JP2006226188A - Fuel property detection device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device capable of practically and accurately detecting the cetane number of a fuel in use. <P>SOLUTION: This fuel property detection device comprises a variable fuel injection means 10 capable of jetting the fuel into a combustion chamber by dividing it into a main injection and a pilot injection prior to the main injection, a pilot combustion state detection means detecting a combustion state produced by the combustion of the pilot injection fuel as a pilot combustion state, and a cetane number detection means 30 detecting the cetane number of the fuel in use based on the detected pilot combustion state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the detection of the properties of fuel used in diesel engines, particularly the cetane number.

Some cetane number sensors detect the cetane number of diesel engine fuel (see Patent Document 1).
Japanese Utility Model Publication 3-45181

  By the way, the cetane number detection method of the said patent document 1 presupposes that there exists a proportional relationship between the viscosity of the light oil which is a fuel for diesel engines, and a cetane number, and the cetane number becomes high, so that the viscosity of light oil is high. To do.

  However, in the research conducted by the present inventors, a result different from that of Patent Document 1 is obtained. That is, as shown in FIG. 15, the correlation between the viscosity of the light oil and the cetane number is low and has an inversely proportional relationship, and the cetane number tends to decrease as the viscosity of the light oil increases. Therefore, the cetane number cannot be detected with high accuracy by detecting the viscosity of the light oil, regardless of whether the relationship between the viscosity of the light oil and the cetane number is proportional or inversely proportional. There was found.

  In the technique of Patent Document 1, a pendulum that falls due to gravity acting on the weight is provided in the fuel tank as a means for measuring the viscosity of light oil, and a mechanism for measuring the drop time of the pendulum that depends on the viscosity of the light oil. The viscosity of the light oil is obtained from the drop time. Then, the detected viscosity is corrected based on the fuel temperature at that time to determine the cetane number. As described above, the technique of Patent Document 1 requires a complicated mechanism for measuring the viscosity of the fuel, which is accompanied by restrictions on the design of the fuel tank and deterioration of productivity. Moreover, if the vehicle is tilted, it is assumed that the friction of the viscosity measuring mechanism itself in the fuel tank changes, and for this reason, accurate viscosity measurement is difficult.

  In view of such circumstances, the present invention has an object to provide an apparatus that can practically and accurately detect the cetane number of fuel actually used.

  The present invention includes variable fuel injection means capable of being divided into main injection and pilot injection preceding the main injection and capable of being injected into a combustion chamber, and a combustion state generated by combustion of the pilot injected fuel is a pilot combustion state. And the cetane number of the used fuel is detected based on the detected pilot combustion state.

  In the present invention, when the pilot injection is performed before the top dead center at which the compression temperature has almost reached the maximum, and combustion is performed in a premixed state by the pilot injection, the cetane number of the fuel is the pilot injected fuel. Is found for the first time to have a very high correlation with the combustion start time of the engine or the peak position of combustion with pilot injected fuel (that is, the maximum angle of combustion with pilot injected fuel or the crank angle position at which the maximum value of combustion with pilot injected fuel is taken) It was made from that. Here, the combustion start timing of the pilot injected fuel or the peak position of the combustion by the pilot injected fuel is an index representing the pilot combustion state.

  That is, according to the present invention, the variable fuel injection means capable of being divided into main injection and pilot injection preceding this main injection and allowing injection into the combustion chamber is provided, and the combustion state caused by the combustion of the pilot injected fuel is determined. Detected as the pilot combustion state, and the cetane number of the fuel used is detected based on the detected pilot combustion state. Therefore, the cetane number of the fuel used can be configured with a simple configuration without requiring a large-scale device such as a viscosity measurement mechanism. Can be detected accurately.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a diesel engine (hereinafter also simply referred to as “engine”) 1 provided with a fuel property detection device of the present invention.

  In FIG. 1, exhaust discharged from an engine main body to an exhaust outlet passage 3a constituting an upstream portion of the exhaust passage 3 passes through a turbine 3b of a supercharger and is disposed downstream of the turbine. For example, an oxidation catalyst and a NOx catalyst) flow into the casing 20 accommodated therein.

  In order to recirculate a part of the exhaust, an EGR passage 4 that connects the intake collector 2c of the intake passage 2 and the exhaust outlet passage 3a, and an EGR valve 5 that can continuously control the flow area of the EGR passage 4 An EGR device (exhaust gas recirculation device) is provided.

  In the intake passage 2, an air cleaner 2a is disposed at an upstream position, and a compressor 2b of a supercharger is disposed downstream thereof.

  An intake throttle valve 6 that is driven to open and close by an actuator (for example, a stepping motor type) is interposed between the compressor 2b and the intake collector 2c. The intake throttle valve 6 is used together with the EGR valve 5 to control the EGR amount (EGR rate).

  Each cylinder of the engine 1 is provided with a pressure sensor 7 (combustion chamber pressure detecting means) for detecting the pressure in the combustion chamber. As the pressure sensor 7, a type facing the combustion chamber or a washer-shaped knocking sensor type can be used.

  The fuel supply device for the engine 1 includes a fuel tank 60 that stores diesel oil as diesel fuel, and a fuel supply for supplying the fuel in the fuel tank 60 to the fuel injection device 10 (variable fuel injection means) of the engine 1. A passage 16 and a fuel return passage 19 for returning return fuel (spill fuel) from the fuel injection device 10 of the engine 1 to the fuel tank 60 are provided.

  The fuel injection device 10 is a well-known common rail fuel injection device, and generally includes a supply pump 11, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valve 15 of each cylinder.

