Note: Descriptions are shown in the official language in which they were submitted.
CA 02794117 2012-10-31
METHOD AND SYSTEM FOR DETECTING AND DIAGNOSING A GASEOUS
FUEL LEAK IN A DUAL FUEL INTERNAL COMBUSTION ENGINE SYSTEM
Technical Field
[0001 ] The present invention relates to a method and a system for detecting
and
diagnosing a leak of gaseous fuel into liquid fuel in a dual fuel internal
combustion engine system. This involves detecting an amount of gaseous fuel in
the liquid fuel return line.
Background of the Invention
[0002] Because of its ready availability, low cost, and potential for reducing
particulate emissions, natural gas has proven to be a good substitute for
replacing diesel fuel for fuelling internal combustion engines. Since the auto-
ignition temperature of natural gas and other gaseous fuels is substantially
greater than that of diesel, some gaseous fuelled engines use a small amount
of
pilot fuel, such as diesel, to ignite the main fuel.
[0003] Some gaseous fuelled engines of this type can use a dual fuel injector
injecting both a liquid pilot fuel and a gaseous main fuel. Such engines are
"dual
fuel" engines which are defined here to mean engines that can be fuelled with
two different fuels at the same time. In preferred embodiments, the two fuels
are
independently and separately injected into the combustion chamber, such that
ignition of the gaseous fuel is assisted by the pilot fuel. Such a dual fuel
injector
is disclosed in the Applicant's co-owned U.S. Patent No. 6,073,862 (the `862
patent) which illustrates a hydraulically actuated dual fuel injector which
comprises two concentric needle valves for injecting controlled quantities of
a
main gaseous fuel and a pilot liquid fuel into the combustion chamber of an
internal combustion engine. The injector comprises liquid seals which surround
the gaseous fuel needle valve and prevent the leakage of gaseous fuel into the
actuating hydraulic fluid around the gaseous fuel needle valve. The hydraulic
CA 02794117 2012-10-31
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fluid can be the same as the pilot liquid fuel, for example diesel fuel. The
pressure in the gaseous fuel common rail which supplies gaseous fuel to the
injector is maintained at a pressure which is slightly less than the pressure
in the
pilot fuel common rail which supplies pilot liquid fuel to the injector to
prevent
leakage of gaseous fuel past the liquid seals into the pilot fuel or into the
hydraulic fluid.
[0004] From U.S. Patent No. 6,298,833 (the '833 patent), which is also co-
owned
by the Applicant, it is known to dynamically control sealing-fluid pressure
and
implicitly pilot fuel pressure to ensure that the gaseous fuel pressure is
slightly
less than pilot fuel pressure for all engine operating conditions. A pressure-
balancing system, comprising for example a dome-loaded regulator helps to
maintain a positive pressure differential between the sealing fluid (the pilot
fuel)
and the gaseous fuel to prevent leakage of the gaseous fuel into the pilot
fuel
throughout the operating range of engine speeds and loads.
[0005] In systems employing a dome-loaded regulator such as those described in
the `833 patent, the pressure differential between the diesel fuel rail
pressure and
the gaseous fuel rail pressure is generally monitored by measuring the
pressures
in the diesel fuel common rail and in the gaseous fuel common rail, downstream
of the dome-loaded regulator. A negative pressure differential between the
diesel
fuel supply pressure and the gaseous fuel supply pressure can indicate gaseous
fuel leaking into the liquid fuel cavities and passages or into the hydraulic
fluid
when the liquid fuel is also used as hydraulic fluid. The measured pressures
are
transmitted to a controller and if, during engine's operation, the calculated
pressure differential between the diesel fuel rail pressure and the gaseous
fuel
rail pressure is negative for a prolonged period of time, the engine is
generally
switched to operate only on diesel (the run-on-diesel (ROD) mode).
[0006] Intrusion of the gaseous fuel into the liquid fuel can affect the
performance of the hydraulic system or can form a combustible mixture in the
liquid fuel drain lines.
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[0007] Known methods measuring the pressure differential between the diesel
fuel supply pressure and the gaseous fuel supply pressure cannot reliably
detect
the gaseous fuel leakage into liquid fuel. Unit to unit variations and system
aging
can influence the accuracy of the sensors placed in the pilot fuel and gaseous
fuel rails. Furthermore, if there is leakage of gaseous fuel into the liquid
fuel, the
methods used in the past cannot accurately diagnose if such leakage is caused
by a fault in the pressure balancing system or in the dual fuel injector.
