Multidimensional Modeling of the Scavenging and Injection Processes of a Small Two-Stroke Engine Compared to LDV Measurements

The scavenging and injection processes on a 50 cc. crankcase-scavenged compressed air-assisted direct fuel injection 2-stroke engine are analyzed by means of multidimensional CFD modeling. A moving mesh including the intake ports, cylinder and exhaust port has been built, solving the interface at ports. The information at boundaries is obtained from a one-dimensional wave action model. A detailed analysis of the scavenging process is presented.

A motored engine with suitable optical access has been used to measure in-cylinder velocities by Laser Doppler Velocimetry LDV. Due to the small engine size some technical problems had to be solved to carry out the measurements. The comparison between the modeled and measured velocities shows good agreement.

Finally, the validated multidimensional modeling has been used for the optimization of the injection process in terms of fuel short-circuit to the exhaust and also of mixture quality. A study of the fuel injection timing and location shows the key points to optimize injection and mixing process.