  The common rail 14 is provided with a pressure sensor 34 and a temperature sensor 35 in order to detect the pressure and temperature of the fuel in the common rail 14. Further, in order to control the fuel pressure in the common rail 14, a part of the fuel discharged from the supply pump 11 is returned to the fuel supply passage 16 via the overflow passage 17 having the one-way valve 18. Yes. Specifically, a pressure control valve 13 that changes the flow passage area of the overflow passage 17 is provided, and the pressure control valve 13 changes the flow passage area of the overflow passage 17 in accordance with a duty signal from the engine control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the fuel pressure in the common rail 14 is controlled.

  The fuel injection valve 15 is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30, and injects fuel into the combustion chamber by the ON signal and stops injection by the OFF signal. The fuel injection amount increases as the period of the ON signal applied to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases.

  Further, a water temperature sensor 31 for detecting the cooling water temperature is attached to an appropriate position of the engine 1 as a representative of the temperature of the engine 1.

  The engine control unit 30 includes a combustion chamber pressure CP signal from the pressure sensor 7, a coolant temperature Tw signal from the water temperature sensor 31, a crank angle from the crank angle detection crank angle sensor 32 (the basis of the engine speed Ne and Signal), cylinder discrimination signal Cyl from cylinder discrimination crank angle sensor 33, common rail pressure (fuel pressure of common rail 14) PCR signal from pressure sensor 34, fuel temperature TF signal from fuel temperature sensor 35, accelerator A signal of the accelerator opening (the amount of depression of the accelerator pedal) L (equivalent to the engine load) from the opening sensor 36 is input.

  The controller 30 performs fuel injection control, EGR control, common rail pressure control, and the like based on the above signals. Here, as fuel injection control, a small amount of fuel is injected prior to the main injection at a time before the top dead center where the compression temperature has almost reached the maximum in order to improve the state of combustion by the main injection fuel. So-called pilot injection is performed. The map values required for these controls, for example, the pilot injection amount, the main injection start timing, and the common rail pressure target value (target reference pressure PCR0) are adapted to the reference cetane number fuel described later. .

  Diesel oil, a fuel used in diesel engines on the market, has a non-uniform composition and properties depending on the crude oil production area and refiner, and is particularly fragrant with a benzene ring structure that is flame-retardant and has low evaporation properties. It is well known that when the amount of the group hydrocarbon or naphthene component is large, the cetane number of the fuel is low, and vice versa.

  Thus, since the cetane number of the fuel marketed on the market is not always constant, fuel different from the standard cetane number may be refueled, and at this time, stable engine operation cannot be expected. It is necessary to detect the cetane number of the fuel, correct the map value with the detected cetane number, and use the corrected map value for each control of the fuel injection control, EGR control, and common rail pressure control. From this point of view, it is important to accurately detect the cetane number of the fuel.

  For this reason, when the present inventors conducted an experiment, the above-described combustion by the pilot-injected fuel is premixed combustion, but between the combustion state by the pilot-injected fuel and the cetane number of the fuel. The inventors found for the first time that there is a strong correlation.

  This will be described with reference to FIG. 2. The upper part of FIG. 2 shows pilot injection fuel injection start timing P start, main injection fuel injection start timing M start, pilot injection period P period, main injection period M period, and pilot injection start. The interval DIT between the timing and the main injection start timing, and the lower part of FIG. 2 is calculated from the combustion chamber pressure at that time, and the heat generation rate by the combustion of the pilot injected fuel (the heat generation rate by the combustion of this pilot injected fuel, Hereinafter, it is simply referred to as “pilot heat generation rate”.) The characteristic of dQ / dθ is shown. Since the abscissa is the crank angle [deg BTDC] measured from the compression top dead center to the advance side, it increases with a positive value as it shifts from the compression top dead center to the advance side, and is delayed from the compression top dead center. The larger the angle, the larger the negative value.

  When the reference cetane number, high cetane number and low cetane number fuel are supplied to the engine with the same injection pattern (that is, the upper pattern in FIG. 2) as shown in the lower part of FIG. 2, the cetane number fuel is higher than the reference cetane number fuel. A valence fuel has good ignitability, and a low cetane number fuel has poor ignitability. Here, the reference cetane number fuel means a fuel whose cetane number is a reference cetane number (standard cetane number). For example, 55 is selected as the reference cetane number. On the other hand, a high cetane number fuel means a fuel having a cetane number higher than the reference cetane number, and a low cetane number fuel means a fuel having a cetane number lower than the reference cetane number.

  Due to the difference in cetane number, the maximum value (peak) of the pilot heat generation rate for the reference cetane number fuel is PQ max std (“dQ max std” in the figure) and the pilot heat generation for the high cetane number fuel is shown in the figure. The maximum value of the rate is PQ max high (“dQ max high” in the figure), the maximum value of the pilot heat generation rate for the low cetane number fuel is PQ max low (“dQ max low” in the figure), and the reference cetane PIT std is the maximum time of pilot heat generation rate for the high-valent fuel (time when the maximum value is shown), PIT high is the maximum time of pilot heat generation rate for the high cetane number fuel, and the pilot heat generation rate of the low cetane number fuel is If the maximum time is PIT low, the maximum value PQma of the pilot heat generation rate with high cetane number fuel high is higher than the maximum value PQmax std of the pilot heat generation rate in the reference cetane number fuel, and the maximum time PIT high of the pilot heat generation rate in the high cetane number fuel is PIT high, the pilot heat generation rate in the reference cetane number fuel It is earlier than the maximum time of PIT std. This is because, in high cetane number fuel, the proportion of pilot injected fuel combusted before the start of injection of the main injected fuel is relatively higher than that of the reference cetane number fuel. The maximum value of the heat generation rate due to combustion is lower than the maximum value of heat generation due to combustion of the main injection fuel for the reference cetane number fuel.

