Thermal Efficiency Analysis on Lean Burn Spark Ignition Engine

Advanced spark ignition (SI) engines can operate under lean conditions in order to improve the efficiency and reduce the emissions. Under extensive lean conditions, the ignition and complete combustion of the charge mixture is a challenge, because of the reduced cylinder charge reactivity, leading to combustion instabilities, thus making the empirical investigations in the vicinity of and beyond the lean limit of current engines, unviable. With further improvements to the ignition and combustion control, the lean operation limit may be extended in future engines. To circumvent this limitation to an extent, in this work, the potential of extremely lean mixtures (well beyond the practical lean limit) for SI engines has been studied using numerical simulations. The main objective of this thesis is to perform a modelling study of lean burn engine using a zero-dimensional engine cycle simulation and aid in acquiring an understanding of the combustion characteristics that have a major impact on the indicated thermal efficiency. The simulations are performed to investigate the impact of combustion phasing, combustion duration and heat transfer independently on the indicated efficiency. The simulations are conducted under various fixed combustion characteristics such as air-fuel ratio, combustion duration, combustion phasing, and more using AVL BOOST™. The empirical in-cylinder pressure data is used to validate the simulation model used. The results show that combustion phasing and heat transfer effect have a major impact and combustion duration has negligible influence on the indicated thermal efficiency