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Homogeneous Charge Compression Ignition (HCCI) offers great promise for excellent fuel economy and extremely low emissions of NOx and PM. HCCI combustion lacks direct control on the "start of combustion" such as spark timing in SI engines and fuel injection timing in CI engines. Auto ignition of a homogeneous mixture is very sensitive to operating conditions of the engine. Even small variations of the load can change the timing from "too early" to "too late" combustion. Thus a fast combustion phasing control is required since it sets the performance limitation of the load control. Crank angle position for 50% heat release is used as combustion phasing feedback parameter. In this study, a dual-fuel approach is used to control combustion in a HCCI engine. This approach involves controlling the combustion heat release rate by adjusting fuel reactivity according to the conditions inside the cylinder. Two different octane fuels (methanol and n-heptane) are used for the study.

Cyclic variations are inherent in the combustion of internal combustion engines. However, extreme cyclic combustion variations limit the operation of spark-ignition (SI) engines, particularly at highly lean and diluted charge operation. Lean charge operation is desired due to its expected benefits in fuel efficiency and engine-out NOx and HC emissions. Studies suggested the existence of the low-dimensional deterministic nature of cyclic variations, which is essential from the perspective of designing a high-frequency controller. The lean limit of a SI engine operation may be extended by controlling the deterministic component of cyclic variations to meet the future strict emissions and fuel economy regulations. This paper presents a review of the evolution of the experimental and analytical understanding of cyclic combustion variations of spark-ignition engines.

Engine design and selection of fuels for automotive applications are required to minimize noise and exhaust emissions without compromising fuel economy. The knocking combustion investigation is essential as it directly affects the performance and durability as well as the thermal efficiency of the engine. Several fuel additives were suggested in the previous studies to mitigate the knocking combustion in spark ignition (SI) engines. The present study reviews the effect of antiknock fuel additives such as ethanol, methanol, prenol, n-butanol, furan mixtures, etc., on knocking behavior in SI engines. Additionally, this paper aims to present a systematic review of the studies conducted to investigate the effect of EGR on the knocking in SI engines. The EGR is often considered an effective means to suppress knocking in SI engines. The thermal effect of EGR in controlling the knocking is well known as EGR affects the temperature and pressure history of the combustion chamber.