Numerical Simulation Of Gas Flow And Internal EGR Rate In A Two-Stroke Diesel Engine

Homogeneous charge compression ignition (HCCI) combustion is a new combustion mode for internal combustion engine, which can greatly reduce NOx and smoke emissions simultaneously, and can also improve engine thermal efficiency. The purpose of this paper was to study premixed charge compression ignition (PCCI) combustion in a two-stroke diesel engine, including influence of fuel properties and internal EGR on PCCI combustion.The gas flow characteristics inside the cylinder and internal EGR rate under different scavenging pressures of the two-stroke engine were investigated by means of numerical simulation. The thermal effect and specific heat capacity effect of internal EGR were analyzed theoretically. The results show that the engine in cylinder gas flow is very sophisticated. In the process of scavenging and exhaust, in-cylinder swirls, tumbles, swirl ratio, tumble ratio, turbulent kinetic energy and its dissipation rate change greatly. The internal EGR rate decreases with increase in the scavenging pressure, which changes from 15% to 70%. The internal EGR rate is also reduced with increase in the engine load under the same engine rate and scavenging pressure. The thermal effect of the internal EGR could advance the ignition while the specific heat capacity effect could decrease the in-cylinder temperature. The thermal effect is predominant in the ignition of PCCI combustion.It could be concluded that the real-time variable internal EGR is necessary for controlling PCCI combustion of the two-stroke engine. As a result, it can be of great significance for determining internal EGR under different load conditions.