Note: Descriptions are shown in the official language in which they were submitted.
CA 02862664 2014-09-04
- 1 -
VAPORIZER SYSTEM AND CONTROL STRATEGY
Field of the Invention
[0001] The present application relates to a vaporizer system and a control
strategy to
operate the vaporizer system for an internal combustion engine.
Background of the Invention
[0002] It is known to use engine coolant from an internal combustion
engine as a
heat exchange medium in a heat exchanger (also known as a vaporizer) that
vaporizes a
liquefied gaseous fuel, such as liquefied natural gas (LNG). The engine
coolant circulates
through what is commonly known as the water jacket of the engine and absorbs
waste
heat as the engine operates. The engine coolant is communicated outside the
engine to the
vaporizer where it and the liquefied gaseous fuel are routed through an
arrangement of
collocated passageways such that the waste heat in the engine coolant is
transferred to the
liquefied gaseous fuel, raising its temperature above the boiling point
causing it to boil
and change from a liquid state to a gas or supercritical state.
[0003] To increase performance of the vaporizer, it is known to arrange the
passageways such that the warmest engine coolant comes in contact with the
coldest
liquefied gaseous fuel, which is at respective inlets to the vaporizer for the
engine coolant
and the liquefied gaseous fuel. In this manner an increased amount of heat,
relative to the
overall performance characteristics of the vaporizer, gets transferred from
the engine
coolant to the liquefied gaseous fuel.
[0004] When the engine cold-starts the temperature of the engine coolant can
be
much lower than the preferred operating temperature for the engine coolant.
Depending
on the ambient temperature, which is the temperature of the engine coolant on
cold-start,
and the temperature of the liquefied gaseous fuel, it is possible for the
engine coolant to
CA 02862664 2014-09-04
-2-
freeze in and around the vaporizer on cold-start. Similarly, when the engine
is running at
a low engine speed, such as at idle or light load conditions, the flow rate of
engine
coolant through the vaporizer relative to the heat transfer rate from the
engine coolant to
the liquefied gaseous fuel in the vaporizer may result, again, in the engine
coolant
freezing in and around the vaporizer. When the engine coolant freezes, the
flow of engine
coolant through the vaporizer can be reduced, but not blocked. In these
situations the
performance of the vaporizer is reduced and the downstream temperature of the
vaporized gaseous fuel decreases. Components downstream from the vaporizer may
experience increased thermal stress due to the cold temperatures, which
decreases
servicing intervals and increases maintenance costs. When the flow of engine
coolant
through the vaporizer is blocked, this could affect the flow of the engine
coolant through
the water jacket, causing the engine temperature to increase until the engine
is shutdown
due to overheating. A minimum amount of time is required after the engine
coolant
freezes to allow it to melt, which is an inconvenience to the operator of the
engine.
100051 Previously, to prevent the engine coolant from freezing in the
vaporizer, the
engine would operate with another fuel, such as Diesel, thereby reducing and
possibly
eliminating the demand for liquefied gaseous fuel, for a predetermined amount
of time
allowing the engine to warm up. The engine would switch to operating with
liquefied
gaseous fuel after the engine coolant temperature was sufficient to reduce the
likelihood
of the engine coolant from freezing. In other circumstances, there could be an
accumulator of vaporized gaseous fuel from which the engine could consume
gaseous
fuel, allowing the engine to warm up, before beginning to vaporize liquefied
gaseous
fuel. When operated in this manner, the pressure of the gaseous fuel in the
accumulator
drops as fuel is consumed, which is not desirable if the pressure drops below
the desired
injection pressure and/or the quantity of fuel that can be delivered to the
engine is limited
on account of the available pressure.
CA 02862664 2014-09-04
-3-
[0006] The state of the art is lacking in techniques for reducing the
likelihood of
engine coolant freezing, under certain operating conditions, when acting as a
heat
exchange medium through a vaporizer. The present system and control strategy
provide a
technique for reducing the likelihood of engine coolant from freezing.