[0008] While the problem of monitoring the pressure differential between the
gaseous fuel rail pressure and the pilot fuel rail pressure has been addressed
in
the past, there is still a need for a more accurate method of detecting and
diagnosing a gaseous fuel leak in a dual fuel internal combustion engine
system.
Summary
[0009] A method is disclosed for detecting and diagnosing a leak of gaseous
fuel
into liquid fuel in a dual fuel internal combustion engine system comprising a
fuel
injector for separately injecting gaseous fuel and liquid fuel into a
combustion
chamber. The method comprises detecting an amount of gaseous fuel in a liquid
fuel return line through which liquid fuel is returned from the fuel injector
to a
liquid fuel supply, and producing a first fault signal ("Gaseous Fuel Leak to
Drain") indicating that gaseous fuel has leaked into the liquid fuel return
line
when said amount of gaseous fuel is detected in the liquid fuel return line.
[0010] For further diagnosing the gaseous fuel leak to detect if it caused by
a
fault in the fuel injector or in the pressure regulating components, the
method can
comprise measuring a liquid fuel rail pressure and a gaseous fuel rail
pressure
downstream of any system components which regulate the liquid fuel rail
pressure and the gaseous fuel rail pressure to respective pressure target
values,
calculating a pressure differential between the liquid fuel rail pressure and
the
gaseous fuel rail pressure by subtracting the measured gaseous fuel rail
pressure from the measured liquid fuel rail pressure, and comparing the
calculated pressure differential to a predetermined range of a nominal
pressure
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differential. The liquid fuel rail pressure is the pressure at which liquid
fuel is
supplied to the fuel injector and the gaseous fuel rail pressure is the
pressure at
which gaseous fuel is supplied to the fuel injector.
[0011 ] If the first fault signal is produced and the calculated pressure
differential
is within or higher than the predetermined range , the method further
comprises
producing an injector fault signal indicating a failure of the fuel injector.
[0012] If the first fault signal is produced and the calculated pressure
differential
is lower than the predetermined range, the method further comprises producing
a
bias fault signal indicating a failure of at least one of the system
components
which regulate the fuel rail pressures. Because the calculated pressure
differential is lower than the predetermined range the bias fault signal is
recorded
as "Bias out of range low" or "BOL".
[0013] If the first fault signal is not produced and the calculated pressure
differential is lower or higher than said predetermined range, the method
further
comprises producing a bias fault signal indicating a failure of at least one
of the
system components which regulate the fuel rail pressures. The bias fault
signal is
recorded as "Bias out of range low" (BOL) or "Bias out of range high" (BOH)
when the calculated pressure differential is lower or respectively higher than
the
predetermined range.
[0014] In preferred embodiments, the presence of gaseous fuel is detected by
measuring the pressure in the liquid fuel return line, comparing the value of
the
measured pressure in the liquid fuel return line to a predetermined nominal
pressure, and producing the first fault signal indicating the gaseous fuel
leak
when the measured pressure in the liquid fuel return line is higher than the
predetermined nominal pressure.
[0015] In other embodiments, the presence of gaseous fuel is detected by a
gaseous fuel detector placed in the liquid fuel return line between the fuel
injector
and the liquid fuel supply or in the liquid fuel supply.
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[0016] In the present method, the predetermined range of the nominal pressure
differential can be constant during engine operation or it can be a function
of the
engine's speed and/or torque.
[0017] The step of detecting the amount of gaseous fuel in the liquid fuel
return
line is done by continuous monitoring. In preferred embodiments of the present
method, during the engine's transient operation the pressure differential is
not
calculated to avoid any inaccurate pressure measurements or, in alternate
embodiments, the pressure differential is calculated based on the filtered
values
of the liquid fuel rail pressure and the gaseous fuel rail pressure.
[0018] Preferably, any of said fault signals are generated after a condition
that
triggers the respective fault signal is recorded for a predetermined period of
time.
