Feasible design of experiment: DOE

Hello everybody,

I am working on “improvement of formulation and process parameters for a process”. For a proper planning of my experiments I need a design of experiment.

I have to show the influence of 8 factors to my process. Whereas five of this factors contain 2 levels, and three factors contain 3 levels. I will have time for 15 runs maximally.

Someone gave me the advice to try Plackett-Burmann, but as I have factors with 3 levels, I am not sure if it really is the right design. You can determine the influence of 11 factors in 12 runs. But as I need just 8 factors, I could combine factors 6 to 11 to three factors of 3 levels, right?

Further someone suggested D-optimal design. Apparently, 2-level, 3-level (or higher) factors can be used directly. Also, the algorithm is more flexible and can be used for any number of runs (i. e. 15 in my case). Unfortunately, I couldn't find too many references. Is this design appropriate for my problem?

Any other suggestions?

As I have no experience with DOE and this question is quite essential in my project, I would be really grateful if someone could help me.

Thank you in advance.

Cheers,