Duel fuelling with hydrogen increases the brake thermal
efficiency with all fuels due to an increase in the premixed
combustion rate. At full load, with hydrogen induction, the
brake thermal efficiency of RSO and RSOME increases from
26.56% to 28.12% and 27.89% to 29.26% at the hydrogen share
of 8.39% and 8.73% on the energy basis. The increase in
brake thermal efficiency with lower loads is minimum.
The maximum hydrogen energy share that can be tolerated
with knock limit was highest with diesel (12.69%) and
decreases with RSOME (11.2%) and RSO (10.76%) at full load.
At full load, the smoke level is reduced from 6.1 BSU to
3.8 BSU at the higher brake thermal efficiency point of
energy share from hydrogen with RSO. Similar trends were
found with RSOME and diesel. This is mainly due to the
reduction in the amount of main fuel injected and improved
combustion rate with hydrogen induction.
There is a reduction in the HC and CO levels at all loads with
the induction of hydrogen for all injected fuels. The values
with RSO are higher than the other fuels on account of
inferior combustion due to poor mixture formation and
higher amount of the main fuel used.
NOx emission increases from 6.9 g/kWh to 10.76 g/kWh for
RSO with 0–8.39% of hydrogen energy share and for RSOME
it increases to the maximum of 11.77 g/kWh at a hydrogen
energy share of 8.73%. This is mainly due to the enhanced
combustion temperature on account of the high premixed
combustion.
The peak pressure and maximum rate of pressure rise
increases mainly at higher power outputs. At 25% and 50%
loads, the peak pressure and the maximum rate of pressure
rise reduces with hydrogen induction due to the weak
ignition source.
The ignition delay increases for all the fuels with hydrogen
induction. This will also contribute to higher heat release
rate in the initial stages of combustion.
The combustion duration decreases with hydrogen induction
at all loads. This is due to the enhanced flame velocity
as a result of the gaseous form of hydrogen.
There is a significant difference in heat release rates between
the neat RSO mode and the RSO–hydrogen dual fuel mode. A
sharp rise in the initial heat release, which is due to the
combustion of the accumulated injected fuel and the
entrained hydrogen, is seen at full load. Similar trends are also
seen when the engine is operated with RSOME and diesel.
On the