[0019] A system is disclosed for detecting and diagnosing a leak of gaseous
fuel
into liquid fuel in a fuel system for a dual fuel internal combustion engine
comprising a fuel injector for separately injecting gaseous fuel and liquid
fuel into
a combustion chamber. The system for detecting and diagnosing said leak
comprises a detection system for detecting the presence of gaseous fuel in a
liquid return line through which liquid fuel is returned from said fuel
injector to a
liquid fuel supply and a controller which receives a signal from the detection
system and is programmed to generate a first fault signal indicating that
gaseous
fuel has leaked to the liquid fuel return line based on the received signal.
[0020] In preferred embodiments, the detection system comprises a first
pressure
sensor for measuring the pressure in the liquid fuel return line which
transmits a
signal indicative of the measured liquid fuel return line pressure to the
controller,
and the controller is programmed to compare the received signal to a stored
predetermined nominal pressure for the liquid fuel return line and generate
the
first fault signal indicating that gaseous fuel has leaked to the liquid fuel
return
line based on the results of this comparison.
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[0021 ] Alternatively, the detection system can comprise a pressure switch
which
makes electrical contact when the pressure in said liquid fuel return line is
higher
than a stored predetermined nominal pressure for the liquid fuel return line
and
sends a signal to the controller and the controller is programmed to generate
the
first fault signal indicating that gaseous fuel has leaked to the liquid fuel
return
line based on the signal received from the pressure switch.
[0022] In yet another embodiment, the detection system can comprise a gaseous
fuel detector placed in the liquid fuel return line or in the liquid fuel
supply which
supplies liquid fuel to the fuel injector, and the gaseous fuel detector sends
a
signal to the controller when it detects an amount of gaseous fuel. The
controller
is programmed to generate the first fault signal indicating that gaseous fuel
has
leaked to the liquid fuel return line based on said signal received from the
gaseous fuel detector.
[0023] The detection system can also comprise a second pressure sensor for
measuring a gaseous fuel rail pressure downstream of a system component
which regulates the gaseous fuel rail pressure, the second pressure sensor
being
configured to send a signal indicative of said measured pressure to the
controller;
and a third pressure sensor for measuring a liquid fuel rail pressure
downstream
of a system component which regulates the liquid fuel rail pressure, the third
pressure sensor being configured to send a signal indicative of the measured
pressure to the controller. The controller is programmed to calculate a
pressure
differential based on received signals from the second and third pressure
sensor
by subtracting the measured gaseous fuel rail pressure from the measured
liquid
fuel rail pressure and comparing the calculated pressure differential to a
predetermined range of a nominal pressure differential. The controller
generates
a bias fault signal indicating a failure of at least one of said system
components
which regulate the gaseous fuel or liquid fuel rail pressures or an injector
fault
signal indicating the failure of the fuel injector based on the results of
this
comparison, thereby diagnosing the causes of the gaseous fuel leak.
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[0024] The controller is programmed to generate the bias fault signal ("Bias
out of
range low" or "BOL") indicating a failure of at least one of said system
components which regulate the gaseous fuel or liquid fuel rail pressure when
the
first fault signal indicating a gaseous fuel leak is produced and the
calculated
pressure differential is lower than the predetermined range of the nominal
pressure differential.
[0025] The controller is programmed to generate an injector fault signal
indicating
the failure of the fuel injector when the first fault signal indicating a
gaseous fuel
leak is produced and the calculated pressure differential is within or higher
than
the predetermined range of the nominal pressure differential.
[0026] The controller is programmed to generate a bias fault signal, "Bias out
of
range low" (BOL) or "Bias out of range high" (BOH) indicating a failure of at
least
one of said system components which regulate the gaseous fuel or liquid fuel
rail
pressure when the first fault signal indicating a gaseous fuel leak is not
produced
and the calculated pressure differential is lower or, respectively higher the
predetermined range of the nominal pressure differential.
[0027] A dual fuel internal combustion engine system is disclosed which
comprises an engine fuelled with gaseous fuel and liquid fuel, the system
further
comprising:
a. a gaseous fuel supply and a liquid fuel supply;
b. a fuel injector for separately injecting gaseous fuel and liquid fuel in a
combustion chamber, the fuel injector being fluidly connected to the
gaseous fuel supply and the liquid fuel supply through a gaseous fuel
supply line and, respectively a liquid fuel supply line, each of said fuel
supply lines being provided with a component for regulating the
pressure in the respective supply line;
c. a liquid fuel return line fluidly connecting a drain outlet of the fuel
injector to the liquid fuel supply line; and
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d. a detection system for detecting the presence of gaseous fuel in the
liquid return line; and
e. a controller which receives a signal from the detection system and is
capable of generating a first fault signal indicating that there is a
gaseous fuel leak to the liquid fuel return line based on said signal.
