The ignition characteristics of a lean primary reference fuel (PRF)/air mixture under reactivity controlled compression ignition (RCCI) and stratified charge compression ignition (SCCI) conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species reduced mechanism of PRF oxidation. For RCCI combustion, n-heptane and iso-octane are used as two different reactivity fuels and the corresponding global PRF number is PRF50 which is also used as a single fuel for SCCI combustion. The 2-D DNSs of RCCI/SCCI combustion are performed by varying degree of fuel stratification, r, and turbulence intensity, u′, at different initial mean temperature, T₀, with negatively-correlated T–r fields. It is found that in the low- and intermediate-temperature regimes, the overall combustion of RCCI cases occurs earlier and its mean heat release rate (HRR) is more distributed over time than those of the corresponding SCCI cases. This is because PRF number stratification, PRF′, plays a dominant role and T′ has a negligible effect on the overall combustion within the negative temperature coefficient (NTC) regime. In the high-temperature regime, however, the difference between RCCI and SCCI combustion becomes marginal because the ignition of the PRF/air mixture is highly-sensitive to T′ rather than PRF′ and ϕ′. The Damköhler number analysis verifies that the mean HRR is more distributed over time with increasing r because the portion of deflagration mode of combustion becomes larger with increasing fuel stratification. Finally, it is found that the overall combustion of both RCCI and SCCI cases becomes more like the 0-D ignition with increasing u′ due to the homogenization of initial mixture by turbulent mixing.

使用2-D直接数值模拟（DNS）对具有反应物种的压缩稀有主要参考燃料（PRF）/混合气在RCCI和分层充气压缩点火（SCCI）条件下的点火特性进行了研究，其中包括116种PRF氧化的机理。对于RCCI燃烧，正庚烷和异辛烷用作两种不同的反应性燃料，相应的全局PRF值为PRF50，它也用作SCCI燃烧的单一燃料。RCCI / SCCI燃烧的二维DNS通过在不同的初始平均温度T ₀下改变燃料分层度r和湍流强度u '来执行，具有负相关的T – r字段。结果发现，在低温和中温状态下，RCCI案例的整体燃烧发生得较早，并且其平均放热率（HRR）随时间的分布比相应的SCCI案例的分布更大。这是因为PRF数分层PRF'起主导作用，而T '在负温度系数（NTC）范围内对总体燃烧的影响可忽略不计。在高温度状态，但是，RCCI和SCCI燃烧之间的差变边际因为PRF /空气混合物的点火是高度敏感的Ť '，而不是PRF'和φ”。Damköhler数分析证明，随着r的增加，平均HRR随着时间的推移会更均匀地分布，因为随着燃料分层的增加，燃烧的爆燃模式部分会变得更大。最后，发现由于湍流混合使初始混合物均质化，RCCI和SCCI两种情况的整体燃烧都变得更像0-D点火，随着u '的增加。