Note: Descriptions are shown in the official language in which they were submitted.
A COMPRESSION IGNI~ION ENGINE
1 This invention relates to a system o gas fuelling of
compression ignition engines preferably of the high-speed
type. These engines would predominantly be in automotive
applications fuelled by CNG and diesel.
The proble~ this invention aims to overcome is -to pro-
vide a way of controlling the gas and diesel fuelling of
engines, when operating in a dual fuel mode, in such a way
as to provide satisfactory and efficient operation of these
engines. A secondary problem the invention aims to overcome
is that of being able to retrofit the control system to
existing engines.
An object of the invention is to provide a means of gas
fuelling which contains the desirable features of retention
of the volumetric and thermodynamic efficiency of the engine
coupled with the simplicity of design and maintenance of
manifold admission of the gas fuel.
In addition, the related problem of control of detona-
tion in the gas fuelled engine is provided for by wide
variation of the air to gas ratio.
A further object is to provide a system that is basi.-
cally fail-safe~ Some of the benefits of satisfying this
requirement should permit compliance with CNG vehicle
instaIlation regulations without the use o ancillary
equipment.
Accordingly the present invention consists in a
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~ compression ignition engine having a pilot\fuel feed to the
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1 engine and a separate gaseous fuel Eeed characteri~ed in
that the separate gaseous fuel feed is controlled by means
controlled by hydraulic pressure dependent on engine speed
and/or engine load.
Preferably said means controlling said separate gaseous
fuel feed is a valve.
Preferably said valve is a piston type valve.
PrefeL~bly said valve is a diaphragm type valve.
Preferably for each engine speed when the engine is
0 running the 'nydraulic pressure has a redetermined maximum
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.value there being bleeding off cir_~it~ to enable reduc-
tions of hydraulic pressure below said maximum value for
each engine speed.
Preferably means is provided whereby under low load con-
ditions engine speed governor means cause the bleeding offc~c~
-C'__~iL~y~tO cause a reduction in hydraulic pressure and
hence gaseous fuel feed for the particular engine speed.
Preferably said hydraulic pressure is dependant on
engine speed and the means which controls the separate
gaseous fuel feed is a regulator valve dependant on such
hydraulic pressure, said regulator valve and the hydraulic
pressure being arranged such that there is no flow of said
separate gaseous fuel feea when the engine is not running.
In a further aspect the invention consists in a
compression ignition engine of a kind having a pilot liquid
fuel feed into each combustion chamber and having a gaseous
fuel feed to each combustion chamber characterized in that
there is provided:
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1 means clependant on gngine speed to generate a hydraulic
pressure which increases with engine speed~
means to govern the effect of load on any engine speed,
means responsive to said means to govern to reduce said
hydraulic pressu.re in low load situations t~ result in a
resultant hydrau.lic pressure less that otherwise would be
the case, and
means dependant on said resultant hydraulic pressure
to.control the feed of said gaseous fuel, the arrangement
being such that when the engine is not running said means
dependant on said resultant hydraulic pressure does not
allow a gaseous fuel feed and such that for each speed there
is a feed rate of gaseous fuel dependant on said resultant
hydraulic pressure, the greatest gaseous feed or each
~5 engine speed being that when the engine is under load
sufficient to minimize the reduction of said hyd.raulic
pressure by said means responsive to said means to govern.
.. Preferably said means to govern is a mechanical
governor, or hydraulic governor, the mechanical movement of
which is constrained from adjusting the liquid fuel feed
and instead arranged to coact with said means responsive
to said means to govern.
Preferably said gaseous feed is into the inlet manifold
or manifolds of the engine.
~5 Preferably saîd means responsive to said means to
govern is a bleeding circuit.
In yet a ~urther aspect the present invention consists
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1 in a fuel system for a compression ignition engine which
results in a compression ignition engine in accordance with
the present invention. The presen-t invention also consists
in componentry for retrofitting~a compression ignition
engine (preferably a governed compression ignition engine)
to provide a compression ignition engine in accordance with
the present invention.
