Closed Loop Control of Exhaust System Fluid Dosing
Field of the Invention
[0001] The present invention relates to exhaust aftertreatment systems for diesel
engines and lean-burn gasoline engines.
Background
[0002] NOx and particulate matter (soot) emissions from diesel engines are an
environmental problem. Several countries, including the United States, have long
had regulations pending that will limit these emissions. Manufacturers and
researchers have put considerable effort toward meeting those regulations. Diesel
particulate filters (DPFs) have been proposed for controlling the particulate matter
emissions. A number of different solutions have been proposed for controlling the
NOx emissions.
[0003] In gasoline-powered vehicles that use stoichiometric fuel-air mixtures, NOx
emissions can be controlled using three-way catalysts. In diesel-powered vehicles,
which use compression ignition, the exhaust is generally too oxygen-rich for three-
way catalysts to be effective.
[0004] One set of approaches for controlling NOx emissions from diesel-powered
vehicles involves limiting the creation of pollutants. Techniques such as exhaust gas
recirculation and partially homogenizing fuel-air mixtures are helpful in reducing NOx
emissions, but these techniques alone are not sufficient. Another set of approaches
involves removing NOx from the vehicle exhaust. These approaches include the use
of lean-burn NOx catalysts, selective catalytic reduction (SCR), and lean NOx traps
(LNTs).
[0005] Lean-burn NOx catalysts promote the reduction of NOx under oxygen-rich
conditions. Reduction of NOx in an oxidizing atmosphere is difficult. It has proven
challenging to find a lean-burn NOx catalyst that has the required activity, durability,
and operating temperature range. Lean-burn NOx catalysts also tend to be
hydrothermally unstable. A noticeable loss of activity occurs after relatively little use.
A reductant such as diesel fuel must be provided, which introduces a fuel economy
penalty of 3% or more. Currently, peak NOx conversion efficiencies for lean-burn
NOx catalysts are unacceptably low.
[0006] SCR generally refers to selective catalytic reduction of NOx by ammonia.
The reaction takes place even in an oxidizing environment. The NOx can be
temporarily stored in an adsorbent or ammonia can be fed continuously into the
exhaust. SCR can achieve high levels of NOx reduction, but there is a disadvantage
in the lack of infrastructure for distributing ammonia or a suitable precursor. Another
concern relates to the possible release of ammonia into the environment.
[0007] To clarify the state of a sometimes ambiguous nomenclature, one should
note that in the exhaust aftertrea.tment art the terms "SCR catalyst" and "lean NOx
catalyst" can be used interchangeably. Often, however, the term "SCR" is used to
refer just to ammonia-SCR, in spite of the fact that strictly speaking ammonia-SCR is
only one type of SCR/lean NOx catalysis. Commonly, when both ammonia-SCR
catalysts and lean NOx catalysts are discussed in one reference, SCR is used in
reference to ammonia-SCR and lean NOx catalysis is used in reference to SCR with
reductants other than ammonia, such as SCR with hydrocarbons.
[0008] LNTs are devices that adsorb NOx under lean exhaust conditions and
reduce and release the adsorbed NOx under rich exhaust conditions. An LNT
generally includes a NOx adsorbent and a catalyst. The adsorbent is typically an
alkaline earth compound, such as BaCO3 and the catalyst is typically a combination
of precious metals, such as Pt and Rh. In lean exhaust, the catalyst speeds
oxidizing reactions that lead to NOx adsorption. In a reducing environment, the
catalyst activates reactions by which adsorbed NOx is reduced and desorbed. In a
typical operating protocol, a reducing environment will be created within the exhaust
from time to time to remove accumulated NOx and thereby regenerate (denitrate) the
LNT.
[0009] During denitration, much of the adsorbed NOx is reduced to N2, although a
portion of the adsorbed NOx is released without having been reduced and another
portion of the adsorbed NOx is released after being deeply reduced to ammonia.
U.S. Pat. No. 6,732,507 describes a system in which an SCR catalyst is configured
downstream from the LNT in order to utilize the ammonia released during
denitration. The ammonia is utilized to reduce NOx slipping past the LNT and
thereby improves conversion efficiency over a stand-alone LNT.
[0010] In addition to accumulating NOx, LNTs accumulate SOx. SOx is the
combustion product of sulfur present in ordinarily fuel. Even with reduced sulfur
fuels, the amount of SOx produced by combustion is significant. SOx adsorbs more
strongly than NOx and necessitates a more stringent, though less frequent,
regeneration. Desulfation requires elevated temperatures as well as a reducing
atmosphere. The temperature of the exhaust can be elevated by engine measures,
particularly in the case of a lean-burn gasoline engine. At least in the case of a diesel
engine, however, it is often necessary to provide additional heat. Once the LNT is
sufficiently heated, then a reducing environment similar to LNT denitration is created.
[0011] Except when the engine can be run stoichiometric, or rich, creating a
reducing environment for LNT regeneration generally involves injecting reductant
into the exhaust. A portion of the reductant is required to eliminate excess oxygen
from the exhaust. The amount of oxygen to be removed by reaction with reductant
can be reduced in various ways, for example, by throttling the engine air intake. At
least in the case of a diesel engine, however, it is generally necessary to eliminate a
substantial amount of oxygen from the exhaust by combustion or reforming reactions
with injected reductant. Reductant is also commonly injected into the exhaust to
heat the LNT for desulfation or to heat a DPF to initiate soot combustion.
[0012] Reductant can be injected into the exhaust by the engine fuel injectors.
For example, the engine can inject extra fuel into the exhaust within one or more
cylinders prior to expelling the exhaust. A disadvantage of this approach is that
engine oil can be diluted by fuel passing around piston rings and entering the oil
gallery. Additional disadvantages of cylinder reductant injection include having to
alter the operation of the engine to support LNT regeneration, excessive dispersion
of pulses of reductant, and forming deposits on turbocharger and EGR valves. As
an alternative to using the engine fuel injectors, reductant can be injected into the
exhaust downstream from the engine using separate exhaust line fuel injectors.
Injecting the exhaust directly into the exhaust line has the advantage of allowing the
point of introduction to be selected.
[0013] An oxidation catalyst or a fuel reformer may be used within the exhaust
line to combust or reform the injected reductant upstream from a pollution control
device. U.S. Pat. No. 7,082,753 (hereinafter "the '753 patent") describes an exhaust
aftertreatment system with a fuel reformer placed in the exhaust line upstream from
an LNT. The reformer includes both oxidation and reforming catalysts. The reformer
both removes excess oxygen from the exhaust and converts the diesel fuel reductant
into more reactive reformate. The inline reformer of the 753 patent is designed to
heat rapidly and to then catalyze steam reforming.
