Accessing the Predictabilities in Cyclic Combustion and Emission Variations in SI Engines for Their Modelling and Control: A Literature Review

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 NO_x 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. First, the methods of characterization of cyclic combustion variations and their contributing factors are discussed, which is a prerequisite for developing a controller. Additionally, the recent studies related to cyclic emission variations and their relation with cyclic combustion variations are also discussed. Various nonlinear dynamics and chaotic methods are also discussed, along with their respective results. Nonlinear dynamical and chaotic methods are a better tool for the analysis of cyclic variations in comparison to statistical methods. It is found that engine combustion dynamics include both deterministic and stochastic components; one dominates over the other depending upon operating conditions.