  On the other hand, the proportion of pilot fuel that cannot be combusted before the start of injection of main injected fuel is relatively larger than that of the reference cetane fuel in the case of low cetane fuel. The maximum value PQmax low is lower than the maximum value PQmax std of the pilot heat generation rate for the reference cetane number fuel, and the maximum time PIT low of the pilot heat generation rate for the low cetane number fuel is the pilot for the reference cetane number fuel. It is later than the maximum heat generation rate PIT std.

  In addition, since the start of combustion of the main injection fuel is delayed from the reference cetane number fuel in the low cetane number fuel, the premixed combustion ratio when the main injection fuel starts combustion is relatively increased as compared to the reference cetane number fuel. As a result, the maximum value of the heat generation rate due to the combustion of the main injection fuel becomes higher than that of the reference cetane number fuel, which leads to an increase in combustion noise and an increase in NOx, HC, etc. compared to the reference cetane number fuel. .

  Instead of the pilot heat generation rate maximum time, the pilot heat generation rate increase start time can be used.

  The characteristics of the pilot heat generation rate dQ / dθ shown in the lower part of FIG. 2 were found for the first time by the present inventors through experiments. Based on the results of these experiments, the cetane number of the fuel used can be detected practically and accurately. Recognize. That is, since the maximum value PQ max std of the pilot heat generation rate for the reference cetane number fuel and the maximum time PIT std of the pilot heat generation rate for the reference cetane number fuel can be known in advance, they are stored in the memory. The maximum value of the pilot heat generation rate for the actual fuel used is detected, and this is compared with the maximum value of the pilot heat generation rate PQ max std for the reference cetane number fuel. When the fuel used is a high cetane fuel when the pilot heat generation rate maximum value PQ max std of the cetane fuel is larger than the maximum, the pilot heat generation rate maximum value of the actual fuel used is the pilot fuel of the reference cetane fuel. When the heat generation rate is smaller than the maximum value PQ max std, the fuel used is detected as a low cetane number fuel (determination). Kill.

  Alternatively, the pilot heat generation rate maximum timing for the actual fuel used is detected, and this is compared with the pilot heat generation rate maximum timing PIT std of the reference cetane number fuel, and the maximum pilot heat generation rate timing of the actual fuel used is the reference cetane. When the fuel used is a high cetane fuel when it is earlier than the maximum pilot heat generation rate timing PIT std, the actual pilot fuel heat generation maximum timing of the actual fuel used is the pilot heat generation of the reference cetane fuel. When it is later than the rate maximum time PIT std, it can be detected (determined) that the fuel used is a low cetane number fuel.

Here, the parameter for detecting the cetane number is not limited to the pilot heat generation rate dQ / dθ. For example, instead of the pilot heat generation rate dQ / dθ, the combustion chamber pressure differential value dP / dθ [kPa / deg] due to the combustion of the pilot injected fuel shown in the lower part of FIG. 3, and the combustion of the pilot injected fuel shown in the lower part of FIG. The combustion chamber pressure twice differential value dP ² / dθ ² [kPa / deg ² ] can be used.

As can be seen from the lower part of FIG. 3 and the lower part of FIG. 4, the characteristics of the combustion chamber pressure differential value dP / dθ due to the combustion of the pilot injected fuel or the combustion chamber pressure twice differential value dP ² / dθ ² due to the combustion of the pilot injected fuel It is sharper than the characteristics of the heat release rate dQ / dθ, and the level of the contribution of combustion by the pilot injected fuel is well understood. Therefore, when importance is attached not only to exhaust emission but also combustion noise, combustion control is performed using these indices (differential pressure in combustion chamber due to combustion of pilot injected fuel and twice differential pressure in combustion chamber due to combustion of pilot injected fuel). It is desirable to do.

  These indices may be obtained by calculation based on the signal from the crank angle sensor 32 for detecting the crank angle, the signal from the crank angle sensor 33 for determining the cylinder, and the signal from the pressure sensor 7, or may be obtained by using a high-pass filter or the like. It is also possible to ask for it.

  Next, the contents of the control including the cetane number detection of the present invention executed by the engine control unit 30 will be described based on the following flowchart.

  FIG. 5 is a basic control routine relating to the control of the entire diesel engine 1 and is repeatedly executed at regular intervals (for example, every 1 msec or every 10 msec).

  In step 100, the coolant temperature Tw detected by the water temperature sensor 31, the engine rotation speed Ne detected by the crank angle detection crank angle sensor 32, the cylinder discrimination signal Cyl detected by the cylinder discrimination crank angle sensor 33, and the pressure sensor The common rail pressure PCR detected by 34, the combustion chamber pressure CP detected by the pressure sensor 7, the fuel temperature TF detected by the temperature sensor 35, and the accelerator opening L detected by the accelerator opening sensor 35 are read.

  Here, the accelerator opening L is used as the engine load, but a fuel injection amount calculated based on the engine speed and the accelerator opening may be used as the engine load.

  In step 200, the common rail pressure is controlled. In the present invention, the control of the common rail pressure itself is not the main part, and will be described briefly. That is, in the common rail pressure control, the target reference pressure PCR0 of the common rail 14 is obtained by searching a predetermined map stored in advance in the ROM of the control unit 30 using the engine rotational speed Ne and the load L as parameters. The flow passage area of the overflow passage 17 is feedback-controlled through the pressure control valve 13 so that the actual common rail pressure (injection pressure) PCR detected by 34 matches the target reference pressure PCR0.

  In step 300, the fuel property (cetane number) is detected. This detection will be described with reference to the flowchart of FIG.

  In FIG. 6 (subroutine of step 300 in FIG. 5), in step 310, it is checked whether or not the cetane number of the used fuel has been detected. For example, a cetane number detected flag (initially set to zero when the engine is started) is prepared, and if this cetane number detected flag = 0, it is determined that the cetane number of the used fuel has not been detected yet. Proceed to, and determine the cetane number detection conditions. The determination of the cetane number detection condition will be described with reference to the flowchart of FIG.

