In this paper, 20%H₂ (20% hydrogen in natural gas-hydrogen
blends, by volume) is selected as the test fuel, and the ignition
timing and EGR ratio are adjusted to optimize the performance,
combustion, and emissions of a natural gas-hydrogen engine. An
experimental investigation on the effect of ignition timings, EGR
ratios on combustion behaviors and emissions of a spark-ignition
engine fuelled with natural-gas and hydrogen blends was
conducted.
When increasing the ignition timing at specified EGR ratio,
engine power output will give its peak value at MBT timing. Large
EGR introduction decreases engine power output and increases
combustion duration. Effective thermal efficiency shows an
increasing trend at the small EGR ratio and a decreasing trend with
further increasing EGR ratio.
With advancing the ignition timing, the flame development
duration is increased, and the rapid combustion duration and total
combustion duration are decreased. All of these three kinds of
combustion duration are increased with the increase of EGR
ratio.
HC concentration is decreased and NOx concentration is increased
with advancing the ignition timing while CO emission varies little
with the ignition timing. NOx concentration is decreased with the
increase of EGR ratio. HC emission is increased with the increase
of EGR ratio. CO and CO₂ emissions show little variations with the
EGR ratio and ignition timing.
Based on the above analysis, a MAP containing ignition timings
and EGR ratios for 20%H₂ fuel blend is presented, and this will
provide the reference and guidance to engine designers and
engineers. In addition, through optimizing ignition timing and EGR
ratio, high efficiency and low emission spark-ignition engine can
be realized fueled with natural gas-hydrogen blends.