Intensifier apparatus and method for supplying high pressure gaseous fuel to an internal combustion engine

The invention relates to an apparatus and method for supplying high pressure gaseous fuel from a storage vessel to a vehicle's internal combustion engine. More particularly, the invention is a fuel supply system with three main components: the storage vessel; an intensifier; and, an accumulator vessel. Fuel passages connect each one of the components directly with the other two components. The intensifier has a plurality of compression chambers and one of the compression chambers can be by-passed when the intensifier is operating in a low capacity mode, depending upon the pressure in the storage vessel. The intensifier operates continuously. When no fuel compression is required, the intensifier runs in an idle mode with the respective inlets and outlets of the compression chambers connected by fuel passages, thus preventing any fuel compression. The loading to the intensifier actuating mechanism is balanced in all modes of operation.

TECHNICAL FIELD OF THE INVENTION 
The invention relates to an apparatus and method for supplying high 
pressure gaseous fuel from a storage vessel to a vehicle's internal 
combustion engine. More particularly, the invention is a fuel supply 
system where the pressure in the storage vessel is variable and it is 
important to consistently maintain fuel injection pressure within a 
pre-determined acceptable operating range. 
BACKGROUND OF THE INVENTION 
To inject gaseous fuel into a combustion engine, the fuel pressure must be 
raised higher than the pressure in the piston chamber. For a compression 
ignition engine, such as a diesel engine, a fuel pressure as high as 200 
bar (approx. 3,000 psi) may be required to inject the fuel and to ensure 
combustion. Compressed fuel is typically supplied from pressure rated 
storage vessels carried on board the vehicle. As the fuel is consumed, the 
pressure in the storage vessels drops. To consistently maintain the 
pressure of gaseous fuels within a pre-determined acceptable operating 
range for injection into the combustion chamber of the internal combustion 
engine, it is necessary to provide a means for increasing the pressure of 
the gaseous fuel. The pre-determined acceptable operating range is 
determinable from the optimal injection pressure which depends upon the 
particular characteristics of a given engine. 
An intensifier is a compressor which increases the pressure of a gas 
supplied from a variable pressure source to a higher pressure. An 
intensifier can be used to increase the fuel pressure from a fuel storage 
tank on a vehicle for injection of the fuel into the engine. 
It is well known to locate a small accumulator vessel near the fuel 
injectors to consistently maintain the gaseous fuel pressure at the 
injectors within a pre-determined acceptable operating range despite the 
varying pressure in the fuel supply system and storage vessel. When the 
pressure decreases in the accumulator, it is known to use an intensifier 
to deliver compressed gaseous fuel from the storage vessel to the 
accumulator vessel. When the pressure in the accumulator rises to the 
upper limit of the pre-determined acceptable operating range the 
intensifier typically shuts off. Accordingly, pressure in the accumulator 
is kept within a pre-determined acceptable operating range. In 
conventional fuel supply systems, the compressor is only activated when it 
is needed to raise the pressure in the accumulator vessel. 
U.S. Pat. No. 4,615,259, Anbe, discloses an intensifier using a Scotch-yoke 
design. The Scotch-yoke mechanism has a crank pin eccentrically extending 
from an end of a main drive shaft. A slider rotatably surrounds the crank 
pin. A yoke defines a pair of opposed parallel sliding surfaces for 
confining the motion of the slider only to the sliding motion along the 
surfaces. The yoke further defines a pair of outwardly extending 
connecting rods for connecting oppositely disposed pistons on either side 
of the yoke. The orbital motion about the axis of the main drive shaft 
causes the slider to reciprocate the yoke and the oppositely disposed 
pistons. Diaphragms separate the volume in which oil is provided to 
lubricate sliding and rolling bearings from the volumes associated with 
oil-free gas compression. 
U.S. Pat. No. 5,033,940, Baumann, also describes a compressor using a 
Scotch yoke design and sliding contact between the slider, which rotatably 
surrounds the crank pin, and the parallel sliding surfaces of the yoke. 
The quantity of lubricating oil entering the compression space from the 
volume occupied by the lubricated bearings is minimized by a dry gap ring 
seal. The piston liner and piston are made of materials having close to 
the same coefficient of thermal expansion. With the object of supporting 
dry (oil-free) compression to pressures as high as 500 bar, the pistons 
each have a ring seal and a guide ring made of a self-lubricating 
material, such as Teflon, suitable for dry running. 
