Effect of Natural Gas/Hydrogen Blends on Spark Ignition Stoichiometric Engine Efficiency 2011-24-0121
Hydrogen (H₂) added to natural gas (NG), improves the combustion
process of the air-fuel mixture. This gives the potentiality to
develop engines with better performance and lower environmental
impact. In any case how hydrogen is produced represents a crucial
aspect. In general, if H₂ is produced utilizing fossil fuels and
not renewable or nuclear sources, the environmental benefit of CO₂
reduction could be reduced.
In this paper two engines, a light-duty (LD) and a heavy-duty
(HD), were tested in stoichiometric conditions. The engines were
fuelled with NG and with two blends of NG with a 20% and a 40% by
volume of H₂, respectively named NG/H₂ 20% and NG/H₂ 40%. The
light-duty engine was tested at different loads and speeds, with
spark advance set by the electronic control unit (ECU). The ECU
actuated a retarded ignition, especially at low load.
With the heavy-duty engine, the tests were carried out only at
high load. Spark advance was tuned to obtain burning gravity center
at the same angular position with NG and the two NG/H₂ blends.
Hydrogen positive effect on combustion development has been
observed, even if global efficiency was only marginally affected
for both the light- and the heavy-duty engine. Moreover, only with
the heavy-duty engine and NG/H₂ 40% blend, knocking phenomena have
been observed, requiring great attention in spark advance, boost
pressure and EGR rate optimization. For best performance with high
H₂ content, a specific combustion system design would be necessary
to fully exploit H₂ characteristics.