Lean Partially Premixed Combustion Investigation of Methane Direct-Injection Under Different Characteristic Parameters

The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane–air partially premixed turbulent combustion have been studied experimentally using a constant volume combustion chamber (CVCC). The fuel–air mixture was ignited by centrally located electrodes at given spark delay times of 1, 5, 40, 75, and 110 ms. Experiments were performed for a wide range of hydrogen volumetric fractions (0% to 40%), simulated diluent volumetric fractions (0% to 25% as a diluent), injection pressures (30–90 bar), chamber pressures (1–3 bar), chamber temperatures (298–432 K) and overall equivalence ratios of 0.6, 0.8, and 1.0. Flame propagation images via the Schlieren/Shadowgraph technique, combustion characteristics via pressure derived parameters and pollutant concentrations were analyzed for each set of conditions. The results showed that peak pressure and maximum rate of pressure rise increased with the increase in chamber pressure and temperature while changing injection pressure had no considerable effect on pressure and maximum rate of pressure rise. The peak pressure and maximum rate of pressure rise increased, while combustion duration decreased with simultaneous increase of hydrogen content. The lean burn limit of methane–air turbulent combustion was improved with hydrogen addition. Addition of diluent increased combustion instability and misfiring while decreasing the emission of nitrogen oxides (NO_x).