U.S. Pat. No. 5,078,017, Zomes, discloses a Scotch yoke mechanism in which 
the slider bearings described by Anbe and by Baumann are replaced by 
rolling contact between the outer race of, or a ring surrounding, a roller 
or ball bearing enclosing the crank pin and the parallel surfaces of the 
yoke, which is rigidly connected to the compression pistons. A further 
distinction of this disclosure from those of Anbe and of Baumann is the 
provision of two laterally offset tracks, on opposite sides of the slot in 
the yoke, each of which engages one of two coaxial rollers, both mounted 
on the same crank pin. 
U.S. Pat. No. 5,327,863, Downton and Feilden, also discloses a Scotch yoke 
mechanism which can be used to actuate pistons from a crankshaft. The 
device includes slider bearings between parallel inner surfaces of the 
yoke and the slider block which is rotatably connected to the crank pin. 
Provision is made for stiffening of the yoke, to withstand deflections due 
to the bending moments associated with high compression load, and for side 
plates which control the relative lateral locations of the slider block 
and yoke. 
These disclosures show that the Scotch yoke mechanism, both with sliding 
and rolling contact at the inner parallel surfaces, of the yoke is well 
known. However, they do not disclose means for non-sliding control of the 
roller motion relative to the track. Nor do they disclose means for coping 
with the special problems associated with compression to a desired high 
pressure from a supply pressure which is variable from some extreme low 
value right up to the desired high pressure. These problems are of 
sufficient importance that the device used for compression in this case is 
designated by the special name intensifier. 
There are particular problems in applying conventional compression 
technology when the flow demand is highly variable, and when the inlet 
pressure varies from a low value to a value near the high outlet pressure. 
1. Fuel consumption requirements vary depending upon the demand made of the 
engine. For example, the engine may consume more fuel while the vehicle is 
accelerating or climbing a hill. At other times much less fuel is needed, 
for example, when the vehicle is maintaining a constant velocity or 
descending a hill. For a vehicle with a compression ignition engine, 
during normal operation, the rate of fuel consumption may vary by about a 
factor of ten. Activating the intensifier only when pressure in the 
accumulator vessel decreases below a pre-determined level causes the 
intensifier to cycle on and off. This kind of operation subjects the 
intensifier to accelerated wear, reducing its service life. Consequently, 
this is a problem in applications where reliability, maintenance costs, 
and long service life are important considerations. 
2. Since the fuel pressure in the storage vessel varies as the fuel is 
consumed, this could cause large unbalanced forces within the intensifier 
if the inlet pressure is high. The supply pressure may vary by a factor of 
10. If the intensifier is designed for full delivery at low inlet 
pressure, there may be a large unbalanced force on the first stage piston 
when the inlet pressure is high and the first compression stage is not 
needed. This can pose a difficulty in design or make the device less 
durable. 
3. Since the supply pressure can rise nearly to the delivery pressure, and 
it is not generally feasible to pressurize the crankcase of the 
intensifier to supply pressure, the blowby gas which escapes from the high 
pressure cylinder with a conventionally sealed piston cannot be directed 
to the supply tank and would need to be vented to the atmosphere with 
undesirable implications for safety and for the environment. 
Accordingly, there is a need for an apparatus which is adapted for 
supplying gaseous fuel consistently at a pressure within an pre-determined 
acceptable operating range, and operating under the difficult and variable 
operating conditions inherent in a gaseous fuel supply system for an 
internal combustion engine. Also there is a need for a means of preventing 
the leakage of gas from the compression space to the crankcase. 
SUMMARY OF THE INVENTION 
The invention provides an intensifying apparatus and method for supplying 
high pressure gaseous fuel at a consistent pressure, within a 
pre-determined acceptable operating range, to an internal combustion 
engine. 
The invention in one embodiment provides a fuel supply system which uses an 
intensifier which runs continuously, to reduce wear caused by cycling 
between on and off modes. The invention also provides a fuel supply system 
supplied by a variable pressure fuel source, which consistently supplies 
gaseous fuel at a pressure within a pre-determined acceptable operating 
range. In another aspect, the invention provides a fuel supply system 
which has the capacity to deliver fuel at the rate required by an internal 
combustion engine where such fuel consumption rates vary by about a factor 
of ten. 
The apparatus of the invention has three main components, connected to each 
other by a plurality of fuel passages. The three main components are a 
storage vessel, an intensifier, and an accumulator vessel. The storage 
vessel is a pressure vessel which stores a quantity of compressed gaseous 
fuel. The accumulator is much smaller than the storage vessel and it 
maintains a quantity of the gaseous fuel at an injection pressure that is 
within a pre-determined acceptable operating range. The intensifier has a 
first compression chamber and a second compression chamber for compressing 
the gaseous fuel to increase the pressure of the gaseous fuel supplied 
from the storage vessel. The intensifier can have more than one 
compression stage, thereby requiring a plurality of chambers. 