  In FIG. 7 (subroutine of step 320 in FIG. 6), in steps 321 and 322, the cooling water temperature Tw detected by the water temperature sensor 31 is compared with a predetermined temperature, and the operating conditions determined from the engine speed and the load L are predetermined. See if you are in the driving range. It is determined that the cetane number detection condition is not satisfied when the coolant temperature Tw is lower than a predetermined temperature (that is, before completion of engine warm-up), or when the operating condition is not within the predetermined operating range even if the coolant temperature Tw is equal to or higher than the predetermined temperature. Then, the process proceeds to step 400 in FIG. 5 without detecting the cetane number.

  On the other hand, when the cooling water temperature Tw is equal to or higher than the predetermined temperature (that is, after the engine warm-up is completed) and the operation condition is in the predetermined operation region, it is determined that the cetane number detection condition is satisfied, and the process proceeds to step 323 and EGR is performed. See if it has stopped. Whether or not EGR is stopped can be determined from a signal output from the engine control unit 30 to the EGR valve 5.

  If the EGR is stopped (a signal for fully closing the EGR valve 5 is output), the process proceeds to step 325 to increase the pilot injection amount, and then proceeds to step 330 in FIG. Further, when the EGR is not stopped (the signal for opening the EGR valve 5 is output), the EGR is stopped at step 324 (a signal for fully closing the EGR valve 5 is issued to forcibly fully close the EGR valve 5). Then, the operation of step 325 is executed, and the process proceeds to step 330 of FIG.

  In this way, the pilot injection amount is increased because the detection of the cetane number is based on the combustion state of the pilot injection fuel. As in EGR, the EGR gas is introduced to lower the combustion temperature and to generate NOx. This is in order to avoid the state in which the combustion is caused by the pilot injection fuel in the suppressed state and the cetane number cannot be accurately detected.

  Returning to FIG. 6, in step 330, a predetermined map stored in advance in the ROM of the engine control unit 30 is searched from the engine speed Ne and the load L, whereby the pilot heat generation rate maximum time of the reference cetane number fuel is determined. Find PIT0. The unit of this PIT0 is, for example, a crank angle [deg BTDC] taken on the advance side with reference to the compression top dead center.

  In step 340, the pilot heat generation rate dQ / dθ [J / deg] of the fuel used is calculated based on the combustion chamber pressure CP detected by the pressure sensor 7. The calculation method of the pilot heat generation rate dQ / dθ may be the same as the calculation method of the heat generation rate due to combustion by the main injection fuel. The calculation method of the heat release rate by combustion with the main injection fuel is known.

  In step 350, the pilot heat generation rate maximum timing PIT of the fuel used is obtained based on the calculated pilot heat generation rate dQ / dθ. The unit of this PIT is also a crank angle [deg BTDC] taken on the advance side with reference to the compression top dead center.

  In Step 360, the pilot heat generation rate maximum timing PIT of the fuel used is divided by the pilot heat generation rate maximum timing PIT0 of the reference cetane number fuel, that is, the pilot heat generation rate maximum timing coefficient KPIT [anonymous number] is calculated by the following equation. calculate.

KPIT = PIT / PIT0 (1)
In step 370, the cetane number C number of the fuel used is calculated by searching a table having the contents shown in FIG. 8 from the pilot heat generation rate maximum timing coefficient KPIT. As shown in FIG. 8, when the pilot heat generation rate maximum timing coefficient KPIT is 1, that is, when the pilot heat generation rate maximum timing PIT of the fuel used matches the pilot heat generation rate maximum timing PIT0 of the reference cetane number fuel, The cetane number C number of the fuel used is equal to the reference cetane number (ie 55). The cetane number C number of the used fuel becomes larger than the reference cetane number as the pilot heat generation rate maximum timing coefficient KPIT becomes larger than 1, and conversely, the cetane number of the used fuel becomes smaller as the pilot heat generation rate maximum timing coefficient KPIT becomes smaller than 1. C number is smaller than the reference cetane number.

  Here, when the pilot heat generation rate maximum timing coefficient KPIT is larger than 1, that is, when the pilot heat generation rate maximum timing PIT of the used fuel is larger than the pilot heat generation rate maximum timing PIT0 of the reference cetane number fuel, the cetane number of the used fuel The reason why C number is made larger than the reference cetane number is that the cetane number of the fuel used at this time is higher than the reference cetane number, as described above in the lower part of FIG. On the contrary, when the pilot heat generation rate maximum timing coefficient KPIT is smaller than 1, that is, when the pilot heat generation rate maximum timing PIT of the fuel used is smaller than the pilot heat generation rate maximum timing PIT0 of the reference cetane number fuel, The reason why the number C number is made smaller than the reference cetane number is that the cetane number C number of the fuel used at this time is smaller than the reference cetane number, as described earlier in FIG. The characteristics of FIG. 8 are actually determined by adaptation.

  When the cetane number C number of the used fuel is detected in this way, this value is stored in a nonvolatile memory such as an EEPROM. Further, since the cetane number of the used fuel is already detected, the above cetane number detected flag = 1 is set. When the cetane number detected flag = 1, it is not possible to proceed from step 310 to step 320 in FIG. 6 from the next time, and immediately proceed to step 400 in FIG. That is, the detection of the cetane number of the fuel used is limited to one time.

  In the embodiment, when the engine is started, the cetane number detected flag = 0 is set to detect the cetane number of the fuel used every time the engine is started. However, the present invention is not limited to this. For example, since the cetane number of the fuel used cannot change unless refueling is performed, it is determined whether or not fuel has been supplied at the start of the engine, and only when there is fuel supply, the cetane number of the fuel used is detected. Therefore, the cetane number detected flag = 0 is set to 0, and the cetane number detected flag = 1 is set when the fuel is not supplied, so that the cetane number stored in the nonvolatile memory is read out and used.