Brief Description of the Drawings
[0028] The drawings illustrate specific preferred embodiments of the
invention,
but should not be considered as restricting the spirit or scope of the
invention in
any way.
[0029] Figure 1 is a schematic view of a fuel system for a dual fuel internal
combustion engine according to one embodiment of the present invention.
[0030] Figure 2 is a schematic view of a fuel system for a dual fuel internal
combustion engine according to a second embodiment of the present invention.
[0031] Figure 3 is a chart illustrating liquid fuel and gaseous fuel rail
pressures
and bias versus engine torque for the internal combustion engine of Figure 1
operating at one engine speed.
[0032] Figure 4 is a chart illustrating the variation of the liquid fuel and
gaseous
fuel rail pressures over time, during transient and steady pressure
conditions.
[0033] Figure 5 is a chart illustrating the variation of the liquid fuel
return line
pressure and the variation of the liquid fuel and gaseous fuel rail pressures
over
time.
[0034] Figure 6 is a diagram illustrating the steps of the present method of
detecting and diagnosing a gaseous fuel leak in the fuel injector of a gaseous
fuelled engine system.
Detailed Description of the Preferred Embodiments
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[0035] Referring to FIG. 1, there is shown a schematic view of fuel system 100
for supplying a pilot fuel and a gaseous fuel to a dual fuel internal
combustion
engine (not illustrated). Fuel system 100 comprises dual fuel injector 102
which
allows the separate and independent injection of a gaseous fuel and of a pilot
fuel into the combustion chamber of the internal combustion engine. The
gaseous fuel is the main fuel for combustion in the engine. In the present
disclosure the gaseous fuel is preferably natural gas, but can be other types
of
gaseous fuels such as methane, propane, butane, hydrogen, and blends of such
fuels that can combust when ignited by a pilot fuel. The pilot fuel is a
liquid fuel,
for example diesel, but can be other types of liquid fuel that are more easily
ignitable when injected inside a combustion chamber. The liquid fuel used as
pilot fuel for the ignition of the gaseous fuel can also be the hydraulic
fluid used
for activating the fuel injector and/or the liquid used for the liquid seals
which
prevent the leakage of gaseous fuel into the hydraulic fluid.
[0036] Fuel system 100 comprises a liquid fuel supply 104 and a gaseous fuel
supply 106. Liquid fuel supply 104 can be a liquid fuel tank, which supplies
liquid
fuel through supply line 108 to liquid fuel pumping apparatus 110. Gaseous
fuel
supply 106 can be an accumulator which accumulates gaseous fuel from an
upstream supply line 112, as illustrated in the present embodiment, or it can
be a
gas cylinder storing compressed natural gas (CNG). In the present embodiment,
the illustrated upstream supply line 112 can be a commercial or residential
gas
line, or a feed pipe from a supply of liquefied gaseous fuel such as liquefied
natural gas (LNG). Gaseous fuel supply 106 supplies gaseous fuel to pressure
regulator 114 through line 116. From pressure regulator 114 gaseous fuel is
supplied through rail 118 to fuel injector 102.
[0037] Liquid fuel pumping apparatus 110 pressurizes the liquid fuel to a
pressure suitable for injection and supplies it through rail 120 to fuel
injector 102.
In the present embodiment, pumping apparatus 110 is a liquid fuel pump. Liquid
fuel rail 120 is fluidly connected to regulator 114 through line 122. The
liquid fuel
pressure in rail 120 is substantially equal to the liquid fuel pressure in
line 122.
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[0038] Although only one fuel injector is shown in FIG. 1, it is understood
that in
most embodiments this fuel injector is one of a plurality of fuel injectors,
each
associated with a respective combustion chamber, and in such embodiments
liquid fuel rail 120 and gaseous fuel rail 118 are known as the common fuel
rails
that supply liquid fuel and respectively gaseous fuel to all the fuel
injectors.
