Note: Descriptions are shown in the official language in which they were submitted.
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DIRECT INJECTION INTERNAL COMBUSTION ENGINE AND METHOD OF
MAKING AND OPERATING SAME
Field of the Invention
[0001] The present invention relates to a direct injection internal combustion
engine, a method of operaring same, and a method of converting a conventional
diesel-
fuelled engine to operate with direct injection of a two different fuels
through two
separate fuel injection valves so that the engine can be fuelled with one
fuel, the other
fuel or a combination of both fuels.
Background of the Invention
[0002] So-called compression ignition engines employ compression ratios that
are
I O much higher than Otto cycle (spark-ignited) engines. The most common
compression
ignition engines are diesel engines. Under normal operating conditions in a
diesel engine,
the heat produced by the mechanical compression of the fuel and air mixture
auto-ignites
the liquid diesel fuel at or near the end of the piston's compression stroke.
In such an
engine a glow plug is employed to provide ignition assist during start-up
conditions when
the engine is cold. The glow plug is normally turned off when the engine
achieves
normal operating conditions. "Glow plug" is defined in this specification to
mean any
type of electrically heated hot surface element employed within an engine's
combustion
chamber to assist with ignition of the fuel.
[0003] Recent developments have been directed to burning gaseous fuels such as
natural gas in a compression ignition engine. By substituting gaseous fuels
for liquid
fuels such as diesel, a compression ignition engine can be operated with much
lower
emissions of undesirable pollutants such as oxides of nitrogen (NOx) and
particulate
matter (Plvi]. Governments around the world are introducing ever more
stringent
regulations aimed at reducing pollution today and in the future by prescribing
increasingly lower levels of engine emissions.
[0004] A problem with burning gaseous fuels in a compression ignition engine
is
that while gaseous fuels are generally cleaner burning, compared to diesel
fuels, they
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typically require higher temperatures and pressures to achieve reliable auto-
ignition. One
approach has been to maintain the same compression ratios found in
conventional diesel
engines, and provide a means for assisting ignition of the gaseous fuel when
the engine is
running, such as, for example, a hot surface provided by a continuously
operable glow
S plug or a pilot fuel that is introduced into the combustion chamber. When a
pilot fuel is
employed, the pilot fuel is a fuel that is more readily auto-ignited compared
to the
gaseous fuel, which in this example is referred to as the main fuel since it
typically
represents the majority of the fuel that is consumed by the engine when
measured on an
energy basis. Since the pilot fuel is more easily ignited, it auto-ignites at
a lower
temperature than the main fuel and the ignition of the pilot fuel triggers the
ignition of the
gaseous fuel.
[0005] A challenge associated with using a pilot fuel is that a different fuel
from
the main fuel is added to the system and apart from requiring two separate
fuel systems,
such a system is also challenged by physical constraints such as allocating
space in the
fire deck of the cylinder head above the combustion chamber to accommodate a
separate
pilot fuel valve in addition to a gaseous (main) fuel valve and a conventional
glow plug.
This can be especially difficult now that recent trends in engine design have
led to the use
of more intake and exhaust valves per cylinder. Instead of only one intake
valve and one
exhaust valve per cylinder, current engine designs employ a total of at least
three or four
intake and exhaust valves, leaving less space for other components that are
mounted in
the cylinder head such as the fuel injection valves) and a glow plug.
[0006] In converting a conventional diesel-fuelled engine to operate with a
main
fuel and a pilot fuel, it is preferable to utilize as many of the same parts
to reduce
development and set up costs and to maintain economies of scale. Accordingly,
it is
desirable to avoid the need to design and manufacture a new cylinder head to
accommodate separate pilot fuel and main fuel injection valves. One solution
is to
employ a single fuel injection valve that can be mounted in the same opening
normally
occupied by a conventional diesel fuel injection valve, and that is capable of
injecting
both the main fuel and the pilot fuel, as taught, for example, by co-owned
United States
patent numbers 5,996,558, 6,073,862, 6,336,598, 6,439,192, and 6,761,325. In
preferred
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embodiments, so-called "dual fuel injectors" allow the separate and
independent injection
of pilot fuel and main fuel, allowing both fuels to be introduced directly
into the
combustion chamber, with the dual fuel injector occupying the space normally
occupied
by a conventional diesel fuel injection valve. The dual fuel injector approach
permits the
use of conventional cylinder heads without any substantial modifications. This
solution
can be employed for all engine sizes but is more suited to larger engines,
compared to
smaller engines, because there is more space in a larger engine to accommodate
a dual
fuel injector.
(0007] However, there remains a need for other arrangements and approaches for
operating a bi-fuel engine with the same power, performance and efficiency of
a
conventional diesel engine. In this disclosure a bi-fuel engine is defined as
an engine that
can burn two different fuels, and in preferred embodiments it can burn one of
the two
fuels or a combination of both fuels. For a bi-fuel engine that employs a
pilot fuel that is
directly injected into the combustion chamber, there is a need for an
arrangement that is
suitable for engines of all sizes, including smaller engines. In the example
of a gaseous-
fuelled engine, by injecting only a pilot quantity of liquid fuel, cleaner
burning gaseous
fuel can be substituted to satisfy the majority of the energy requirements,
thereby
reducing emissions. However, emissions can be further reduced in some
operating
modes if under certain. conditions a means other than the introduction of a
pilot fuel can
be employed to assist with ignition of the gaseous fuel. The present
disclosure relates to
a novel solution for addressing these needs with an apparatus that allows
separate and
independent introduction of two different fuels directly into an engine's
combustion
chamber without requiring any substantial modification of the cylinder head.
The present
disclosure also relates to an apparatus and method that allows an engine to be
operated in
several operating modes responsive to real-time operating conditions, with
flexibility to
burn two different fuels separately or together.
Summary of the Invention
[0008] An internal combustion engine is provided that can be fuelled with a
first
fuel atone or a combination of the first fuel and a second fuel or the second
fuel alone. The
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engine comprises the following components that cooperate with one another to
combust the
first fuel and/or the second fuel within a combustion chamber to produce
mechanical work
without ignition assistance from glow plugs:
an engine block defining the combustion chamber in cooperation with a
piston reciprocable within the combustion chamber, and a cylinder head
covering
one end of the combustion chamber opposite the piston;
an intake air manifold through which air can flow into the combustion
chamber by operation of an intake valve;
a piston rod operatively connecting the piston to a crankshaft, whereby
reciprocating movement of the piston is linked to rotation of the crankshaft;
a first fuel injection valve disposed in the cylinder head and operative to
inject the first fuel directly into the combustion chamber through a first
nozzle;
a second fuel injection valve distinct from the first fuel injection valve and
disposed in the cylinder head and operative to inject the second fuel directly
into the
I 5 combustion chamber through a second nozzle;
an ignition-assist apparatus associated with the intake air manifold that can
be activated to change a property of air inside the intake air manifold to
promote
ignition of the first or second fuel that is directly injected into the
combustion
chamber; and
an electronic controller programmable to command operation of the first fuel
injection valve, the second fuel injection valve nd the ignition-assist
apparatus
responsive to measured engine operating conditions.