The fuel passages direct the flow of the gaseous fuel from the storage 
vessel to the accumulator vessel. The fuel passages also provide 
connections between each of the storage vessel, the intensifier, and the 
accumulator vessel. A first passage connects an outlet from the storage 
vessel to an inlet to the first compression chamber. A second passage 
connects an outlet from the first compression chamber to an inlet to the 
second compression chamber. A third passage connects an outlet from the 
second compression chamber to an inlet to the accumulator vessel. A first 
by-pass passage, can be selected for fuel flow to by-pass the first 
compression chamber. A second by-pass passage, can be selected for fuel 
flow to by-pass the second compression chamber. 
In an embodiment of the invention a control apparatus is provided for 
automatically controlling fuel flow through the first and second by-pass 
passages according to the fuel pressures measured in the accumulator 
vessel and the storage vessel. Valves mounted in each of the first and 
second by-pass passages are used to control fuel flow through the by-pass 
passages. A first pressure measuring instrument is mounted to the 
accumulator vessel to measure pressure of the gaseous fuel inside the 
accumulator vessel. A second pressure measuring instrument is mounted to 
the first fuel passage for measuring pressure of the gaseous fuel supplied 
from the storage vessel. 
In another embodiment of the invention, provision of complementary 
curvatures on the surfaces of the roller and tracks for non-sliding 
control of the rolling contact motion between the yoke and the rolling 
ring rotatably surrounding the crank pin. 
In another embodiment of the invention, a separate high pressure source of 
oil is connected to the sealing space between the piston and the cylinder 
of each stage of compression such that the sealing oil supply pressure 
always exceeds the gas pressure in the compression space, so that no gas 
can leak past the piston into the crankcase volume. 
In another embodiment of the invention, a fourth passage connects the first 
passage to a compartment in the intensifier. The compartment is located 
behind a piston of the first compression chamber such that the compartment 
is separated from the compression chamber by the piston. 
In one specific aspect, the invention is directed to an apparatus for 
supplying high pressure gaseous fuel to a fuel injector of an internal 
combustion engine, said apparatus comprising: (a) a fuel storage vessel; 
(b) an intensifier having a first compression chamber with a first piston 
therein, and a second compression chamber with a second piston therein; 
(c) an accumulator vessel for holding a quantity of gaseous fuel at an 
injection pressure within a pre-determined acceptable operating range; 
and, (d) a plurality of fuel lines for directing flow of said gaseous fuel 
from said storage vessel to said accumulator vessel and for providing 
direct connections between said fuel storage vessel, said intensifier, and 
said accumulator vessel, said fuel passages including: (i) a first fuel 
line for connecting an outlet from said fuel storage vessel to a first 
inlet to said first compression chamber; (ii) a second fuel line for 
connecting a first outlet from said first compression chamber to a second 
inlet to said second compression chamber; (iii) a third fuel line for 
connecting a second outlet from said second compression chamber to an 
inlet to said accumulator vessel; (iv) a first closeable by-pass passage, 
connecting the first fuel line with the second fuel line; and (v) a second 
closeable by-pass passage, connecting the fuel line with the third fuel 
line. 
The apparatus can further include a control apparatus for automatically 
controlling fuel flow through one or the other or both of said first and 
second closeable by-pass passages based upon fuel pressure measurements at 
said accumulator vessel and said fuel storage vessel. The control 
apparatus can further include: (a) a first valve mounted in said first 
by-pass passage for controlling fuel flow through said first by-pass 
passage; and (b) a second valve mounted in said second by-pass passage for 
controlling fuel flow through said second by-pass passage. 
The apparatus can further include a passage connecting a compartment 
located behind the first piston of the first compression chamber on a side 
opposite to the first compression side of the first piston for enabling 
pressures in said first compression chamber to balance. The apparatus can 
further include a check valve on each of the first and second inlets and 
the first and second outlets of the first and second compression chambers 
for controlling the direction of flow of the gaseous fuel. 
The apparatus can further include a heat exchanger associated with the 
second fuel line for cooling gaseous fuel after it has been compressed by 
the first piston in the first compression chamber. The apparatus can 
further include a heat exchanger associated with the third fuel line for 
cooling gaseous fuel after it has been compressed by the second piston in 
the second compression chamber before it enters the accumulator vessel. 
