Note: Descriptions are shown in the official language in which they were submitted.
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"LIQUID FUEL VAPOURISATION APPARATUS FOR FUEL INJECTED INTERNAL
COMBUSTION ENGINES"
TECHNICAL FIELD
THIS INVENTION relates to liquid fuel vapourisation
apparatus for spark ignition fuel injected internal combustion
engines. The invention also has application to carbureted
internal combustion engines which can be converted to fuel
injection internal combustion engines.
BACKGROUND ART
Internal combustion engines designed to run on petrol
(sometimes called gasoline) are often converted to run on liquid
petroleum gas (LPG). More recently, automotive manufacturers
have provided vehicles having LPG instead of petrol as the fuel
source, avoiding the need for conversion. There are many forms
of conversion available, however, the method of carburetion or
fuel injection arising from the conversion may result in some
drawbacks, such as, for example, difficulty in starting hot
engines. While it has been found that using a fuel in the
gaseous phase may have benefits, running LPG fuel as a vapour
from the LPG tank creates a heat sink in the tank due to the
energy required to evaporate the LPG fuel. On the other hand,
petrol is liquid at ambient conditions, and vapourisation of the
liquid fuel requires heat input, such as from the engine coolant.
There have been proposals for dual fuel internal combustion
engines, however, such proposals usually require the LPG to be
delivered to the combustion chamber as a liquid under much the
same phase conditions as liquid fuels, thus foregoing the
benefits of having a vapour and air mix in the combustion chamber
prior to ignition.
Sometimes, engines with liquid fuel injection systems
converted to run on LPG merely inject gas into the throat of the
air intake manifold and rely on natural or forced aspiration to
control fuel supply, bypassing the fuel injectors, foregoing the
advantages of precise fuel delivery time and quantity offered by
fuel injection.
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It has also been suggested that the fuels used in internal
combustion engines are not necessarily ideal in that combustion
occurs relatively slowly due to the fuel consisting of a range
of molecular weights of hydrocarbon. The lighter fractions
ignite before heavier fractions which sometimes remain unburnt
and may contribute to photochemical smog unless catalytically
oxidised prior to emission from the tail pipe of the vehicle.
A narrower range of molecular weights in the constituents of the
fuel may lead to better efficiency since the combustion will be
more predominantly percussive than would be the case for fuel
having a wider range of molecular weights in its constituents.
The present invention aims to provide vapourised liquid fuel
injection apparatus for internal combustion engines which
alleviates one or more of the aforementioned problems, or at
least to provide a useful alternative to present fuel systems for
internal combustion engines. Other aims and advantages may
become apparent from the following description.
SUNINIARY OF THE INVENTION
With the foregoing in view, this invention in one aspect
resides broadly in liquid fuel vapourisation apparatus for a fuel
injected internal combustion engine having a throttle body and
an intake manifold, the apparatus including:
first pressure reduction means for receiving liquid fuel and
reducing the pressure of the liquid fuel to a first controlled
pressure, at which at least some of the fuel may be vapourised;
a vapouriser in fluid communication with the first pressure
reduction means for receiving the partly vapourised fuel
therefrom and vapourising the remainder of the liquid fuel to
provide a gaseous fuel at the first controlled pressure;
second pressure reduction means in fluid communication with
the vapouriser for receiving the gaseous fuel and reducing the
pressure thereof to a second controlled pressure for delivery to
one or more of the fuel injectors of the internal combustion
engine to which the apparatus is fitted.
The first and second pressure reduction means may be adapted
to be operatively interposed between the throttle body and the
intake manifold of the engine, or alternatively, the first and
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second pressure reduction means being operatively incorporated
into a throttle body which in turn is adapted to be operatively
connected to the intake manifold of the engine. It will be
appreciated that the internal combustion engine may have been
converted from an a carbureted combustion engine to a fuel
injected internal combustion engine.
In another aspect the invention resides broadly in an
internal combustion engine having an intake manifold and a
throttle body in fluid communication with the intake manifold,
characterised in that liquid fuel vapourisation apparatus as
previously described is operatively connected between the
throttle body and the intake manifold. The first and second
pressure reduction means described above may be formed as a two-
stage regulator.
