Ammonia/Hydrogen and Cracked Ammonia Combustion

Area of Science:

• Combustion science
• Energy systems
• Decarbonization technologies

Background:

• Ammonia (NH3) is a promising carbon-free energy carrier, but its combustion presents challenges.
• Moderate or Intense Low-oxygen Dilution (MILD) combustion and hydrogen (H2) addition are strategies to improve NH3 combustion efficiency and reduce emissions.
• Partial cracking of NH3 produces H2, offering a potential pathway for enhanced fuel reactivity.

Purpose of the Study:

• To investigate the effectiveness of MILD combustion for NH3/H2 blends in a cyclonic reactor.
• To analyze the impact of equivalence ratio and H2 addition on combustion stability and NOx emissions.
• To compare combustion behavior with pure NH3, pure H2, and cracked NH3 mixtures (NH3/H2/N2).

Main Methods:

• Experimental investigation of NH3/H2 blends in a cyclonic reactor under MILD conditions.
• Systematic variation of equivalence ratio and H2 addition percentage.
• Direct comparison of results with cracked NH3 mixtures (NH3/H2/N2).

Main Results:

• The cyclonic reactor demonstrated fuel flexibility, achieving total conversion of NH3/H2 blends at temperatures below 1400 K.
• H2 addition increased NH3 reactivity but also led to higher NOx emissions compared to pure NH3.
• For cracked NH3 mixtures, N2 dilution did not significantly alter combustion behavior under MILD conditions, except for a 75%H2-25%N2 mixture where it promoted a more uniform reaction zone and limited NOx formation.

Conclusions:

• MILD combustion in a cyclonic reactor is effective for stable and low-emission combustion of NH3/H2 blends.
• H2 addition enhances reactivity but requires careful management to control NOx emissions.
• N2 dilution in cracked NH3 mixtures can be a viable strategy to further mitigate NOx formation by ensuring a more uniform reaction zone.