[0039] Pressure regulator 114 is responsive to liquid fuel pressure in line
122 to
regulate gaseous fuel pressure in rail 118 below liquid fuel pressure in line
122
and rail 120. Regulator 114 operates as described in more detail in the afore-
mentioned `833 patent. In the present embodiment, regulator 114 is illustrated
as
a dome-loaded regulator, known to those familiar with this technology.
Pressure
regulator 114 maintains a pressure differential between liquid fuel pressure
in rail
120 and gaseous fuel in rail 118 to prevent gaseous fuel from leaking past the
liquid seals into the liquid fuel as described in the aforementioned `862 and
`833
patents. Because of the construction of pressure regulator 114, the pressure
differential between liquid fuel rail pressure (LFP) and gaseous fuel rail
pressure
(GFP) is maintained constant as illustrated in FIG. 3 which represents the
liquid
fuel and gaseous fuel supply pressures and the pressure differential between
them (bias) versus engine torque. In other embodiments, pressure regulator 114
can be replaced by a variable pressure regulator as further described in
relation
with the embodiment illustrated in FIG. 2.
[0040] Fuel system 100 further comprises a liquid fuel pressure sensor 124
which
monitors the pressure in the liquid fuel rail 120 and a gaseous fuel pressure
sensor 126 which monitors the pressure in the gaseous fuel rail 118. The
pressures measured by sensors 124 and 126 are communicated to electronic
controller 130. Electronic controller 130 can be a standalone computer for
controlling the fuel system or it can be the engine control unit (ECU) for the
engine. Electronic controller 130 commands pumping apparatus 110 responsive
to the signals received from pressure sensors 124 and 126. The gaseous fuel
pressure (GFP) and the liquid fuel pressure (LFP) are preferably measured when
the pressures in respective fuel rails 118 and 120 have stabilized, for
example at
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a time T1 as illustrated in FIG. 4. Transient pressure conditions which are
present in respective fuel rails 118 and 120 when liquid fuel pressure and/or
gaseous fuel pressure are being changed from one pressure to another
according to engine demand can generate inaccurate readings of pressure
sensors 124 and 126. For example, liquid fuel pressure LFP can change at a
different rate than gaseous fuel pressure GFP during transients, which can
result
in inaccurate pressure differential readings. The controller preferably uses
pressure measurements that are taken when the engine speed and torque have
stabilized or filters the pressure measurements taken during transients.
[0041 ] Fuel system 100 further comprises a liquid fuel return line 132
through
which liquid fuel is returned from fuel injector 102 to liquid fuel supply
104. The
pressure in liquid fuel return line 132 is continuously monitored by pressure
sensor 134. The measurements of pressure sensor 134 on the liquid fuel return
line are communicated to controller 130.
[0042] Another embodiment of the present fuel system is illustrated in FIG. 2.
Fuel system 200 supplies liquid fuel and gaseous fuel to dual fuel injector
102
which is associated to a combustion chamber of an internal combustion engine
(not illustrated). Similar to the fuel system illustrated in FIG. 1, dual fuel
injector
102 allows the separate and independent injection of a gaseous fuel and of a
pilot fuel into the combustion chamber of the internal combustion engine. The
pilot fuel is a liquid fuel and the same liquid fuel can also be used as the
hydraulic fluid used for activating the fuel injector and/or as the fluid for
the liquid
seals in the fuel injector. The fuel system illustrated in FIG. 2 is similar
to the fuel
system illustrated in FIG. 1 and therefore only the differences are discussed
here.
[0043] Pressure regulator 214 is a variable pressure regulator that is
controlled
by controller 230 to regulate the gaseous fuel pressure in gaseous fuel rail
118.