In the apparatus as defined, the first piston can have a larger end area 
than the second piston, for balancing the forces during respective 
compression strokes and to accommodate differences in volumetric flow 
through the first and second compression chambers caused by compression of 
the gaseous fuel in the first compression chamber. 
The apparatus as defined can include: (e) a sealing oil storage tank; (f) a 
sealing oil pump connected to the sealing oil tank; (g) a first sealing 
oil line from the sealing oil pump to a high pressure sealing location 
associated with the first compression chamber; and (h) a second sealing 
oil line from the sealing oil pump to a high pressure sealing location 
associated with the second compression chamber. 
The apparatus can include at least two gaseous fuel storage vessels and the 
effect of two stage operation can be obtained by sequential use of a 
single stage in first compressing the gaseous fuel from a low pressure 
tank to an intermediate pressure tank, and then compressing the gaseous 
fuel from the intermediate pressure tank to the accumulator vessel which 
directly supplies the engine. 
The invention in another specific aspect includes intensifier for supplying 
high pressure gaseous fuel to a fuel injector of an internal combustion 
engine comprising: (a) a hollow chamber; (b) a reciprocating member in 
said chamber; (c) a first piston and a first fuel compression chamber, 
said first piston being driven by said reciprocating member; (d) a second 
piston and a second fuel compression chamber, said second piston being 
driven by said reciprocating member; (e) a one-way inlet and a one-way 
outlet associated with the first fuel compression chamber; (f) a one-way 
inlet and a one-way outlet associated with the second fuel compression 
chamber; and (g) a passageway connecting the one-way outlet of the first 
fuel compression chamber with the one-way inlet of the second fuel 
compression chamber. 
The method of supplying high pressure gaseous fuel to fuel injectors for an 
internal combustion engine includes the following steps: 
(a) Supplying gaseous fuel from a variable pressure source; 
(b) Regulating the pressure of the gaseous fuel to maintain an injection 
pressure within a pre-determined acceptable operating range using an 
intensifier having a plurality of compression chambers; and 
(c) By-passing a compression chamber of the intensifier when the pressure 
inside the storage vessel is higher than a pre-determined pressure. 
Another embodiment of the method of the invention includes the step of 
by-passing the intensifier and continuing to operate the intensifier in an 
idle mode without compressing any gaseous fuel. 
In the method as defined, the step of providing back pressure to the piston 
in a first of the compression chambers can be added to balance operating 
loads applied to the intensifier during idle running speed. The sealing 
oil from a high pressure sealing oil source can be directed to sealing 
spaces between the plurality of pistons and cylinders in which the pistons 
travel at a pressure which is higher than the pressures of the compression 
chambers, thereby preventing leakage of gas past the plurality of pistons. 
In a specific aspect, the invention is directed to a method of supplying 
high pressure gaseous fuel to a fuel injector for an internal combustion 
engine, the method comprising the steps of: (a) drawing the gaseous fuel 
from a variable pressure fuel source; (b) regulating the pressure of the 
gaseous fuel to maintain a fuel injection pressure within a pre-determined 
acceptable operating range using an intensifier having a plurality of 
pistons and compression chambers; (c) operating the intensifier without 
compressing any gaseous fuel when the injection pressure is greater than a 
first pressure P1 which is equal to an upper limit of the pre-determined 
acceptable operating range; (d) compressing gaseous fuel in first and 
second compression chambers of the intensifier when the injection pressure 
decreases to a second pressure P2 which is equal to a lower limit of the 
pre-determined acceptable operating range and the fuel source pressure is 
less than a pre-determined supply pressure P3; and, (e) compressing 
gaseous fuel in the second compression chamber and by-passing the first 
compression chamber when the injection pressure decreases to P2 and the 
fuel source pressure is greater than P3. 
The method can include at least two fuel sources, and the effect of two 
stage operation can be obtained by sequential use of a single stage in 
first compressing the gas from a low pressure tank to an intermediate 
pressure tank and then compressing the gas from the intermediate pressure 
tank to an accumulator which directly supplies the engine. 
An advantage of the apparatus of the invention is that the by-pass passages 
allow the apparatus to be operated in three modes: a first mode where the 
intensifier is completely by-passed and gas is not compressed; a second 
mode where only one of the compression chambers is by-passed; and a third 
mode where all of the compression chambers are used to compress gaseous 
fuel. These three modes provide flexibility which enables the apparatus to 
operate efficiently over a broad range of supply pressures and fuel 
consumption rates. 
