Calculation new compression ratio for CNG engine

The main function of the piston modifications is to reduce the compression ratio of the engine.
Calculate the compression ratio for the gas converted engine, considering that the ideal compression
ratio must be:
- for N.A. CNG engines: 12 ÷ 13
- for turbocharged CNG engines: ~ 11,5
- for N.A. GPL engines: 9,5 ÷ 10
- for turbocharged GPL engines: 8,5 ÷ 9

The necessary data for the execution of the calculations of the new compression ratio are:
- original compression ratio of the engine
- displacement
- number of cylinders
- type of intake of air (turbo engine or N.A. engine)
- original dimensions of the original piston (with an original drawing)
- verify that the disposition of possible oil conduits in the original piston allows the necessary
workings (if it is possible, dissect an original piston).

COMPRESSION RATIO CALCULATION

(01). Calculate the UNITARY DISPLACEMENT (U):
        U= TOTAL DISPLACEMENT / NUMBER OF CYLINDERS
(02). Calculate the VOLUME OF THE COMBUSTION CHAMBER when the piston is at the    TDC    (V2):
         V2= UNITARY DISPLACEMENT / (ORIGINAL COMPRESSION RATIO – 1)
(03). Measure the volume of the original diesel bowl (Vbowl) filling it up with the water.   Measure
       the quantity of water that enters in the original diesel bowl.
      Subtract the volume of the ORIGINAL BOWL (Vbowl) to the VOLUME OF THE   COMBUSTION     CHAMBER (V2),
     to find the volume included between the piston head and the engine head      when the   piston is at the TDC:
                  Vt = V2 – Vbowl

Take away 0,5 mm from the top of the piston and measure the new volume Vt:
Vt new = originalVt + (π * D2) / 4 * 0,5
Calculate the volume of the bowl gas, working material until to the lateral (picture 04) and
inferior (picture 05) tangent of the original diesel bowl.
Vgas bowl = (π * D2) / 4 * H





Calculate the new compression ratio with the formula:
ρ = U / (V2 gas) + 1
VERIFY IF THE NEW COMPRESSION RATIO IS ACCEPTABLE, LOOKING THE
VALUES WRITTEN AT THE BEGINNING OF THE PARAGRAPH. IF IT ISN’T
ACCEPTABLE, MODIFY THE VALUES OF D AND H (SEE THE PICTURE 06) IN
ORDER TO HAVE THE CORRECT VALUES TO OBTAIN A CORRECT
COMPRESSION RATIO