[0009] An important feature of the ignition-assist apparatus is that, unlike a
conventional glow plug or spark plug, it is associated with the intake air
manifold and not
the combustion chamber. This allows more space in the cylinder head above the
combustion chamber for installing the first and second fuel injection valves,
which
require two separate mounting positions since these fuel injection valves are
distinct from
each other. The ignition-assist apparatus is operable to change a property of
the air inside
the intake manifold to promote ignition of the first or second fuel that is
directly injected
into the combustion chamber. For example, the ignition-assist apparatus can be
operable
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to increase the temperature of the intake air, or to introduce a fluid into
the intake air that
helps to promote combustion when the intake charge is compressed and heated in
the
combustion chamber.
[0010] In a preferred embodiment, the ignition-assist apparatus is a heater
that is
S operative to heat air within the intake air manifold when activated, whereby
the property
of the air that is changed is its temperature. The heater can comprise, for
example, an
electrical resistance heating element disposed within the intake air manifold,
or a burner that
can burn the gaseous fuel in a burner combustion chamber proximate to the air
intake
manifold. If the heater is a burner, the burner can be operable to emit hot
combustion
products from the burner combustion chamber directly into the intake air
manifold. In
another embodiment, the ignition-assist apparatus can be an injection valve
for
introducing a fuel into the intake air manifold that is more readily ignited
within the
combustion chamber compared to the first or second fuels. Dimethylether is an
example
of a fuel that would be suitable for conditioning the intake air to prime the
intake charge
1 S for ignition. An advantage of the ignition-assist apparatus being a heater
is that there is
no need to supply a third fuel to the engine. For this reason, while persons
skilled in the
technology will understand that other embodiments of the ignition-assist
apparatus are
possible, in the detailed description of the preferred embodiments set out
below and in
the accompanying figures, the ignition-assist apparatus is described and
illustrated as a
heater.
[0011] The disclosed engine is a bi-fuel engine since two different fuels may
be
employed to provide the energy needed to service the load applied to the
engine. In a
preferred embodiment, one fuel is a liquid fuel and the other fuel is a
gaseous fuel,
wherein the gaseous fuel is cleaner burning than the liquid fuel, and the
liquid fuel has a
2S Iower auto-ignition temperature compared to the gaseous fuel. When both
fuels are
introduced into the combustion chamber, the liquid fuel can a.ct as a pilot
fuel to ignite
the gaseous fuel. In preferred operating modes the quantity of liquid fuel is
limited,
allowing the majority of the fuel, on an energy basis, to be the cleaner
burning gaseous
fuel. In addition to the environmental benefits associated with most of the
burned fuel
being a cleaner burning gaseous fuel, there can also be economic advantages
because in
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many markets, gaseous fuels such as natural gas are less expensive than
conventional
liquid fuels such as diesel, when fuel costs are calculated on an energy
basis.
(0012] The first and second fuel injection valves can be any type of valve
suitable
for regulating the injection of fuel directly into a combustion chamber, as
long as they
can be manufactured with dimensions that allow them to be installed in the
openings
available in the cylinder head. For example, one or both of the fuel injection
valves can
employ inward opening valve needles if such valves can provide the desired
performance
characteristics while also meeting the dimensional constraints imposed by the
space
available for installing the valves in the cylinder head. Modern four-stroke
internal
combustion engines typically accommodate four intake and exhaust valves, in
addition to
the two fuel injection valves of the disclosed engine, and in a preferred
embodiment, if
there is not enough available space in the cylinder head to accommodate a fuel
injection
valve with an inward opening needle, at least one of the fuel injection valves
can be a
poppet valve. Poppet valves can be made with smaller outside diameters
compared to
valves with inward opening needles, and this can be advantageous if one of the
fuel
injection valves is mounted in an opening that is normally occupied by a glow
plug.
[0013] When one of the fuel injection valves is a poppet valve, it can be
desirable
to break up the fuel spray so that instead of being introduced in a conical
sheet, the fuel is
introduced in plumes with more contact interfaces with the oxygen in the
intake charge.
To divide the fuel spray into plumes, a nozzle tip can be disposed over the
end of each
poppet valve, the nozzle tip comprising orifices whereby fuel spray plumes can
be
introduced into the combustion chamber through the poppet valve. Such a nozzle
tip can
be detached from the nozzle tip and attached to the cylinder head, whereby the
poppet
valve is removable from the cylinder head separately from the nozzle tip. If
the nozzle
tip is damaged, worn, or clogged, it can be desirable to remove and clean or
replace the
nozzle tip. In preferred embodiments the nozzle tip is removably attached to
the cylinder
head. Instead of using a nozzle tip with orifices, a poppet valve can further
comprise
posts projecting from the end of the poppet valve, whereby the posts extend
into the path
of a fuel spray introduced into the combustion chamber through the poppet
valve, thereby
breaking up fuel spray to provide more contact surfaces with the oxygen in the
intake
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charge. In yet another embodiment, the poppet valve can comprise a fluted
plenum
provided between a valve stem and a nozzle body adjacent to a valve seat. The
fluted
plenum channels the fuel into the plenum openings so that when the valve is
opened the fuel
flows into the combustion chamber in plumes.
[0014] In preferred embodiments the electronic controller is programmable to
operate the engine in one of a plurality of selectable predetermined operating
modes. Each
one of the plurality of selectable operating modes determines the commands
that the
electronic controller sends to operate the first fuel injection valve, the
second fuel injection
valve, and the ignition-assist apparatus. Under some engine operating
conditions it may not
be necessary to operate the ignition-assist apparatus to auto-ignite the fuel
in the combustion
chamber. In some embodiments, the ignition-assist apparatus will only be
commanded to
operate during special operating conditions such as during a cold start up. In
other
embodiments, the electronic controller can be programmed to operate the
ignition-assist
apparatus whenever air temperature within the intake air manifold is less than
a
predetermined value. In another embodiment, if the ignition-assist apparatus
is a heater, the
electronic controller can be further programmed to determine heat input from
the heater,
quantity of the first fuel, quantity of the second fuel, and timing and
duration for each
injection event with reference to an engine map and data inputs received by
the electronic
controller, with the data inputs comprising measured engine operating
parameters and
operator inputs. In the embodiment wherein the ignition-assist apparatus is a
heater, in a
start-up mode, the electronic controller can be programmed to:
switch on the heater to heat air in the intake manifold before cranking the
engine;
inject a pilot quantity of the first fuel into the combustion chamber through
the first fuel injection valve; and
inject a main quantity of the second fuel into the combustion chamber
through the second fuel injection valve.