Another advantage of the apparatus is that the intensifier is continuously 
activated. This avoids the wear caused in conventional fuel supply systems 
by cycling between on and off modes, dictated by the demand for compressed 
gaseous fuel. With the apparatus of the invention, when no compression is 
needed, the intensifier is simply by-passed, and the intensifier continues 
to run idle. 
Another advantage of the apparatus is the ability to compensate by pressure 
balancing for the large out-of-balance forces would otherwise be 
encountered when the inlet pressure rises to near the outlet pressure. 
Another advantage of the apparatus is the possibility of preventing any 
gaseous fuel reaching the environment.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION 
The invention is an apparatus and method for supplying high pressure 
gaseous fuel to an internal combustion engine. The subject intensifier 
application differs from conventional compressors in a number of aspects. 
Firstly, the intake pressure varies considerably, by a factor of 10. It is 
thus a variable intake pressure compressor or intensifier. Secondly, the 
mass flow requirements at the exhaust of the intensifier vary. This 
variation exists because sometimes the internal combustion engine is 
subject to heavy load and needs a lot of high-pressure gas, but other 
times it is idling and needs very little gas. Generally, there is a 
variation by a factor of 10 in the mass flow requirements. The intensifier 
according to the invention deals with the variable mass flow requirement 
by compressing gas only when it is needed to maintain high pressure in an 
accumulator. The applicant has determined that the best way to suppress 
the compression of gas when it is not required to operate the intensifier 
with equal pressure on intake and exhaust. This strategy essentially 
requires that the intensifier run "unloaded", or without compressing any 
gas. The intensifier according to the invention incorporates special 
features to deal with this situation and with the variable pressure ratio. 
These are described below. 
FIG. 1 represents an enlarged sectional view of an intensifier according to 
an embodiment of the invention. FIG. 2 represents a flow diagram 
illustrating the components and operation of an intensifier for raising 
fuel pressure from a fuel storage tank to a higher pressure for injection 
into an engine. 
Referring to FIG. 2, there are three main components. These three 
components are joined by fuel passages which connect each one of the 
components to the other two components. The first main component is fuel 
storage vessel 18. Storage vessel 18 is a pressure rated vessel which 
holds compressed gaseous fuel. While only one vessel 18 is shown, it will 
be understood that a vehicle may use several storage vessels to increase 
the amount of gaseous fuel which can be stored on board the vehicle. As 
the fuel is consumed, the fuel pressure decreases in storage vessel 18. 
The second component is an intensifier 1, as described previously. The 
third component is an accumulator 17. 
The intensifier is composed of a first stage I and of a second stage II, as 
illustrated in FIG. 1. The intensifier 1 is constructed of a hollow 
housing 2 with hollow protrusions on opposite sides. The pistons 3 and 4 
in each protrusion reciprocate respectively in compression chambers 24 and 
25 and are actuated by a scotch yoke mechanism. The scotch yoke mechanism 
comprises a rotating shaft 5 which drives an eccentric disk 6 which 
reciprocally forces a moving bloc 7 to oscillate from side to side, 
thereby sequentially actuating pistons 3 and 4. The pistons 3 and 4 are 
guided and supported by bushings 8 on each piston 3 and 4. The cylinders 
in the two protrusions are sealed to prevent leakage to the actuating 
chamber of the housing. Each compression chamber 24, 25 has a respective 
intake valve 10, 11 and a respective exhaust valve 12, 13. 
When the block 7 moves to the left, as indicated by the directional arrow, 
it moves piston 3 to the left, and also piston 4 to the left. On the 
return stroke, the block 7 forces the pistons 3 and 4 to move to the 
right. Gas is thereby sequentially forced in through the intake valves 10 
and 11, in alternating strokes, and out through exhaust valves 12 and 13 
on reverse alternating strokes. The piston 3 of the first stage I is 
larger than that of the piston 4 of the second stage II because of the 
different volumetric gas flows and because of the need to balance the 
forces acting on the actuating mechanism 7. 
For stage I, the intake port 10 is connected to a back-pressure port 14, 
thereby allowing a back pressure to be applied to the back of piston 3. 
This back pressure on piston 3 permits the operation of the unloaded 
intensifier 1 to be balanced when no compression takes place. 
Referring to FIG. 2, there are three main components of the overall system. 
These three components are joined by fuel passages which connect each one 
of the components to the other two components. The first main component is 
fuel storage vessel 18. Storage vessel 18 is a pressure rated vessel which 
holds compressed gaseous fuel. While only one vessel 18 is shown, it will 
be understood that a vehicle may use several storage vessels to increase 
the amount of gaseous fuel which can be stored on board the vehicle. As 
the fuel is consumed, the fuel pressure decreases in storage vessel 18. 
