DESCRIPTION
FUEL-CETANE-NUMBER ESTIMATION METHOD AND APPARATUS
TECHNICAL FIELD
[0001] The present invention relates to a fuel-Cetane-number estimation method of
estimating a Cetane number of fuel used in a compression ignition type inner combustion
engine such as a diesel engine, and an apparatus for implementing the fuel-Cetane-number
estimation method.
10 BACKGROUND
[0002] Fuel such as light oil is used in a compression ignition type inner combustion
engine such as a diesel engine. However, the Cetane numbers of commercially-supplied
fuels are not necessarily constant. Thus, usage of fuel having a Cetane number other than a
predetermined Cetane number may cause a misfire and white smoke, as well as an increase in
15 harmful substances contained in exhaust gas and reduction of the fuel consumption
performance. As a way to solve such a problem, a Cetane number may be estimated for the
fuel actually used in an internal combustion engine, and the estimation result may be reflected
in the operation control of the internal combustion engine.
[0003] There are various methods proposed to estimate a Cetane number of fuel, such as
20 those disclosed in Pate.nt Documents 1 and 2.
In Patent Document 1, when an internal combustion engine is in an idle state, a fuelinjection
timing is gradually retarded to make a combustion state gradually unstable and cause
a misfire on purpose. Then, the amount of retard at which the misfire occurs is determined,
and the Cetane number of the fuel is estimated on the basis of a map that specifies in advance
25 a relationship between the amount of retard and the Cetane number.
In Patent Document 2, a Cetane number is estimated on the basis of a fuel-injection
timing at which a relationship "~PI ~CA = a" is substantially satisfied. ~p is a difference
between: an in-cylinder pressure peak value after a top dead center of compression due to
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combustion caused by fuel injection; and an in-cylinder pressure peak value of a top dead
center of compression or in the vicinity of the same due to combustion caused by pilot
injection before fuel injection or compression of in-cylinder gas due to piston motion. /1CA
is a difference in crank angles corresponding to the respective in-cylinder pressure values.
Citation List
Patent Literature
[0004]
Patent Document l: JP2007-l54699A
l 0 Patent Document 2: JP2009-l44634A
SUMMARY
Problems to be Solved
[0005] In Patent Document 1, a Cetane number is estimated on the basis of a misfire
15 caused in a combustion state by retarding a fuel-injection timing. However, a misfire is a
phenomenon that occurs as a result of the combustion state becoming extremely unstable, and
thus unfavorable for an internal combustion engine. Further, occurrence of a misfire in a
combustion state leads to a considerable decrease in the fuel consumption performance, which
is another problem.
20 In Patent Document 2, the Cetane number is estimated on the basis of in-cylinder
pressure peak values. Thus, it is necessary to provide an additional in-cylinder pressure
sensor in an internal combustion engine to implement the estimation method, which results in
an increase in the implementation cost.
[0006] The present invention was made in view of the above issues. An object is to
25 provide a method and an apparatus for estimating a fuel-Cetane number that can be
implemented with a simplified and inexpensive configuration that does not cause a misfire in
a combustion state.
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Solution to the Problems
[0007]
To achieve the above object, a fuel-Cetane-number estimation method of
estimating a Cetane number of a fuel used in an internal combustion engine which performs
compression ignition combustion according to the present invention includes: preparing in
5 advance a map which specifies a relationship between the Cetane number of the fuel and a
control parameter of the internal combustion engine at which NOx concentration of exhaust
gas of the internal combustion engine reaches a predetermined concentration value;
controlling the control parameter of the internal combustion engine variably to detect
transition of the NOx concentration of the exhaust gas of the internal combustion engine;
l 0 obtaining the control parameter of the internal combustion engine at which the NOx
concentration has reached the predetermined concentration value on the basis of the detected
NOx concentration; and estimating the Cetane number which corresponds to the obtained
control parameter on the basis of the map.
[0008] According to the present invention, it is possible to estimate a Cetane number
15 without causing a misfire in the combustion state of the internal combustion engine on the
basis of the control parameter at which the NOx concentration of the exhaust gas of the
internal combustion engine has reached the predetermined value by focusing on the NOx
concentration of the exhaust gas which shows a remarkable change in response to the variable
control of the control parameter of the internal combustion engine. Especially, it is possible
20 to estimate a Cetane number with a simplified and inexpensive configuration by preparing in
advance the map which specifies a relationship between the Cetane number of the fuel and the
control parameter at which the NOx concentration of the exhaust gas of the internal
combustion engine reaches the predetermined concentration value by a method based on a test,
an experiment or a theory, and applying an actual measurement value ofNOx concentration of
25 the exhaust gas to the map.
[0009] In one embodiment of the present invention, the method further includes:
detecting a state factor which affects the NOx concentration of the exhaust gas of the internal
combustion engine; and correcting the map by using a predetermined correction value which
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corresponds to the detected state factor.
