Development and comparative experimental investigations of laser plasma and spark plasma ignited hydrogen enriched compressed natural gas fueled engine

A customized port-fuel-injection (PFI) SI engine was operated in spark ignition (SI) and laser ignition (LI) modes at varying brake mean effective pressure (BMEP) and relative air-fuel ratio (λ) under naturally aspirated conditions. Test fuel used were hydrogen enriched compressed natural gas (HCNG) mixtures and results were compared with baseline CNG. For H2 enrichment of CNG, a customized dynamic fuel mixing system was developed. For LI, a solid state Q-switched Nd:YAG laser (200 mJ; 30 Hz; 6–9 ns) was used, and the laser beam was focused using a converging lens of 50 mm focal length. Experiments of HCNG fueling exhibited relatively higher peak pressure (Pmax) with its peak shifted closer to the top dead center (TDC). H2 enrichment of CNG led to increase in peak in-cylinder Pmax (by ∼2.9 bar), RoPR (by ∼0.72 bar/deg) and HRR (by ∼7.2 kJ/m3.deg) for 40HCNG compared to baseline CNG. The maximum BTE was observed to be ∼42.8% (at λ = 1.4) in LI mode for 30HCNG fueled engine. The lowest BSFC obtained were at λ = 1.2 for HCNG in SI mode, while corresponding value in LI mode was obtained at λ = 1.4. BSHC emissions were always lower for LI mode than the SI mode. At 3.96 bar BMEP, BSHC emissions reduced from 0.54 g/kWh (for CNG) to 0.35 g/kWh (for 40HCNG), which further reduced to 0.21 g/kWh (for H2) in LI mode. BSNOx emissions increased with increasing BMEP but reduced from 0.89 g/kWh at λ = 1.5 for CNG to 0.17 g/kWh for 30HCNG at λ = 1.7 at 30 Nm load.