Anderson J.D.- Computational fluid dynamics. The basics with applications. This is very a very good book and easy to understand how to discritize the PDE's into algebraic form.
Try the book: " Difference Equations" , 2/e, (2001) by Walter G Kelley and Allan C Peterson, Academic Pre4ss- Elsevier. I found it extermely readable and accessible to an Engineering student
For an applied mathematician's perspective that might also appeal to the engineers, I can suggest Bender and Orzsag's "Advanced Mathematical Methods for Scientists and Engineers". There is a short chapter on finite difference equations with plenty of worked out examples. Its a gem of a book and has lots of other wonderful chapters dealing with applied math techniques.