
© 2023 Elsevier Ltd

PY - 2023/9

Y1 - 2023/9

N2 - Recent discoveries and developments on the dynamic process of premixed turbulent spark ignition are reviewed. The focus here is on the variation of turbulent minimum ignition energies (MIET) against laminar MIE (MIEL) over a wide range of r.m.s. turbulence fluctuation velocity (uʹ) alongside effects of the spark gap between electrodes, Lewis number, and some other parameters on MIE. Two distinguishable spark ignition transitions are discussed. (1) A monotonic MIE transition, where MIEL sets the lower bound, marks a critical uʹc between linear and exponential increase in MIET with uʹ increased. (2) A non-monotonic MIE transition, where the lower bound is to be set by a MIET at some uʹc, stems from a great influence of Lewis number and spark gap despite turbulence. At sufficiently large Lewis number >> 1 and small spark gap (typically less than 1 mm), turbulence facilitated ignition (TFI), where MIET < MIEL, occurs; then MIET increases rapidly at larger uʹ > uʹc because turbulence re-asserts its dominating role. Both phenomena are explained by the coupling effects of differential diffusion, heat losses to electrodes, and turbulence on the spark kernel. In particular, the ratio of small-scale turbulence diffusivity to reaction zone thermal diffusivity, a reaction zone Péclet number, captures the similarity of monotonic MIE transition, regardless of different ignition sources (conventional electrodes versus laser), turbulent flows, pressure, and fuel types. Furthermore, TFI does and/or does not occur when conventional spark is replaced by nanosecond-repetitively-pulsed-discharge and/or laser spark. The latter is attributed to the third lobe formation of laser kernel with some negative curvature segments that enhance reaction rate through differential diffusion, where MIEL < MIET (no TFI). Finally, the implications of MIE transitions relevant to lean-burn spark ignition engines are briefly mentioned, and future studies are suggested.

AB - Recent discoveries and developments on the dynamic process of premixed turbulent spark ignition are reviewed. The focus here is on the variation of turbulent minimum ignition energies (MIET) against laminar MIE (MIEL) over a wide range of r.m.s. turbulence fluctuation velocity (uʹ) alongside effects of the spark gap between electrodes, Lewis number, and some other parameters on MIE. Two distinguishable spark ignition transitions are discussed. (1) A monotonic MIE transition, where MIEL sets the lower bound, marks a critical uʹc between linear and exponential increase in MIET with uʹ increased. (2) A non-monotonic MIE transition, where the lower bound is to be set by a MIET at some uʹc, stems from a great influence of Lewis number and spark gap despite turbulence. At sufficiently large Lewis number >> 1 and small spark gap (typically less than 1 mm), turbulence facilitated ignition (TFI), where MIET < MIEL, occurs; then MIET increases rapidly at larger uʹ > uʹc because turbulence re-asserts its dominating role. Both phenomena are explained by the coupling effects of differential diffusion, heat losses to electrodes, and turbulence on the spark kernel. In particular, the ratio of small-scale turbulence diffusivity to reaction zone thermal diffusivity, a reaction zone Péclet number, captures the similarity of monotonic MIE transition, regardless of different ignition sources (conventional electrodes versus laser), turbulent flows, pressure, and fuel types. Furthermore, TFI does and/or does not occur when conventional spark is replaced by nanosecond-repetitively-pulsed-discharge and/or laser spark. The latter is attributed to the third lobe formation of laser kernel with some negative curvature segments that enhance reaction rate through differential diffusion, where MIEL < MIET (no TFI). Finally, the implications of MIE transitions relevant to lean-burn spark ignition engines are briefly mentioned, and future studies are suggested.

KW - Lean-burn premixed turbulent combustion

KW - Minimum ignition energy (MIE)

KW - Monotonic MIE transition

KW - Non-monotonic MIE transition

KW - Turbulence facilitated ignition

KW - Turbulent premixed spark ignition

UR - http://www.scopus.com/inward/record.url?scp=85161616172&partnerID=8YFLogxK

U2 - 10.1016/j.pecs.2023.101099

DO - 10.1016/j.pecs.2023.101099

M3 - 回顧評介論文

AN - SCOPUS:85161616172

SN - 0360-1285

VL - 98

JO - Progress in Energy and Combustion Science

JF - Progress in Energy and Combustion Science

M1 - 101099

ER -