Plotting phase curves Mathematica

[Dustinsfl]

I was talking to my professor and I am tying to generate a phase curve that looks like (see attached).However, I am only been able to generate phase portraits.View attachment 94I need to generate a plot that does that.From these equations,$$\dot{x} = -x + ay +x^2y$$$$\dot{y} = b -ay-x^2y$$Here is what I have been able to generate thus farView attachment 95

 

[Dustinsfl]

$$\dot{x} = -x + ay +x^2y$$
$$\dot{y} = b -ay-x^2y$$

Ok I found an example
http://demonstrations.wolfram.com/PhasePlanePlotOfTheVanDerPolDifferentialEquation/#
The left graph where it plots x (t) vs x' (t) with parametric plot.
How can I do this with my ODEs?

http://demonstrations.wolfram.com/VanDerPolOscillator/
Here is another example plot