Particle emissions in a turbocharged gasoline direct injection engine under Atkinson cycle operation through late intake valve closure

Abstract

However, despite of their effectiveness in improving the thermal efficiency, these strategies are vulnerable to particle emissions due to the fuel being directly injected into the cylinder. Although various studies regarding particle emissions have been conducted, the correlated mechanism between particle emissions and the late intake valve closing (LIVC), which is a type of Atkinson cycles frequently utilized in modern engines, has yet to be discovered. Therefore, in this research, the effect of LIVC on particle number emissions of a turbocharged gasoline direct injection (T-GDI) engine had been investigated. Through particle number measurement, combustion analysis, and visualization techniques (borescope and particle image velocimetry), the flame propagation and in-cylinder flow characteristics associated with the LIVC had been investigated. The experimental data showed that the retardation of the intake valve closing (IVC) timing resulted in the reduction of particle number emissions. The retardation of IVC timing decreased the in-cylinder pressure and temperature at the ignition timing while it increased the in-cylinder flow velocity, and thereby, the turbulent kinetic energy. From the research findings, the decreased in-cylinder temperature and improved mixture formation seemed to inhibit pyrolysis process, leading to the decreased formation of particles at a cost of decelerated initial flame propagation. The decelerated flame propagation, however, was compensated by the accelerated combustion speed from the increased turbulent kinetic energy during the late stage of combustion, leading to the increased oxidation of the produced particles. Therefore, in this research, it was found that the retardation of the IVC timing effectively reduced particle number emissions in a T-GDI engine.

As the CO2 emission problems become serious concerns of modern societies, the need for carbon neutrality is rapidly increasing. In the transport sector, numerous types of researches have been conducted for achieving carbon-neutrality, ranging from hydrogen combustion to the development of renewable synthetic fuels. Among these types of studies, the thermal efficiency improvement of the internal combustion engines has been considered as one of the most practical and feasible solutions for achieving carbon-neutrality because of its convenient compatibility with the utilization of renewable synthetic fuels. The combinations of downsizing, Atkinson cycle and direct injection have been frequently utilized for maximizing the thermal efficiency of gasoline engines