[0014] Temperatures from about 500 to about 700 °C are required for steam
reforming. These temperatures are substantially higher than typical diesel exhaust
temperatures. To achieve a sufficient reformer temperature when LNT regeneration
is required, the reformer of the 753 patent is heated by first injecting fuel at a rate
that leaves the exhaust lean, whereby the injected fuel combusts in the reformer,
releasing heat. After warm up, the fuel injection rate is increased to provide a rich
exhaust. Ideally, the reformer of the 753 patent can be operated auto-thermally,
with endothermic steam reforming reactions balancing exothermic combustion
reaction. In practice, however, at high exhaust oxygen concentrations the reformer
. unavoidably and excessively heats if reformate is produced continuously. To avoid
overheating, the 753 patent proposes pulsing the fuel'injection.
[0015] U.S. Pat. No. 6,006,515 suggests that an LNT may be regenerated more
efficiently by either longer or shorter chain hydrocarbons, depending on the LNT
composition and the temperature at which regeneration takes place. In order to be
able to control the selection between long and short chain hydrocarbons, the patent
proposes two fuel injectors, one in the exhaust manifold upstream from the
turbocharger and one in the exhaust line immediately before the LNT. Due to the
high temperatures in the exhaust upstream from the turbocharger, fuel injected with
the manifold fuel injector is said to undergo substantial cracking to form shorter chain
hydrocarbons.
[0016] Diesel particulate filters must also be regenerated. Regeneration of a DPF
is to remove accumulated soot. Two general approaches are continuous and
intermittent regeneration. In continuous regeneration, a catalyst is provided
upstream of the DPF to convert NO to NO2. NO2 can oxidize soot at typical diesel
exhaust temperatures and thereby effectuate continuous regeneration. A
disadvantage of this approach is that it requires a large amount of expensive
catalyst.
[0017] Intermittent regeneration involves heating the DPF to a temperature at
which soot combustion is self-sustaining in a lean environment. Typically this is a
temperature from about 400 to about 700 °C, depending in part on what type of
catalyst coating has been applied to the DPF to lower the soot ignition temperature.
A typical way to achieve soot combustion temperatures is to inject fuel into the
exhaust upstream from the DPF, whereby the fuel combusts generating heat in the
DPF or an upstream device.
[0018] Various exhaust line reductant injection systems for injecting diesel fuel for
LNT regeneration have been proposed. A common issue addressed by these
systems concerns the heat of the exhaust line. Heat from the exhaust line can
cause fuel that remains stagnant within the fuel injectors between fuel injections to
decompose into substances that eventually clog the fuel injectors.
[0019] One approach is to physically separate the injector from the exhaust line
by providing a relatively long line between the injector and a point of entry into the
exhaust line. A difficulty with this approach is that the injector is generally designed
to provide the fuel in finely distributed droplets. These droplets may recombine
within the relatively long line before reaching the point of entry.
[0020] Another approach is to design exhaust line fuel injectors with cooling
jackets. Water or air cooling can be used. Alternatively, an injector can be cooled
with the reductant being injected; an excess flow of reductant is provided to the
injector. The excess flow is returned to a reservoir. The return flow carries away
heat.
[0021] Robert Bosch GmbH has proposed an exhaust line fuel injection system
with a separate metering valve and injection unit. The injection unit is a simple
nozzle surrounded by a cooling jacket. The metering valve, which comprises a pulse
width modulated (PWM) pulse width modulated valve, is kept some distance away
from the exhaust line to protect temperature sensitive components of the valve, such
as electrical insulators. The metering valve is designed to draw fuel from the low
pressure portion of the engine fuel injection circuit or from a separate pump and/or
pressure regulator. The flow rate is regulated through the duty cycle of the metering
valve.
[0022] The Bosch system is configured with two pressure measuring devices, one
upstream from the PWM valve and the other downstream from the PWM valve. A
conventional way to control the flow through this system would be to relate the
pressure drop across the metering valve together with the duty cycle of the valve to
the flow rate. The duty cycle (the fraction of time the valve is open) can be increased
or decreased until the desired flow rate is reached.
[0023] In spite of advances, a long felt need continues for an exhaust
aftertreatment system that is durable, is reliable, has acceptable manufacturing and
operating costs, and can reduce NOx emissions from diesel engines enough to meet
U.S. Environmental Protection Agency (EPA) regulations effective in 2010 and other
such regulations.
Summary
[0024] One of the inventors' concepts relates to a method of operating an exhaust
aftertreatment system with exhaust line fuel injection. The method comprises
opening a flow regulating valve to allow fuel to flow from a pressurized fuel source to
an exhaust system fuel supply line. The exhaust system fuel supply line is
connected to a nozzle. The nozzle generally comprises a check valve, whereby the
nozzle sprays the fuel into the exhaust line whenever the pressure drop across the
nozzle is sufficiently high to open the check valve. Using a pressure measuring
device, an indication of the exhaust system fuel supply line pressure is obtained.
The indication of the exhaust system fuel supply line pressure is used to provide
feedback for controlling the regulating valve.
[0025] The method uses a predetermined relationship between the flow rate
through the nozzle and either the indication of the exhaust system fuel supply line
pressure or a difference between the indication of the exhaust system fuel supply
line pressure and an exhaust line pressure. The relationship can be used to relate
pressures or pressure drops to flow rates, in which case the valve is controlled to
cause the flow rate to approach a flow rate target. Equivalently, the predetermined
relationship can be used to obtain a target pressure indication from the target flow
rate (and optionally the exhaust line pressure), in which case the valve is controlled
to cause the pressure indications to approach the target.
[0026] One advantage of this method is that it can be implemented with a single
pressure measuring device. Another advantage is that it provides accurate control,
particularly where the exhaust line pressure does not vary much. A further
advantage is that the same pressure indication used for control can provide useful
diagnostic information. In particular, it has been found that the frequency spectrum
of the pressure indication can signify that the fuel injection system is functioning
properly.
[0027] The flow rate is related to either the pressure drop across the nozzle or an
exhaust system fuel supply line pressure independent of any other system pressure.
Although the pressure drop can be used even when the exhaust line does not
include a DPF, using the pressure drop is particularly desirable and convenient to
implement when the exhaust line has a DPF. Pressure variations in the exhaust line
tend to be higher when the exhaust line contains a DPF, with pressures increasing
as the DPF fills. The exhaust line pressure is typically measured for DPF control.
The pressure drop across the nozzle is the difference between the pressure in the
exhaust system fuel supply line and the exhaust line. The pressure drop can track
the flow rate even more accurately than the exhaust system fuel supply line
pressure.
