This study investigates cycle-by-cycle variations in a gasoline fuelled, homogeneous charge compression ignition (HCCI) engine with internal exhaust gas recirculation. In order to study the effects of exhaust-fuel reactions occurring prior to the main combustion event fuel was injected directly into the cylinder at two selected timings during the negative valve overlap period. The engine was operated as both autonomous HCCI and spark assisted HCCI (SA-HCCI). The primary interest in this work was the operating region where the engine is switched between HCCI and spark ignition modes, thus operation with stoichiometric air–fuel mixture, which is typical for this region, was considered. Cycle-by-cycle variations in both combustion timing and indicated mean effective pressure (IMEP) were investigated. It was found that long-period oscillations of the IMEP occur when fuel injection is started at early stages of the negative valve overlap period, and that these can be suppressed by delaying the start of injection. This behaviour remained even when fuel injection was split into early and late-negative valve overlap injections. Spark assisted operation allowed eliminating late combustion cycles, thus improving thermal efficiency. However, characteristic patterns of IMEP variations were found to be the same for both HCCI and SA-HCCI operations, irrespective of the adopted negative valve overlap fuel injection strategy, as evidenced by using symbol-sequence statistics.

中文翻译：

---

自主和火花辅助的均质充气压缩点火燃烧的化学计量空气-燃料混合物的逐周期变化

这项研究调查了带有内部废气再循环的汽油燃料，均质充气压缩点火（HCCI）发动机的逐周期变化。为了研究在主燃烧事件之前发生的废气反应的影响，在负气门重叠期间内，在两个选定的正时将燃油直接喷入气缸。该发动机既作为自动HCCI也作为火花辅助HCCI（SA-HCCI）运行。这项工作的主要兴趣是在HCCI和火花点火模式之间切换发动机的工作区域，因此考虑了该区域典型的化学计量空气-燃料混合物的工作。研究了燃烧正时和指示平均有效压力（IMEP）的逐周期变化。已经发现，当在负气门重叠期的早期开始燃料喷射时，发生IMEP的长时间振荡，并且可以通过延迟喷射开始来抑制这些振荡。即使将燃料喷射分为早期和晚期负气门重叠喷射，这种行为仍然保持。火花辅助操作可消除后期的燃烧循环，从而提高热效率。但是，无论采用哪种负气门重叠燃油喷射策略，HCCI和SA-HCCI操作的IMEP变化特征模式都是相同的，这通过使用符号序列统计得以证明。即使将燃料喷射分为早期和晚期负气门重叠喷射，这种行为仍然保持。火花辅助操作可消除后期的燃烧循环，从而提高热效率。但是，无论采用哪种负气门重叠燃油喷射策略，HCCI和SA-HCCI操作的IMEP变化特征模式都是相同的，这通过使用符号序列统计得以证明。即使将燃料喷射分为早期和晚期负气门重叠喷射，这种行为仍然保持。火花辅助操作可消除后期的燃烧循环，从而提高热效率。但是，无论采用哪种负气门重叠燃油喷射策略，HCCI和SA-HCCI操作的IMEP变化特征模式都是相同的，这通过使用符号序列统计得以证明。