Summary of the Invention
[0007] An improved method for vaporizing a gaseous fuel stored in liquefied
form
for consumption by an internal combustion engine comprises counter flowing the
gaseous
fuel with a heat exchange medium through a heat exchanger during a first
operating
mode; and co-flowing flowing the gaseous fuel with the heat exchange medium
through
the heat exchanger during a second operating mode. In a preferred embodiment,
the heat
exchange medium is engine coolant from the internal combustion engine, which
in a
common heat exchange loop circulates through the heat exchanger and the engine
water
jacket. In those embodiments where the heat exchange loop is separate from the
water
jacket, the heat exchange medium can be glycol or other known heat exchange
mediums.
[0008] There are several possible enabling conditions that determine which
operating
mode the engine is currently in. In a preferred embodiment, the internal
combustion
engine is in the second operating mode when at least one of heat exchange
medium
temperature is below a first predetermined value; and gaseous fuel temperature
downstream from the heat exchanger is below a second predetermined value. When
the
heat exchange medium is engine coolant, the internal combustion engine can be
in the
second operating mode when at least one of engine coolant temperature is below
a first
predetermined value; gaseous fuel temperature downstream from the heat
exchanger is
below a second predetermined value; engine speed is below a third
predetermined value;
engine coolant mass flow rate is below a fourth predetermined value; gaseous
fuel mass
flow rate is above a fifth predetermined value; and a differential mass flow
rate between
the gaseous fuel and the engine coolant is above a sixth predetermined value.
Alternatively, or additionally, the internal combustion engine is in the
second operating
CA 02862664 2014-09-04
-4-
mode when at least one of the internal combustion engine is starting,
especially cold-
starting; the internal combustion engine is idling; and the internal
combustion engine is
operating under a light load condition. The first operating mode can be
entered after a
predetermined time interval in the second operating mode. The internal
combustion
engine can be in the first operating mode when it is not in the second
operating mode. In
another preferred embodiment there is a third operating mode where the heat
exchange
medium is made to by-pass the heat exchanger, such as when the engine is being
fuelled
with another fuel other than the gaseous fuel, such that the gaseous fuel does
not need to
be vaporized. When the internal combustion engine is not in both the second
operating
mode and the third operating mode, it is in the first operating mode.
[0009] In those embodiments where the heat exchange medium is not part of the
engine water jacket heat exchange loop, the heat exchange medium can be heated
in a
variety of ways. For example, the heat exchange medium can be heated by at
least one of
heating the heat exchange medium with an electric heater; heating the heat
exchange
medium with a burner; and heating the heat exchange medium with a boiler.
[0010] In another preferred embodiment, when the internal combustion engine is
in
the second operating mode, the method further comprises one of by-passing an
engine
coolant radiator; and turning an engine coolant fan off
[0011] An improved apparatus for vaporizing a gaseous fuel, stored in
liquefied form
in a fuel supply, for consumption by an internal combustion engine comprises a
supply of
a heat exchange medium; a heat exchanger having a first passageway for the
heat
exchange medium and a second passageway for the gaseous fuel; a fluid switch
fluidly
connected to the heat exchanger and one of the supply of the heat exchange
medium and
the fuel supply; and a controller operatively connected with the fluid switch
and
programmed to command the fluid switch to a first position in a first
operating mode
where the heat exchange medium counter flows with the gaseous fuel in the heat
exchanger; and command the fluid switch to a second position in a second
operating
CA 02862664 2014-09-04
- 5 -
mode where the heat exchange medium co-flows flows with the gaseous fuel in
the heat
exchanger. In a preferred embodiment the apparatus further comprises at least
one of a
heat exchange medium temperature sensor arranged to measure at least one of
heat
exchange medium temperature upstream from the heat exchanger and heat exchange
medium temperature downstream from the heat exchanger; and a gaseous fuel
temperature sensor arranged to measure at least one of gaseous fuel
temperature upstream
from the heat exchanger and gaseous fuel temperature downstream from the heat
exchanger.
[0012] In another preferred embodiment, the apparatus further comprises a
heater for
heating the heat exchange medium. The heater can comprise at least one of an
electric
heater; a burner; and a boiler.
Brief Description of the Drawings
[0013] FIG. 1 is a schematic view of a vaporizer system illustrated in a
first operating
mode according to a first embodiment.
[0014] FIG. 2 is a schematic view of the vaporizer system of FIG. 1
illustrated in a
second operating mode.
[0015] FIG. 3 is a schematic view of a vaporizer system illustrated in a
first operating
mode according to a second embodiment.