[0028] Another aspect of the inventors' concepts relates to a power generation
system. The power generation system has an engine operative to produce an
exhaust, which is channeled through an exhaust line. The power generation system
also has a fuel pump operative to pump fuel from a fuel tank to a conduit, a flow
regulating valve configured to admit fuel from the conduit and to release the fuel to
an exhaust system fuel supply line, a nozzle, which generally comprises a check-
valve and is configured to admit fuel from the exhaust system fuel supply line to the
exhaust line, a pressure measuring device configured to measure a pressure of the
exhaust system fuel supply line, and a controller configured to control the flow
regulating valve using feedback from the measured pressures. In one embodiment,
the controller is configured to use a predetermined relationship between the flow rate
through the nozzle and the pressure in the exhaust system fuel supply line. In
another embodiment, the controller is configured to use a predetermined relationship
between the flow rate through the nozzle and a pressure drop across the nozzle.
The system can be used to implement the methods described above.
[0029] Another one of the inventors' concepts relates to a method of dosing fuel
to an exhaust aftertreatment system. According to the method, the fuel is passed
through a regulating valve to an exhaust system fuel supply line. From there, the
fuel is injected into an exhaust line through a nozzle, which generally comprises a
check-valve. A pressure in the exhaust system fuel supply line is measured to
obtain pressure data. A relationship is provided giving the flow rate through the
check-valve as a function of the exhaust system fuel supply line pressure, or the
pressure drop across the check-valve. An integration using the pressure data and
the relationship is carried out to obtain a total amount of fuel passing through the
check-valve over a period. The fuel dosing can be controlled based on the total For
example, an injection can be terminated when a certain total amount of fuel has
been injected. When fuel injection is being pulsed, a pulse period, frequency, or
amplitude can be adjusted based on the total.
[0030] The primary purpose of this summary has been to present certain of the
inventors' concepts in a simplified form to facilitate understanding of the more
detailed description that follows. This summary is not a comprehensive description
of every one of the inventors' concepts or every combination of the inventors'
concepts that can be considered "invention". Other concepts of the inventors will be
conveyed to one of ordinary skill in the art by the following detailed description and
the accompanying drawings. The specifics disclosed herein may be generalized,
narrowed, and combined in various ways with the ultimate statement of what the
inventors claim as their invention being reserved for the claims that follow.
Brief Description of the Drawings
[0031] Fig. 1 is a schematic illustration of an exemplary exhaust line hydrocarbon
injection system.
[0032] Fig. 2 is a schematic illustration of an example of a nozzle in an open
position.
[0033] Fig. 3 is a schematic illustration of the exemplary nozzle of Figure 2 in a
closed position.
[0034] Fig. 4 is a schematic illustration of another example of a nozzle in an open
position.
[0035] Fig. 5 is a schematic illustration of the exemplary nozzle of Figure 4 in a
closed position.
[0036] Fig. 6 is a schematic illustration of a further example of a nozzle in an
open position.
[0037] Fig. 7 is a schematic illustration of the exemplary nozzle of Figure 6 in a
closed position.
[0038] Fig. 8 is a schematic illustration of an example of a two-way PWM pulse
width modulated valve in a closed position.
[0039] Fig. 9 is a schematic illustration of the exemplary nozzle of Figure 8 in an
open position.
[0040] Fig. 10 is a schematic illustration of an example of a three-way PWM pulse
width modulated valve in a closed position.
[0041] Fig. 11 is a schematic illustration of the exemplary nozzle of Figure 10 in
an open position.
[0042] Fig. 12 is a schematic illustration of an example of a proportional control
spool valve in a closed position.
[0043] Fig. 13 is a schematic illustration of the valve of Figure 12 in an open
position.
[0044] Fig. 14 is a schematic illustration of an exemplary power generation
system.
[0045] Fig. 15 is a plot showing the relationships between duty cycle, flow rate
exhaust system fuel supply line pressure.
[0046] Fig. 16 is a schematic illustration of an exemplary exhaust line
hydrocarbon injection system.
[0047] Fig. 17 is a plot showing a frequency spectrum of a series of exhaust
system fuel supply line pressure measurements taken with an unclogged nozzle and
a PWM flow control valve at 100% duty cycle (continuously open).
[0048] Fig. 18 is a plot showing a frequency spectrum of a series of exhaust
system fuel supply line pressure measurements taken for the same system and
under the same conditions as used to obtain the measurements plotted in Fig. 17,
except that the nozzle is artificially partially clogged.
Detailed Description
[0049] Figure 1 is a schematic illustration of an exemplary exhaust line
hydrocarbon injection system 10 that is part of a power generation system 1 that can
embody some of the inventors' concepts. The hydrocarbon injection system 10
draws fuel from an engine fuel supply system 20 and injects the fuel into an exhaust
line 30. The hydrocarbon injection system 10 includes a flow regulating valve 11, a
nozzle 12, a pressure sensor 13, and a controller 14. The pressure sensor 13 is
configured to read the pressure in an exhaust system fuel supply line 15, which
carries fuel from the flow regulating valve 11 to the nozzle 12.
[0050] The flow regulating valve 11 is adapted to selectively admit fluid from a
pressurized source. In this example, the pressurized source is the low pressure
portion of the engine fuel supply system 20. The engine fuel supply system 20 has a
low pressure fuel pump 22 that pumps fuel from a tank 21 to a conduit 23. The
conduit 23 connects to a high pressure fuel pump 24, which supplies a high pressure
common rail 25. Fuel injectors 26 admit fuel from the common rail 25 to the
cylinders of a diesel engine (not shown), which is operative to produce the exhaust
carried by the exhaust line 30. A high pressure relief valve 27 can return fuel from
the common rail 27 to the fuel tank 21.
[0051] In this example, the flow regulating valve 11 is configured to selectively
admit fuel from the conduit 23. Drawing fuel for exhaust line fuel injection from the
conduit 23 has the advantage of eliminating the need for an additional fuel pump
separate from the engine fuel supply system 20, but has the disadvantage that the
pressure in the conduit 23 varies significantly during normal operation of the engine.
[0052] The fuel enters the exhaust line 30 through the nozzle 12. A nozzle can
be any structure that provides a narrow passage for the fuel it passes. In the present
context, the passage is narrow in the sense of causing the fuel to undergo a large
pressure drop in comparison to the pressure drop caused by the exhaust system fuel
supply line 15. The nozzle 12 comprises a check valve, whereby fuel only flows
through the nozzle 12 if the pressure drop across the nozzle exceeds a critical value.