The NOx concentration of the exhaust gas of the internal combustion engine may be
affected by a particular state factor (e.g. an engine state or an environmental condition).
Thus, accuracy of the map may decrease in accordance with a change in the state factor. In
5 the present embodiment, the map is corrected by a correction value corresponding to a
detection result of the state factor, which makes it possible to eliminate the influence of a
change in the state factor and to estimate a Cetane number accurately under various
conditions.
[001 0] Further, the method may further include: detecting a state factor which affects the
10 NOx concentration of the exhaust gas of the internal combustion engine; and correcting the
predetermined concentration value by using a predetermined correction value which
corresponds to the detected state factor.
The influence of a change in the state factor can be also eliminated by correcting the
predetermined concentration value which is used as a standard for determining the NOx
15 concentration. In the present embodiment, the predetermined concentration value is
corrected by a correction value corresponding to a detection result of the state factor, which
makes it possible to estimate a Cetane number accurately under various conditions.
[00 11] Specifically, the state factor may include at least one of a temperature of a coolant
water, a temperature of an inlet of a cylinder, a pressure of the inlet of the cylinder, oxygen
20 concentration of the cylinder, an amount of intake air, a pressure of the intake air, or a
humidity of the intake air ofthe internal combustion engine.
[00 12] In another embodiment of the present invention, execution of the fuel-Cetanenumber
estimation method is automatically started if a predetermined starting condition is
satisfied.
25 According to the present embodiment, the fuel-Cetane-number estimation method is
executed if a starting condition suitable to execute the control for estimating a Cetane number
is satisfied, such as detection of an idling state and detection of operation of an execution
button for starting a control by an operator.
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[0013] The control parameter may be an amount of retard in a fuel injection timing in a
combustion chamber of the internal combustion engine. Furthermore, the control parameter
may be an amount of recirculation of the exhaust gas to the intake air of the internal
combustion engine.
5 The NOx concentration of the exhaust gas is affected by an amount of retard of a fuelinjection
timing or an amount of recirculation of the exhaust gas to the intake air, which are
thus suitable as control parameters for a transition control for estimating a Cetane number.
[0014] To achieve the above object, a fuel-Cetane-number estimation apparatus for
estimating a Cetane number of a fuel used in an internal combustion engine which performs
10 compression ignition combustion according to the present invention includes: a NOx
concentration detection unit for detecting NOx concentration of exhaust gas of the internal
combustion engine; an internal-combustion-engine control unit for variably controlling a
control parameter of the internal combustion engine; a storage unit for storing a map which
specifies a relationship between the Cetane number of the fuel and the control parameter of
15 the internal combustion engine at which the NOx concentration of the exhaust gas of the
internal combustion engine reaches a predetermined concentration value; and a Cetanenumber
estimation unit for variably controlling the control parameter with the internalcombustion-
engine control unit to vary the NOx concentration of the exhaust gas of the
internal combustion engine, obtaining the control parameter at which the NOx concentration
20 reaches the predetermined concentration value, and estimating the Cetane number which
corresponds to the obtained control parameter on the basis of the map.
[0015] With the above apparatus, it is possible to execute the above method of estimating
a Cetane number of a fuel (including the above embodiments) appropriately.
[0016] The fuel-Cetane-number estimation apparatus may further include: a state-factor
25 detection unit for detecting a state factor which affects the NOx concentration of the exhaust
gas of the internal combustion engine; and a correction unit for correcting the map by using a
predetermined correction value which corresponds to the state factor detected by the statefactor
detection unit.
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With the above correction unit, it is possible to eliminate the influence of a change in the
state factor and to estimate a Cetane number accurately under various conditions by correcting
the map with a correction value corresponding to a detection result of the state factor.
[0017] Further the fuel-Cetane-number estimation apparatus may include: a state-factor
5 detection unit for detecting a state factor which affects the NOx concentration of the exhaust
gas of the internal combustion engine; and a correction unit for correcting the predetermined
concentration value by using a predetermined correction value which corresponds to the state
factor detected by the state-factor detection unit.
With the above correction unit, it is possible to eliminate the influence of a change in the
1 0 state factor and to estimate a Cetane number accurately under various conditions, by
correcting the predetermined value with a correction value corresponding to a detection result
of the state factor.
[0018] Further, the NOx concentration detection unit may also be used as a NOx sensor
used to calculate a purification rate in an exhaust-gas purification device for purifying the
15 exhaust gas ofthe internal combustion engine.
There are an increasing number of vehicles equipped with an exhaust-gas purification
device in response to tightening of the exhaust-gas regulations. Such an exhaust-gas
purification device often includes a NOx sensor for calculating a purification rate. Thus,
using such a NOx sensor also as a NOx concentration detection unit of the present invention
20 makes it no longer necessary to provide an additional sensor or the like, which is effective in
reducing cost.