The second component is an intensifier 1, as described previously. The 
third component is an accumulator 17. 
The storage tank 18 is connected to the intake valve 10 of the piston 3 
side of the intensifier by fuel line 21. The exhaust valve 12 is connected 
through an intercooler 19 and line 22 to intake valve 11. A solenoid valve 
15 is located between lines 21 and 22. The exhaust valve 13 is connected 
by line 23 and intercooler 20 to gas accumulator 17. Lines 22 and 23 are 
also bridged by a solenoid valve 16. 
Unloaded conditions are allowed by opening the solenoid valves 15 and 16 
between the intake and exhaust stroke of each stage. (Balancing is 
important to reduce wear on parts. This is particularly important in 
heavy-duty applications where reliability is a priority.) 
The operation of the intensifier system is as follows. When the pressure in 
the accumulator 17 is below pressure P1, as indicated by pressure gauge 
P1, the solenoid valve 16 is closed. If the fuel storage tank 18 pressure 
is below pressure P3, as indicated by pressure gauge P3, which is below 
pressure P1, the solenoid valve 15 is also closed. As the moving bloc 7 
moves to the right, gas from the fuel tank 18 flows into the first stage 
cylinder housing piston 3 through intake valve 10. As the moving bloc 7 
moves to the left, the gas is compressed by the piston 3 in the first 
stage I and then flows out the exhaust valve 12. The gas is cooled in an 
inter-cooler 19 before entering the second stage II. Gas is introduced in 
the second stage II and the second chamber housing piston 4 upon leftward 
motion of the moving bloc 7, and is subsequently compressed upon rightward 
motion of the bloc 7. The compressed high-pressure gas is transmitted 
through line 23 and then through a heat exchanger 20 before entering the 
accumulator 17. 
Another operating mode occurs when the pressure in the storage tank 18 is 
greater than pressure P3. The solenoid valve 15 is then opened, and the 
first stage I produces no compression of the gas. Only the second stage II 
is then used to bring the gas to high pressure P1. 
Another operating mode occurs when the pressure of the accumulator 17 
reaches pressure P2, as indicated by pressure gauge P2, which is greater 
than operating P1. Pressure P1 is below and pressure P2 is above the 
required injection pressure respectively. The accumulator 17 is then 
considered full and intensification is not needed. The solenoid valves 15 
and 16 are then opened, leaving the intake and exhaust of each stage 
connected thereby producing no compression. 
The following table summarizes the features of the intensifier that permit 
it to deal with the special application. 
______________________________________ 
Application 
Particularity 
Feature Device 
______________________________________ 
Variable Intake Pressure 
Sizing of first and 
ratio of piston sizes 
second stage 
optimized for best 
balance under a wide 
range of pressure 
ratios 
Capability of running 
control system 
only second stage 
Variable Fuel Flow 
Connect exhaust to 
control system 
intake when no 
compression needed 
Balancing of use back pressure on 
intensifier for idle 
back of first stage to 
running balance 
______________________________________ 
Accumulator 17 is a pressure vessel, and is typically much smaller than 
fuel storage vessel 18. Accumulator 17 is used to hold gaseous fuel at a 
pressure within a pre-determined acceptable operating range. Compressed 
gaseous fuel from accumulator 17 is supplied to the fuel injectors of an 
internal combustion engine in known fashion. Exhaust valve 13, which is 
one-way, prevents the compressed gaseous fuel in accumulator 17 from 
flowing back to fuel storage vessel 18 when the pressure in accumulator 17 
is higher than the pressure in fuel storage vessel 18, which is virtually 
all of the time. 
A feature of the invention is the arrangement of the fuel passages which 
connect the three main components together. The fuel passages must be 
pressure rated to handle high pressure gaseous fuel. The fuel passages may 
be tubing, pipes, hoses, or passages formed in the housing 2 of 
intensifier 1. 
A control apparatus, which is typically a computer, is used to control fuel 
flow through first and second by-pass passages 38, 40 respectively. The 
control apparatus includes first by-pass solenoid valve 15 which controls 
the flow through the first by-pass passage between lines 21 and 22, and 
second solenoid by-pass valve 16 which controls the flow through the 
second by-pass passage between lines 22 and 23. The control apparatus also 
includes first, second and third pressure gauges P1, P2 and P3 
respectively, which measure fuel injection pressure and the fuel pressure 
in accumulator 17 and fuel storage vessel 18. 