The critical value is preferably from about 0.5 to about 3 atmospheres, more
preferably from about 1 to about 2 atmospheres. Typically the pressure drop is
approximately equal to the gauge pressure of the exhaust system fuel supply line 15,
as the pressure in the exhaust line 30 generally remains close to atmospheric
pressure.
[0053] Figures 2 and 3 illustrate an exemplary nozzle 40, which can be used as
the nozzle 12. The nozzle 40 comprises a poppet 43 biased against a valve seat 41
by a spring 44. When the pressure drop across the nozzle 40 exceeds a critical
amount, the poppet 43 lifts off the seat 41 as shown in Figure 2, allowing fuel to flow
from the inlet 42 through the valve body 45 and to exit as a spray though the orifice
47. When the pressure drop across the nozzle 40 falls below the critical value, the
poppet 43 collapses against the seat 41 blocking the flow as shown in Figure 3. The
pressure drop across the nozzle 40 is preferably primarily a pressure drop across the
opening between the poppet 43 and the seat 41.
[0054] The nozzle 12 is designed for intermittent hydrocarbon injection into the
exhaust line 30. Accordingly, the nozzle 12 must generally be cooled to prevent fuel
remaining in the nozzle 12 between fuel injections from being heated by the exhaust.
If the nozzle 12 is allowed to heat between fuel injections, stagnant fuel within the
nozzle 12 can decompose and eventually clog the fuel injector. To prevent the
stagnant fuel from being excessively heated, the nozzle 40 is provided with a cooling
jacket 46 through which a cooling fluid, such as engine coolant or air, can be
circulated.
[0055] As an alternative, the nozzle 12 can be cooled using an excess fuel flow.
An excess fuel flow is fuel supplied to a nozzle, but not injected through the nozzle
12. Rather, the excess fuel is carried away from the nozzle 12 taking with it heat.
Figures 4 and 5 illustrate a nozzle 50 configured for cooling by an excess fuel flow.
The nozzle 50 has many of the same components as the nozzle 40. The inlet 52
has an opening to cooling jacket 56. When fuel injection is not required, a valve 51
is opened allowing fuel to flow from the inlet 52 through the cooling jacket 56, cooling
the valve body 55 as illustrated in Figure 5. When fuel injection is required, the valve
51 is closed, whereby fuel flows through the valve body 55, as illustrated in Figure 4,
provided that the fuel supply is at sufficient pressure to lift the poppet 43 off its seat
41. When the valve 51 is again opened, the fuel flow through the cooling jacket 56
relieves pressure from the inlet 52, causing the poppet 43 to return to its seat 41,
and preventing fuel flow through the valve body 55 as illustrated in Figure 5.
[0056] Figures 6 and 7 schematically illustrate another exemplary nozzle 140.
The nozzle 140 comprises a poppet 143 biased against a seat 141 by a spring 144.
When the pressure from the inlet 142 is sufficiently great, the poppet 143 lifts off the
seat 141 and fuel flow through the nozzle body 145 as illustrated in Figure 6. When
the pressure drops, the poppet 143 closes with the seat 141 and the fuel flow is
stopped. The nozzle 141 is configured for cooling by circulation of a coolant through
passages 146. If a nozzle is not configured for cooling, it is preferably configured to
be purged with air between fuel injections. An air purge can remove fuel from the
nozzle, which fuel might otherwise form nozzle clogging substances between fuel
injections. In one example, purge air is drawn from a truck braking system.
[0057] The flow regulating valve 11 can be of any suitable type. Examples of
suitable valve types include proportional control valves and pulse width modulated
(PWM) valves. A proportional flow control valve is a valve that regulates the volume
of flow through a degree of opening. A PWM valve is a valve that regulates flow by
rapidly opening and closing, with the volume of flow through the valve being
regulated by the fraction of time the valve is open (the duty cycle). A PWM valve
comprises an actuator. Examples of actuators include solenoids and hydraulic
actuators.
[0058] Figures 8 and 9 are schematic illustrations of an exemplary two port PWM
pulse width modulated solenoid valve 60 that can be used as the flow regulating
valve 11. The valve 60 comprises a valve body 61 defining an inlet 62 and an outlet
63. In a closed position, illustrated by Figure 8, a poppet 64 rests against a seat 65
blocking flow through the valve body 61 between the inlet 62 and the outlet 63. A
solenoid is energized to lift the poppet 64 off its seat 65 as illustrates in Figure 9.
The valve 60 comprises a spring 66 that biases the poppet 64 against the valve seat
65 and an armature 67 that lifts the poppet 64 off the valve seat 65 when the coil 68
is energized. The poppet 64 and seat 65 are configured whereby the pressure of the
supply fluid within the valve body 61 biases the poppet 64 against the seat 65 when
the coil 68 is not energized.
[0059] Figures 10 and 11 illustrate an exemplary three port PWM valve 70 that
can also be used as the flow regulating valve 11. The valve 70 comprises many of
the same components as the valve 60. A principal difference is that when the valve
70 is in the closed position illustrated by Figure 10, fluid from the entrance 62 flows
through the valve body 71 to a return port 72. When the valve 70 is in an open
position illustrated by Figure 11, the poppet 64 rests against a second seat 73
blocking the flow between the entrance 62 and the return port 72.
[0060] Figures 12 and 13 illustrate an exemplary spool valve 80, which is one
type of proportional control valve that can be used as the flow regulating valve 11.
The spool valve 80 can be cylindrically symmetrical except for the entrance port 81,
the exit port 82, and the control passage 83. The valve 80 comprises a valve body
84 within which a spool 85 slides. The axial position of the spool 85 within the valve
body 86 determines a degree of opening of a passage 87, which is a bottleneck for
flow between the entrance port 81 and the exit port 82. Figure 12 shows the valve
80 in a fully closed position and Figure 13 shows the valve 80 in a partially open
position. The exit port 82 is in fluid communication with a chamber 88 through the
control passage 83.
[0061] During operation, the spool 85 moves to an equilibrium position in which
the various forces acting upon the spool 85 are in balance. A solenoid 89 and a
spring 90 exert axial forces on the spool 85. The fluid in the chamber 88 also exerts
an axial on the spool 85. In the equilibrium position, the pressure force from the
. chamber 88, the spring force from the spring 90, and the force from the solenoid 89
balance. Preferably, the forces from the spring 90 and the solenoid 89 are made
largely independent of the axial position of the spool 89. The valve 80 provides a
steady pressure at the exit port 82 that depends predictably on the power provided to
• the solenoid 89.