  When the detection of the cetane number of the fuel used is completed in this way, the process returns to FIG. 5 and the engine exhaust control is performed at step 400 to end the current process. This engine exhaust control will be described with reference to the flowchart of FIG.

  In FIG. 9 (subroutine of step 400 in FIG. 5), fuel injection control and EGR control are performed based on the operating region of the engine 1 and the engine temperature (for example, the cooling water temperature Tw) so as to obtain a predetermined engine exhaust performance. And exhaust aftertreatment control is performed. Since these three controls themselves are not the main part of the present invention, each of the three controls will be briefly described first, and then the correction based on the cetane number detected as described above will be referred to.

  First, at step 410, fuel injection control is performed. For example, with engine speed Ne and load L as parameters, pilot injection amount Q pilot, main injection amount Q main, pilot injection period P period, main injection period M period, main injection start time M start, pilot injection start time P start, The pilot injection interval DIT and the like are respectively obtained by searching predetermined maps stored in advance in the ROM of the engine control unit 30. Based on the crank angle signal of the crank angle detection crank angle sensor 32 and the cylinder discrimination signal Cyl of the cylinder discrimination crank angle sensor 33, the pilot injection amount Q pilot and the main injection amount Q main are supplied. During the pilot injection period P period from the injection start timing P start and during the main injection period M period from the main injection start timing M start, the fuel injection valves 15 of the cylinders to be injected are driven to open (see the upper part of FIG. 2). . Thus, pilot injection and main injection are performed.

  As for EGR control, first, it is checked whether EGR is necessary. Specifically, it is determined whether or not there is an operating condition determined from Ne and Q main at that time in a predetermined EGR region set using the engine rotation speed Ne and the main injection amount Q main as parameters. In other words, because the operation frequency is high and the air excess ratio is relatively large, even if EGR is executed and NOx is reduced, other exhaust components and fuel efficiency are not deteriorated, or the EGR is performed. And whether it is a region where the smoke or PM (exhaust particulate) emission increases or the output decreases (outside the EGR region).

  If the operating condition determined from Ne and Q main is in the EGR region, target EGR data (drive signals for the EGR valve 5 and the intake throttle valve 6) for executing an appropriate EGR, for example, the engine speed Ne and The main injection amount Q main is used as a parameter to obtain a predetermined map stored in the ROM of the engine control unit 30 in advance, and the opening degree of the EGR valve 5 is controlled and intake air so that this target EGR data can be obtained. The throttle valve 6 is controlled to close. When the cooling water temperature Tw is low, the EGR amount is corrected to decrease. On the other hand, if the operating condition is outside the EGR region, the EGR valve 5 is fully closed and the intake throttle valve 6 is fully opened in order to stop or hold the EGR.

  With regard to exhaust aftertreatment control, for example, NOx is adsorbed (trapped) when the air-fuel ratio of the inflowing exhaust is lean, and NOx is desorbed when the air-fuel ratio of the inflowing exhaust is rich or the stoichiometric air-fuel ratio. In addition, a so-called NOx trap catalyst for reducing and purifying the desorbed NOx using HC and CO in the exhaust gas as a reducing agent is provided in the casing 20, and this operation is performed during the lean operation. NOx generated frequently in the state is adsorbed to the NOx trap catalyst, and when the amount of adsorption to the NOx trap catalyst increases and the time for regeneration of the NOx trap catalyst is reached, the intake throttle is strengthened (the opening of the intake throttle valve 6). Small), EGR enhancement or post injection (small amount of fuel injection after main injection) is executed alone or in combination to exhaust the exhaust from the engine. By setting the ratio to rich, to reproduce the NOx trap catalyst.

  This completes the overview of each of the three controls. Next, the correction using the cetane number of the fuel used will be described. The pilot injection amount Q pilot and the main injection start timing M start are all relative to the reference cetane number fuel. Is suitable. Therefore, if the cetane number of the fuel used deviates from the reference cetane number, these map values (map data) become inappropriate. Here, the pilot injection amount Q pilot and the main injection start timing M start are used as the fuel used. It is corrected by the cetane number C number. That is, a pilot injection amount correction coefficient K PLTQ is obtained by searching a table having the contents shown in FIG. 10 from the cetane number C number of the fuel used, and a value obtained by multiplying the pilot injection amount Q pilot (map value) by the pilot injection amount correction coefficient K PLTQ. Is again set as the pilot injection amount Q pilot. As shown in FIG. 10, the pilot injection amount correction coefficient K PLTQ becomes smaller than 1.0 when the cetane number C number of the fuel used is larger than the reference cetane number (that is, when the high cetane fuel is used), and the fuel used Is a value larger than 1.0 when the cetane number C number is smaller than the reference cetane number (that is, when a low cetane number fuel is used).

  Further, the main injection start timing correction amount is obtained by searching a table having the contents shown in FIG. 11 from the cetane number C number of the used fuel, and this value is added to the main injection start timing M start (map value). Is again set as the main injection start timing Mstart. As shown in FIG. 11, the main injection start timing correction amount is positive when the cetane number C number of the used fuel is larger than the reference cetane number (that is, when the high cetane number fuel is used), and the cetane number C number of the used fuel. Is negative when the value is smaller than the reference cetane number (that is, when low cetane number fuel is used). Here, the main injection start timing is a value taken on the advance side with respect to the compression top dead center. Therefore, when the positive value is subtracted from the main injection start timing, the main injection start timing is retarded, and conversely, when the negative value is subtracted from the main injection start timing, the main injection start timing is advanced.

