Air shroud for air assist fuel injector

A fuel injector for a spark ignition internal combustion engine includes a fuel injector having inlet and discharge ends. The discharge end includes a fuel injection port for supplying a fuel stream directed along an axis. An air shroud supplies assist air. The air shroud includes a first end mountable over the injector discharge end. The air shroud also includes a second end having an air assist passageway coaxially aligned with the fuel injection port for directing the fuel stream through the passageway along a common axis and guiding a flow of assist air through the passageway. The air flowing through the passageway coaxially surrounds the fuel stream to mix with the fuel upon discharge from the passageway, thereby providing a precisely targeted atomized fuel spray.

FIELD OF THE INVENTION 
This invention relates to fuel injectors for spark-ignition, internal 
combustion engines and more particularly to an air assist fuel injector. 
BACKGROUND OF THE INVENTION 
The function of air assist fuel injectors is to provide enhanced 
atomization so that exhaust emissions can be minimized through more 
complete combustion. Prior designs, while providing better atomization, 
have failed to maintain accurate fuel spray targeting. 
Fuel which wets the intake port impairs both emissions and driveability as 
the fuel film causes acceleration driving modes to be lean and 
decelerations to be rich. This problem is aggravated during cold engine 
conditions as the fuel film thickness is inversely related to port wall 
temperature. (The first two minutes of the cold engine phase of the 
emission test accounts for most of the emissions as the catalyst initially 
has zero conversion efficiency and tailpipe emissions are strongly 
dependent upon the raw emissions from the engine.) 
While there are algorithms which compensate for this rich/lean condition, 
the finely atomized fuel which hits the port walls is not finely atomized 
when it flashes off the walls and/or runs down the walls. Thus much of the 
benefit is lost. 
Known air assist fuel injectors for distributing fuel from a fuel injection 
valve in the vicinity of an intake port to two intake valves in a 
combustion chamber utilize a sleeve nozzle having fuel flow separating 
holes provided on the fuel injection downstream side of a fuel injection 
port means to separate a spray of fuel jetted from the fuel injection port 
means into flows in a plurality of different directions. The sleeve nozzle 
also has a plurality of slit-like air holes for jetting assist air in a 
band-like manner such that the assist air impinges against fuel sprays 
separately jetted from the fuel flow separating holes from the opposite 
sides of the fuel sprays. With this arrangement, flat jets of air impinge 
obliquely against the jetted fuel. With such an arrangement, the fuel 
cannot be directly targeted as a well defined spray. 
SUMMARY OF THE INVENTION 
The present invention provides an air assist fuel injector that introduces 
an air assist airflow coaxial to an axially directed fuel stream. The 
co-axial air/fuel flow allows for precise targeting of the resulting spray 
pattern. 
The invention provides a fuel injector for a spark ignition internal 
combustion engine including a fuel injector having inlet and discharge 
ends. The discharge end includes a fuel injection port for supplying a 
fuel stream directed along an axis. An air shroud supplies assist air. The 
air shroud includes a first end mountable over the injector discharge end. 
The air shroud also includes a second end having an air assist passageway 
coaxially aligned with the fuel injection port for directing the fuel 
stream through the passageway along a Common axis and guiding a flow of 
assist air through the passageway. The air flowing through the passageway 
coaxially surrounds the fuel stream to mix with the fuel upon discharge 
from the passageway thereby providing a precisely targeted atomized fuel 
spray. 
The air shroud is of a cup like shape having a generally cylindrical 
sidewall extending from the second end. The second end has an inside 
surface spaced from the injector discharge end allowing air to be directed 
therebetween. The injector discharge end includes an orifice plate 
including the fuel injection port. 
Optionally the orifice plate includes multiple injection ports and the 
shroud second end includes a corresponding multiple of air assist 
passageways. 
The invention also provides a method of delivering an air fuel mixture in a 
fuel injected spark ignition engine having a fuel injector including inlet 
and discharge ends. The method includes the steps of providing a fuel 
injection port in the discharge end of the fuel injector for supplying a 
fuel stream directed along an axis. An air shroud is provided having an 
air assist passageway coaxially aligned with the fuel injection port for 
supplying assist air. A fuel stream is directed through the passageway 
along the common axis and the air flow of assist air is guided through the 
passageway and coaxially surround the fuel stream to mix with the fuel 
upon discharge from the passageway thereby providing a precisely targeted 
atomized fuel spray. 
These and other features and advantages of the invention will be more fully 
understood from the following detailed description of the invention taken 
together with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1-3, there is shown a fuel injector 10 for a spark 
ignition internal combustion engine, not shown, used to supply an atomized 
fuel spray into an internal combustion engine. As is hereinafter more 
fully described, the fuel injector 10 provides a precisely targeted 
atomized fuel spray. 
Referring to FIG. 1 the fuel injector 10 includes inlet and discharge ends 
12, 14. The discharge end 14, includes a fuel injection port 16 for 
supplying a fuel stream 18 directed along an axis 20. Fuel injector 10 
includes an air shroud 22 for supplying assist air. Air shroud 22 includes 
a first end 24 mountable over the injector discharge end 14. The air 
shroud also includes a second end 26 having an air assist passageway 28 
coaxially aligned with the fuel injection port 16 for directing the fuel 
stream 18 through the passageway along a common axis. Air assist 
passageway 28 also guides a flow of assist air through the passageway so 
that the air coaxially surrounds the fuel stream 18 to mix with the fuel 
upon discharge from the passageway. The fuel and air discharged from the 
air assist passageway 28 becomes a precisely targeted atomized fuel spray. 
With further reference to the drawings, air shroud 22 is of a cup shape 
having a generally cylindrical sidewall 30 extending from the second end 
26. The second end 26 has an inside surface 32 spaced from the injector 
discharge end 14 allowing air to be directed therebetween. 
The discharge end 14 of the fuel injector 10 includes an orifice plate 34 
including the fuel injection port 16. 
In the embodiment illustrated, orifice plate 34 includes two injection 
ports 16 for supplying separate fuel streams 18 directed along axes 20. In 
other applications where the invention is used there are more than two 
fuel streams having a coaxially aligned air assist flow. 
Shroud 22 includes a corresponding multiple, two, of air assist passageways 
28 extending through the second end 26 of the shroud. 
With this arrangement, the assist air is coaxially aligned and directed 
with the fuel streams jetted from the injection ports of the orifice plate 
34. The fuel stream is coaxially surrounded by the assist air, thereby 
allowing the atomized fuel spray to be precisely targeted. 
Turning now to the method of delivering an air fuel mixture in a fuel 
injected spark ignition engine, not shown, having a fuel injector 
including inlet and discharge ends, the method includes the steps of 
providing a fuel injection port in the discharge end of the fuel injector 
for supplying a fuel stream directed along an axis. An air shroud is 
provided having an air assist passageway coaxially aligned with the fuel 
injection port for supplying assist air. A fuel stream is directed and/or 
jetted through the passageway along a common axis and the assist air flow 
is guided through the passageway coaxially surrounding the fuel stream to 
mix with the fuel stream upon discharge from the passageway. Thus the 
method of delivering the air fuel mixture provides an atomized spray that 
is precisely targeted. 
Although the invention has been described by reference to a specific 
embodiment, it should be understood that numerous changes may be made 
within the spirit and scope of the inventive concepts described. 
Accordingly, it is intended that the invention not be limited to the 
described embodiment, but that it have the full scope defined by the 
language of the following claims.