[0062] ' Configured within the exhaust line 30 are one or more pollution control
devices. Figure 14 provides a schematic illustration of an exemplary power
generation system 110 comprising an exhaust line 100, which can be the exhaust
line 30. The power generation system 110 includes an engine 111, a manifold 112
that guides exhaust from the engine 111 to the exhaust line 100, and a controller 119
that controls the fuel injection system 10 based on data such as data from the
temperature sensor 114. The controller 119 can be the same unit as the controller
14 or a separate unit that issues instructions to the controller 14. Likewise, the
controller 119 can be an engine control unit (ECU) or a separate device that
communicates with the ECU.
[0063] The exemplary exhaust line 100 includes an oxidation catalyst 113, a fuel
reformer 115, a diesel particulate filter 116, an LNT 117, and an SCR catalyst 118.
The fuel injection system 10 is used intermittently to warm the fuel reformer 115, to
heat the DPF 116, and to provide fuel for the fuel reformer 115 for removing oxygen
from the exhaust and producing reformate to regenerate the LNT 117. The fuel
injection system 10 may also be used to provide fuel in pulses over an extended
period of time, as when fuel injection is pulsed to regulate the temperature of the
reformer 115 over extended periods of desulfating the LNT 117.
[0064] A fuel injection system 10 is typically designed to accurately dose fuel to
the exhaust line 30 over a broad range of rates in order to fulfill one or more of the
foregoing function. A broad range typically spans two orders of magnitude. For
heavy duty diesel engines, exemplary ranges are from about 20 to about 1200
grams per minute and from about 40 to about 1200 grams. For a medium duty
diesel engine, from about 20 to about 800 grams per minute is typical. For an
automotive engine, from about 20 to about 400 grams per minute is typical.
Relatively low fuel injection rates are used to heat the reformer 114 and downstream
devices. Relatively high fuel injection rates are used to make the exhaust rich for
LNT regeneration. The accuracy of fuel injection rate control is preferably to within
about ± 5% of the full scale over the entire range, more preferably to within about ±
3%, ad even more preferably to within about ± 1%.
[0065] The fuel injection system 10 preferably remains operative as the exhaust
pipe temperature varies from about 110 °C to about 550 °C. Optionally, the fuel
injection system 10 is configured to inject fuel into the exhaust manifold 112 of the
engine 111. In such a case, the fuel injection system is preferably operative up to
exhaust pipe temperatures of about 600 °C. Operability at these temperatures
includes the property of the fuel injection system not being adversely affected over
the extended periods between fuel injections during which the nozzle 12 remains
idle.
[0066] In order to achieve the required accuracy over the required range using
simple and reliable equipment, the inventors conceived a method of controlling the
flow rate based on the pressure drop across the nozzle 12. The pressure drop
across the nozzle 12 is the difference between the pressure in the exhaust system
fuel supply line 15 and the pressure in the exhaust line 30. The flow rate though the
nozzle 12 depends primarily on the pressure drop across the nozzle 12.
Accordingly, the flow rate can be obtained from a predetermined relationship
between the flow rate and the pressure drop across the nozzle 12.
[0067] The inventors recognized that the pressure in the exhaust system fuel
supply line 15 is the primary determinant of pressure drop across the nozzle 30. In
one embodiment, the pressure in the exhaust line 30 is treated as a constant, in
which case flow rate though the nozzle 12 can be obtained from a predetermined
relationship involving the pressure in the exhaust system fuel supply line 15 as the
only measured pressure. A typical pressure variation for the exhaust line 30 is ±0.2
atm or less. If the check valve of the nozzle 12 requires a pressure drop of at least
about 2.0 atm to open, then the uncertainty in the pressure drop when a constant
exhaust line pressure is assumed will typically be ±10% or less.
[0068] Figure 15 is a plot relating duty cycle of the PWM flow regulating valve 11
to flow rate through nozzle 12 for three different pressures in the exhaust system fuel
supply line 15. The plot shows that the flow rate is reproducibly related to the
pressure and varies linearly with duty cycle.
[0069] In another embodiment, the pressure in the exhaust line 30 is measured or
estimated, in which case the flow rate across the nozzle 12 can be obtained from a
predetermined relationship involving the difference between pressure in the exhaust
system fuel supply line 15 and the pressure in the exhaust line 30.
[0070] The pressure in the exhaust line 30, when required, can be measured
directly. A sensor can be configured to measure a pressure in the exhaust line 30.
Alternatively, a pressure difference between the exhaust line 30 and the exhaust
system fuel supply line 15 can be measured with a device connected to both lines.
As a further option, the pressure drop can be calculated using an estimate of the
exhaust line pressure. The exhaust line pressure can be estimated based on the
operating state of the power generation system 110. For example, the pressure can
be estimated based on the amount of soot accumulated in the DPF 116, which can
in turn be based on an estimate of the amount of soot produced by the engine 111
since the last regeneration of the DPF 116.
[0071] The largest variations in exhaust line pressure occur when the DPF 116 is
designed for intermittent regeneration and is configured downstream from the fuel
injection point. As the DPF 116 accumulates soot, the pressure drop across the
DPF 116 and the pressure upstream from the DPF 116 increase. In such a case,
the pressure upstream of the DPF 116 or the pressure drop across the DPF 116 is
generally measured in order to determine when to regenerate the DPF 116. Thus, in
exhaust lines with the largest pressure variations, the exhaust line pressure is
generally readily available for calculating the pressure drop across the nozzle 12. In
exhaust lines with smaller pressure variations, the pressure drop across the nozzle
12 can be estimated with sufficient accuracy from the pressure in the exhaust
system fuel supply line 15 alone.
[0072] At the beginning of a fuel injection, the flow regulating valve 11 can be set
to a first duty cycle or position based on feed forward control. In one example, feed
forward control is based on an estimated or measured value for the pressure of the
fuel supply for the valve 11. Based on a predetermined relationship, a duty cycle or
degree of opening can be set in order to cause the flow rate to approach a desired
flow rate.
[0073] In one embodiment, an integration is carried out using the pressure
information and a relationship between that information and flow rate in order to
calculate a cumulative fuel injection amount. The pressure information can pertain to
either the pressure in the exhaust system fuel supply line 15 or the pressure drop
across the nozzle 12.
[0074] The cumulative fuel injection amount can be used in control methods. In
one example, a period of fuel injection is terminated when the cumulative fuel
injection amount reaches a target value, indicating that a certain dose of fuel has
been provided. In another example, one or more parameters of fuel pulsation are
adjusted based on the calculated amount. Parameters of fuel pulsation include
pulse width, pulse frequency, and pulse amplitude. The adjustment can be used to
control the amount of fuel injected per pulse and/or the amount of fule injected per
unit time.