Regulator 214 can be a variable pressure regulator or any other pressure
regulating valve that controls the pressure in gaseous fuel rail 118 according
to at
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least one of the engine's operating parameters, for example engine speed or
load. Pressure regulator 214 is not directly responsive to the pressure in
liquid
fuel rail 120. Controller 230 monitors the pressure signals from pressure
sensors
124 and 126 and commands liquid fuel pumping apparatus 110 and pressure
regulator 214 to maintain a target pressure differential between liquid fuel
pressure in rail 120 and gaseous fuel pressure in rail 118 within a
predetermined
range of tolerance. The pressure differential between the liquid fuel pressure
and
the gaseous fuel pressure is selected to prevent gaseous fuel from leaking
past
the liquid seals into the liquid fuel as described in the aforementioned `862
and
`833 patents. In this embodiment, the pressure differential is not constant
and
can be optimized for each engine operating condition, for example by reducing
the pressure differential at idle and lower load conditions and progressively
increasing the pressure differential at higher load conditions. The embodiment
illustrated in FIG. 2 has the advantage of independently controlling the
liquid fuel
pressure and the gaseous fuel pressure such that an optimum pressure
differential is maintained during transients when the liquid fuel pressure
(LFP)
and the gaseous fuel pressure (GFP) fluctuate as illustrated in FIG. 4.
[0044] In Fig. 2 electronic controller 230 can be a standalone computer for
controlling the fuel system or it can be the engine control unit (ECU) for the
engine.
[0045] In both embodiments illustrated in Figures 1 and 2 liquid fuel rail
pressure
and gaseous fuel rail pressure are measured by pressure sensor 124 and,
respectively 126, and the pressure in liquid fuel return line 132 is
continuously
monitored by pressure sensor 134. Signals from pressure sensors 124, 126 and
134 are communicated to controller 130 and respectively 230 which record the
pressure variation in the respective fuel lines. An example of such a map that
can
be recorded by controller 130 or 230 is illustrated in FIG. 5.
[0046] The pressure differential between liquid fuel pressure (LFP) in rail
120 and
gaseous fuel pressure (GFP) in rail 118 is preferably maintained positive,
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meaning that the liquid fuel pressure is preferably higher than the gaseous
fuel
pressure to prevent any gaseous fuel leakage in the fuel injector. If at a
time T2,
during the engine operation, gaseous fuel pressure GFP becomes higher than
liquid fuel pressure LFP and such negative pressure differential is maintained
over a period of time, gaseous fuel may leak into liquid fuel within fuel
injector
102 and further into liquid fuel return line. Pressure sensor 134 will
therefore
record at a time T3, after time T2, an increase in liquid fuel return pressure
(LFRP)
thereby indicating that there is gaseous fuel leak into the liquid fuel return
line
132. If gaseous fuel pressure GFP drops at a time T4 and becomes lower than
liquid fuel pressure LFP, the condition of positive pressure differential is
re-
established and pressure sensor 134 will indicate at a delayed time T5 a drop
in
liquid fuel return pressure LFRP. Pressure sensor 134 can be located in liquid
fuel return line 132 anywhere between dual fuel injector 102 and liquid fuel
supply 104. The time delay in recording a pressure increase or a pressure drop
in liquid fuel return line 132 will be shorter if pressure sensor 134 is
located
closer to fuel injector 102.
[0047] In an alternative embodiment, the detection system for detecting a leak
of
gaseous fuel into the liquid fuel return line comprises a pressure switch
instead of
pressure sensor 134 and the pressure switch establishes electrical contact
when
the pressure in liquid fuel return line 132 exceeds a predetermined nominal
value
and communicates this information to the controller without recording a
pressure
trace as illustrated in FIG. 5.
[0048] Furthermore, in other embodiments, the detection system for detecting a
leak of gaseous fuel into the liquid fuel return line can comprise a gaseous
fuel
detector instead of pressure sensor 134 and the gaseous fuel detector can be
placed in the liquid fuel return line 132 between fuel injector 102 and liquid
fuel
supply 104 or directly within liquid fuel supply 104. Controller 130 or 230
receives
a signal from the gaseous fuel detector indicating if an amount of gaseous
fuel
has been detected in the liquid fuel return line 132 and generates a fault
signal
indicating a gaseous fuel leak into the liquid fuel return line.
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[0049] The diagram of FIG. 6 illustrates the steps of the present method which
is
performed within controller 130 illustrated in FIG. 1 for detecting and
diagnosing
a gaseous fuel leak in a dual fuel internal combustion engine system. The same
method can be applied to the fuel system illustrated in FIG. 2 and the steps
of the
method will then be executed in the memory of controller 230.
[0050] Pressure sensor 134 measures the pressure (LFRPm) in liquid fuel return
line 132 and sends a signal indicative of the LFRPm pressure to controller
130.