Advantageous Effects
[0019] According to the present invention, it is possible to estimate a Cetane number
25 without causing a misfire in the combustion state of the internal combustion engine on the
basis of the control parameter at which the NOx concentration of the exhaust gas of the
internal combustion engine has reached the predetermined value by focusing on the NOx
concentration of the exhaust gas which shows a remarkable change in response to the variable
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control of the control parameter of the internal combustion engine. Especially, it is possible
to estimate a Cetane number with a simplified and inexpensive configuration by preparing in
advance a map which specifies a relationship between the Cetane number of the fuel and the
control parameter at which the NOx concentration of the exhaust gas of the internal
5 combustion engine reaches the predetermined concentration value by a method based on a test,
an experiment or a theory and applying an actual measurement value ofNOx concentration of
the exhaust gas to the map.
l 0 BRIEF DESCRIPTION OF ORA WINGS
[0020] FIG. l is a configuration diagram of an overall structure of a fuel-Cetane-number
estimation apparatus according to the present embodiment.
FIG. 2 is a conceptual diagram of an interior configuration of ECU illustrated as
function blocks for implementing a method of estimating a fuel-Cetane-number.
15 FIG. 3 is a graph showing a change in NOx concentration of exhaust gas in a case where
the amount of retard of a fuel-injection timing is controlled variably.
FIG. 4 is an example of a map that specifies a correlation between the amount of retard
and the Cetane number of fuel used in an engine.
FIG. 5 is a flowchart of control operation of a fuel-Cetane-number estimation apparatus
20 according to the present embodiment.
FIG. 6 is a conceptual diagram of an interior configuration ofECU according to the first
modified embodiment, illustrated as function blocks for implementing the method of
estimating a fuel-Cetane-number.
FIG. 7 is a graph of relationships between a control parameter and NOx concentration of
25 exhaust gas at different coolant-water temperatures, for an engine using a fuel having the
same Cetane number.
FIG. 8 is a map including the amount of correction according to the first modified
embodiment.
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FIG. 9 is a characteristic graph including the amount of correction according to the
second modified embodiment.
5 DETAILED DESCRIPTION
[0021] Embodiments of the present invention will now be described in detail with
reference to the accompanying drawings. It is intended, however, that unless particularly
specified, dimensions, materials, shapes, relative positions and the like of components
described in the embodiments shall be interpreted as illustrative only and not limitative of the
10 scope of the present invention.
[0022] FIG. 1 is a configuration diagram of an overall structure of a fuel-Cetane-number
estimation apparatus according to the present embodiment.
The reference numeral l is a diesel engine which is an internal combustion engine
including a fuel-injection device of a common-rail type (hereinafter, referred to as an "engine"
15 where appropriate). Fuel is directly injected into a combustion chamber of each cylinder
from a fuel injection valve, and thereby compression ignition combustion is performed. The
fuel-injection timing and the amount of injection of the fuel injection valves are electrically
controlled by an electronic control unit (hereinafter, suitably referred to as "ECU") 10.
[0023] The engine l includes an exhaust turbine 2a and an exhaust turbocharger 2 having
20 a compressor 2b that is driven coaxially with the exhaust turbine 2a. Air incorporated from
an intake pipe 3 is compressed and heated by the compressor 2b, and then cooled by an
intercooler 4 disposed at the downstream side of the compressor 2b. The supply air cooled
by the intercooler 4 is supplied to a combustion chamber 7 via an intake manifold 6.
[0024] Compression ignition combustion is performed in the combustion chamber 7, and
25 exhaust gas generated by the combustion is discharged to the outside from an exhaust pipe 9
via an exhaust manifold 8. An exhaust-gas recirculation (EGR) pipe 11 is branched from the
exhaust pipe 9 at the upstream side of the exhaust turbine 2a and connected to the intake pipe
3 at the downstream side of a throttle valve 5, so that a part of exhaust gas is re-circulated.
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An EGR cooler 12 is disposed in the EGR pipe 11, so that the high-temperature exhaust gas is
cooled. The amount of recirculation of the EGR gas (EGR amount) is adjusted by the EGR
valve 13 disposed in the EGR pipe 11.
[0025] The exhaust gas of the engine 1 drives the exhaust turbine 2a disposed in the
5 exhaust pipe 9a to serve as a power source ofthe compressor 2b, before being supplied to an
exhaust aftertreatrnent system 14. The exhaust aftertreatment system 14 is formed integrally
with an oxidation catalyst (DOC) 15 and a diesel particulate filter (DPF) 16. The DOC 15
utilizes oxygen contained in the exhaust gas to oxidize and break down non-combusted
substances that mainly contain hydrocarbon (HC) in the exhaust gas into water (H20) and
10 carbon dioxide (C02).