[0075] In another embodiment, the pressure information and relationship with flow
rate is used to adjust the flow regulating valve 11 to achieve a desired flow rate in a
feedback control loop. The set point and error for the control loop can be expressed
in terms of pressure in the exhaust system fuel supply line 30, pressure drop across
the nozzle 12, or flow rate through the nozzle 12. If the error is expressed in terms
of pressure or pressure drop, then a set point is determined from a target flow rate
and a predetermined relationship between the flow rate and the pressure or the
pressure drop. If the error is expressed in terms of flow rate, then the predetermined
relationship is used to obtain the flow rate from the pressure or pressure drop. The
flow rate thus obtained is compared to the target flow rate to calculate the error. Any
suitable control algorithm can be used. Examples of potentially suitable control
algorithms include proportional, proportional-integral, proportional-integral-differential
control, and state based control schemes.
[0076] While a typical sampling frequency for a pressure measuring device is
1000 Hz, in one embodiment the controller is operated at 40 Hz. At 40 Hz, the
control algorithm tends to cause noticeable oscillations in the pressure of the
exhaust system fuel supply line 15. Nevertheless, the inventors have found that the
fuel injection system can be operated satisfactorily in spite of these oscillations. The
oscillations can be mitigated by smoothing the pressure data, or by using a moving
time average. A moving time average involves averaging a series of measurements
obtained in a preceding time period. An average can be a simple average or a
weighted average. Operating at 40 Hz has the advantage of allowing the controller
to be integrated into a standard engine control unit (ECU). A standard ECU has a
clock speed of 25 ms.
[0077] The pressure within the exhaust system fuel supply line 15 is measured by
a pressure sensor 13. This sensor may be conveniently integrated with the flow
regulating valve 11. The data from this sensor may be processed in several ways
before being used in a control algorithm. For example, the data may be normalized,
conditioned, and/or filtered. In particular, filtering may be used to remove high
frequency oscillation in the pressure data. High frequency oscillations are often
present in the data when the nozzle 12 comprises a check valve having a spring and
poppet, such as the nozzle 40. The pressure oscillations are caused by the poppet
43, which typically oscillates on the spring 44 whenever there is flow through the
valve body 45. These oscillations cause small variations in the pressure within the
exhaust system fuel supply line 15, which can be detected.
[0078] In one embodiment, the flow regulating valve 11 is a pulse width
modulated valve operated at a relatively low frequency. A low frequency could be 20
hertz, more typically 10 hertz or less. At such a low frequency, the pressure in the
exhaust system fuel supply line 15 varies significantly with the pulsations of the valve
11. In such a case, am average or integration over a series of pressure
measurements can be used in place of instantaneous values in the control algorithm.
For example, an average pressure can be obtained by summing over the previous n
pressure measurements and dividing by n.
[0079] In another embodiment, the pulse width modulate valve is operated at a
relatively high frequency to mitigate pressure variations in the exhaust system fuel
supply line 15 that could affect feedback control based on this pressure. A relatively
high frequency would be about 40 hertz, more typically about 50 hertz or higher.
[0080] Figure 16 is a schematic illustration of another exemplary exhaust line
hydrocarbon injection system 200 conceived by the inventors. The exhaust line
hydrocarbon injection system 200 contains many of the same components as the
hydrocarbon injection system 10, but also contains a pressure accumulator 16. The
pressure accumulator 16 smoothes pressure variation in the supply pressure to the
flow regulating valve 11 and thus reduces perturbations affecting the flow rate. The
accumulator 16 can be as simple as a length of pipe with a diameter significantly
larger than that of the surrounding pipe. The. hydrocarbon injection system 200 also
comprises a pressure sensor 18 upstream from the flow regulating 11. This
pressure sensor can be used for fault diagnostics and to provide open loop control in
the event that closed loop control of the flow regulating 11 cease to function
correctly.-
[0081] The hydrocarbon injection system 200 comprises a nozzle 12 configured
for cooling with an excess fuel flow. Check valve 17 is provided to control the flow of
fuel used for cooling. The nozzle 50 can be used as the nozzle 12 with the check
valve 51 in place of the check valve 17.
[0082] The exhaust line hydrocarbon injection systems disclosed herein
preferably includes some form of fault detection Exhaust system components are
operated over long periods of time under conditions that may cause failure in the
best designed systems. A failure in a hydrocarbon fuel injection system can have
significant consequences. An over injection of fuel can cause overheating of and
damage to expensive exhaust system components. Under injection can cause
under performance of pollution control devices. If the reformer 114 is designed for
auto-thermal operation, under injection can cause over heating by reducing the
extent of endothermic steam reforming reactions while the rate of exothermic
combustion reactions remains essentially constant.
[0083] Severe faults in the fuel injection system can be detected by conventional
methods. For example, a leak can be detected by a rapid fall of the pressure in the
exhaust system fuel supply line 15 after the end of a fuel injection, provided the fuel
is not used to cool the nozzle 12 between injections. When the flow regulating valve
11 comprises a solenoid, the proper functioning of that solenoid can be determined
by electrical means, such as by measuring the current to the solenoid or by
measuring a current induced by the solenoid motion. Various techniques are
available for determining whether the solenoid is functioning as commanded from
this type of information.
[0084] More difficult to detect types of faults include partial clogging and sticking
of the nozzle 12. In one embodiment, fault detection is accomplished by comparing
a flow rate determined from the pressure drop across the nozzle 12, or from the
pressure in the exhaust system fuel supply line 15, to a flow rate determined from a
different source. An example of a different source that can be used to determine the
flow rate is the pressure drop across the flow regulating valve 11 or the pressure
upstream from the valve 11 in combination with the duty cycle of the valve 11, when
the valve 11 is a PWM valve. Another example of a different source is a flow meter.
A significant discrepancy between two flow rates determined from different sources
indicates a fault. The discrepancy can be signaled and/or used to trigger a fault
correction procedure.
[0085] A temperature reading in the exhaust line 30 can be used to determine a
flow rate using a thermal model. For example, a thermal model can be used to
predict the temperature of the fuel reformer 115 as a function of the flow rate. The
model can take into account the fuel injection rate, the exhaust conditions, and the
properties of the reformer 115. If the result of applying the thermal model is
inconsistent with a temperature measured by the temperature measuring device 114,
a difference between the actual fuel injection rate and the fuel injection rate used as
an input to the model can be inferred.
[0086] Another of the inventors' concepts is to detect faults through the frequency
spectrum of the pressure in the exhaust system fuel supply line 15. Figures 17 and
18 are plots of exemplary frequency spectra obtained using a fully open flow control
valve 11 and a 43 psi supply pressure. Figure 17 is the base case, and shows a
large peak at 380 Hz and a comparatively small peak at 245 Hz. Figure 18 was
obtained by simulating a partial obstruction of the nozzle. With the obstruction
present, the spectrum is greatly altered, with a single peak at about 170 Hz. While
the exact locations of these peaks are expected to depend on many particulars of
the system used in this experiment, differences like this can be expected in most
systems. If in some particular system variations in these frequency spectra are not
observed as the nozzle 12 clogs, it is suggested that a different nozzle be used,
preferably one in which the size of the opening between the poppet and the seat
varies continuously with flow rate through the nozzle.
