buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

82 Victor Pantilie et al.
many researchers have studied the effect of using hydrogen as a fuel (pure or
mixed with another fuel) on pollutant emissions and engine performance (Das et
al., 2000), (Al-Baghdadi & Al-Janabi, 2000), (Yamin et al., 2000), (Maher et
al., 2003).
The combustion of hydrogen does not create pollutant emissions such as
CO2, CO, HC or PM because hydrogen does not contain any carbon. From the
oil combustion, some fractions of unburned hydrocarbons are present inside the
engine combustion chamber but these are negligible (Pantile, 2010). The massspecific
lower heating value of hydrogen is almost three times as high as that of
gasoline thus the brake specific fuel consumption is reduced ant the thermal
efficiency of the engine is increased. Hydrogen has antiknock quality due to the
self-ignition temperature of the hydrogen/air mixture which is greater than that
of gasoline. A combustible mixture is produced by a small amount of hydrogen
mixed with air, which can be burned in a conventional spark ignition engine at
an equivalence ratio below the lean flammability limit of gasoline/air mixture.
The resulting ultra-lean combustion produces low flame temperature and leads
directly to lower heat transfer to the walls, higher engine efficiency and lower
NOx emissions in the exhaust (Al-Baghdadi & Al-Janabi, 2003). The laminar
flame speed of a hydrogen-air mixture at stoichiometric conditions is almost 6
times higher than that of gasoline. At lean dosage conditions (λ=2) the laminar
flame speed of hydrogen is approximately equivalent to that of a stoichiometric
gasoline-air mixture (Verhelst & Wallner, 2009). The hydrogen flammability
limits are wider compared to gasoline. This means that the load of the spark
ignition engine can be controlled by the excess air-fuel ratio – the load engine
qualitative adjustment. Furthermore, the compression ratio of the engine can be
increased due to the higher octane number. The main disadvantage comes from
the low density of hydrogen which influences the storage of hydrogen and the
power output which is lower compared to liquid fuels (when comparing engines
with external mixture formation), (Pantile et al., 2011).
The U.S. Department of Energy and Department of Transportation have
taken initiatives to shift towards a hydrogen-based transportation system. The
aim of these researches is to develop and commercialize hydrogen fuel cell
vehicles in an economic manner. However, hydrogen can be used as a fuel for
transportation in internal combustion engines rather than in fuel cells at least for
some decades (Romm, 2006), (Sukumaran & Kong, 2010).
The lack of efficient and economical hydrogen infrastructure represents
one of the major issues in exploiting hydrogen energy. Internal combustion
engines can be considered as a transition technology for achieving economical
hydrogen infrastructure (Safaria et al., 2009). Developing hydrogen programs
are conducted by several automotive companies especially by BMW Group and
Ford Motor Company. BMW has introduced its hydrogen engine in the 7 series;
6.0 L V12 bi-fuel (gasoline – hydrogen) engine which operates with liquid
hydrogen stored on board (Kiesgen et al., 2006). Also, Ford has optimized