[0015] If the heater is an electrical resistance heater, the electronic
controller is
preferably programmed to switch off the heater before cranking the engine, so
that the
electrical load during start up is not excessive.
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[0016] 'The predetermined operating modes define for each combustion cycle
whether the first fuel is injected alone or in combination with the second
fuel or if the
second fuel is injected alone. The predetermined operating modes also define
whether the
ignition-assist apparatus is operated or not. The electronic controller is
programmed with at
least two operating modes wherein each of the first and second fuels is
introduced into the
combustion chamber in at least one of the selectable predetermined operating
modes. The
plurality of selectable predetermined operating modes from which the
electronic controller
is programmed to select comprise at least two of
operating mode I in which the ignition-assist apparatus is operated and both
of the first fuel injection valve and the second fuel injection valve are
commanded to
open;
operating mode 2 in which the ignition-assist apparatus is not operated and
both of the first fuel injecfion valve and the second fuel injection valve are
commanded to open;
operating mode 3 in which the ignition-assist apparatus is operated, the first
fuel injection valve is held closed and the second fuel injection valve is
commanded
to open;
operating mode 4 in which the ignition-assist apparatus is not operated, the
first fuel injection valve is held closed and the second fuel injection valve
is
commanded to open;
operating mode 5 in which the ignition-assist apparatus is operated, the first
fuel injection valve is commanded to open and the second fuel injection valve
is held
closed; and
operating mode 6 in which the ignition-assist apparatus is not operated, the
first fuel injection valve is commanded to open and the second fuel injection
valve is
held closed.
[0017) For example, in one embodiment, when starting up the internal
combustion
engine, the electronic controller can be programmed to operate the ignition-
assist apparatus
as part of a predetermined start up sequence. After start up, the electronic
controller can be
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programmed to select between operating mode 2 and operating mode 6 responsive
to
measured engine operating parameters and operator inputs.
[0018] A method is also disclosed of manufacturing an internal combustion
engine that comprises at least one combustion chamber defined by a cylinder
bore
provided within an engine block, a piston reciprocable within the cylinder
bore, and a
cylinder head covering an end of the cylinder bore opposite to the piston,
wherein the
cylinder head comprises a first opening suitable for receiving a conventional
diesel fuel
injection valve and a second opening suitable for receiving a glow plug. The
method
comprises:
installing a first fuel injection valve in one of the first and second
openings
in the cylinder head;
installing a second fuel injection valve in the one of the first and second
openings in the cylinder head that is not occupied by the first fuel injection
valve;
installing an ignition-assist apparatus in an intake air manifold through
which
air is flowable enroute to the combustion chamber; and
programming an electronic controller to operate the engine in one of a
plurality of operating modes wherein in at least one operating mode a first
fuel and a
second fuel are injectable directly into the combustion chamber, and in
another
operating mode the first fuel alone is injectable directly into the combustion
chamber, and in all operating modes the electronic controller is programmed to
switch on the ignition-assist apparatus responsive to predetermined operating
conditions to assist with promoting combustion in the combustion chamber.
(OOI9] If the second fuel is auto-ignitable within the combustion chamber
without
ignition assistance from the first fuel, the method of manufacturing the
engine can further
comprise programming the electronic controller to detect engine operating
conditions in
which the second fuel is auto-ignitable without assistance from the first
fuel, so that when
such engine operating conditions are detected, the electronic controller is
programmed to
select an operating mode in which the first fuel injection valve is held
closed and the
second fuel injection valve is opened. When the first fuel is diesel fuel and
the second
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fuel is a cleaner burning gaseous fuel, in some operating modes this feature
enables the
engine to run without burning any diesel fuel, thereby reducing engine
emissions.
(0020] In a preferred manufacturing method the internal combustion engine is
made with many of the same parts that are used to make a conventional diesel
engine,
such as the engine block, the cylinder head, pistons, and other major
components. The first
fuel is a liquid fuel and the second fuel is a gaseous fuel, and by practising
the method,
glow plugs are removed or not installed, and the engine is made to be operable
as a
gaseous-fuelled engine with liquid pilot fuel ignition assistance.
(0021) A method is disclosed of operating an internal combustion engine that
can be
fuelled with a first fuel alone or a combination of the first fuel and a
second fuel. The
method comprises:
pre-conditioning air within an intake air manifold by pre-heating the air or
introducing an ignition-assisting fluid to promote auto-ignition of the first
or second
fuel within the combustion chamber by operating an ignition-assist apparatus
associated with the intake air manifold;
introducing the first fuel directly into the combustion chamber through a
first
fuel injection valve;
introducing the second fuel directly into the combustion chamber through a
second fuel injection valve; and
selecting one of a plurality of predetermined operating modes for
determining when to pre-condition the air, when to introduce the first fuel,
and when
to introduce the second fuel, with these deterniinations being made responsive
to
measured engine operating conditions and operator inputs.
(0022) In a preferred method, one of the plurality of operating modes is a
start-up
mode for starting up the engine. In the start-up mode the method can further
comprise:
measuring engine temperature;
switching on the ignition-assist apparatus to pre-condition air in the intake
manifold before cranking the engine if the engine temperature is below a
predetermined value;
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determining a quantity of the first fuel and a quantity of the second fuel,
and timing for starting and ending respective injection events, with reference
to
data inputs received by the electronic controller and an engine map, the data
inputs
comprising measured engine operating parameters and operator inputs;
introducing the first fuel directly into the combustion chamber through the
first fuel injection valve; and
introducing the second fuel directly into the combustion chamber through
the second fuel injection valve.
I O [0023) In a preferred method the ignition-assist apparatus is a heater and
in the start-
up mode, the method further comprises switching offthe heater before cranking
the engine.
[0024) In preferred methods each of the first and second fuels is introduced
into the
combustion chamber in at least one of the plurality of selectable
predetermined operating
modes, which comprise at least two of
a first operating mode in which the ignition-assist apparatus is operated and
both of the first fuel and the second fuel are introduced directly into the
combustion
chamber;
a second operating mode in which the ignition-assist apparatus is not
operated and both of the first fuel and the second fuel are introduced
directly into the
combustion chamber;
a third operating mode in which the ignition-assist apparatus is operated, the
first fuel injection valve is held closed and the second fuel is introduced
directly into
the combustion chamber;
a fourth operating mode in which the ignition-assist apparatus is not
operated, the first fuel injection valve is held closed and the second fuel is
directly
introduced into the combustion chamber;
a fifth operating mode in which the ignition-assist apparatus is operated, the
first fuel is introduced directly into the combustion chamber and the second
fuel
injection valve is held closed; and
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a sixth operating mode in which the ignition-assist apparatus is not operated,
the first fuel is introduced directly into the combustion chamber and the
second fuel
injection valve is held closed.
