Hydrogen is an energy carrier that can be produced without CO2 emissions (green hydrogen) and can be used in existing devices (such as stationary power plants) that are currently fuelled by natural gas. Therefore, hydrogen is one of the possible alternatives to replace fossil fuels, lowering the impact of the energy sector on the emissions of harmful and/or greenhouse gases.

RSE objective is to evaluate the impact of hydrogen addition on performance, emissions, and mechanical degradation of the components of a cogenerative engine fed by mixtures of hydrogen (up to a volumetric concentration of 8%) and natural gas.

The long duration tests (500h for each concentration of H2) can be divided in:

• Load following: the engine load is continuously regulated to match the desired temperature of water sent to the user.
• Intermittent operation (ON-OFF): the cogenerator is turned on and runs at nominal load if the tank temperature is below a minimum threshold, while it is shut down if the temperature exceeds a maximum threshold.

Some conclusions may be drawn after this first set of experimental tests:

• Efficiencies do not show evident differences between the different fuel compositions (0% to 8% of H2).
• CO2, NOx and CO emissions do not show perceptible variations in comparison with pure natural gas operation.
• The concentration of CH4 (unburned hydrocarbons) decreases with the addition of hydrogen, as expected.
• ON-OFF tests have greater electrical efficiency and lower thermal efficiency than thermal tracking tests. This is due to the fact that engine runs for longer in nominal and optimized conditions. This also causes the catalyst to work better, in fact both CH4 and NOx emissions are lower.

The duration of the tests was about 3000 hours so far, and the cogenerator showed no reliability issues due to the addition of hydrogen to the fuel mixture.

All these results should be confirmed with other tests up to maximum 20% of H2 in the mixture; after that, the same tests will be performed with variable H2 concentrations.

The document is available on the site in Italian