[0087] In one embodiment, sticking of the nozzle 12 is determined from the
pressure in the exhaust system fuel supply line 15. For example, oscillations of a
poppet 43 in the nozzle 40 can cause measurable high frequency oscillation in the
pressure. These oscillations begin when the poppet 43 lifts off its seat 41 and cease
when the poppet 43 returns to rest on its seat 41. If the pressure at which these
oscillations begin is significantly higher than the pressure at which these oscillations
end, sticking can be inferred.
[0088] Fault detection based on frequency spectra may be enhanced by the use
of a proportional control valve for the flow regulating valve 18. The use of a
proportional control valve eliminates pressure fluctuations caused by a PWM valve
and thus increases the signal to noise ratio in the frequency spectra.
[0089] Detection of a fault can trigger any suitable response. Examples of
suitable responses include altering a driver by illuminating a light, recording a fault
code in an electronic method, and initiating a fault correction procedure. A fault
correction procedure could include disabling feedback control until the fault is
cleared.
[0090] In one embodiment, upon detection of a fault in feedback control of the
flow regulating valve 11, the power generation system 1 switches from feedback to
open loop (feed forward) control. Preferably, feed forward control involves a
pressure measurement upstream from the flow regulating valve 11. The duty cycle
can be set based on a predetermined relationship between the duty cycle of the flow
regulating valve 11 and the flow rate through the valve, the relationship being a
function of the pressure.
[0091] Advantages of configuring the system 1 for feed forward control based on
a pressure measured upstream from the flow regulating valve 11 include the
possibility of operating in the event of failure of the device measuring pressure in the
exhaust system fuel supply line 15 and the possibility of using the upstream and
downstream pressure indication to detect faults through. A flow rate determined
using the upstream pressure reading can be compared to a flow rate estimated
without that reading in order to detect faults.
[0092] While the engine 111 is preferably a compression ignition diesel engine,
the various concepts of the inventors are applicable to power generation systems
with lean-burn gasoline engines or any other type of engine that produces an oxygen
rich, NOx-containing exhaust. For purposes of the present disclosure, NOx consists
of NO and NO2.
[0093] The power generation system 110 can have any suitable type of
transmission. A transmission can be a conventional transmission such as a counter-
shaft type mechanical transmission, but is preferably a CVT. A CVT can provide a
much larger selection of operating points than can a conventional transmission and
generally also provides a broader range of torque multipliers. The range of available
operating points can be used to control the exhaust conditions, such as the oxygen
flow rate and the exhaust hydrocarbon content. A given power demand can be met
by a range of torque multiplier-engine speed combinations. A point in this range that
gives acceptable engine performance while best meeting a control objective, such as
minimum oxygen flow rate, can be selected. In general, a CVT prevents or
minimizes power interruptions during shifting.
[0094] Examples of CVT systems include hydrostatic transmissions, rolling
contact traction drives, overrunning clutch designs, electrics, multispeed gear boxes
with slipping clutches, and V-belt traction drives. A CVT may involve power splitting
and may also include a multi-step transmission.
[0095] A preferred CVT provides a wide range of torque multiplication ratios,
reduces the need for shifting in comparison to a conventional transmission, and
subjects the CVT to only a fraction of the peak torque levels produced by the engine.
These advantages an be achieved using a step-down gear set to reduce the torque
passing through the CVT. Torque from the CVT passes through a step-up gear set
that restores the torque. The CVT is further protected by splitting the torque from the
engine and recombining the torque in a planetary gear set. The planetary gear set
mixes or combines a direct torque element transmitted from the engine through a
stepped automatic transmission with a torque element from a CVT, such as a band-
type CVT. The combination provides an overall CVT in which only a portion of the
torque passes through the band-type CVT.
[0096] The fuel reformer 115 is a device that converts heavier fuels into lighter
compounds without fully combusting the fuel. The fuel reformer 115 can be a
catalytic reformer or a plasma reformer. Preferably, the fuel reformer 115 is a partial
oxidation catalytic reformer comprising a steam reforming catalyst. Examples of
reformer catalysts include precious metals, such as Pt, Pd, and Rh, and oxides of Al,
Mg, and Ni, the latter group being typically combined with one or more of CaO, K2O,
and a rare earth metal such as Ce to increase activity. The fuel reformer 115 is
preferably small compared to an oxidation catalyst that is designed to perform its
primary functions at temperatures below 450 °C. The reformer 115 is generally
operative at temperatures within the range of about 450 to about 1100 °C.
[0097] The LNT 117 can comprise any suitable NOx-adsorbing material.
Examples of NOx adsorbing materials include, without limitation, oxides, carbonates,
and hydroxides of alkaline earth metals such as Mg, Ca, Sr, and Ba or alkali metals
such as K or Cs. Generally, the NOx-adsorbing material is an alkaline earth oxide.
The adsorbent is typically combined with a binder and either formed into a self-
supporting structure or applied as a coating over an inert substrate.
[0098] The LNT 117 also comprises a catalyst for the reduction of NOx in a
reducing environment. The catalyst can be, for example, one or more transition
metals, such as Au, Ag, and Cu, group VIII metals, such as Pt, Rh, Pd, Ru, Ni, and
Co, Cr, or Mo. A typical catalyst includes Pt and Rh. Precious metal catalysts also
facilitate the adsorbent function of alkaline earth oxide adsorbers.
[0099] Adsorbents and catalysts according to the present invention are generally
adapted for use in vehicle exhaust systems. Vehicle exhaust systems create
restriction on weight, dimensions, and durability For example, a NOx adsorbent bed
for a vehicle exhaust system must be reasonably resistant to degradation under the
vibrations encountered during vehicle operation
[0100] The ammonia-SCR catalyst 118 is functional to catalyze reactions
between NOx and NH3 to reduce NOx to N2 in lean exhaust. Examples of SCR
catalysts include some oxides of metals such as Cu, Zn, V, Cr, Al, Ti, Mn, Co, Fe, Ni,
Pd, Pt, Rh, Mo, W, and Ce, and 'some zeolites, such as ZSM-5 or ZSM-11,
substituted with metal ions such as cations of Cu, Co, Ag, Zn, or Pt. Preferably, the
ammonia-SCR catalyst 118 is designed to tolerate temperatures required to
desulfate the LNT117.