[0025] When the engine is operating in a mode in which the ignition-assist
apparatus is not operated, the method can further comprise changing operating
modes and
operating the ignition-assist apparatus when air temperature within the intake
air
manifold is less than a predetermined fixed value. Instead of a predetermined
fixed
value, the method can comprise changing operating modes and operating the
ignition-
assist apparatus when air temperature within the intake air manifold is less
than a
predetermined value that is determined from an engine map. That is, the
threshold
temperature for triggering operation of the ignition-assist apparatus can be
different
depending upon the selected operating mode and/or the current operating point
on the
engine map.
[0026] If the ignition-assist apparahts is a heater, the method can further
comprise
regulating air temperature inside the intake air manifold by controlling heat
output from
the heater. For example, if the heater comprises an electrical resistance
element disposed in
the intake air manifold, and the method can further comprise controlling the
electrical
current delivered to the resistance element to control heat output from the
heater. If the
heater comprises a burner that is fuelled with the gaseous fuel, the method
can further
comprise regulating the flow of gaseous fuel to the burner to control heat
output from the
heater.
[0027] If the ignition-assist apparatus is a burner the method can further
comprise
releasing hot combustion products from the burner directly into the intake air
manifold.
[0028] In preferred methods, one of the fuels is a gaseous fuel selected from
the
group consisting of natural gas, methane, ethane, liquefied petroleum gas,
lighter
flammable hydrocarbon derivatives, hydrogen, and blends thereof. A "gaseous"
fuel is
defined herein to mean a fuel that is combustible in an internal combustion
engine and
that is in the gaseous phase when it enters the combustion chamber.
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[0029] Normally one of the two fuels has a lower auto-ignition temperature
than the
other fuel. If it is the first fuel that has a lower auto-ignition temperature
than the second
fuel, the first fuel can be a liquid fuel selected from the group consisting
of diesel fuel,
dimethylether, bio-diesel, kerosene, and mixtures thereof. In preferred
embodiments, the
fixst fuel is a liquid fuel that has a cetane number greater than or equal to
40.
[0030] The method can further comprise recirculating exhaust gas produced by
combustion inside the combustion chamber, back into the combustion chamber.
Brief Description of the Drawin~(s)
[0031] Figure 1 is a schematic view of an engine's intake air manifold and
combustion chamber, showing a heater disposed in the intake air manifold, and
mounted
separately in the cylinder head above the combustion chamber: a f rst fuel
injection valve
and a second fuel injection valve.
[0032] Figure 2 shows the cylinder head above the combustion chamber, viewed
looking up from within the combustion chamber.
[0033] Figure 3 is an axial view of a cross section of a fuel injection valve
with a
fluted valve stem, which provides channels for dividing the fuel into separate
spray jets.
[0034] Figure 4 is a side view of a nozzle tip for a poppet-style fuel
injection
valve with posts extending from the tip to break up the fuel spray into
plumes.
[0035] Figure 5 is a side view of a domed nozzle tip for a poppet-style fuel
injection valve with orifices for introducing the fuel into the combustion
chamber in
plumes.
[0036) Figure 6 is a flow diagram illustrating a control strategy for starting
up an
internal combustion engine with direct injection of liquid and gaseous fuels
into the
combustion chamber with a heater for pre-heating the intake air.
(0037] Figures 7 through 9 are flow diagrams that each illustrates a different
embodiment of a control strategy for selecting an operating mode for an
internal
combustion engine with direct injection of liquid and gaseous fuels into the
combustion
chamber with a heater for pre-heating the intake air.
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Detailed Description of Preferred Embodimeat(s)
[0038] In the figures illustrating the physical embodiments of the disclosed
engine, like-named features in different illustrated embodiments are referred
to with like
reference numbers increased by increments of 100.
[0039] The schematic view of Figure 1 shows part of the intake air manifold
and
a combustion chamber for an internal combustion engine. The disclosed engine
can be
fuelled with liquid fuel alone or a combination of gaseous fuel and liquid
fuel or gaseous
fuel alone. Like a conventional engine, the engine components cooperate with
one
another to combust fuel within a combustion chamber to produce mechanical
work, but
the presently disclosed engine operates without glow plugs. Instead of glow
plugs an
ignition-assist apparatus is associated with the intake air manifold, whereby
the ignition-
assist apparatus can be activated to promote conditions in the combustion
chamber that
result in the ignition of the directly injected fuel.
[0040] Figure I is illustrative of the disclosed system but the components are
not
drawn to scale. Engine block 102, piston I04 and cylinder head 106
collectively define
the boundaries of combustion chamber 108. Like a conventional internal
combustion
engine, a piston rod (not shown) is operatively connected to piston 104 and a
crankshaft,
whereby reciprocating movement of piston 104 is linked to rotation of the
crankshaft.
Intake air is directed to combustion chamber I08 through intake manifold 1 I 0
and intake
valve 112.
[0041) In the embodiment illustrated by Figure 1, the ignition-assist
apparatus is
heater I 14. Heater 114 is operative to heat air within intake manifold 1 I0.
As illustrated
in Figure l, heater I I4 can comprise, for example, electrical resistance
heating element
116 disposed within intake manifold 110 for direct contact with the intake
air. In another
embodiment (not shown) heater 1 I4 can comprise a burner fueled with the same
gaseous
fuel that is burned by the engine. In such an arrangement, the burner can
comprise a
burner combustion chamber proximate to intake manifold 110 but not within the
intake
manifold, and a burner exhaust port for releasing hot combustion products into
intake
manifold 110. An advantage of a burner is that it reduces the electrical load
on the
battery at start up.
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[0042) For a number of reasons, heater 114 is not as efficient as glow plugs
that
are installed in each cylinder. For example, there is some heat dissipation
between heater
114 and combustion chamber 108, more energy is required to heat air in intake
manifold
110 to a temperature that will promote ignition, compared to the energy
required to heat a
glow plug to provide a hot surface inside combustion chamber 108 towards which
fuel
can be directed to promote ignition. Also, by heating the air inside intake
manifold 110,
the hot air expands and less air can be inducted into combustion chamber 108.
