To provide a method and a device to roughly estimate hydrogen concentration in the reformate flow generated by a fuel processor of a fuel cell.

The sensor measures carbon monoxide, carbon dioxide and water in the reformate flow (58). A fuel level indicator (64) controls the fuel input into the fuel processor (56). An air flow-meter (60) controls the air input into the fuel processor. A water flow-meter (68) controls the water input into the fuel processor. A transportation delay roughly-estimating machine (144) repeatedly estimates the transportation delay of the fuel processor. A hydrogen roughly-estimating machine is related to the transportation delay roughly- estimating machine, the air flow-meter, the water flow-meter and the fuel level indicator, and the sensor roughly estimates the hydrogen concentration in the reformate flow. The hydrogen roughly-estimating machine includes a fuel processor model adjusted by employing the roughly estimated transportation delay. Carbon monoxide, carbon dioxide and water are measured by employing a non-dispersion infrared ray (NDIR) sensor.