Hydrogen
273
An excessive introduction of the preliminary fuel may cause autoignition
by itself thus giving rise to rough combustion. About 30% hydrogen can be
replaced by this method. Introduction of a higher percentage of hydrogen
leads to uncontrolled pressure rise.
Das and Polly (2005) conducted investigations on CI engines to achieve
knock-free operation in various proportions by using diluents such as nitrogen, helium, and water. A comparative assessment among the three diluents
shows that conventional diesel engines can be converted to operate on hydrogen-diesel dual mode with up to about 38% of full-load energy substitution
without any sacrifice on the performance parameters such as power and efficiency. A long-term endurance study on this system showed that there was
no problem related to material compatibility on such configurations and as
such they can be safely adopted.
Kumar, Ramesh, and Nagalingam (2003) reported that with hydrogen
induction, due to high combustion rates, the NO level was increased at full
output. They reported that ignition delay, peak pressure, and the maximum
rate of pressure rise were increased in the dual-fuel mode of operation.
Combustion duration was reduced due to higher flame speed of hydrogen.
Moreover, a higher premixed combustion rate was observed with hydrogen
induction. Welch and Wallace (1990) conducted investigations on hydrogen
combustion by its autoignition with glow plug assist in a reciprocating engine
at a compression ratio of 17. Hydrogen-fueled diesel engines can produce
higher power than an ordinary diesel engine with reduction in NO x and nil
smoke emissions.
9.11.2 Direct injection
In this method, hydrogen is directly introduced into the cylinder at the
end of compression. The gas impinges on the glow plug in the combustion chamber and hence surface ignition burning of fuel occurs. Moreover,
it is possible to introduce lean hydrogen–air during intake of an engine
and then inject the bulk of hydrogen toward the end of compression.
The advantage of this method is that surface ignition is not dependant
on the compression ratio for ignition. Literature shows that a very small
difference in brake thermal efficiency was observed in the compression
ratio 12–18.
With hydrogen directly injected into the combustion chamber in a CI
engine, the power output would be approximately double that of the same
engine operated in the premixed mode. The use of hydrogen DI in a diesel
engine has given a higher power to weight ratio when compared to conventional diesel-fueled operation, with the peak power being approximately
14% higher. The power output of such an engine would also be higher than
that of a gasoline engine, since the stoichiometric heat of combustion per
standard kilogram of air is higher for hydrogen (approximately 3.37 MJ
for hydrogen compared with 2.83 MJ for gasoline). Higher diffusivity and
273
An excessive introduction of the preliminary fuel may cause autoignition
by itself thus giving rise to rough combustion. About 30% hydrogen can be
replaced by this method. Introduction of a higher percentage of hydrogen
leads to uncontrolled pressure rise.
Das and Polly (2005) conducted investigations on CI engines to achieve
knock-free operation in various proportions by using diluents such as nitrogen, helium, and water. A comparative assessment among the three diluents
shows that conventional diesel engines can be converted to operate on hydrogen-diesel dual mode with up to about 38% of full-load energy substitution
without any sacrifice on the performance parameters such as power and efficiency. A long-term endurance study on this system showed that there was
no problem related to material compatibility on such configurations and as
such they can be safely adopted.
Kumar, Ramesh, and Nagalingam (2003) reported that with hydrogen
induction, due to high combustion rates, the NO level was increased at full
output. They reported that ignition delay, peak pressure, and the maximum
rate of pressure rise were increased in the dual-fuel mode of operation.
Combustion duration was reduced due to higher flame speed of hydrogen.
Moreover, a higher premixed combustion rate was observed with hydrogen
induction. Welch and Wallace (1990) conducted investigations on hydrogen
combustion by its autoignition with glow plug assist in a reciprocating engine
at a compression ratio of 17. Hydrogen-fueled diesel engines can produce
higher power than an ordinary diesel engine with reduction in NO x and nil
smoke emissions.
9.11.2 Direct injection
In this method, hydrogen is directly introduced into the cylinder at the
end of compression. The gas impinges on the glow plug in the combustion chamber and hence surface ignition burning of fuel occurs. Moreover,
it is possible to introduce lean hydrogen–air during intake of an engine
and then inject the bulk of hydrogen toward the end of compression.
The advantage of this method is that surface ignition is not dependant
on the compression ratio for ignition. Literature shows that a very small
difference in brake thermal efficiency was observed in the compression
ratio 12–18.
With hydrogen directly injected into the combustion chamber in a CI
engine, the power output would be approximately double that of the same
engine operated in the premixed mode. The use of hydrogen DI in a diesel
engine has given a higher power to weight ratio when compared to conventional diesel-fueled operation, with the peak power being approximately
14% higher. The power output of such an engine would also be higher than
that of a gasoline engine, since the stoichiometric heat of combustion per
standard kilogram of air is higher for hydrogen (approximately 3.37 MJ
for hydrogen compared with 2.83 MJ for gasoline). Higher diffusivity and