Accordingly, in a conventional diesel engine, these are some of the reasons
why glow
plugs are employed instead of an intake manifold heater to assist with
ignition at start up
when the diesel fuel may not auto-ignite. All of these disadvantages remain
disadvantages associated with the use of an intake manifold heater in the
presently
disclosed invention. However, unlike a conventional engine, with the presently
disclosed
engine, these disadvantages are offset by the advantages gained by the
presently
disclosed engine, which is capable of burning a f rst fuel alone, a
combination of the first
fuel and a second fuel, or the second fuel alone without ignition assistance
from a glow
plug. Removing the glow plugs provides space for the installation of a second
fuel
injection valve, so that two fuel injection valves can be installed in
cylinder head 106 for
each combustion chamber without requiring a custom-designed cylinder head or
major
modifications to a conventional cylinder head. Even though heater 114 is less
efficient
than glow plugs, heater 1 I4 need only be used when the engine is in a start-
up operating
mode or when the intake air temperature is below a predetermined value.
Normally, once
the engine is running and the engine block is heated to normal operating
temperatures,
heater 114 can be turned off since the retained heat of combustion and the
normal in-
cylinder operating temperature near top dead center can be hot enough to auto-
ignite at
least one of the two directly injected fuels, which can in turn cause the
ignition of the
other fuel.
[0043] In addition, since heater 114 need only be normally employed when the
engine is starting up and optionally under specific predefined conditions such
as idle or
low load conditions, the reduced air mass flow caused by the lower density of
heated air
is not a detriment. Higher air mass flow rates are needed when the engine is
running
CA 02524146 2005-11-18
-16-
under high load operating conditions, but under such conditions, the heat
generated in the
combustion chamber is normally sufficient to make pre-heating the intake air
unnecessary. Under low load and idle conditions, with the smaller amounts of
fuel being
combusted, the heat of combustion may be relatively low and with the disclosed
engine it
is possible to activate the heater to increase the temperature in the
combustion chamber
for improved combustion and lower emissions. Accordingly, the performance of
the
disclosed engine is not affected by the effect of pre-heating the intake air
on the air mass
flow rate into the combustion chamber.
[0044] Therefore, while heater 114 may not be a desirable substitute for glow
plugs in a conventional diesel engine, it is an advantageous solution for the
presently
disclosed engine since it allows two separate fuel injection valves to each be
installed in
the cylinder head that was originally designed to accommodate only one fuel
injection
valve and a glow plug. The disclosed engine arrangement is also advantageous
for new
engines designed from the outset as bi-fuel engines because the disclosed
engine
arrangement simplifies the design of the cylinder head, which might otherwise
be
required to accommodate two fuel injection valves in addition to a glow plug
or spark
plug.
[0045] A first fuel can be injected directly into combustion chamber 108
through
first fuel injection valve 122. A second fuel can be injected directly into
combustion
chamber 108 through second fuel injection valve 120. Both fuel injection
valves are
mounted in cylinder head 106. As noted above in the discussion relating to
heater 114,
the installation of two fuel injection valves associated with each combustion
chamber and
using a conventional cylinder head designed for a diesel engine, is made
possible by
removing the glow plugs, and substituting an ignition-assist apparatus such as
heater 114
to assist with ignition during start-up by preheating air in intake manifold
110.
[0046] Compared to a single dual fuel injector that is capable of injecting
both
gaseous fuel and liquid fuel, an advantage of having two separate fuel
injection valves is
that the fuel supply systems can be completely segregated. With a dual fuel
injector,
because there are moving parts, and two types of fuel, dynamic seals, such as
fluid seals,
are needed to keep the gaseous and liquid fuels separate. To reduce leakage in
a dual fuel
CA 02524146 2005-11-18
17-
injection valve, it is desirable to substantially balance the pressures of the
gaseous fuel
and the liquid fuel. With the presently disclosed arrangement there can be
separate
gaseous and liquid fuel injection valves, allowing gaseous and liquid fuel
pressures to be
selected based on operational requirements. In the case of the liquid fuel,
operational
requirements can include, for example, the pressure required to atomize the
fuel. In the
case of the gaseous fuel, operational requirements can include, for example,
the pressure
that is needed to introduce the desired amount of fuel with the desired mass
flow rate, and
fuel spray velocity since this may be controlled to promote fuel penetration
into
combustion chamber 108 as well as turbulence and mixing therein.
[0447] In addition, the design of two separate fuel injection valves is less
complex than the design of a single fuel injection valve that separately and
independently
injects a gaseous fuel and a liquid fuel. Depending upon an engine's fuel
requirements
fuel injection valves that are currently mass-produced can be employed with
minor
modifications, or without any modifications at all. Accordingly, the presently
disclosed
engine can be less expensive to manufacture compared to an engine that employs
a single
custom-designed dual fuel injection valve.
[0048] In one embodiment, at least one of first fuel injection valve 122 and
second fuel injection valve 120 is a poppet valve (also known as an outward
opening
pintle valve). Such poppet valves can be made with dimensions suitable for
fitting in the
cylinder head opening normally provided for accommodating a glow plug.
[0049] In the simplified illustration of Figure 1, the exhaust system is not
shown,
but like a conventional engine, combustion products are exhausted through
exhaust
valves and an exhaust manifold. The disclosed engine can employ an exhaust gas
recirculation system, such as the system disclosed by co-owned published
Patent
Cooperation Treaty Application serial number PCT/CA03/01466, entitled,
"Exhaust Gas
Recirculation Methods and Apparatus for Reducing NOx Emissions from Internal
Combustion Engines". .
[0050] As is known by persons skilled in the technology, an electronic control
unit (ECU) can be programmed to control the operation of the engine. With the
presently
disclosed engine, the ECU also controls activation of heater 114, and
operation of second
CA 02524146 2005-11-18
-18-
fuel injection valve 120 and first fuel injection valve 122. In Figure 1,
solid lines are
drawn from ECU 140 to heater 114 and second fuel injection valve 120 and first
fuel
injection valve 122 to indicate that they can be controlled responsive to
signals
transmitted from ECU 140. ECU 140 receives measured data representative of
engine
operating parameters which can comprise, for example, one or more of the
following:
engine speed, actual engine load, commanded engine load, boost pressure, and
oil
temperature, ambient air temperature, air temperature inside intake manifold
110, engine
block temperature, pilot fuel rail pressure, gaseous fuel rail pressure, and
start of
combustion. Dashed lines are shown to indicate data inputs that ECU 140 can
receive
that can be of particular relevance to embodiments of the presently disclosed
engine. The
dashed line from temperature sensor 142 indicates that in the illustrated
embodiment
ECU 140 can receive data representative of the air temperature measured in
intake
manifold 110 by temperature sensor 142. Similarly, the dashed line from
temperature
sensor 144 shows that ECU 140 can receive data representative of the
temperature of
engine block 102 measured by sensor 144. For example, one or both of these
temperature measurements can be processed by ECU 140 to determine when to
activate
heater 114.
