Ignition of a lean PRF/air mixture under RCCI/SCCI conditions: A comparative DNS study

Prediction of Ignition Regimes in DME/Air Mixtures with Temperature and Concentration Fluctuations

“…Note that the prediction of F Sa,S for the previous n-heptane and other fuels under various conditions [25][26][27][28][29][30][31][32][33][34] is validated by comparing F Sa,S with F S of the previous DNS studies that shows a satisfactory agreement between F Sa,S and F S (not shown here). For example, with T = 15 K, both F Sa,S and F S are approximately equal to unity for T 0 of 850 K, 934 K, and 1008 K, confirming a purely spontaneous ignition for all these three cases [25].…”

“…∂φ > 0). It was found in the previous DNS results [23,24,[28][29][30][31]] that a NC T-φ distribution attributed to the cooling effect of heat vaporization has a canceled-out effect on producing deflagration if T 0 outside the NTC regime while it has synergistic effect if T 0 inside the NTC regime. However, the deterministic prediction of the combustion modes by the extended Sa p criterion applied for the NTC fuels for a wide range of T 0 at distinct temperature regimes together with different combinations of T and φ levels merits further investigation.…”

“…Early direct injection may result in uncorrelated T-φ fields because of turbulent mixing and heat transfer. Late direct injection may produce negatively-correlated T-φ fields attributed to the evaporative cooling of fuel vaporization and incomplete mixing [23,27,[29][30][31]68]. As a result, the temperature and equivalence ratio fields have a comparable integral length scale, l T ∼ l φ .…”

On the effect of injection timing on the ignition of lean PRF/air/EGR mixtures under direct dual fuel stratification conditions

“…Due to the inhomogeneities in the n -heptane field, the fluctuation in the reactivity (PRF) and equivalence ratio can be attained. As in [19,21,26,[28][29][30]35,43,[57][58][59][60] , the initial turbulent flow field is prescribed by an isotropic kinetic energy spectrum function of Passot and Pouquet [61] . Initial fuel concentration and temperature fields are also generated by the same energy spectrum with different random numbers.…”

“…In previous direct numerical simulation (DNS) studies, the ignition characteristics of HCCI [18][19][20][21][22][23][24][25][26][27][28] , SCCI [29][30][31][32][33][34] , and RCCI [35,36] combustion have been investigated at constant volume. In real IC engines, however, the combustion process is highly affected by both the compression heating before TDC and the expansion cooling after the TDC by the piston motion.…”