Therefore, the COVimep of HICEs varies with throttle position,
as determined using the conditions shown in Table 6.
Fig. 7 shows that when throttle position is less than 20%,
COVimep decreases as throttle position rapidly increases.
However, COVimep tends to be constant as throttle position
further increases. This result is attributed to the increase in
vacuum degree as throttle position decreases, and to the
slowing down of the mass flow of air. The intake process is
then easily affected by hydrogen injection. Therefore, COVimep
increases at a small throttle position and stays almost constant
when the throttle position is large.