The control apparatus operates the solenoid by-pass valves 15 and 16 
according to the pressure in accumulator 17 and fuel storage vessel 18. 
When the pressure in accumulator 17 is greater than a pre-determined 
pressure P1, which is greater than the desired injection pressure into the 
engine, accumulator 17 is full and there is no current need for compressed 
fuel. Intensifier 1 continues to operate but the fuel supply system is 
operating in an idle mode without compressing any fuel. 
In the idle operating mode, both of the solenoid by-pass valves 15 and 16 
are open. Fuel pressure in all fuel lines is equalized and because the 
inlets and outlets of the first and second compression chambers 24, 25 
containing pistons 3 and 4 are all connected, there is no compression. 
When the first compression chamber 24, with first piston 3, is undergoing 
a compression stroke, the second compression chamber 25 with second piston 
4 is undergoing an intake stroke. 
Because fuel pressure in the fuel supply system is equalized in the idling 
mode, fuel pressure in first and second compression chambers 24, 25 is 
also equalized during respective intake and compression strokes. First and 
second pistons 3, 4 are both driven by the same actuating mechanism 6, 7. 
Since the end surface area of second piston 4 is less than the end surface 
area of first piston 3, the load applied to the actuating mechanism 6, 7 
would not be balanced without the existence of back pressure port 14 
behind first piston 3. 
Intercooler 20 is a heat exchanger and is installed in line 23 to cool the 
compressed gaseous fuel before it enters accumulator 17. Without heat 
exchanger 20, heat energy transferred from second compression chamber 25 
might otherwise ignite the compressed fuel in accumulator 17. 
No gaseous fuel is compressed in first compression chamber 24 while by-pass 
passage 15 is open since the inlet and outlet of first compression chamber 
24 remain connected. 
If the pressure in fuel storage vessel 18 is less than a pre-determined 
pressure P3, first solenoid by-pass valve 15 is also closed, initiating a 
high capacity mode of operation. In the high capacity mode first and 
second compression chambers 24, 25 operate in series. The gaseous fuel 
compressed in first compression chamber 24 flows through second line 22 to 
the inlet of second compression chamber 25. First compression chamber 24 
increases the pressure of the gaseous fuel entering second compression 
chamber 25. By utilizing both first and second compression chambers 24, 25 
the supply fuel pressure increases more rapidly, allowing intensifier 1 to 
accommodate fuel supplied at a lower pressure. 
Intercooler 19, which is a heat exchanger, is installed in line 22 to cool 
the fuel from first compression chamber 24 before entering second 
compression chamber 25. Without heat exchanger 19, heat transferred from 
first compression chamber 24, combined with the heat generated in second 
compression chamber 25 might cause the fuel in second compression chamber 
25 to ignite. 
FIG. 3 shows, in one embodiment of the intensifier, a tank 31 containing 
sealing oil which is pressurized by pump 32 and conducted by line 33 to 
the high pressure sealing location 34 of the first compression stage, and 
likewise conducted by line 35 to the high pressure sealing location 36 of 
the second compression stage. 
Mode of Operation with Variable Inlet Pressure 
FIG. 4 shows, as an example, the characteristics of the operation of the 
intensifier 1 when the inlet-to-outlet pressure ratio P.sub.1 /P.sub.2 
varies from 0.1 to 1.0 (with the outlet pressure P.sub.2 being held 
constant). 
Shown are the curves of volumetric efficiency N.sub.V1 and N.sub.V2 for the 
first and second stages I and II, respectively. Also shown is the ratio 
P.sub.interstage /P.sub.2, in which P.sub.interstage is the interstage 
pressure. At the lowest inlet pressure this interstage pressure ratio is 
about 0.33 in this example, which implies about equal pressure ratio per 
stage. 
As the inlet pressure rises above 0.1 times P.sub.2, the interstage 
pressure in line 22 rises till at some point it is close to the outlet 
pressure. Accompanying this pressure increase is a small increase in the 
first-stage I volumetric efficiency, and a large increase in the 
second-stage II volumetric efficiency, as the pressure ratio across the 
second stage approaches 1.0. Past that point, the first stage I is 
bypassed and only the second stage II is used for compression. The 
interstage pressure therefore drops to the inlet pressure P.sub.1 which is 
now the same as P.sub.intercooler. 