  Thus, the reason why the pilot injection amount is increased when the low cetane number fuel is used is as follows. That is, in the case of the low cetane number fuel, the pilot heat generation rate maximum timing becomes smaller than that in the case of the reference cetane number fuel. In this case, the pilot injection amount Q pilot is increased, and the ignitability and main injection of the pilot injected fuel are increased. This is to improve the ignitability of the fuel, shorten the ignition delay period of the main injection, improve the combustion state, and suppress an increase in unburned HC emissions and an increase in combustion noise.

  Similarly, the main injection start timing is advanced when low cetane number fuel is used for the same reason. In other words, with the low cetane number fuel, the maximum pilot heat generation rate timing is smaller than that with the reference cetane number fuel. In this case, the main injection start timing is advanced to improve the ignitability of the main injected fuel. This is because the ignition delay period of the main injection is shortened to improve the combustion state, and the increase in unburned HC emissions and the increase in combustion noise are suppressed.

  Further, since the target reference pressure PCR0 of the common rail 14 is also a value adapted to the reference cetane number fuel, the target reference pressure PCR0 is corrected by the cetane number of the used fuel.

  That is, the common rail pressure correction coefficient is obtained by searching a table having the contents shown in FIG. 12 from the cetane number C number of the fuel used, and the target pressure PCR1 is obtained by multiplying the target reference pressure PCR0 (map value) by the common rail pressure correction coefficient. The common rail pressure is feedback-controlled so that the actual common rail pressure coincides with the target pressure PCR1. As shown in FIG. 12, the common rail pressure correction coefficient becomes larger than 1.0 when the cetane number C number of the used fuel is larger than the reference cetane number (that is, when the high cetane number fuel is used), and vice versa. Is a value smaller than 1.0 when the cetane number C number is smaller than the reference cetane number (that is, when a low cetane number fuel is used).

  As described above, the target reference pressure PCR0 is lowered when the low cetane number fuel is used for the following reason. That is, in the low cetane number fuel, the pilot heat generation rate maximum timing is smaller than that in the case of the reference cetane number fuel, and in this case, the target reference pressure PCR0 is decreased and the fuel is injected from the fuel injection valve 15 at a low pressure. This is because the diffusion of the spray from the fuel injection valve 15 is suppressed to promote the formation of a rich air-fuel mixture in the combustion chamber, and the ignitability is improved.

  Here, the operation of the present embodiment will be described.

  In the present embodiment (the invention described in claim 1), when the pilot injection is performed before the top dead center where the compression temperature reaches almost the maximum, and combustion is performed in the premixed state by the pilot injection, This is because the cetane number of the fuel has been found for the first time to have a very high correlation with the peak position of combustion by the pilot injected fuel (or the combustion start timing of the pilot injected fuel). Here, the peak position of combustion by pilot injected fuel (or the combustion start timing of pilot injected fuel) is an index representing the pilot combustion state.

  That is, according to the present embodiment (the invention described in claim 2), the fuel injection device 10 (variable fuel) that can be divided into main injection and pilot injection preceding the main injection and injected into the combustion chamber 6), the pilot heat generation rate maximum timing PIT is detected as a pilot combustion state, and the cetane number C number of the fuel used is detected based on the detected pilot heat generation rate maximum timing PIT (step in FIG. 6). 330-370), the cetane number of the fuel used can be accurately detected with a simple configuration without requiring a large-scale device such as a viscosity measuring mechanism.

  Before the warm-up of the engine is completed, the combustion state of the pilot injected fuel deteriorates after the warm-up is completed, and an error may occur in the detection of the cetane number. In this embodiment, the cooling water temperature is detected when the cetane number is detected. The condition is that Tw is equal to or higher than a predetermined temperature (see step 321 in FIG. 7). That is, according to the present embodiment (the invention described in claim 8), since the condition for detecting the cetane number of the fuel used is after completion of warming up of the engine, no error occurs in the detection of the cetane number.

  When the operating conditions deviate from the predetermined operating range, the combustion state due to the pilot injected fuel deteriorates and an error may occur in the detection of the cetane number. In this embodiment, the engine operating conditions are determined when detecting the cetane number. Is in a predetermined area (see step 322 in FIG. 7). That is, according to the present embodiment (the invention described in claim 9), since the condition for detecting the cetane number of the fuel used is when the operating condition is in a predetermined operating region, there is an error in the detection of the cetane number. It does not occur.

  When the operating condition is in the EGR region, the combustion state due to the pilot injected fuel deteriorates and an error may occur in the detection of the cetane number, but in this embodiment, the EGR is stopped when the cetane number is detected. (See step 323 in FIG. 7). That is, according to the present embodiment (the invention according to claim 10), the condition for detecting the cetane number of the fuel used is that the operating condition is not in the EGR region, so that an error occurs in the detection of the cetane number. There is no.

  According to the present embodiment (the invention described in claim 11), when the operating condition is in the EGR region, the cetane number of the fuel used is detected in a state where the EGR device is forcibly deactivated. Opportunities can be increased.

  According to the present embodiment (the invention described in claim 12), the pilot injected fuel is increased when the cetane number of the fuel used is detected (see step 325 in FIG. 7), so that the pilot injected fuel is not increased. Also, the cetane number can be detected with high accuracy.

  FIG. 13 is a flowchart for explaining the detection of the fuel property of the second embodiment, which replaces FIG. 6 of the first embodiment. The same steps as those in FIG. 6 are given the same step numbers.

  Steps 510, 520, 530, and 540 are different from FIG. The difference from FIG. 6 will be mainly described. In step 510, a predetermined map stored in advance in the ROM of the engine control unit 30 is searched from the engine rotational speed Ne and the load L to thereby determine the reference cetane number fuel. A pilot heat release rate maximum value PQ max0 [J / deg] is obtained.

