2
Air to fuel equivalence ratio λ (–)
5
3.3
2.5
2
1.7
1.4
1.25
1.1
1
200
180
160
140
120
100
80
60
40
20
0
Power density H PFI compared to
stoichiometric gasoline (%)
Naturally aspirated
Supercharged (1 bar boost)
0.2 0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Fuel to air equivalence ratio φ (–)
Hydrogen
271
Figure 9.11
Theoretical power density of a PFI H 2 engine compared to stoichiometric gasoline operation
as a function of equivalence ratio and charging strategy. (From Verhelst, S. and Wallner, T.,
Progress in Energy and Combustion Science, 35, 490–527, 2009. Reprinted with permission from
Elsevier Publications.)
late in the compression stroke generally ending just before spark timing. In
order to avoid displacement of a fresh charge by hydrogen of low density,
the start of injection even for early injection is usually set after intake valve
closing. During fuel injection, the inlet valve is closed completely thereby
avoiding premature ignition during the suction stroke. The DI fuel system
requires higher fuel rail pressure than other fuel systems.
In order to flow hydrogen directly into the combustion chamber, the pressure inside the injection system has to exceed the pressure inside the cylinder;
that is, critical injection condition. The amount of fuel injected is determined
only as a function of injection pressure and injection duration for engine calibrations and accurate fuel metering. Critical conditions are that the injection
pressure has to be approximately twice the cylinder pressure to guarantee
critical conditions (choked flow). Therefore, operating strategies with early
DI require injection pressures in the range of approximately 5 and 20 bar,
late injection strategies up to 100 bar, and multiple injection strategies with
injection pulses during the actual combustion event of 100–300 bar (Verhelst
and Wallner 2009).
9.10.4 Preignition Problems in Hydrogen engines
Hydrogen burns cleanly and operates efficiently as it has the characteristics
to operate in ultra-lean combustion conditions. This will drastically reduce
the NO x formation and have better performance at low load conditions.
Air to fuel equivalence ratio λ (–)
5
3.3
2.5
2
1.7
1.4
1.25
1.1
1
200
180
160
140
120
100
80
60
40
20
0
Power density H PFI compared to
stoichiometric gasoline (%)
Naturally aspirated
Supercharged (1 bar boost)
0.2 0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Fuel to air equivalence ratio φ (–)
Hydrogen
271
Figure 9.11
Theoretical power density of a PFI H 2 engine compared to stoichiometric gasoline operation
as a function of equivalence ratio and charging strategy. (From Verhelst, S. and Wallner, T.,
Progress in Energy and Combustion Science, 35, 490–527, 2009. Reprinted with permission from
Elsevier Publications.)
late in the compression stroke generally ending just before spark timing. In
order to avoid displacement of a fresh charge by hydrogen of low density,
the start of injection even for early injection is usually set after intake valve
closing. During fuel injection, the inlet valve is closed completely thereby
avoiding premature ignition during the suction stroke. The DI fuel system
requires higher fuel rail pressure than other fuel systems.
In order to flow hydrogen directly into the combustion chamber, the pressure inside the injection system has to exceed the pressure inside the cylinder;
that is, critical injection condition. The amount of fuel injected is determined
only as a function of injection pressure and injection duration for engine calibrations and accurate fuel metering. Critical conditions are that the injection
pressure has to be approximately twice the cylinder pressure to guarantee
critical conditions (choked flow). Therefore, operating strategies with early
DI require injection pressures in the range of approximately 5 and 20 bar,
late injection strategies up to 100 bar, and multiple injection strategies with
injection pulses during the actual combustion event of 100–300 bar (Verhelst
and Wallner 2009).
9.10.4 Preignition Problems in Hydrogen engines
Hydrogen burns cleanly and operates efficiently as it has the characteristics
to operate in ultra-lean combustion conditions. This will drastically reduce
the NO x formation and have better performance at low load conditions.