[0026] The DPF 16 collects particulate matters (PM) contained in the exhaust gas to
purify the exhaust gas. When the amount of accumulated PM collected by the DPF 16
increases, the purifying performance decreases. Thus, regeneration process is performed on
the DPF 16 at a predetermined timing. When the DPF 16 is regenerated, the DOC 15 at the
15 upstream side oxidizes fuel in the exhaust gas to heat the exhaust gas, and the exhaust gas
having a high temperature is supplied to the DPF 16, thereby combusting the accumulated PM.
[0027] In the exhaust pipe 9 at the downstream side of the exhaust aftertreatment system
14, disposed is a NOx selective catalytic reduction (SCR) 17 (hereinafter, referred to as
"denitration catalyst") for decomposing nitrogen oxide (NOx) in the exhaust gas into water
20 (H20) and nitrogen (N2). A urea injection nozzle 18 for spraying urea solution, which is a
reductant, into the exhaust pipe 9 is disposed at the upstream side of the denitration catalyst
17.
[0028] When the urea solution is sprayed to the exhaust gas, ammonia is produced from
the urea solution by hydrolysis as shown in the following formula (1).
25 (NH2)2CO + H20 - C02 + 2NH3 ( 1)
Further, the denitration reaction between the ammonia (NH3) and the nitrogen oxide
(NOx) at the denitration catalyst 17 is varied depending on the reaction rate, taking place
according to one ofthe following formulas (2) to (4).
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4NH3 + 4NO+O ~ 4N2 + 6H20 (2)
2NH3 + NO+N02 ~ 2N2 + 3H20 (3)
8NH3 + 6N02 ~ 7N2 + 12H20 (4)
[0029] The ECU 10 obtains detection values of NOx sensors 19a and 19b disposed at the
5 upstream side and the downstream side of the denitration catalyst 17, calculates the NOx
purification rate at the denitration catalyst 17, and performs various controls such as a control
of the additive amount of the urea solution on the basis of the calculation result. For
instance, the ECU 10 obtains a target NOx purification rate on the basis of the operation state
(such as an engine load and a rotation speed) ofthe engine 1 and the catalyst temperature of
10 the denitration catalyst 17, and compares the target NOx purification rate to an actual NOx
purification rate calculated on the basis of detection values detected by the NOx sensors 19a
and 19b, so as to control the additive amount of reductant or the timing to start addition.
[0030] In the present embodiment, in addition to the above general control, the ECU 10
achieves efficient operation by estimating a Cetane number of fuel used in the engine 1, and
15 reflecting the estimation result on a normal operation control (e.g. by performing correction
based on the estimation results on engine-control parameters in a normal operation such as a
fuel-injection control parameter, an EGR control parameter, and a variable-turbo control
parameter). Specifically, the ECU 10 functions as an arithmetic unit for implementing the
method of estimating a Cetane number according to the present invention.
20 {0031] FIG. 2 is a conceptual diagram of an interior configuration of the ECU 10
illustrated as function blocks for implementing a method of estimating a fuel-Cetane-number.
A control-parameter control part 20 performs a variable control on a control parameter
of the engine 1 by transmitting control signals. The control parameters to be controlled here
only need to be parameters related to the operation state of the engine 1 and capable of
25 affecting the NOx concentration in the exhaust gas. Preferably, the amount of retard of the
fuel-injection timing or the EGR amount may be used as the control parameters.
The series of fuel-Cetane-number estimation controls described below can be applied
regardless of the type of control parameters. Hereinafter, to make it easier to understand, the
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controls will be described in detail with reference to a case where the amount of retard of the
fuel-injection timing is used as a control parameter.
[0032] Here, FIG. 3 is a graph showing a change in NOx concentration of exhaust gas in a
case where the amount of retard MI of a fuel-injection timing is controlled variably. The
5 horizontal axis is the amount of retard MI of the fuel-injection timing, and the vertical axis is
the NOx concentration C of exhaust gas. Further, in FIG. 3, the solid line (a) represents the
characteristic of a fuel having a higher Cetane number, while the dotted line (b) represents the
characteristic of a fuel having a lower Cetane number.
[0033] The graph shows a trend that, when the amount of retard MI of the fuel injection
I 0 timing is gradually increased, the combustion state of the engine 1 gradually becomes
unstable, and the NOx concentration C of exhaust gas decreases. In the characteristic graph,
the slope of the amount of retard MI becomes steep across a predetermined value, and the
decreasing speed of NOx concentration increases. The amount of retard at which the slope
becomes steep depends on the Cetane number. As illustrated in FIG. 3, the slope changes
15 rapidly at a smaller amount of retard in the characteristic graph (b) having a lower Cetane
number than in the characteristic graph (a) having a higher Cetane number.
