This engine has as a similar effect to the Curve engine but gives smoother, more smokelike effects. There is no connection line like there is in the Curve engine. The absence of a connection line will give the result a smoother effect.
The unique settings to the engine are all in the Brush size area. Increasing the particle size will give you more lines and make the brush appear to get larger. The dx and dy scales will affect how much your brush strokes speed up as you move your pen. Using negative values gives unexpected results, so be careful with this setting. The Gravity option is also tricky. The default is .986, simulating gravity on Earth. Higher values will make the brush go faster. Modifying the Gravity option can quickly make your brush unusable, so be careful with it.