[0101] Although not illustrated in any of the figures, a clean-up catalyst can be
placed downstream from the other aftertreatment device. A clean-up catalyst is
preferably functional to oxidize unbumed hydrocarbons from the engine 111, unused
reductants, and any H2S released from the LNT 117 and not oxidized by the
ammonia-SCR catalyst 118. Any suitable oxidation catalyst can be used. To allow
the clean-up catalyst to function under rich conditions, the catalyst may include an
oxygen-storing component, such as ceria. Removal of H2S, when required, may be
facilitated by one or more additional components such as NiO, Fe2O3, MnO2, CoO,
and CrO2.
[0102] The invention as delineated by the following claims has been shown
and/or described in terms of certain concepts, components, and features. While a
. particular component or feature may have been disclosed herein with respect to only
one of several concepts or examples or in both broad and narrow terms, the
components or features in their broad or narrow conceptions may be combined with
one or more other components or features in their broad or narrow conceptions
wherein such a combination would be recognized as logical by one of ordinary skill in
the art. Also, this one specification may describe more than one invention and the
following claims do not necessarily encompass every concept, aspect, embodiment,
or example described herein.
Industrial Applicability
[0103] The present invention is useful in controlling emissions from diesel and
lean-burn gasoline engines.
The claims are:
1. A power generation system (110), comprising:
an engine (111) operative to produce an exhaust that is channeled
through an exhaust line (100);
a fuel pump (22) operative to pump fuel from a fuel tank (21) to a
conduit (23);
a flow regulating valve (11, 60, 70, 80) configured to selectively admit
fuel from the conduit (23) and to release the fuel to an exhaust system fuel supply
line (15);
a nozzle (12, 40, 50) configured to admit fuel from the exhaust system
fuel supply line (15) to the exhaust line (30, 100);
a pressure measuring device (13) configured to obtain a pressure
measurement from the exhaust system fuel supply line (15); and
a controller (14, 119) configured to control the flow regulating valve (11,
60, 70, 80) based on the pressure measurement and a predetermined relationship
between the flow rate through the nozzle (12, 40, 50) and one of:
i) the pressure in the exhaust system fuel supply line (15) and
ii) a difference between the pressure in the exhaust system fuel
supply line (150 and a pressure of the exhaust line (30, 100).
2. The system (110) of claim 1, wherein the fuel pump (21) supplies fuel
to the engine (111).
3. The system (110) of claim 2, further comprising an accumulator (16)
configured between the conduit (23) and the flow regulating valve (11, 60, 70, 80)
and functional to ameliorate pressure fluctuations in the fuel entering the flow
regulating valve (11, 60, 70, 80).
4. The system (110) of claim 1, wherein the flow regulating valve (11, 60,
70, 80) is a pulse width modulated valve (60, 70).
5. The system (110) of claim 4, wherein the pulse width modulated valve
(60, 70) is configured to operate at a frequency of about 50 Hz or more.
6. The system (110) of claim 4, wherein the pulse width modulated valve
(60, 70) is configured to operate at a frequency of about 10 Hz or less.
7. The system (110) of claim 4, wherein the controller (14, 119) is
configured to use a pressure or a flow rate that is averaged or integrated over a
series of the pressure measurements in controlling the flow regulating valve (60, 70).
8. The system (110) of claim 1, further comprising a valve (17) that allows
fuel from the exhaust system fuel supply line (15) to return to the fuel tank (21).
9. The system (110) of claim 1, further comprising:
a fuel reformer (115) or a diesel oxidation catalyst (116) configured
within the exhaust line. (30, 100);
wherein the nozzle (12, 40, 50) is configured to inject the fuel into the
exhaust line (30, 100) upstream from the fuel reformer (115) or the diesel oxidation
catalyst (116).
10. The system (110) of claim 1, further comprising:
a lean NOx trap (117) or a diesel particulate filter (116) configured
within the exhaust line (30,100);
wherein the controller (14, 119) is configured to initiate fuel flow
through the nozzle (12, 40, 50) intermittently to regenerate the lean NOx trap (117)
or a diesel particulate filter (116).
11. The system (110) of claim 1, wherein the flow regulating valve (11, 60,
70, 80) is a proportional flow control valve (80).
12. The system (110) of claim 1, wherein the nozzle (12, 40, 50) comprises
a check-valve.
13. The system (110) of claim 12, wherein:
the controller (14, 119) is configured to obtain a frequency spectrum of
the exhaust system fuel supply line pressure and to analyze the frequency spectrum
to check for an exhaust line fuel injection system fault.
14. The system (110) of claim 1, further comprising a diesel particulate
filter (116) configured in the exhaust line (30, 100) and a second pressure measuring
device configured to obtain a measurement of the pressure of the exhaust line (30,
100).
15. A method of providing fuel to an exhaust aftertreatment system,
comprising:
passing the fuel through a regulating valve (11, 60, 70, 80) comprising
an inlet (62, 81) and an outlet (63, 83), the inlet (62, 81) being connected to a first
fuel line (23), the outlet being connected to an exhaust system fuel supply line (15);
passing the fuel from the exhaust system fuel supply line (15) to an
exhaust line (30,100) through a nozzle (12, 40, 50, 60);
obtaining an indication of a pressure difference between the exhaust
system fuel supply line (15) and the exhaust line (30,100);
providing a predetermined relationship between the pressure difference
and a flow rate through the nozzle (12, 40, 50, 60); and
controlling the flow rate through the nozzle (12, 40, 50, 60) using the
regulating valve (11, 60, 70, 80), the predetermined relationship, and feedback from
the indication of the pressure difference.

An exhaust line fuel injection system (1) and
associated methods of operation and control are
disclosed. The fuel passes through a regulating valve
(11, 60, 70, 80) having an inlet (62, 81) connected to
a pressurized fuel source (20) and an outlet (63, 82)
connected to an exhaust system fuel supply line (15).
The exhaust system fuel supply line (15) is connected
to a nozzle (12, 40, 50, 60), which generally comprises
a check-valve and is configured to inject the fuel into
the exhaust line (30, 100) . Using a pressure measuring
device (13), an indication of the exhaust system fuel
supply line pressure is obtained. A controller (14,
119) provides control over the flow regulating valve
(11, 60, 70, 80) using feedback from the pressure
indication and a predetermined relationship between the
flow rate through the nozzle (12, 40, 50, 60) and one
of the exhaust system fuel supply line pressure and the
pressure drop across the nozzle (12, 40, 50, 60) . The
method can be implemented with a single pressure
measuring device (13) . The same pressure measurements,
especially their frequency spectrum, can be used to
detect system faults.