Product Description
Multec 3.5 Fuel Injector Application Manual
3-34
Delphi Energy and Chassis Systems
Revision: 11/05-1
Figure 3-18 - Injector Working Flow Range
.
3.11
Tip Leakage
Tip leakage is defined as unmetered fuel that leaks from the injector tip
due to imperfect sealing in the closed valve position. The injector valve
seals through metal-to-metal contact between the valve and seat for
cycling wear durability reasons. The design and manufacture of this
interface controls the tip leak rate.
Loss of fuel pressure during engine shutdown due to injector tip leak can
result in fuel vapor formation in the fuel system. This may lead to long
engine restart times and possible stalling.
In addition, injector tip leakage has been identified as a source of
evaporative hydrocarbon (HC) emission during engine shutdown and
tailpipe HC emissions during engine restart. As government regulations
further restrict these emissions, injector tip leakage requirements are
becoming more stringent.
Injector tip leak rate is normally specified using a gaseous medium such as
Nitrogen. This is to avoid the limitations of fluid leak test equipment in
the manufacturing environment. Vehicle testing with limit leak rate
injectors is recommended to verify that the tip leak design specification
provides the expected level of performance.
0 .0
0 .5
1 .0
1 .5
2 .0
2 .5
3 .0
0 .0
1 .0
2 .0
3 .0
4 .0
5 .0
6 .0
7 .0
8 .0
9 .0
1 0 .0
M e a n F lo w C u r v e
0 .0
5 .0
1 0 .0
W o rk in g F lo w R a n g e
P u ls e W id th (m s )
F
low
Ra
te
(g
/s)
3
σ
Dev
iat
io
n
Fr
o
m
M
e
an
Fl
ow
(%
)