[0051] With the disclosed engine, ECU I40 can be programmed to choose from
at least two different predetermined operating modes, depending upon measured
operating parameters. With the understanding that the disclosed engine enables
operation
with two different fuels that can both be liquid or both gaseous or one liquid
and one
gaseous, by way of example, six operating modes are set out in Table 1 below
for an
engine that burns a liquid fuel and a gaseous fuel and that uses a heater
associated with
the intake air manifold as the ignition-assist apparatus. That is, in Table 1,
"LIQUID
FUEL" could be replaced with "FIRST FUEL" and "GASEOUS FUEL" could be
replaced with "SECOND FUEL".
CA 02524146 2005-11-18
- 19-
(0052] Table 1: Operating Modes
MODE HEATER LIQUID FUEL GASEOUS FUEL
1 ON INJECTED INJECTED
2 OFF INJECTED INJECTED
3 ON NOT INJECTED INJECTED
4 OFF NOT INJECTED INJECTED
ON INJECTED NOT INJECTED
6 OFF INJECTED NOT INJECTED
[0053] Refernng to Table 1, ECU 140 can select operating mode 1, for example,
when the engine is cold or when the engine is operating in a cold climate, and
when the
heat of compression alone is not sufficient to ensure auto-ignition of the
liquid fuel. Such
5 conditions can be detected by data inputs from engine block temperature
sensor 144 and
intake manifold temperature sensor 142, respectively. When operating mode I is
selected, ECU 140 commands heater 114 to pre-heat the intake air, and both
first fuel
injection valve I22 and second fuel injection valve 120 are commanded to
respectively
inject liquid and gaseous fuel into the combustion chamber with the liquid
fuel acting as a
pilot fuel to initiate combustion of the gaseous fuel.
j0054] Operating mode 2 is selectable, for example, if ECU 140 determines that
combustion chamber 108 is at a temperature that is consistently above a
predetermined
value at which pre-heating the intake air is unnecessary to ensure combustion
of at least
one of the fuels (normally it is the liquid fuel that has the lower auto-
ignition
temperature). ECU 140 can determine when this condition is met from data input
from
engine block temperature sensor 144. For example, if ECU 140 determines that
the
engine block temperature is above a predetermined threshold value when the
piston is at
top dead center at the end of a compression stroke, ECU 140 can command heater
114 to
turn off. In operating mode 2, ECU 140 commands both first fuel injection
valve 122 and
second fuel injection valve 120 to respectively inject liquid and gaseous
fuels directly
into the combustion chamber with the fuel with the lower auto-ignition
temperature
acting as a pilot fuel to assist with combustion of the other fuel. That is,
in this example
the gaseous fuel is the main fuel that is metered to satisfy the energy needs
demanded by
CA 02524146 2005-11-18
-20-
the engine load while the quantity of liquid fuel is limited to only that
amount which is
needed to ignite the gaseous fuel.
[0055] The disclosed engine can be controlled by employing only operating
modes 1 and 2, but under certain operating conditions operating modes 3
through 6 can
S be advantageously employed for improved performance, reduced emissions
and/or
improved operational flexibility. Operating modes 3 and 4 can only be used
with gaseous
fuels that can auto-ignite without ignition assistance from a pilot fuel, and
these operating
modes allow the disclosed engine to operate using gaseous fuel alone.
Operating modes
S and 6 provide operational flexibility by allowing the disclosed engine to
operate using
liquid fuel alone.
[0056] ECU 140 can be programmed to select operating mode 3, for example, if
the temperature inside the combustion chamber at the end of the compression
stroke is
above a predetermined temperature such that the gaseous fuel will auto-ignite
with
ignition assistance from pre-heated intake air, but without requiring ignition
assistance
from the liquid pilot fuel. ECU 140 can determine when combustion chamber
temperatures at the desired ignition timing are above this predetermined
temperature
from data received from engine block temperature sensor 144. This operating
mode is
desirable for reducing emissions since gaseous fuels are generally cleaner
burning
compared to liquid fuels. In this operating mode ECU 140 commands heater 114
to
switch on, while no command signal is sent to actuate first fuel injection
valve 122 so
that it remains closed. ECU 140 commands second fuel injection valve 120 to
open to
inject the desired amount of gaseous fuel into the combustion chamber. With
the ignition
assistance provided by the pre-heated intake air, the gaseous fuel auto-
ignites.
[0057) ECU 140 can be programmed to select operating mode 4, for example, if
2S ECU 140 determines that the projected temperature of engine block I02 at
the desired
ignition time is already above a predetermined temperature at which the
gaseous fuel is
known to auto-ignite without ignition assistance from the liquid pilot fuel
and without the
need to pre-heat the intake air. The auto-ignition temperature of the gaseous
fuel depends
upon the properties of the gaseous fuel. When operating mode 4 is selected,
ECU 140
commands heater 114 to switch off and an actuating command is not sent to
first fuel
CA 02524146 2005-11-18
-2I -
injector 122 so that it remains closed, while ECU 140 sends an actuating
command to
second fuel injector 120 so that gaseous fuel is injected into combustion
chamber 108.
[0058] Operating modes 5 and 6 both define operating modes where only liquid
fuel is injected. For example, if a vehicle runs out of gaseous fuel before it
reaches a re-
fueling station or if the engine is idling and requires only a very small
amount of fuel and
it is not practical to inject two different fuels and gaseous fuel will not
auto-ignite on its
own. In operating mode 5 the heater is switched on and in operating mode 6 the
heater is
switched off. In these operating modes, heater 114 is switched on when ECU 140
determines that pre-heating the intake air is necessary to assist with
ignition of the liquid
fuel.
(0059] In operating modes 1, 3, and 5, heater 114 is switched on, and ECU 140
can determine from the measured operating parameters whether to regulate the
heater to
increase or decrease the level of heating provided by heater 114. For example,
if the
heater is an electrical resistance heater, the amount of electrical current
directed to the
heating coil can be adjusted to raise or lower the temperature of the intake
air. If the
heater is a burner, a flow regulator can be adjusted to control the amount of
fuel that is
sent to the burner to raise or lower the temperature of the intake air. An
open or closed
loop control system can be employed to control intake air temperature.
[0060] Using the operating modes set out in Table 1 that are described above,
many different control strategies are possible. Figures 6 through 9 are
control diagrams
that provide examples of a few control strategies made possible by the
disclosed engine
with references to the "operating modes" being the operating modes of Table 1.
As with
Table 1, these descriptions relate to a preferred embodiment in which the
ignition-assist
apparatus is a heater, and the first fuel is a liquid fuel and the second fuel
is a gaseous
fuel.
