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Abstract
Laminar and turbulent minimum ignition energies (MIE_{L} and MIE_{T}) of a lean primary reference automobile fuel (PRF95; 95% isooctane/5% nheptane) and air mixture at the equivalence ratio of 0.8 at 373 K with large Lewis number Le ≈ 2.95 >> 1 using small and large pintopin electrode spark gaps (d_{gap}) are measured in a dualchamber, constant temperature/pressure, fanstirred 3D cruciform burner capable of generating nearisotropic turbulence. Each MIE datum is statistically determined at 50% ignitability by 18–30 repeated runs over a range of ignition energy (E_{ig}). We find two ignition transition (IT) modes. (1) A nonmonotonic IT at small d_{gap} = 0.8 mm with the lowest MIE_{T} = 13.9 mJ (< MIE_{L} = 30.1 mJ) occurring at a critical u′_{c} ≈ 1.82 m/s due to the coupling effects between differential diffusion and turbulence, where u′ is the r.m.s. turbulent fluctuating velocity. When u′ > u′_{c}, MIE_{T} increases drastically (>> MIE_{L}), because turbulence reasserts its dominant role. (2) A regular IT at large d_{gap} = 2 mm is found where MIE_{L} is only 2.05 mJ, in which the increasing slopes of MIE_{T} with u′ change from gradually to exponentially when u′ > u′_{c} ≈ 2.3 m/s. In the posttransition when u′ ≥ u′_{c}, the averaged ratio of MIE at d_{gap} = 0.8mm and 2mm (MIE_{0.8}/MIE_{2.0}) is 1.64 > 1, suggesting that using large d_{gap} = 2mm has a higher ignition probability than using small d_{gap} = 0.8mm for the leanburn gasoline surrogate in intense turbulence. Finally, we estimate the uncertainties of burning velocities at u′ = 0 and 2.76 m/s, which are respectively less than 2% and 6% when using small/large E_{ig} ≈ MIE/70 mJ and/or d_{gap} = 0.8mm/2mm. These results are relevant to spark ignition gasoline engines operated in leanburn turbulent condition.
Original language  English 

Pages (fromto)  340348 
Number of pages  9 
Journal  Combustion and Flame 
Volume  225 
DOIs  
State  Published  Mar 2021 
Keywords
 Differential diffusion
 Electrodespark gap
 Laminar and turbulent burning velocities
 Lean primary reference fuel
 Minimum ignition energy
 Nonmonotonic and regular ignition transition
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Dive into the research topics of 'Two ignition transition modes at small and large distances between electrodes of a lean primary reference automobile fuel/air mixture at 373 K with Lewis number >> 1'. Together they form a unique fingerprint.Projects
 1 Finished

Advanced Experimental Studies on HighPressure, HighTemperature Premixed Turbulent Combustion(3/3)
Shy, S.Y. (PI)
1/08/19 → 31/03/21
Project: Research