Autozone brake cleaner is the best substitute I have found for nitro wash. Simple Green has it's place, but for cleaning greasy parts, glow plugs, etc. quickly you need a degreaser that dries quick. I buy a lot of it for basic degreasing and surface prep around my shop.

Please note - I have tried other types and brands of brake cleaners and some WILL eat plastic. I know the Autozone doesn't so I stick with it.