[0034] A storage part 21 of the ECU 10 stores in advance a NOx-concentration threshold
value CO (reference numeral 22 in FIG. 2) which is information required to estimate a Cetane
number, and a map 23. FIG. 3 illustrates an example of the NOx-concentration threshold
20 value CO stored in the storage part 21. The NOx-concentration threshold value CO is set so
as to cross lines in a region of the characteristic graph where the slope rapidly changes.
[0035] Here, the amount of retard at which a line in the characteristic graph crosses the
NOx-concentration threshold value CO is defined as MIO. In the example of FIG. 3, the
retard amount MIO of the lines (a), (b) in the characteristic graph is respectively MIO-h and
25 MI0-1. The amount of retard MIO depends on the Cetane number of fuel used in the engine 1.
The map 23 specifies the correlation between the amount of retard MIO and the Cetane
number.
Here, FIG. 4 is an example of a map 23 which specifies a correlation between the
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amount of retard MIO and the Cetane number CN of fuel used in an engine. According to
the map 23, the Cetane numbers corresponding to the amounts of retard MIO-h and MI0-1
illustrated in FIG. 3 are estimated to be respectively CN 1 and CN 2.
[0036] As illustrated in FIG. 2, a Cetane-number estimation part 24 of the ECU 10
5 determines the NOx concentration of the exhaust gas by obtaining a detection value detected
by the NOx sensor 19a at the upstream side, and estimates a Cetane number by the above
process on the basis of the NOx concentration threshold value CO and the map 23 read out
from the storage part 21.
[0037] With reference to FIG. 5, the control operation of the fuel-Cetane-number
10 estimation device according to the present embodiment will be described in sequence.
FIG. 5 is a flowchart of control operation of a fuel-Cetane-number estimation apparatus
according to the present embodiment.
First, under a condition in which the engine 1 is in normal operation, the ECU 10
determines whether a predetermined starting condition is satisfied (step S1 01). If the
15 starting condition is satisfied (step S101: YES), the ECU 10 starts a Cetane-number
determination operation mode to execute estimation of a Cetane number of fuel according to
the procedures described below (step S 1 02).
[0038] Here, the starting condition is a trigger condition for starting the Cetane-number
determination operation mode. For instance, it is determined whether a condition suitable to
20 execute controls for estimating a Cetane number is satisfied, such as detection of an idling
state and detection of operation of an execution button for starting a control by an operator.
To mention a specific example, in a case where determination is performed on the basis
of an idling state, it is possible to execute the Cetane number estimation under a condition in
which the operation state of the engine is stable by starting the Cetane number determination
25 operation mode when the idling state has lasted for a predetermined period, which makes it
possible to obtain good estimation accuracy.
Further, when determination is performed on the basis of detection of operation ofan
execution button, it is possible to start the Cetane number determination operation mode at an
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optional timing intended by an operator (mainly a driver). Thus, it is possible to prevent a
driver from being disturbed by the Cetane-number determination operation mode starting at a
unintended timing.
[0039]
In another example of the starting condition, the Cetane-number estimation may
5 be automatically executed by detecting replenishment operation when a fuel tank is
replenished with additional fuel. In this case, the Cetane number of stored fuel may change
due to the additional fuel supplied to the fuel tank. Thus, it is possible to control the engine
suitably by executing the Cetane-number determination operation mode to re-evaluate an
accurate Cetane number and reflect the accurate Cetane number on the operation control.
10 [0040]
Once the Cetane-number determination operation mode is started, the ECU 10
transmits a control signal to the engine 1 from the control parameter control part 20 to control
the control parameters variably (step S 1 03).
Especially in step S 103, the control parameter control part 20 variably controls the
amount of retard to increase by 1 degree, and then the ECU 10 obtains the NOx concentration
15 C of exhaust gas on the basis of the detection value detected by the NOx sensor 19 (step
S 104 ). Then, the ECU 10 determines whether the NOx concentration C obtained in step
S 104 is smaller than the NOx concentration threshold value CO obtained from the storage part
21 (step S105). If the NOx concentration Cis not less than the NOx concentration threshold
value CO (step S l 05: NO), the ECU 10 returns the process to step S 103, and increases the
20 amount of retard MI by another 1 degree.
[0041] While increasing the amount of retard MI by 1 degree every time as described
above, the process is repeated until the NOx concentration C of exhaust gas becomes smaller
than the NOx concentration threshold value CO. Then, once the NOx concentration C
becomes smaller than the NOx concentration threshold value CO (step S105: YES), the ECU
25 10 determines the amount of retard at this time as MIO (step S 1 06). Specifically, the ECU 10
specifies the amount of retard MIO at the time when the NOx concentration C reaches the
NOx concentration threshold value CO by obtaining the NOx concentration C of exhaust gas
while variably controlling the amount of retard MI ofthe amount of fuel injection.