  In step 520, the pilot heat generation rate maximum value PQ max [J / deg] of the used fuel is obtained from the calculated pilot heat generation rate dQ / dθ.

  In step 530, the pilot heat generation rate maximum value PQ max of the used fuel is divided by the pilot heat generation rate maximum value PQ max0 of the reference cetane number fuel, that is, the pilot heat generation rate maximum value coefficient KPQ [unknown number] ] Is calculated.

KPQ = PQ max / PQ max 0 (2)
In step 540, a cetane number C number of the fuel used is calculated by searching a table having the contents shown in FIG. 14 from the maximum pilot heat generation rate coefficient KPQ. As shown in FIG. 14, when the pilot heat generation rate maximum value coefficient KPQ is 1, that is, the pilot heat generation rate maximum value PQ max of the fuel used matches the pilot heat generation rate maximum value PQ max0 of the reference cetane number fuel. Sometimes the cetane number C number of the fuel used is equal to the reference cetane number (ie 55). As the pilot heat generation rate maximum value coefficient KPQ becomes larger than 1, the cetane number C number of the used fuel becomes larger than the reference cetane number, and conversely, the cetane number of the used fuel becomes smaller as the pilot heat generation rate maximum value coefficient KPQ becomes smaller than 1. C number is smaller than the reference cetane number.

  Here, when the pilot heat generation rate maximum value coefficient KPQ is larger than 1, that is, when the pilot heat generation rate maximum value PQ max of the used fuel is larger than the pilot heat generation rate maximum value PQ max0 of the reference cetane number fuel, The reason why the cetane number C number is made larger than the reference cetane number is that the cetane number of the fuel used at this time is higher than the reference cetane number, as described above in the lower part of FIG. On the contrary, when the pilot heat generation rate maximum value coefficient KPQ is smaller than 1, that is, when the pilot heat generation rate maximum value PQ max of the used fuel is smaller than the pilot heat generation rate maximum value PQ max0 of the reference cetane number fuel, the used fuel The reason why the cetane number C number of the fuel is made smaller than the reference cetane number is that the cetane number C number of the fuel used at this time is smaller than the reference cetane number, as described in the lower part of FIG. The characteristics shown in FIG. 14 are actually determined by adaptation.

  The second embodiment also has the same operational effects as the first embodiment. That is, according to the present embodiment (the invention described in claim 5), the fuel injection device 10 (variable fuel) that can be divided into main injection and pilot injection preceding the main injection and injected into the combustion chamber. Injection means), the pilot heat generation rate maximum value PQ max is detected as a pilot combustion state, and the cetane number C number of the fuel used is detected based on the detected pilot heat generation rate maximum value PQ max (FIG. 13). Steps 510, 340, 520, 530, 540), and the cetane number of the fuel used can be accurately detected with a simple configuration without requiring a large-scale device such as a viscosity measuring mechanism.

  In the embodiment, the pilot heat generation rate maximum timing PIT is detected (calculated) based on the pilot heat generation rate dQ / dθ, and the detected pilot heat generation rate maximum timing PIT is set to the pilot combustion state. However, the combustion start timing of the pilot injected fuel may be calculated based on the pilot heat generation rate PIT, and the calculated combustion start timing of the pilot injected fuel may be set to the pilot combustion state. Described invention).

Further, based on the combustion chamber pressure differential value dP / dθ due to the combustion of the pilot injected fuel and the combustion chamber pressure twice differential value dP ² / dθ ² due to the combustion of the pilot injected fuel, the combustion chamber pressure differential value due to the combustion of the pilot injected fuel. The time at which dP / dθ or the combustion chamber pressure twice differential value dP ² / dθ ² due to combustion of pilot injected fuel becomes maximum is calculated, and the calculated combustion chamber pressure differential value dP / dθ due to combustion of pilot injected fuel is calculated. The combustion chamber pressure differential value dP ² / dθ ² due to the combustion of the pilot injected fuel may be set to the pilot combustion state, or the combustion chamber pressure differential value dP / dθ due to the combustion of the pilot injected fuel may be used. and based on the combustion chamber pressure second derivative value dP ² / d [theta] ² by the combustion of the pilot injection fuel, combustion start timing of the pilot injection fuel Calculated, it may be a pilot combustion state of the combustion start timing of the calculated pilot injection fuel (claim 3 and 4).

Further, based on the combustion chamber pressure differential value dP / dθ due to the combustion of the pilot injected fuel and the combustion chamber pressure twice differential value dP ² / dθ ² due to the combustion of the pilot injected fuel, the combustion chamber pressure differential value due to the combustion of the pilot injected fuel. And a value in which the combustion chamber pressure twice differential value dP ² / dθ ² resulting from the combustion of the pilot injected fuel becomes maximum, and the calculated combustion chamber pressure differential value dP / dθ and the pilot injected fuel due to the combustion of the pilot injected fuel are calculated. A value that maximizes the differential value dP ² / dθ ^{2 in the} combustion chamber pressure twice due to the combustion may be set to the pilot combustion state (inventions according to claims 6 and 7).

  The function of the pilot combustion state detecting means according to claim 1 is performed by steps 340 and 350 in FIG. 6, and the function of the cetane number detecting means is performed by steps 360 and 370 in FIG.