FIG. 4 also shows what happens to the mass flow per revolution of the 
intensifier 1. Here the dimensionless quantity (m R T.sub.1)/(V.sub.d1 
P.sub.2) is used, in which m is the quantity of fuel mass delivered per 
stroke, R is the gas constant, T.sub.1 is the gas inlet temperature, 
V.sub.d1 is the first stage displacement volume, and P.sub.2 is the outlet 
pressure. All quantities except m being constant, the curve with this 
designation directly indicates the relative variation of mass flow per 
revolution as the inlet pressure changes. 
The stage displacement volumes are chosen so that at minimum inlet pressure 
the intensifier 1 will meet maximum engine fuel demand (and, in this 
example, so that at minimum inlet pressure the stage pressure ratios are 
about equal). As FIG. 4 indicates, the fuel supply rate will rise with 
rising inlet pressure reaching as high as 5 or 6 times the maximum engine 
demand. When the intensifier fuel supply exceeds the engine demand both 
first and second stages I and II of the intensifier 1 are bypassed, while 
the engine draws directly from the gas accumulator 17 placed at the 
intensifier outlet 13. 
Also shown in FIG. 4 is the variation in work per revolution with inlet 
pressure ratio. Here the dimensionless work parameter employs the 
constants previously mentioned as well as Cp which is the gas specific 
heat. The curve indicates that the work per revolution (while the 
intensifier is in operation) reaches a maximum which is about 45% higher 
than when the inlet pressure is minimum. As the inlet pressure has risen, 
the work per unit mass has dropped but the mass ingested per revolution 
has risen disproportionately. 
A potentially serious problem might occur when the intensifier 1 is 
operating with both stages I and II bypassed during relatively long 
periods when the inlet pressure is high and there is unbalanced pressure 
loading. FIG. 5 indicates that in this case (V=0.3), the maximum 
unbalanced pressure load on the yoke could approach approximately 2P.sub.2 
A.sub.2, in which A.sub.2 is the area of the second stage piston. The 
product 2P.sub.2 A.sub.2 could be of the order of two tons of force. 
The calculations whose results are shown in FIG. 4 employed the concept of 
polytropic compression with polytropic compression index assumed to be 
1.25 for both first and second stages. The stage clearance ratios were 
assumed to be 0.25 and 0.35 for the first and second stages, respectively. 
For each stage, the volumetric efficiency N.sub.v was estimated from 
EQU N.sub.v =1-.epsilon.(PR)1/n=1, 
in which .epsilon. is the stage clearance ratio and n is the polytropic 
index. The symbols PR indicate the outlet-to-inlet pressure ratio for the 
stage in question. For these calculations the stage volume displacements 
were related (as an example) by 
##EQU1## 
in which V.sub.d1 and V.sub.d2 are the displacements of the first and 
second stages, respectively. T.sub.1 is the first stage inlet temperature, 
and T.sub.intercooler is the second stage inlet temperature. In the 
calculations for FIG. 3, the ratio T.sub.intercooler /T.sub.1 was assumed 
to be 1.16. The interstage pressure was determined by equating mass 
delivered by first and second stages I and II. 
As a second example, FIG. 6 shows the operation of an intensifier over the 
same range of pressure ratio as FIG. 4 but with a different displacement 
volume ratio (defined above), taken as V=1. Here at minimum supply 
pressure, the first and second stage pressure ratios are about 2.5 and 4, 
respectively, and the corresponding volumetric efficiencies differ 
considerably. In this case, however, the interstage pressure ratio 
approaches unity only at the upper end of the inlet pressure range; both 
stages are active throughout and there is need for only one bypass valve. 
The unbalanced pressure load during intermittent unloaded operation is 
much less, as is shown by FIG. 5. 
FIGS. 4, 5 and 6 indicate the need for a strategy to match the intensifier 
supply and the compressor demand over the range of inlet pressures and 
call for controlled intermittent operation of either both stages or the 
second stage only with due attention to force unbalance. 
Where two or more gaseous fuel tanks are provided, as is common in fueling 
vehicle engines, the intensifier can be used in this environment. In this 
case, the effect of two-stage operation at lowest fuel tank pressure can 
be obtained with a first stage by using the first compression end of the 
intensifier to compress the gas from the tank with the lowest pressure to 
an intermediate pressure tank and subsequently, the second compression end 
of the intensifier can be used for compression taking place between the 
intermediate pressure tank and the accumulator which supplies the gaseous 
fuel directly to the engine. 
As will be apparent to those skilled in the art in the light of the 
foregoing disclosure, many alterations and modifications are possible in 
the practice of this invention without departing from the spirit or scope 
thereof. Accordingly, the scope of the invention is to be construed in 
accordance with the substance defined by the following claims.