Preferably, catalytic cracking means is operatively
connected in the fluid flow path between the second pressure
reduction means and the intake manifold for thermal catalytic
reduction of the gaseous fuel received therefrom to produce a
cracked fuel having constituents of substantially lower molecular
weight.
Preferably, the second pressure reduction means is operable
to regulate the pressure of the fuel in the vapour state so that
the ratio of the absolute gas supply pressure to the injectors
to the absolute manifold pressure is 1.85 or greater. It is
believed that this ratio will ensure that the gas flowing through
the injectors reaches sonic velocity, thereby causing the mass
flow rate to be close to proportionate to the supply pressure.
Using supply pressure as an analogue for mass flow rate, under
sonic conditions, an accurate quantity of fuel may be delivered
by accurately controlling supply pressure of the fuel. It will
be appreciated that for supercharged or turbocharged engines, a
higher pressure will be required.
Pressure regulators typically reduce the pressure of LPG
drawn from the top of the tank as a vapour using a needle and
seat together with a spring loaded diaphragm to regulate the
pressure relative to the vent port. In the present invention,
it is preferred that the first pressure reduction means comprises
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a first needle and seat type valve through which liquid fuel may
enter and a second needle and seat type valve comprising the
second pressure reduction means, the ratio of the effective cross
sectional area of the first needle and seat to that of the second
needle and seat being selected to reflect the expected increase
in volume accompanying the phase change. In a preferred form the
ratio is about 1:270 for LPG.
In a preferred form, the first and second needles are
opertively connected by a common shaft to a spring loaded
diaphragm. More preferably, the first and second needles are
formed in the common shaft. The side of the diaphragm remote
from the needles may be either vented to atmosphere or arranged
for fluid connection with the intake manifold making the output
pressure of the vapouriser apparatus relative to either
atmospheric pressure or to manifold pressure respectively. In
the case of supercharged or turbocharged engines, the vent is
provided with a fluid connection such that the extra pressure
supplied to the engine is also transmitted to the remote side of
the diaphragm. In the case of centrifugal superchargers, the
spring may be selected to exhibit non-linear compression
characteristics to provide the pressure regulation which may be
necessary for such engines.
Where a catalytic cracking means is provided, it is
preferred that the vaporisation means heats the gaseous fuel to
a temperature of between 190° and 235°C for unleaded standard
grade petrol, and that a quantity of water is provided to
vaporise and provide a source of hydrogen and/or oxygen in
reactive form for catalytic combination with some components of
the petrol and produce lower molecular weight hydrocarbons and/or
alcohols. A thermal catalyst is believed to be suitable for this
purpose, and may be selected for example, from the zeolites, to
catalytically crack the fuel from the liquid fuel source to a
desired cracked fuel composition consisting of components of a
narrow range of molecular weights which will produce a more
percussive type combustion in the combustion chamber of the
engine than the liquid fuel prior to catalytic cracking.
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The injector or injectors may be fitted to a plate between
the throttle body and the manifold. In such an arrangement, it
is preferred that the plate also supports the two-stage
regulator, filter and a shut-off solenoid valve such that all of
the desired components are in a unitary assembly. It will be
seen that this arrangement may have the advantage of reducing
complexity and cost. Alternatively, a separate injector may be
used for each cylinder or bank of cylinders and operatively
connected into the manifold at the appropriate position. This
approach may be necessary in the case of engines which have their
idle air control motor/valve located between banks of cylinders
to equalise gas distribution to all cylinders.
It is believed that in addition to pressurised, liquified
gaseous fuels, the apparatus of present invention may be used for
fuels which are normally liquid at standard atmospheric
conditions, such as petrol, diesel oil, arid low molecular weight
alcohols, in which case the fuel may be stored in a non-
pressurised tank and pressurised by a pump before being
vapourised and injected. It will be appreciated that non-
fractionating fuels would be suitable for use with the liquid
fuel vapouriser apparatus of the present invention. If the engine
is to be supplied with more than one type of fuel, a separate
vapouriser would be necessary, each vapouriser having the ratio
of the respective effective cross sectional areas of the first
and second needle seats selected to reflect the expected volume
increase in the change of phase for each particular fuel to be
used.