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When the amount of retard MI of the fuel injection timing is increased, the combustion
state gradually becomes unstable, and a misfire occurs eventually. However, the range in
which the control parameters are variably controlled in step S 103 is within a range in which a
misfire does not occur. That is, in the present embodiment, it is possible to evaluate a
5 Cetane number on the basis of the NOx concentration at the time when the control parameters
are variably controlled in a range where a misfire does not occur.
[0042] Subsequently, the ECU 10 estimates the Cetane number by applying the amount of
retard MIO obtained in stepS 106 to the map 23 (step S107). As descried above, in the map
23 prepared in advance in the storage part 21, a relationship between the amount of retard
10 MIO and the Cetane number CN is specified in advance, and the ECU 10 applies the amount
of retard MIO obtained in steps S 106 to the map 23 to obtain the corresponding Cetane
number CN as an estimation value.
[0043] As described above, it is possible to estimate a Cetane number without causing a
misfire in the combustion state of the engine 1, by controlling the control parameters of the
15 engine 1 variably and using the control parameter MIO of the time when the NOx
concentration C of exhaust gas has reached the predetermined concentration value CO. In
particular, the map 23 specifying a relationship between the Cetane number CN and the
control parameter MIO of the time when the NOx concentration C of exhaust gas reaches a
predetermined concentration value CO is prepared in advance by a method based on a test,.an
20 experiment or a theory, which makes it possible to estimate a Cetane number with a simplified
and inexpensive configuration by applying the actual measurement value of the NOx
concentration of exhaust gas to the map.
[0044] Further, the NOx concentration used to estimate a Cetane number is obtained on
the basis of the detection value detected by the NOx sensor 19a, while the NOx sensor 19a is
25 also used to calculate the purification rate of the denitration catalyst 17. Thus, it is possible
to estimate a Cetane number without providing an additional sensor or the like, and thus the
present embodiment is advantageous in terms of cost as well.
[0045] Although the fuel injection timing is selected as a control parameter in a
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substantial part of the above description, the EGR amount or the like may be used as a control
parameter. Also in this case, it is possible to estimate the Cetane number by a similar
method by evaluating the NOx concentration of exhaust gas when the EGR amount is
controlled variably.
[0046] (First modified embodiment)
In the above embodiment, a Cetane number of fuel is estimated on the basis of the map
23 specifying a relationship between a Cetane number CN of fuel and a control parameter
MIO at the time when the NOx concentration C of exhaust gas reaches a predetermined
concentration value CO set in advance. According to the research of the present inventors,
10 the relationship specified in the map 23 as described above is affected by state factors that
affect the NOx concentration of exhaust gas (e.g. the temperature of the coolant water for the
engine, the temperature of a cylinder inlet, the pressure of the cylinder inlet, the oxygen
concentration of the cylinder inlet, the amount of intake air, the pressure of the intake air, and
the humidity ofthe intake air).
15 While an example of the map 23 is illustrated in FIG. 4, the relationship in the drawing
is specified for a case in which the engine 1 has constant state factors. When the state
factors change, there is a problem that an error in the map 23 increases and the accuracy in
estimating a Cetane number decreases. In the modified embodiment 1, to solve the above
problem, the map 23 is corrected in accordance with the state factors of the engine 1, which
20 makes it possible to improve the accuracy in estimating a Cetane number.
[0047] FIG. 6 is a conceptual diagram of an interior configuration of the ECU 10
according to the first modified embodiment, illustrated as function blocks for implementing
the method of estimating a fuel-Cetane-number. Here, elements similar to those in the above
embodiment are indicated by the same reference numerals, and not described in detail again.
25 The state factor of the engine 1 is detected by a state-factor detection unit 25, and
monitored by a Cetane-number estimation unit 24. Here, the state-factor detection unit 25 is
a plurality of sensors corresponding to the types of the state factors. Further, the storage part
21 stores collection data 26 which specifies correction values for correcting the map 23, and
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the detection value of the state-factor detection unit 25 is associated with a correction value
corresponding to the detection value in a form of a map.
The Cetane-number estimation part 24 calculates a correction value corresponding to
the detection value obtained from the state-factor detection unit 25 on the basis of the
5 correction data 26, and corrects the map 23.
[0048] Here, with reference to FIG. 7, the effect of the coolant-water temperature T of the
engine being an example of the state factors will be examined. FIG. 7 is a graph of
relationships between a control parameter and NOx concentration of exhaust gas at different
coolant-water temperatures, for an engine using a fuel having the same Cetane number. The
10 temperature of the coolant water is 80°C in the solid line, and 40°C in the dotted line.
