Modeling of thermo-fluid dynamic processes in a new, Low-Emission two-stroke IC engine

Abstract

A comprehensive numerical technique has been developed to simulate the various processes in a two?stroke engine. More specifically, detailed multi?dimensional models that can simulate compressible, turbulent, two?phase flow with pressure and velocity boundary conditions, as well as moving boundaries to represent piston motion, have been developed. In particular, these models are used to simulate various processes in a new, low?emission, air?assisted injection?based two?stroke engine that has been under development at the Indian Institute of Science, Bangalore, over the past few years. The primary objectives are: (1) to better understand the working of the system in order to address certain problems faced by the early prototypes, and (2) to study the parametric dependence with a view to optimizing the engine configuration. The simulation of atomization, transport, and vaporization of the liquid fuel in the air?assisted injection system in a multi?dimensional domain suggests a speed dependency of the fuel transport and a delayed response to transitions in operating conditions, which were observed in the early prototypes. The simulation of the scavenging flow indicates tilting of the inlet flow in directions significantly different from the inlet port angles, highlighting the importance of computing conditions at the port instead of prescribing them. The existence of a low?purity swirling loop in the exhaust?side top corner of the engine cylinder (in the absence of a boost port) is observed. In the presence of a boost port, the scavenging front is found to sweep the potential dead?pocket region in the exhaust?side top corner. Finally, the simulation of in?cylinder charge injection, mixing, and stratification shows that there is substantial variation in the state of charge with operating conditions. Increasing the injection pressure by delaying the injection with respect to the mixture?preparation unit is seen to substantially enhance the flammable proportion, indicating a possible improvement in engine performance. A computation of the combustion process supports and reinforces this recommendation. Parametric dependence is established for each process in terms of certain geometric parameters. A detailed study over the parameter space is conducted to determine the optimal range of parameters for a 70?cc engine configuration.