Scavenging Flow in Poppet-Valved Two-Stroke Engines

A three dimensional computations were performed to investigate the scavenging characteristics in poppet-valved two-stroke engines using the KIVA-3V code. The code was modified to handle the valve shroud.

The flows of engines with different configurations were simulated at a speed of 5000 r/min. The stroke bore ratio (0.3 ~ 0.89), valve shroud angle, shroud turned angle and distance between the valves were considered to investigate their effects on the scavenging flows. Additionally, vertical valve, valve shroud style, valve timing and boost pressure have also been studied.

The results show the development of the scavenging processes and indicate the reverse tumble flow pattern. The stroke bore ratio of 0.4 to 0.6, shroud angle of 69 degrees to 108 degrees, turn angle of shroud of 18 degrees to 28 degrees and average tumble ratio of 1.2-1.6 were found to be the optimal range for effective scavenging. For the case with S/D=0.5, shroud angle=107 degrees and shroud turn angle=18 degrees as an optimum configuration, The scavenging efficiency and trapping efficiency improve 30.7% and 69.0% respectively, and the DR decrease 17.3%, compared to the case with S/D=0.89, shroud angle=0 degree and shroud turn angle=0 degree.

Visualization of scavenging flow on a modified two-stroke transparent cylinder engine were used for validation of the code and compared well in flow pattern.

For a larger image, click on the picture.

Flagship poppet valved two-stroke enging of AVL

New air mass fraction contours and velocity field in the cylinder of base engine of AVL

New air mass fraction contours and velocity field in the cylinder of engines with different stroke/bore ratio