(0061] Figure 6 illustrates a start-up control strategy. In the first step,
the ECU
determines the engine block temperature and if the temperature is higher than
a
predetermined temperature T;, the ECU proceeds with cranking the engine. If
the engine
block temperature is less than T;, then the ECU commands the heater to turn
on. When
the intake air temperature is greater than a predetermined temperature TS, if
the heater is
CA 02524146 2005-11-18
-22-
an electric heater, the ECU can turn off the heater to reduce the load on the
electrical
system while the engine is being cranked. If the heater is a burner it can be
left on during
the cranking step. While the engine is being cranked, the ECU commands pilot
fuel to be
injected, followed by gaseous fuel. If fuel ignition is not detected, then the
start up
process can be repeated. Once fuel ignition is detected, the ECU can proceed
with
selecting the desired operating mode.
(0062] Figure 7 shows a control strategy for selecting one of operating modes
l,
2, 5, or 6 as described in Table 1. With this control strategy, the first
query is to
determine if the engine block temperature is greater than predetermined
temperature TA.
For example, temperature TA can be an engine block temperature that correlates
to when
the conditions in the combustion chamber ensure auto-ignition of the liquid
fuel at a
desired ignition time at or near the beginning of the power stroke. As with
all of the
described control strategies, the engine block temperature is preferably
measured with the
same timing in each combustion cycle, for example, at a fixed time in the
engine cycle
defined by the position of the crankshaft measured in degrees before the
piston is at top
dead center. From the measured engine block temperature and other measured
operating
parameters such as engine speed, engine load, and intake air temperature, the
ECU can
predict the temperature in the combustion chamber at the desired ignition
time, for
example by referring to an engine map or by computation. Accordingly, it is
anticipated
that when the engine block temperature from the preceding combustion cycle is
greater
than TA, the liquid fuel that is injected directly into the combustion chamber
in the next
combustion cycle auto-ignites at the desired time, at or near the beginning of
the power
stroke. If the engine block temperature is less than TA then the ECU turns the
heater on,
or leaves it on if already on. Conversely, if the ECU determines that the
engine block
temperature is greater than TA then the ECU turns the heater off or leaves it
off if already
off.
[0063) After determining whether to turn the heater on or off, the next step
is to
determine if gaseous fuel is available. If gaseous fuel is available, then the
ECU
commands the injection of a pilot quantity of liquid fuel followed by the
injection of
gaseous fuel to supply the energy needed for the current engine load. If
gaseous fuel is
CA 02524146 2005-11-18
- 23 -
not available, the ECU commands the liquid fuel injection valve to inject
enough liquid
fuel to supply the energy needed for the current engine load, up to the
maximum flowrate
that can be injected through the Liquid fuel injection valve. If the operator
decides to shut
down the engine, then the heater is turned off and the process stops. If the
operator
wishes to continue running the engine the control strategy can be repeated
when a change
is detected in the engine operating conditions, or periodically after a fixed
number of
engine cycles or a f xed time interval, or the control strategy for selecting
the operating
mode can be repeated for each combustion cycle.
[0064] In the control strategy illustrated in Figure 7, liquid fuel is
injected in
every operating made. In operating modes 1 and 2 the amount of liquid fuel is
limited to
pilot quantities for ignition assistance. In operating modes 5 and 6 the
liquid fuel
represents the entire quantity of fuel is that injected into the combustion
chamber.
Accordingly, because there is liquid fuel introduced into the combustion
chamber in
every operating mode, and the liquid fuel is more readily ignited compared to
the gaseous
fuel, the engine block temperature that correlates to the combustion chamber
conditions
that promote auto-ignition of the liquid fuel is the predetermined temperature
TA which is
employed by this control strategy to determine whether to turn the heater on
or off.
[0065] Figure 8 shows a control strategy that can be used when under some
conditions the gaseous fuel is auto-ignitable without ignition assistance from
the injection
of a liquid pilot fuel. For example, the operating conditions in the
combustion chamber
can promote auto-ignition of the gaseous fuel with the help of residual heat
of
combustion, heat returned to the combustion chamber by exhaust gas
recirculation and
heat provided from the intake air manifold heater. Under other operating
conditions, the
engine can be fuelled with a combination of a pilot quantity of liquid fuel
and a main
quantity of gaseous fuel. In still other situations, such as when gaseous fuel
is not
available, the engine can be fuelled with only liquid fuel. With reference to
Figure 8, if
gaseous fuel is not available, the ECU considers the engine block temperature
to
determine if the intake air heater is required to assist with ignition of the
Liquid fuel. In
this embodiment, Like in the embodiment of Figure 7, temperature TA correlates
to
conditions in the combustion chamber that promote auto-ignition of the liquid
fuel. If the
CA 02524146 2005-11-18
-24-
engine block temperature is greater than TA then the ECU selects operating
mode 6 and
the heater is turned off or left off if already off. Liquid fuel is injected
and auto-ignites
without any ignition assistance from the heater. If the engine block
temperature is not
greater than TA then the ECU selects operating mode S and the heater is turned
on, or left
S on if already on to pre-heat the intake air to assist with ignition of the
liquid fuel.
[0066) If gaseous fuel is available, then according to the control strategy of
Figure 8, the ECU computes the average engine block temperature for the last
"n"
number of cycles, where n is a predetermined number programmed into the ECU.
The
heater is turned off (or left off) if the average engine block temperature is
greater than
threshold temperature TB, which in this embodiment is the temperature of the
engine
block that correlates to when the temperature in the combustion chamber at the
desired
timing for ignition is the auto-ignition temperature for the gaseous fuel.
According to the
strategy diagramed in Figure 8, the ECU selects operating mode 1 if the
average engine
block temperature is not greater than TB and the engine block temperature from
the
1 S immediately preceding engine cycle is also not greater than TB. The ECU
selects
operating mode 2 if the average engine block temperature is greater than TB
but the
engine block temperature from the immediately preceding engine cycle is not
greater than
than TB. The ECU selects operating mode 3 if the average engine block
temperature is
not greater than TB and the engine block temperature from the immediately
preceding
cycle is greater than TB. The ECU selects operating mode 4 if the average
engine block
temperature and the engine block temperature from the immediately preceding
engine
cycle are both greater than T$.
[0067] 'The control strategy shown in Figure 9 is the same as the control
strategy
shown in Figure 8 but with one additional feature. If the required quantity of
fuel on an
2S energy basis is less than a predetermined value ef, then the ECU commands
only the
liquid fuel injection valve to inject fuel into the combustion chamber. Under
these
operating conditions, because of the small quantity of fuel required, it can
be difficult to
inject both a pilot quantity of liquid fuel and gaseous fuel, so under these
conditions
according to the strategy of Figure 9, the ECU determines that only liquid
fuel will be
injected.
