Division 1.1.5 In the case of natural gas/biomethane engines, the ratio of the emission results ‘r’ shall be determined for each pollutant as follows:F1F2

$r=\frac{\mathrm{emission\; result\; on\; reference\; fuel\; 2}}{\mathrm{emission\; result\; on\; reference\; fuel\; 1}}$

or

$r_a=\frac{\mathrm{emission\; result\; on\; reference\; fuel\; 2}}{\mathrm{emission\; result\; on\; reference\; fuel\; 3}}$

and

$r_b=\frac{\mathrm{emission\; result\; on\; reference\; fuel\; 1}}{\mathrm{emission\; result\; on\; reference\; fuel\; 3}}$