[0016] FIG. 4 is a schematic view of the vaporizer system of FIG. 3
illustrated in a
second operating mode.
[0017] FIG. 5 is a schematic view of a vaporizer system illustrated in a
first operating
mode according to a third embodiment.
CA 02862664 2014-09-04
-6-
100181 FIG. 6 is a schematic view of the vaporizer system of FIG. 5
illustrated in a
second operating mode.
[0019] FIG. 7 is a schematic view of a vaporizer system illustrated in a third
operating mode according to a fourth embodiment.
Detailed Description of Preferred Embodiment(s)
100201 Referring to FIG. 1, vaporizer system 10 is shown according to a
first
embodiment in a first operating mode for vaporizing a gaseous fuel stored in
liquefied
form in fuel supply 20 for consumption by internal combustion engine 30. A
gaseous fuel
is any fuel that is in a gas state at standard pressure and temperature, which
in the context
of this application is defined as 1 atmosphere (atm) and 20 degrees Celsius (
C)
respectively. Vaporizer system 10 comprises heat exchanger 40, also known as a
vaporizer, and fluid switch 50. Heat exchanger 40 has first passageway 42 for
a heat
exchange medium and second passageway 44 for gaseous fuel. Engine coolant from
engine 30 is made to circulate by pump 60 through heat exchanger 40, where it
operates
as the heat exchange medium, by way of passageways 70, fluid switch 50 and
passageways 80.Within engine 30, the engine coolant circulates through water
jacket 35
where it absorbs waste heat from the engine. Fuel supply 20 supplies liquefied
gaseous
fuel to heat exchanger 40 by way of shut-off valve 90 and passageway 100. As
the
gaseous fuel flows through heat exchanger 40, it vaporizes, and exits heat
exchanger 40
in a gas or supercritical state, where it is then communicated to engine 30
through
passageway 110. Accumulator 120 is employed to provide a buffer of pressurized
gaseous fuel, in the gas or supercritical state, to engine 30, and is shown in
a t-connection
to passageway 110 but can alternatively be in-line with the passageway in
other
embodiments. Instead of accumulator 120, passageway 110 can be sized to
function as
an accumulator.
CA 02862664 2014-09-04
-7-
100211 Controller 130 is operatively connected with fuel supply 20, engine
30, fluid
switch 50 and shut-off valve 90, as indicated by the dashed lines
therebetween, to
command the operation of these components as will become evident in the course
of this
description. As used herein fluid switch 50 can be a single device and/or
apparatus, or can
be a collection of devices and/or components that operate together to achieve
the
specified functionality. Fuel supply 20 can be commanded by controller 130 to
supply
liquefied gaseous fuel at a predetermined pressure, for example by operating a
cryogenic
pump (not shown). Shut-off valve 90 is commanded to cut-off supply of
liquefied
gaseous fuel to downstream components, for example when engine 30 is shutdown,
as
well as during other circumstances. Temperature sensor 135 provides signals
representative of engine coolant temperature to controller 130, and
temperature sensor
140 provides signals representative of gaseous fuel temperature to the
controller, both
temperatures being measured downstream of the heat exchanger in the
illustrated
embodiment. In alternative embodiments temperature sensor 135 can be arranged
upstream of heat exchanger 40 in the first operating mode, or can integrated
within the
heat exchanger. Alternatively, or additionally, there can be a temperature
sensor
measuring engine coolant temperature within engine 30.
100221 In the first operating mode, controller 130 commands fluid switch 50
into a
first position illustrated in FIG. 1 such that engine coolant counter flows
with gaseous
fuel in heat exchanger 40. Counter flow with respect to fluid flow through
heat exchanger
40 is defined to be that condition when the warmest engine coolant first
delivers heat to
the warmest gaseous fuel. As the engine coolant circulates through heat
exchanger 40 it
transfers heat to the liquefied gaseous fuel, such that the engine coolant
drops in
temperature and the liquefied gaseous fuel increases in temperature, which
eventually
begins to vaporize. That is to say, the warmest engine coolant is that engine
coolant
entering an inlet of heat exchanger 40, and the warmest gaseous fuel is that
gaseous fuel
exiting an outlet of the heat exchanger, as is illustrated schematically in
FIG. 1. Counter
flow occurs, generally, when the engine coolant and gaseous fuel flow in
opposite
CA 02862664 2014-09-04
-8-
forward directions. As a simplified example, when heat exchanger 40 comprises
two
parallel pipes, one for engine coolant and one for gaseous fuel, in the
counter flow
scenario the engine coolant and the gaseous fuel flow through their respective
pipes in the
opposite direction. In another example, heat exchanger 40 can comprise a
helically
wound pipe for gaseous fuel arranged in a chamber through which engine coolant
flows,
in what is known as a 'bath'. In the counter flow scenario the gaseous fuel
flows through
the helically wound pipe such that is has the opposite forward direction as
the engine
coolant in the chamber. As can be appreciated, there are other configurations
for heat
exchangers 40, in which a counter flow scenario can be defined.
