My own project is like this:
1.I have a diesel truck and I want to add CNG to get better fuel economy and extra power...
2. I only need 2 GGE for my daily driving. 50% CNG 50% diesel will give me 60-70 mile range. If I need more I can just use diesel...
3. As a DIY project I will try to keep pressure as low as possible/practical. My tanks are 3 ft3. To get 2 GGE@ 3 ft3 I need to pressure CNG to 1200-1300 Psi.
4. I don't like 3-4 stage air compressors because they are noisy, expensive, run very hot, expensive to fix/rebuild....
5. I am thinking about "hybrid" system:
1 stage is going to be AC compressor (York 210 style). It will boost pressure from 2 Psi to 200 Psi. This compressor is a real beast and can run 200 Psi all day long. Cost is low ($50 used-$150 new) parts are cheap. Easy to fix. Compressor will be turned by hydraulic motor.
2 stage is going to be hydraulic cylinder pushed/pulled by another hydraulic cylinder
I decided to use hydraulic power unit to run compressor (via hydraulic motor) and hydraulic cylinder (hydraulic side). In this case I can put power pack isolated from gas compression unit and I don't need to worry about arks and sparks....
Now let't talk about CNG....