1 is a schematic configuration diagram of an engine according to a first embodiment of the present invention. The change waveform figure of the pilot heat release rate when making the cetane number of used fuel differ. The change waveform figure of the combustion chamber pressure differential value by combustion of pilot injection fuel when making the cetane number of used fuel differ. The change waveform figure of a combustion chamber pressure twice differential value by combustion of pilot injection fuel when making the cetane number of used fuel differ. The flowchart for demonstrating a basic control routine. The flowchart for demonstrating the detection of a fuel property (cetane number). The flowchart for demonstrating determination of cetane number detection conditions. The characteristic figure of the cetane number to the pilot heat release rate maximum time coefficient. The flowchart for demonstrating engine exhaust control. The characteristic view of a pilot injection amount correction coefficient. The characteristic diagram of the main injection start timing correction amount. The characteristic diagram of a common rail pressure correction coefficient. The flowchart for demonstrating the detection of the fuel property of 2nd Embodiment. The characteristic figure of the cetane number to the pilot heat release rate maximum value coefficient of a 2nd embodiment. The characteristic view which shows the correlation of the viscosity and cetane number of light oil.

Explanation of symbols

1 Engine body 7 Pressure sensor (combustion chamber pressure detection means)
10 Fuel Injection Device (Variable Fuel Injection Means 15 Fuel Injection Valve 30 Engine Control Unit

Claims (12)

Variable fuel injection means capable of being divided into main injection and pilot injection preceding the main injection and capable of being injected into the combustion chamber;
Pilot combustion state detecting means for detecting a combustion state generated by the combustion of the pilot injected fuel as a pilot combustion state;
A diesel engine fuel property detection device comprising: a cetane number detection means for detecting a cetane number of a fuel used based on the detected pilot combustion state. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, heat generation rate calculation means for calculating a heat generation rate due to combustion of the pilot injected fuel in the combustion chamber,
Based on the calculated heat generation rate due to the combustion of the pilot injected fuel, calculation means for calculating the combustion start timing of the pilot injected fuel or the timing at which the heat generation rate due to the combustion of the pilot injected fuel is maximized;
The diesel engine according to claim 1, further comprising means for setting the calculated combustion start timing of the pilot injected fuel or the timing at which the heat generation rate by the combustion of the pilot injected fuel is maximized to the pilot combustion state. Fuel property detection device. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, differential value calculating means for calculating a pressure value in the combustion chamber due to combustion of the pilot injected fuel,
Based on the calculated combustion chamber pressure differential value due to the combustion of the pilot injected fuel, calculation means for calculating the combustion start timing of the pilot injected fuel or the timing at which the combustion chamber pressure differential value due to the combustion of the pilot injected fuel becomes maximum,
The means for setting the pilot combustion state to the time when the calculated combustion start time of the pilot injected fuel or the time when the pressure differential value in the combustion chamber due to the combustion of the pilot injected fuel becomes maximum is provided. Diesel engine fuel property detection device. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, a twice-derivative value calculating means for calculating a pressure in the combustion chamber twice due to the combustion of the pilot injected fuel,
Based on the calculated twice differential value in the combustion chamber pressure due to the combustion of the pilot injected fuel, a timing at which the combustion start time of the pilot injected fuel or the double differential value in the combustion chamber pressure due to the combustion of the pilot injected fuel becomes maximum is calculated. A calculation means;
And a means for setting the calculated combustion start timing of the pilot injected fuel or the maximum differential value of the pressure in the combustion chamber due to combustion of the pilot injected fuel to the pilot combustion state. The diesel engine fuel property detection device as described. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, heat generation rate calculation means for calculating a heat generation rate due to combustion of the pilot injected fuel in the combustion chamber,
Based on the calculated heat generation rate due to the combustion of the pilot injected fuel, a calculation means for calculating a value at which the heat generation rate due to the combustion of the pilot injected fuel becomes maximum;
The diesel engine fuel property detection device according to claim 1, further comprising means for setting the calculated value of the heat generation rate due to combustion of the pilot injected fuel to a maximum value in the pilot combustion state. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, differential value calculating means for calculating a pressure value in the combustion chamber due to combustion of the pilot injected fuel,
Based on the calculated differential pressure value in the combustion chamber due to the combustion of the pilot injected fuel, calculation means for calculating a value that maximizes the differential pressure value in the combustion chamber due to the combustion of the pilot injected fuel;
The diesel engine fuel property detection device according to claim 1, further comprising means for setting the calculated maximum value in the combustion chamber pressure due to combustion of the pilot-injected fuel to the pilot combustion state. The pilot combustion state detection means includes
Combustion chamber pressure detection means for detecting the pressure in the combustion chamber;
Based on the detected pressure in the combustion chamber, a twice-derivative value calculating means for calculating a pressure in the combustion chamber twice due to the combustion of the pilot injected fuel,
Calculation means for calculating a value at which the double differential value in the combustion chamber pressure due to the combustion of the pilot injected fuel is maximum based on the calculated double differential value in the combustion chamber pressure due to the combustion of the pilot injected fuel;
2. The fuel property detection of a diesel engine according to claim 1, further comprising: means for setting the value at which the calculated differential pressure in the combustion chamber twice due to combustion of the pilot-injected fuel is maximum to the pilot combustion state. apparatus.   The diesel engine fuel property detection device according to any one of claims 1 to 7, wherein the condition for detecting the cetane number of the used fuel is after completion of warm-up of the engine.   The diesel engine fuel property detection device according to any one of claims 1 to 7, wherein the condition for detecting the cetane number of the used fuel is when the operation condition is in a predetermined operation region. When the EGR device is provided and the EGR device is operated when the operating condition is in a predetermined EGR region,
The fuel property detection device for a diesel engine according to any one of claims 1 to 7, wherein the condition for detecting the cetane number of the fuel used is that the operating condition is not in an EGR region.   11. The fuel property detection device for a diesel engine according to claim 10, wherein the cetane number of the used fuel is detected in a state where the EGR device is forcibly deactivated when the operation condition is in an EGR region.   The diesel engine fuel property detection device according to any one of claims 1 to 7, wherein the amount of pilot injection fuel is increased when detecting the cetane number of the fuel used.

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