100231 With reference to FIG. 2, vaporizer system 10 is illustrated in a
second
operating mode, where controller 130 has commanded fluid switch 50 into a
second
position such that engine coolant co-flows with respect to gaseous fuel in
heat exchanger
40. Co-flow with respect to fluid flow through heat exchanger 40 is defined to
be that
condition opposite to the counter-flow condition, which is when the warmest
engine
coolant first delivers heat to the coldest gaseous fuel. The coldest gaseous
fuel is that
gaseous fuel entering an inlet of heat exchanger 40. Co-flow occurs,
generally, when the
engine coolant and gaseous fuel flow in the same forward direction through the
heat
exchanger. In the simplified example described above, when heat exchanger 40
comprises the two parallel pipes, in the co-flow scenario the engine coolant
and the
gaseous fuel flow through their respective pipes in the same direction. In the
other
example described above, when heat exchanger 40 comprises the helically wound
pipe
for gaseous fuel arranged in the chamber (the "bath") through which engine
coolant
flows, in the co-flow scenario the gaseous fuel flows through the helically
wound pipe
such that is has the same forward direction as the engine coolant in the
chamber. As can
be appreciated, there are other configurations for heat exchangers 40, in
which a co-flow
scenario can be defined.
CA 02862664 2014-09-04
-9-
[0024] Under normal operating conditions, controller 130 commands vaporizer
system 10 into the first operating mode where heat exchanger 40 counter flows
engine
coolant with gaseous fuel. Controller 130 commands vaporizer system 10 into
the second
operating mode when there is a risk of engine coolant freezing, such as when
engine 30 is
cold-started and the temperature of engine coolant is relatively low, or when
engine 30 is
idling or operating under a light load condition, when the mass flow rate of
engine
coolant through heat exchanger 40 is low. Controller 130 can monitor ambient
temperature and/or engine coolant temperature, to determine whether under a
cold-start
condition or a light load condition there is a risk of engine coolant
freezing. Alternatively,
controller 130 can be programmed to command the second operating mode upon
cold-
start, for a predetermined amount of time, after which the controller commands
the first
operating mode. Similarly, controller 130 can command the second operating
mode
whenever engine 30 is operating under a light load condition, and when engine
30
transitions away from the light load condition the controller can command the
first
operating mode. Further, controller 130 can be programmed to command the
second
operating mode as function of gaseous fuel temperature downstream of heat
exchanger
40. As gaseous fuel temperature drops below a predetermined temperature the
controller
commands the second operating mode (co-flow).
[0025] Engine 30 comprises a radiator (not shown) and a fan (not shown)
employed
to cool the engine coolant when its temperature rises above a predetermined
value, as is
known. In addition to being in the second operating mode, or alternatively,
the engine
coolant can be made to by-pass the radiator or the fan can be turned off when
the engine
coolant temperature is too low and there is a risk of freezing the engine
coolant in and
around heat exchanger 40. Techniques for by-passing the radiator are well
known in the
art.
[0026] Referring now to FIGS. 3 and 4, vaporizer system 12 is shown according
to a
second embodiment similar to the first embodiment where like parts to this and
other
CA 02862664 2014-09-04
- 10 -
embodiments have like reference numerals that may not be described in detail,
if at all.
Fluid switch 52 is fluidly connected with fuel supply 20, by way of valve 90
and
passageway 100, and is commanded by controller 130 to switch the direction of
flow of
gaseous fuel through passageways 82 and passageway 44 of heat exchanger 40.