Controller 130 compares measured liquid fuel return pressure LFRPm to a
predetermined nominal pressure LFRPc stored in the controller's memory and it
produces a fault signal indicating that there is a gaseous fuel leak into the
liquid
fuel return line ("Gaseous Fuel Leak to Drain") if measured liquid fuel return
pressure LFRPm is higher than predetermined liquid fuel return pressure LFRPC.
This means there is a gaseous fuel leak in the fuel injector and that gaseous
fuel
has leaked into the liquid fuel return line. Controller 130 can be programmed
such that the measured liquid fuel return pressure has to be higher than the
predetermined liquid fuel return pressure by a predetermined threshold before
it
generates the fault signal indicating a gaseous fuel leak to the liquid fuel
return
line. In engine systems designed to be less tolerant to gaseous fuel - liquid
fuel
mixtures controller 130 or 230 can be programmed to generate a fault signal
immediately after pressure sensor 134 detects a pressure increase in the
liquid
fuel return line over a predetermined value.
[0051] In alternative embodiments, if a pressure switch is used instead of a
pressure sensor and if the measured pressure in the liquid fuel return line
LFRPm
is higher than the predetermined nominal pressure LFRPc the switch sends an
electrical signal to the controller which outputs a fault signal indicating
that there
is a gaseous fuel leak to drain. Similarly, if a gaseous fuel detector is used
instead of the pressure sensor in the liquid fuel return line, the controller
receives
a signal from the gaseous fuel detector that an amount of gaseous fuel is
detected in the liquid fuel return line and outputs a fault signal indicating
the
gaseous fuel leak to drain.
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[0052] In parallel to the measurements of pressure sensor 134, pressure
sensors
124 and 126 measure the pressure (LFP) in liquid fuel rail 120 and
respectively
the pressure (GFP) in gaseous fuel rail 118 and send signals indicative of the
measured pressures to controller 130 which calculates the pressure
differential
between the measured liquid fuel rail pressure and gaseous fuel rail pressure
and records it as bias B. The pressure in fuel rails 118 and 120 are measured
downstream of any system components that regulate the pressure in the rails to
their respective target values. The calculated pressure differential (bias B)
is
compared to a predetermined range of the nominal pressure differential which
comprises values between a predetermined minimum (Bmin) and a predetermined
maximum (Bmax).
[0053] The controller can then further correlate between the comparisons of
the
liquid fuel return pressure and of the calculated pressure differential to
their
respective predetermined nominal values or range of values and can produce
additional fault signals diagnosing an existing gaseous fuel leak to drain as
explained below.
[0054] If measured liquid fuel return pressure LFRPm is higher than
predetermined nominal pressure LFRPc (LFRPm > LFRPc) and calculated
pressure differential B is within the predetermined range of the nominal
pressure
differential (Bmin < B < Bmax) or is higher than a maximum value of the
predetermined range of a nominal pressure differential (B > Bmax) the
controller
produces an additional fault signal indicating a failure of the fuel injector.
This
means that the system components regulating the pressure in the fuel rails
(e.g.
pressure regulator 114 or 214 and pumping apparatus 110) work within the
prescribed parameters, but that fuel injector 102 is defective which causes a
gaseous fuel leak to the liquid fuel.
[0055] If measured liquid fuel return pressure LFRPm is higher than a
calibrated
nominal pressure LFRPc (LFRPm > LFRPc) and calculated pressure differential B
is lower than the minimum value of the predetermined range of a nominal
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pressure differential Bmin (B < Bmin) the controller produces an additional
signal
indicating that at least one of the system components which regulate the fuel
pressure in the fuel rails, for example pumping apparatus 110 or regulator 114
or
214) has failed. This means that a smaller pressure differential than
predetermined has caused gaseous fuel to leak to liquid fuel drain and the
fault is
recorded as "Bias out of range low" (BOL).