Preferred forms of the present invention will now be
described with reference to the accompanying drawings in
which:
Figure 1 is a flow diagram showing part of the com-
ponentry in accordance with the present invention,
T designating a diesel or other liquid fuel tank,
P designating a fuel pump,
V designating a change over valve,
G designating a governor ,
G.F. designating a gaseous fuel supply,
R designating a regulator which is the prefexred
form of valve in accordance with the present invention, and
E designates the engine and preferably the engine
manifold to receive the gaseous fuel flow,
components P and R being shown diagrammatically in
section,
Figure 2 is a diagrammatic view of a hydraulic governor
having the accelerator linkage designated as A and the flow
into the governor being designated by an arrow, the flow out
from the governor being designated by an arrow and the two~
way flow also designated by arrow between the governor and
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1 the regulator e.g, R of Figure 1,
Figure 3 is a governor valve se~sing mechanical movement
of the engines centrifugal governor to provide the bleeding
wanted in low load situations again with the arrows
designating the same features and
Figure 4 shows an alternative governor valve to that
of Figure 3, again sensing mechanical movement of the engine's
centrifugal governor to provide the bleeding wanted in
low load situations, again with the arrows designating the
same features~
In a preferred form the present.invention cons.ists in
a compression ignition engine of a kind having a pilot
liquid fuel eed into each combustion.chamber and having
a gaseous fuel feed to each combustion chamber characterized
in that there is provided:
means dependent on engine speed to generate a
hydraulic pressure which increases with engine speed,
means to govern the effect of load on any engine
speed,
means responsive to said means to govern to reduce said
hydraulic pressure in low load situations to result in a
resultant hydraulic pressure less that otherwise would be
the case, and
means dependent on said resultant hydraulic pressure
to control the feed of said gaseous fuel, the arrangement
being such that when the engine is not running said means
dependent on said resultant hydraulic pressure does not
allow a gaseous fuel feed and such that for each speed
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1 there is a feed rate of gaseous fuel dependent on said
resultant hydraulic pressure, the greatest gaseous feed
for each engine speed being that when the engine is under
load sufficient to ~ln;m; ze the reduction of said hydraulic
pressure by said means responsive to said means to govern.
More broadly however the invention consists in a
compression ignition engine having a pilot liquid fuel
feed to the engine and a separate gaseous fuel feed
characterized in that the separate gaseous fuel feed is
controlled by means controlled by hydraulic pressure
depend~ent on engine speed and/or engine load.
The invention also consists of apparatus for providing
such fèed(s) and/or control and various conversion methods.
The basic operation of the invention can now be
described. Gas flow to the inlet manifold of an engine
possessing duel fuel capability is metered by hydraulic
servo-control of a gas pressure regulator. Hydraulic
fluid, which may be a fuel such as diesel, is admitted
to one side of the regula~or diaphragm to balance gas
pressure on the other side. Gas flow is therefore
primarily regulated by the hydraulic fluid circuit
although final adjus~ment of gas flow is by an adjustable
metering orifice.
In a preferred embodiment of this invention, shown
in Fig. 1, the hydraulic pump is a fuel injection pump
used in diesel engines, and the hydraulic regulating
fluid is diesel fuel. The hydraulic regulating pressure
may then be tapped directly from the engine fuel injection
line.
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1 For variable speed engines the system is described as
ollows. A fixed displacement hydraulic pump such as
the fuel injection pump described above, driven by the
engine, in combination with a bleed orifice produces an
output pressure related to engine speed. For certain
rotary fuel injection pumps as fitted to these engines
this variable pressure may be tapped directly from its
trans~er pump. This output is led via a valve, the purpose
of which is to change over from operation on diesel or
single fuel to gas/pilot liquid fuel operation and thence
via a governor valve for speed control of the engine to
one side of the pressure regulating valve. Gas pressure
produced in the regulator is thus in balance with the
pressure output of the fuel injection or hydraulic fluid
pump unless the governor valve is shut and is therefore
related to the engine speed. By virtue of the pressure
related flow characteristics through the gas metering
orifice m~;rllm gas fuel to the engine at any given speed
is determined for control of combustion chamber detonation.
Under engine acceleration conditions restrictive damping
of the hydraulic line between the governor assembly and
the regulator may be used to control combustion chamber
detonation. Figure 1 of the accompanying drawings out
line the system in the manner of a flow chart.