Engine
coolant from engine 30 is circulated through passageway 72 and passageway 42
of the
heat exchanger, always in the same direction. Vaporizer system 12 is
illustrated in the
first operating mode in FIG. 3 where gaseous fuel and engine coolant are
counter flowed
through heat exchanger 40, and in the second operating mode in FIG. 4 where
gaseous
fuel and engine coolant are co-flowed through the heat exchanger. Although the
result of
switching the direction of gaseous fuel instead of engine coolant is identical
with respect
to the heat exchanger, it is preferred in general to switch the flow of the
engine coolant
instead of the gaseous fuel. The extremely low temperatures associated with
liquefied
gaseous fuels may require a more expensive version of fluid switch 52 and
temperature
sensor 142, which both must be able to operate both at extremely low
temperatures, and
over a wide temperature range, when the direction of the gaseous fuel is
switched. As an
example, the temperature of LNG can be around -160 C and when vaporized its
temperature can be between -20 C and as high as +80 C depending upon the
operating
conditions of the engine. Fluid switch 52 must direct the flow of the gaseous
fuel when it
is in the liquid state and the gas or supercritical state, and therefore has
more stringent
sealing requirements compared to fluid switch 50, which directs the flow of
engine
coolant that is normally in the liquid state. Depending upon the application,
gaseous fuel
pressure can be very much higher than engine coolant pressure, which puts even
further
demands on fluid switch 52 for both sealing and switching under high pressure
conditions.
100271 Referring now to FIGS. 5 and 6, vaporizer system 13 is shown according
to a
third embodiment. Heat exchange loop 25 is employed to provide heat exchanger
40 with
a heat exchange medium instead of using the heat exchange loop from engine 30
(comprising water jacket 35). As an example, the heat exchange medium can be
glycol,
CA 02862664 2014-09-04
- 1 1 -
but as would be known to those familiar with the technology other types of
heat exchange
medium can be employed. Heater 45 elevates the temperature of the heat
exchange
medium that is circulated through heat exchanger 40. Examples of heater 45 can
be an
electric heater, a burner and a boiler, and other heater types are possible.
The burner and
boiler can burn a fuel, such as boil-off gas from a cryogenic vessel in fuel
supply 20. In
other embodiments, waste heat in the engine coolant of engine 30 can be
transferred to
the heat exchange medium in loop 25 by way of a heat exchanger (not shown).
Vaporizer
system 13 is illustrated in the first operating mode in FIG. 5 where gaseous
fuel and the
heat exchange medium are counter flowed through heat exchanger 40, and in the
second
operating mode in FIG. 6 where gaseous fuel and the heat exchange medium are
co-
flowed through the heat exchanger. In other embodiments, heat exchange loop 25
can be
employed in those embodiments where the fluid switch is employed to switch the
flow of
the gaseous fuel, like fluid switch 52 in FIGS. 3 and 4, instead of the heat
exchange
medium.
100281 Referring now to FIG. 7, vaporizer system 14 is shown according to a
fourth
embodiment, illustrating vaporizer system 14 in a third operating mode, where
fluid
switch 54 redirects the heat exchange fluid (engine coolant in this
embodiment)
bypassing heat exchanger 40. This is advantageous when engine 30 is being
fuelled with
a fuel other than gaseous fuel from fuel supply 20, such as when the engine
runs on diesel
(ROD). Fluid switch 54 can be commanded by controller 30 such that vaporizer
system
14 is in one of the first, second and third operating modes. Fluid switch 54
can be
employed in the previously discussed embodiments, particularly those
illustrated in
FIGS. 1 through 4 where engine coolant must continue to be circulated
regardless of
which fuel engine 30 consumes. When engine 30 runs on a fuel other than the
gaseous
fuel, it is advantageous to reduce the heat transfer from the engine coolant
to the gaseous
fuel, which if not reduced could cause the pressure of the gaseous fuel to
increase
excessively. In the embodiment of FIGS. 5 and 6, fluid switch 54 can be
employed,
CA 02862664 2014-09-04
- 12-
alternatively, pump 60 can be stopped when engine 30 is fuelled with a fuel
other than
gaseous fuel from supply 20.
100291 While particular elements, embodiments and applications of the present
invention have been shown and described, it will be understood, that the
invention is not
limited thereto since modifications can be made by those skilled in the art
without
departing from the scope of the present disclosure, particularly in light of
the foregoing
teachings.