In comparison of the lines, when the coolant-water temperature T is lower, the NOx
concentration C of exhaust gas starts to decrease at a smaller amount of retard MI. Thus,
there are two different parameters MIO that cross the NOx concentration threshold value CO
depending on the temperature: MI0-1 and MI0-2. As described above, the control
15 parameters MI being a standard of estimation of a Cetane number are dispersed. Thus, if a
Cetane number were obtained without correcting the map 23, the estimate value would vary
even though the same fuel is used.
[0049] In view of this, a correction value corresponding to the temperature of the coolant
water is specified in the correction data 26 to correct the map 23 so that the dispersion of
20 estimation results due to the difference in the temperature of the coolant water becomes zero.
Specifically, the difference in the characteristic graph between different temperatures of the
coolant water is accumulated in the correction data 26 in advance as correction values as
illustrated in FIG. 8, and a correction value corresponding to the detection value detected by
the state-factor detection unit 25 (a coolant-water thermometer in this case) is read out,
25 thereby correcting the map 23. As a result, it is possible to match the estimation value ofthe
Cetane number corresponding to each of the control parameters MI0-1 and MI0-2 to an
accurate value CN3.
In the first modified embodiment, the map 23 is corrected in accordance with the state
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factors, which makes it possible to estimate a Cetane number accurately under various
conditions.
[0050] Here, the accuracy in estimating a Cetane number can be improved on the basis of
a similar technical idea also in a case where the temperature of the cylinder inlet, the pressure
5 of the cylinder inlet, the oxygen concentration of the cylinder inlet, the amount of intake air,
the pressure of the intake air, the humidity of the intake air or the like is used as a st1;1te factor
instead of the temperature of the coolant water of the engine 1. Specifically, possible errors
that occur in the map 23 when the above factors are varied are accumulated as correction
values in the correction data 26, and a corresponding correction value is read out from the
10 correction data 26 on the basis of the actual measurement value measured by a corresponding
sensor or the like to correct the map 23, which makes it possible to improve the accuracy in
estimating a Cetane number.
[0051] (Second modified embodiment)
In the above first modified embodiment, the correction value for the map 23 is specified
15 as the correction data 26 to eliminate an influence of a change in the state factors. On the
other hand, the second modified embodiment is different in that the correction value
corresponding to the NOx concentration threshold value NOxO is specified as the correction
data 26 to eliminate an influence of a change in the state factor. Here, elements similar to
those in the above embodiment are indicated by the same reference numerals, and not
20 described again in detail.
[0052] FIG. 9 is a graph of relationships between a control parameter (the amount of
retard MI) and NOx concentration C of exhaust gas at different coolant-water temperatures,
for an engine 1 using fuel having the same Cetane number, like FIG. 7. The temperature of
the coolant water is 80°C in the solid line, and 40°C in the dotted line. As described above,
25 when a Cetane number is estimated on the basis of a constant NOx concentration threshold
value CO, there is an error in the characteristic graph due to the temperature of the coolant
water, and the amount of retard MIO at which the NOx concentration reaches the NOx
concentration threshold value CO is also dispersed (see FIG. 7). Thus, a Cetane number
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cannot be estimated accurately.
[0053] In view of this, in the present modified embodiment, as illustrated in FIG. 9, a
correction value is set so that the amount of retard MIO at which the NOx concentration
reaches the NOx concentration threshold value CO stays consistent regardless of the
5 temperature of the coolant water, and the NOx concentration threshold value corresponds to
the temperature of the coolant water. The correction value is associated with the temperature
of the coolant water and accumulated in the correction data 26 stored in the storage part,
similarly to the first modified embodiment.
In FIG. 9, the correction value is set such that the NOx concentration threshold value is
10 CO-l in a case where the temperature of the coolant water is 80°C, and the NOx concentration
threshold value is C0-2 in a case where the temperature of the coolant water is 40°C. In this
way, the NOx concentration threshold value is corrected so that the amounts of retard MIO at
which the NOx concentration reaches the NOx concentration threshold value are consistent.
[0054] In the second modified embodiment, the NOx concentration threshold value is
15 corrected in accordance with the state factors, which makes it possible to estimate a Cetane
number accurately under various conditions.
Industrial Applicability
[0055]
20 The present invention can be applied to a fuel-Cetane-number estimation method of
estimating a Cetane number of fuel used in a compression combustion type internal
combustion engine such as a diesel engine, and to an apparatus for implementing the same
method.