[0056] If the measured liquid fuel return pressure LFRPm is within the
predetermined limits, more specifically if it is equal to or smaller than the
predetermined nominal pressure LFRP,
, (LFRPm = or < LFRP,.) and if the
calculated pressure differential B is outside of the predetermined range for
the
pressure differential, more specifically if it is higher or lower than a
maximum
value or respectively a minimum value of this predetermined range (B < Bmin or
B
> Bmax) the controller produces an additional fault signal indicating a
failure of at
least one of the system components which regulate the pressure in fuel rails
118
and 120. The fault signal is recorded as "Bias out of range high" (BOH) if the
pressure differential is higher than apredetermined maximum value and the
fault
signal is recorded as "Bias out of range low" (BOL) if the pressure
differential is
lower than a predetermined minimum value. This means that gaseous fuel is not
leaking into the liquid fuel return line, but because the calculated pressure
differential between the pressure in liquid fuel rail 120 and the pressure in
gaseous fuel rail 118 is out of range at least one the system components
regulating the pressure in the fuel rails is not working properly.
[0057] In alternative embodiments, the above steps can also be implemented
when detecting a gaseous fuel leak using a pressure switch or a gaseous fuel
detector instead of comparing the measured liquid fuel return pressure to a
predetermined nominal pressure.
[0058] In the present method if the calculated pressure differential B is
outside of
the predetermined range for the pressure differential, more specifically if it
is
higher or lower than a maximum value or respectively a minimum value of this
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predetermined range (B < Bmin or B > Bmax) the controller produces an
additional
fault signal indicating a failure of at least one of the system components
which
regulate the pressure in fuel rails or, depending on the measured pressure in
the
fuel return line, a failure of the fuel injector The controller can be
programmed to
generate this additional fault signal right away after the calculated pressure
differential B is greater than Bmax or smaller than Bmin, or it can generate
this
additional fault signal at a predetermined time after this condition is
detected.
Alternatively, the calculated pressure differential B has to be greater than
Bmax
or smaller than Bmin by a predetermined threshold before the controller
generates a fault signal. The predetermined threshold for generating a fault
signal indicating a failure of the injector can be different than the
threshold for
generating a fault signal indicating a failure of at least one of the system
components which regulate the pressure in fuel rails.
[0059] The described method relies on the measurements received from
pressure sensors 124, 126 and 134. If the system detects an alarm indicating
that any of these sensors stopped working properly the controller aborts the
entire method.
[0060] At a predetermined time after controller 130 generates a fault signal
indicating that there is a gaseous fuel leak in the liquid fuel return line
the engine
is switched to the run-on-diesel operation mode whereby the engine is fuelled
only with liquid fuel. The predetermined time after which the engine is
switched to
the run-on-diesel mode depends on the engine system design, especially its
other existing safety features addressing the hazard posed by a gaseous
fuel/liquid fuel mixture present in the fuel injector, in the liquid fuel
return line or in
the liquid fuel supply.
[0061 ] The controller in the fuel system described here can be programmed
such
that it generates a fault signal after a predetermined period of time after
the
condition which triggers such a fault signal is detected. For example,
controller
130 or 230 will generate a fault signal indicating that there is a gaseous
fuel leak
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to the liquid fuel return line at a predetermined period of time after
detecting that
the pressure signal sent by pressure sensor 134 is higher than a predetermined
liquid fuel return line pressure. The delay time for generating a gaseous fuel
leak
fault signal depends on the engine system's tolerance to gaseous fuel/liquid
fuel
mixtures. Similarly controller 130 or 230 will generate an additional fault
signal
indicating a failure of at least one of the system components which regulate
the
pressure in fuel rails (e.g. BOL, BOH) at a predetermined period of time after
the
condition which triggers this fault signal is detected.
[0062] The predetermined nominal pressure in the liquid fuel return line and
the
predetermined range of the nominal pressure differential between liquid fuel
rail
pressure and gaseous fuel rail pressure are stored in the memory of the
controller. The predetermined nominal pressure in the liquid fuel return line
is
generally a constant value for a particular engine system, determined by
testing.
The predetermined range of the nominal pressure differential (bias B) can be
constant, for example for an engine fuel system illustrated in FIG. 1 or it
can be
variable, for example for an engine fuel system illustrated in FIG. 2. When
bias B
is variable, the memory of controller 130 can comprise a two-dimensional look-
up
table which correlates the values of bias B with the engine speed and torque,
for
example.
[0063] The preferred method has the advantage that it can detect a gaseous
fuel
leak to the liquid fuel return line and at the same time it can identify the
cause of
the failure mode as either a defective pressure regulating system component or
a
defective fuel injector.
[0064] 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.