CA 02524146 2005-11-18
- 25 -
[0068] Returning now to the description of the physical embodiments, Figure 2
is
a view of cylinder head 206 viewed from inside the combustion chamber. The
circular
outlines of two intake valves 212 and two exhaust valves 250 are shown. Second
fuel
injection valve 220 is shown centrally located with first fuel injection valve
222
S positioned nearby. A conventional diesel engine can be converted to operate
according to
the disclosed method by installing second fuel injection valve 220 in the
opening that
would normally be occupied by a diesel fuel injection valve and installing
first fuel
injection valve 222 in the opening that would normally be occupied by a glow
plug. First
fuel injection valve 222 can be employed to inject a liquid fuel and second
fuel injection
valve 220 can be employed to inject a gaseous fuel. With a conventional diesel
engine,
the central opening typically has a larger diameter than that of the opening
for the glow
plug, and with the presently disclosed engine, since gaseous fuel has a lower
density than
liquid fuel, and in preferred operating modes, the large majority of the fuel
that is injected
is gaseous fuel, in preferred embodiments second fuel injection valve 220 is
installed in
the central opening that has the larger diameter, and first fuel injection
valve 222 is
installed in the opening with the smaller diameter that is normally occupied
by a glow
plug in a conventional diesel engine. In another embodiment, the positions of
the two
valves can be exchanged so that first fuel injection valve 222 can be a
conventional diesel
fuel injection valve that is designed to fit in the central opening normally
occupied by a
diesel injection valve.
[0069] For example, a poppet valve for injecting a quantity of liquid pilot
fuel can
be made with the requisite diameter to be installed in the opening normally
filled by a
glow plug. The desired quantity of liquid pilot fuel is less than ten percent
and more
preferably less than five percent of the total fuel burned on an energy basis
when the
engine is operating at full load. Poppet valves open when the outward opening
valve
member moves away from the valve seat allowing the fuel to be sprayed into the
combustion chamber. A simple poppet valve disperses the fuel in a conical
sheet, but it
can be desirable to break up this fuel spray sheet to provide more surfaces
between the
fuel spray and the air inside the combustion chamber. Fuel flow can be divided
into
separate streams by using a poppet valve with a fluted plenum like the one
shown in
CA 02524146 2005-11-18
-26-
Figure 3. Figure 3 is an axial cross section view of a poppet valve with a
fluted valve
stem. Fuel can flow parallel to the axis of valve stem 330 in channels defined
between
valve body 326 and grooves 332. Grooves 332 are shown as having a circular
profile, but
it would be understood by persons skilled in this technology that other shapes
would
S function in substantially the same manner. In another embodiment, it is also
possible to
provide a fluted plenum by providing the grooves in the valve body near the
valve seat,
with the raised areas between the grooves acting as guides for the valve stem.
[0070] In other embodiments, the nozzle tip of the fuel injection valve
downstream from the valve seat can comprise features that break up the fuel
spray into
separate spray plumes. With reference to Figure 4, to break up the fuel spray
and provide
more fuel/air interfaces, features can be added to poppet valve 422 achieve
this, such as
posts 428. Posts 428 extend from valve body 426 and into the path of the fuel
spray
thereby breaking up the fuel spray sheet that is introduced through valve 422
into the
combustion chamber.
I S [0071] With reference to Figure S, poppet valve S22 can be provided with
domed
nozzle tip 528, which comprises orifices S29 so that fuel is introduced into
the
combustion chamber in the form of spray plumes emerging from orifices 529.
Domed
nozzle tip S28 can be integral to the nozzle tip as shown in Figure 5 or a
dome-shaped
cover with orifices can be attached to the cylinder head. If a dome-shaped
cover is
attached to the cylinder head, poppet valve S22 can be removed without
removing the
dome-shaped cover. In such an embodiment, the dome-shaped cover is preferably
removably attached to the cylinder head so that it can be replaced if damaged
or fouled.
[0072] Also disclosed is a method of manufacturing the disclosed engine by
converting a conventional internal combustion engine which has a cylinder head
with a
2S first opening suitable for receiving a conventional diesel fuel injection
valve and a second
opening suitable for receiving a conventional glow plug. The manufacturing
method
comprises the steps of
installing a first fuel injection valve in one of the first and second
openings
in the cylinder head;
CA 02524146 2005-11-18
-27-
installing a second fuel injection valve in the other one of said first and
second openings that is not occupied by the first fuel injection valve;
installing a heater that is operative to heat air in an intake air manifold
through which air is flowable enroute to the combustion chamber; and
programming an electronic controller to operate the engine in one of a
plurality of operating modes wherein in at least one operating mode the second
'
fuel and a pilot fuel quantity of the first fuel are injected directly into
the
combustion chamber through the respective fuel injection valves, and in
another
operating mode the first fuel alone is injected directly into the combustion
chamber, and in all operating modes the electronic controller is programmed to
switch on the heater responsive to predetermined operating conditions to
assist
with promoting combustion in the combustion chamber when the piston is at or
near top dead center.
[0073] In operating modes in which gaseous fuel is introduced into the
combustion chamber, responsive to engine operating conditions the electronic
controller
can determine whether to assist with ignition of the gaseous fuel by: (a)
heating intake
air by switching on the heater; and/or (b) introducing a quantity of liquid
fuel through the
liquid-fuel injection valve, whereby the liquid fuel auto-ignites to in turn
ignite the
gaseous fuel.
[0074] For embodiments in which the liquid fuel is normally only used as a
pilot
fuel, the conversion method can further comprise replacing the diesel fuel
storage tank
with a smaller liquid fuel storage tank, and/or replacing the conventional
fuel pump with
a smaller fuel pump.
[0075] 'The disclosed engine provides operational flexibility since it is
capable of
being fuelled with only liquid fuel, only gaseous fuel, or a combination of
liquid pilot
fuel and gaseous fuel. However, since engine emissions are higher when
fuelling the
engine with only liquid fuel, in locations where government regulations
mandate that
pollutant emissions must be lower than prescribed levels, the liquid fuel
injection valve
can be designed to restrict fuel flow so that full power cannot be achieved
when fuelling
the engine with only liquid fuel. This would make a vehicle impractical to
operate
CA 02524146 2005-11-18
-28-
normally using only liquid fuel. However, if the vehicle runs out of gaseous
fuel, even
when a liquid fuel injection valve has limited flow capacity, it is still
possible for the
vehicle to "limp" home, or to a re-fueling station, or move to a safe location
where it can
be parked out of harms way.
[0076] While particular elements, embodiments and applications of the present
invention have been shown and described, it will be understood, of course,
that
modifications may be made by those skilled in the art without departing from
the scope
of the present disclosure, particularly in light of the foregoing teachings.