25 Description of Reference Numerals
[0056]
Engine
2 Exhaust turbocharger
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3 Intake pipe
4 Intercooler
5 Throttle valve
6 Intake manifold
5 7 Combustion chamber
8 Exhaust manifold
9 Exhaust pipe
10 ECU
11 EGR pipe
10 12 EGR cooler
13 EGR valve
14 Exhaust aftertreatment system
15 Oxidation catalyst (DOC)
16 Diesel particulate filter (DPF)
15 17 NOx selective catalytic reduction (SCR)
18 Urea injection nozzle
19 NOx sensor
20 Control parameter control part
21 Storage part
20 22 NOx concentration threshold value
23 Map
24 Cetane-number estimation part
25 State-factor detection unit
26 Correction data

We Claim:
1. A fuel-Cetane-number estimation method of estimating a Cetane number of a fuel
used in an internal combustion engine which performs compression ignition combustion,
comprising:
5 preparing in advance a map which specifies a relationship between the Cetane number
of the fuel and a control parameter of the internal combustion engine at which NOx
concentration of exhaust gas of the internal combustion engine reaches a predetermined
concentration value;
controlling the control parameter of the internal combustion engine variably to detect
10 transition of the NOx concentration of the exhaust gas of the internal combustion engine;
obtaining the control parameter of the internal combustion engine at which the NOx
concentration has reached the predetermined concentration value on the basis of the detected
NOx concentration; and
estimating the Cetane number which corresponds to the obtained control parameter on
15 the basis of the map, wherein the predetermined concentration value is set to be smaller than a
value in the relationship at which a slope of the NOx concentration with respect to the control
parameter changes discontinuously.
20
25
2. The fuel-Cetane-number estimation method according to claim 1, further comprising:
detecting a state factor which affects the NOx concentration of the exhaust gas of the
internal combustion engine; and
correcting the map by using a predetermined correction value which corresponds to
the detected state factor.
3. The fuel-Cetane-number estimation method according to claim 1, further comprising:
detecting a state factor which affects the NOx concentration of the exhaust gas ofthe
5
10
15
20
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internal combustion engine; and
correcting the predetermined concentration value by using a predetermined correction
value which corresponds to the detected state factor.
4. The fuel-Cetane-number estimation method according to claim 2 or 3,
wherein the state factor includes at least one of a temperature of a coolant water, a
temperature of an inlet of a cylinder, a pressure of the inlet of the cylinder, oxygen
concentration of the cylinder, an amount of intake air, a pressure of the intake air, or a
humidity of the intake air of the internal combustion engine.
5. The fuel-Cetane-number estimation method according to any one of claims 1 to 4,
wherein execution of the fuel-Cetane-number estimation method is automatically
started if the fuel is additionally supplied to a fuel tank.
6. The fuel-Cetane-number estimation method according to any one of claims 1 to 5,
wherein the control parameter is an amount of retard in a fuel injection timing in a
combustion chamber of the internal combustion engine.
7. The fuel-Cetane-number estimation method according to any one of claims 1 to 5,
wherein the control parameter is an amount of recirculation of the exhaust gas to the
intake air of the internal combustion engine.
8. A fuel-Cetane-number estimation apparatus for estimating a Cetane number of a fuel
used in an internal combustion engine which performs compression ignition combustion,
25 comprising:
a NOx concentration detection unit for detecting NOx concentration of exhaust gas of
the internal combustion engine;
an internal-combustion-engine control unit for variably controlling a control parameter
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of the internal combustion engine;
a storage unit for storing a map which specifies a relationship between the Cetane
number of the fuel and the control parameter of the internal combustion engine at which the
NOx concentration of the exhaust gas of the internal combustion engine reaches a
5 predetermined concentration value; and
a Cetane-number estimation unit for variably controlling the control parameter with
the internal-combustion-engine control unit to vary the NOx concentration of the exhaust gas
of the internal combustion engine, obtaining the control parameter at which the NOx
concentration reaches the predetermined concentration value, and estimating the Cetane
10 number which corresponds to the obtained control parameter on the basis of the map, wherein
the predetermined concentration value is set to be smaller than a value in the relationship at
which a slope of the NOx concentration with respect to the control parameter changes
discontinuously.
15
9. The fuel-Cetane-number estimation apparatus according to claim 8, further
compnsmg:
a state-factor detection unit for detecting a state factor which affects the NOx
concentration of the exhaust gas of the internal combustion engine; and
20 a correction unit for correcting the map by using a predetermined correction value
which corresponds to the state factor detected by the state-factor detection unit.
10. The fuel-Cetane-number estimation apparatus according to claim 8, further
compnsmg:
25 a state-factor detection unit for detecting a state factor which affects the NOx
concentration of the exhaust gas of the internal combustion engine; and
a correction unit for correcting the predetermined concentration value by using a
predetermined correction value which corresponds to the state factor detected by the state13
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factor detection unit.
11. The fuel-Cetane-number estimation apparatus according to any one of claims 8 to 10,
wherein the NOx concentration detection unit is also used as a NOx sensor used to
5 calculate a purification rate in an exhaust-gas purification device for purifying the exhaust gas
of the internal combustion engine.