The vapouriser may also include means for enhancing the
phase change from liquid to vapour, such as a catalyst, or such
like, or what is sometimes known in the art as an ebulator. The
vapouriser includes a housing to enclose the vapour and liquid
and house the ebulator.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more readily understood
and put into practical effect, reference will now be made to the
accompanying drawings which illustrate a preferred embodiment of
the invention, and wherein:
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Fig. 1 is a schematic diagram of a fuel supply system for
an internal combustion engine incorporating liquid fuel
vapourisation apparatus according to the invention and, in
dotted outline, a combined vapourisation apparatus and
thermal catalytic cracker, and in which the engine has four
vapour fuel injectors;
Fig. 2 is a schematic diagram showing the location of the
liquid fuel vapourisation apparatus between a throttle body
and an intake manifold for an internal combustion engine
similar to that of Fig. 1, but having two vapour fuel
injectors; and
Fig. 3 is a diagrammatic sectional view of a dual seat
valve assembly for the liquid fuel vapourisation apparatus
of Figs. 1 and 2.
The fuel supply system 10 illustrated in Fig. 1 includes a
fuel tank for liquid fuel (pressurised LPG) 13, for supplying
fuel in liquid form from the tank through a fuel tank valve 12
to a liquid fuel line 15. Alternatively, or in addition thereto,
a fuel tank for petrol (shown in dotted outline at 11) is
provided with a fluid connection to a fuel pump 14 which in turn
has its output in fluid connection to the liquid fuel line 15.
A fuel pump would be necessary for LPG if the ambient temperature
is insufficient for the vapour pressure to be above the required
regulated pressure (after allowing for pressure losses through
the tubing, valves etc.) for the particular composition of the
LPG.
In the case of the LPG fuel tank, the liquid fuel line is
in fluid communication with the liquid fuel vapourisation
apparatus 20, which in turn is in fluid communication with a
vapour fuel line 17 feeding four fuel injectors shown typically
at 25. In the case of the petrol fuel tank, the liquid fuel line
is in fluid communication with the combined vaporisation
apparatus and thermal catalytic cracker 21, which in turn is in
fluid communication with the vapour fuel line 17 shown in dotted
outline, and which also feeds the fuel injectors described above.
The fuel injectors are controlled by four respective
injector control cables shown typically at 26 which are in
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electrical connection with an electronic control unit 28. In
use, the liquid fuel is fed through the fuel tank valve and then
through the liquid fuel line to the liquid fuel vapourisation
apparatus by the pump or under pressure of the liquid and gas in
the fuel tank. The liquid fuel is vapourised in the liquid fuel
vapourisation apparatus and fed into the vapour fuel line, and
thence to the individual injectors which inject the vapourised
fuel into the respective combustion chambers of the engine under
control of the electronic control unit. In the case of the
petrol fuel, the gas phase fuel emerging from the second stage
of the pressure reduction is heated and passed over zeolite
catalyst to crack the heavier fractions to lighter molecular
weight components. Optionally, water may be added from a water
tank 18 to provide reactive hydrogen and/or hydroxyl groups to
assist the cracking process.
Referring to Fig. 2, the liquid fuel vapourisation apparatus
is mounted on a plate 33 having therethrough a throat 34, and
which is inserted between the throttle body 32 and the manifold
31. Two fuel injectors 25 are also mounted to the plate for
20 injecting vapourised fuel into the manifold 31 for transport to
the combustion chambers of the engine (not shown), the gas from
the injectors being injected through respective vapour nozzles
35 in the throat of the plate.
