An Analysis of Mechanical and Thermal Stresses, Temperature and Displacement within the Transparent Cylinder and Piston Top of a Small Direct-Injection Spark-Ignition Optical Engine

Abstract

Two- and three-wheeled vehicles account for a significant portion of the automobile market in several countries worldwide. In order to advance the capabilities of these vehicles, the integration of direct-injection (DI) technology is essential, given its potential benefits such as high thermal efficiency and low engine-out emissions. Direct injection in small-bore engines, however, further complicates the challenges involved (of DI technology) like fuel impingement and mixture inhomogeneity inside the engine cylinder, driving the need for an in-depth exploration of in-cylinder processes. Consequently, the necessity arises to develop a small-bore direct-injection spark-ignition (DISI) optical engine that incorporates a transparent cylinder and piston top. In this scenario, these transparent components are required to endure a combination of intricate loads and boundary conditions, hence the potential to result in failures. This work aims to assess numerically the effects of these loads and boundary conditions on the transparent components and optimize their thicknesses. For this purpose, a computer-aided design model of a small-bore DISI optical engine (displacement volume of 200 cm3) is developed. The mechanical and thermal loads are extracted from the experimental data and validated computational fluid dynamics model of the same engine configuration. A coupled temperature-displacement finite element analysis methodology is developed in ABAQUS/CAE, and simulations are performed under both steady and transient conditions. Temperature and combined stress distributions within the transparent cylinder and piston top are obtained and analyzed to find their optimum thicknesses. Knowing thermal gradients, combined stresses and displacements under actual conditions helped design the small optical engine with an improved factor of safety.