For constant speed engines the control system is
able to be constructed more simply by connecting the
governor valve to the engine lubrication oil pressure
supply. The system as described above can then be adjusted
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1 give the appropriate gas fuelling for the oil pressure
available. A restrictor orifice ensures a minimum bleediny
off of the lubrication oil.
For engines consuming gas from a flow pressure
supply, normally constant speed engines fuelled by pro-
ducer gas or biomass digestor gas of suitable calorific
value, the control system is described as follows. A
constant pressure oil supply is used as noted above. A
changeover valve and governor valve are incorporated.
A pressurising fan is required to yield a positive pressure
at the regulator valve. The pressure regulating valve is
of a diferent type and would comprise either a large bore
regulator valve as diagrammed or a butterfly yalve in the
gas admission pipe under hydraulic control.
With reference to the operation of the governor and
the pilot fuel control two systems are used.
Firstly a system has been devised in which the
existing engine fuel control mechanism is restrained in
the pilot fuel position mechanically, or by use`of a
solenoid or a small pressure-operated ram and the existing
engine governor is not used for speed control. The speed
related output pressure of the system pump is used in a
hydraulic governor valve one form o~ which is shown in
Figure 2. ~Iere hydraulic pressure moves a control piston
against spring pressure determined by the accelerator posi-
tion to produce a reduced pressure in the static line
between the governor valv~ and the gas pressure ~egulator.
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1 'rhat reduced pressure is related to the demand require-
ments for engine speed.
Secondly a system has been devised in which the
speed related hydraulic pressure of the pump is only used
to control maximum fuelling of the engine and governing is
obtained by the action of the engine's own centrifugal
governor or hydraulic governor with a mechanical movement
on a small hydraulic valve. Restraint of the engine's fuel
control rack or equ~valent is obtained by action of a small
hydraulic piston-two forms of which are shown in Figures 3
and 4~ These have a shut-down piston and governing valve
combined into one unit. Admission of hydraulic pressure
by the changeaver valve causes the piston to move forcing
the control rack to move to the pilot fuel position which
may be variable according to engine speed as determined
by a stiff spring. Movement of the piston to the pilot
fuel position uncovers a port admitting governor control
pressure`to the static line between the governor valve ~nd
the gas pressure regulatox. The movement of the engine's
fuel control rack to operate the governor valve is con-
fined to a small range about the pilot fuel position. On
some engines on which heavy overload cannot be sustained on
gas provision is made for the fuel control rack orce to
overcome the force on the piston which returns the engine
to diesel operation until the load reduces.
For constant speed engines a pressure as set or
that engine can be used rather than a speed related hydraulic
pressure as noted aboveO The descriptions of the operation
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1 of the governor and the pilot fuel control in both systems
is unchanged however.
On the basis of the foregoing the many advantages of
the present invention can readily be seen, for example,
it can be seen that by using a small diesel or other liquid
fuel pilot feed CNG or other combustible gas can be
effectively employed in a wide range of engine usages
without the draw-backs of most pre-existant systems. Also
it can be seen that the choice of a higher than usual gas
delivery pressure would permit a number of advantages
including:-
(i~ small bore plumbing with overall size
reductions,
~ small physical size of the gas regulator
allowing precise control,
~iii) remoteness of the gas regulator from the
manifold,
(iv) with high flows gas expansion is less so
cooling effects are reduced.
It can also be seen that the use of hydraulic con-
txol circuitry reduces the need for engine model specific
parts in control linkages.
It can also be seen that the use of control within
the hydraulic circuit itself yields the following benefits:-
(i~ the need is obviated for low friction gas
tight seals,
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1 (i.i) any failure or loss of control pressure makes
the system failsafe.
It can also be seen that the provision for control
of the amount of pilot fuel permits:-
- (i) the governor to allow the engine to lapse
back onto diesel under heavy overload,
(ii) variation of pilot injection with engine
speed particularly to compensate for variations of
injection pump efficiency at different speeds.
It is believed therefore that the present invention
in the form as~claimed or the more preferred form
hereinbefore described should find wide spread acceptance.
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