The liquid fuel vapourisation apparatus 20 illustrated in
Fig. 3 has a housing 40 with a fuel entry port 55 to which the
liquid fuel line 15 is connected, and a vapour fuel outlet port
57 to which the vapour fuel line 17 is connected. A first seat
plate 42 extends across the housing, and has an aperture therein
forming a first seat 44. The first seat plate and part of the
housing define a liquid intake chamber 41 and the liquid fuel
line leads into the liquid intake chamber to substantially fill
the liquid intake chamber with liquid fuel. A first needle 43 on
the distal end of a needle shaft 45 extending substantially
axially at least part way through the vapouriser housing is
sealingly enagagable with the first seat. A second seat plate 46
extends across the housing at right angles to the housing axis
to form a vapourisation chamber 50 intermediate the first and
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second seat plates. The second seat plate, in a similar fashion
to the first seat plate, has an aperture therethrough forming a
second seat 48 into which a second needle 47 is sealably
engagable. The first needle and second needle are integrally
formed on the needle shaft and extend from a diaphragm 49 which
is biassed to close the first and second needles against the
first and second needle seats by a spring 56 interposed between
the diaphragm and the top of the housing. Also, a vent port 52
is provided in the housing on the other side of the diaphragm
from the needle shaft. A vapour chamber 51 is formed between the
diaphragm and the second seat plate.
Additionally, to vapourise the fuel in the vapourisation
chamber, engine coolant is introduced through a coolant feed port
63 into a coolant chamber 64 which has a convoluted coolant
chamber wall 61 dividing the coolant chamber from the
vapourisation chamber. Engine coolant introduced through the
coolant feed port is returned to the engine cooling system by way
of a coolant return port 66. The compression of the spring 56 may
be adjusted by an adjusting screw 54 thereby adjusting the
biassing force on the first and second needles. The liquid fuel
vapourisation apparatus may be secured at a desired location by
an annular mounting flange 58 extending radially outward from the
vapouriser housing.
In use, liquid fuel pumped or led through the liquid fuel
line is fed into the liquid intake chamber, and flow of the
liquid from the liquid intake chamber is controlled by the
biassing force applied by the spring to the first needle against
the first seat. The liquid which passes through the first needle
and seat is vapourised in the vapourisation chamber by virtue of
both the pressure reduction and the transfer of heat from the
engine coolant being re-circulated through the coolant chamber
through the coolant chamber walls. If desired, the vapourisation
chamber may be packed with contact material to enhance the change
of phase from liquid to vapour. The flow of vapour from the
vapourisation chamber to the vapour chamber is controlled by the
second needle and seat, both the first and second needles and
seats being movable axially by action of the pressure of the
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liquid and gas on the first and second needles respectively
acting against the compensating biassing force of the spring, the
biassing force of which is adjustable by virtue of the adjusting
screw. The gas pressure in the vapour chamber is equilibrated
either to atmosphere through the vent port or to the manifold
pressure. The vapour chamber may also be packed with thermal
cracking catalyst and a water or steam inlet port to facilitate
the catalytic cracking of heavier fractions in the fuel.
In a preferred form, the plate is cast as a body having flow
passages provided for connecting injectors, the vapouriser
apparatus, fuel filters, shut off solenoids and such other
components as desired or required by threaded engagement
therewith so that the plate and all of the components can be
conveniently interposed between the throttle body and the
manifold.
Where the engine is converted from a petrol fuel injection
to a vapour fuel injection in accordance with the invention, the
vapour injectors are used instead of the petrol injectors of the
engine, the preferred vapour injector being a fast response
solenoid valve of the type disclosed in United States Patent No.
4,610,267 to Neils J. Beck, Edward T. Gilbert, William E. Weseloh
and Kenneth Rudolf.
The existing electronic control unit of the petrol injection
engine is used to control the vapour injectors used with the
vapouriser apparatus of the present invention which inject the
vapour directly into the throat of the intake manifold so that
a mixture very close to the stoichiometric ratio of fuel and air
is delivered to each combustion chamber in turn under the control
of the electronic control unit receiving its signals from sensors
typically provided in operative association with the engine. For
installation of the liquid fuel vapourisation apparatus in a non-
fuel injected engine, vapour fuel injectors may be substituted
for liquid fuel injectors from a fuel injection conversion kit,
and the electronic control unit of the fuel injection conversion
kit can be used to control the vapour fuel injectors fed with the
vapourised fuel from the liquid fuel vapourisation apparatus of
the present invention.
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Although the invention has been described with reference to
one or more specific examples, it will be appreciated by persons
skilled in the art that the invention may be embodied in other
forms within the broad scope and ambit of the invention as
defined by the following claims.
