Fuel property determination device

Abstract

To properly grasp a use time of alternate fuel when fuel higher in cetane number and lower in heating value than diesel fuel is used as the alternate fuel.SOLUTION: An ECU 50 includes: an ignition timing determination portion for calculating an ignition timing when fuel injected from a fuel injection valve 17 is ignited in a combustion chamber 12 of an engine 10 and determining whether preignition enhancing an ignition timing occurs or not on the basis of the ignition timing; an exhaust determination portion acquiring an amount of a specific component containing at least any one of NOx and PM in an exhaust gas and determining whether degradation of the exhaust gas in which the amount of the specific component becomes excessive occurs or not on the basis of the amount of the specific component; and a fuel determination portion determining the use of alternate fuel in a case where the ignition timing determination portion determines the occurrence of the preignition and the exhaust determination portion determines that the degradation of exhaust does not occur.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The disclosure of the present specification relates to a fuel property determining device. [Background technology]

[0002] Diesel engines and other compression-ignition internal combustion engines primarily use diesel fuel. When diesel fuel has a high cetane number, which indicates how easily the fuel ignites, pre-ignition occurs, meaning that the fuel ignites early after injection from the fuel injection valve. This pre-ignition is thought to increase the amount of NOx in the exhaust gas.

[0003] Conventionally, there is known a technique for detecting whether the ignition timing of fuel after fuel injection from a fuel injection valve is more advanced than the standard ignition timing, i.e., whether pre-ignition has occurred, and, if an advance in the ignition timing is detected, performing control to retard the fuel injection timing in order to retard the ignition timing (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-171818 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the use of hydrogenated biodiesel fuel (HVO: Hydro-treated Vegetable Oil) and GTL (Gas to Liquid) fuel has been considered as alternative fuels to diesel. These alternative fuels have a higher cetane number and a lower calorific value than diesel, which affects the combustion state in internal combustion engines. Therefore, a technology that can properly grasp the use of such alternative fuels is desired.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a fuel property determination device that can properly determine when an alternative fuel that has a higher cetane number and a lower heating value than diesel is being used as an alternative fuel. [Means for solving the problem]

[0007] The present invention provides It is applied to compression ignition internal combustion engines that use diesel as the standard fuel, but also allow the use of alternative fuels that have a higher cetane number and lower heating value than diesel. an ignition timing determination unit that calculates an ignition timing at which fuel injected from a fuel injection valve in a combustion chamber of the internal combustion engine is ignited, and determines whether or not pre-ignition, in which the ignition timing is advanced, is occurring based on the ignition timing; an exhaust determination unit that acquires the amount of specific components including at least one of NOx and PM in the exhaust gas discharged from the combustion chamber, and determines whether or not exhaust gas deterioration has occurred, resulting in an excessive amount of the specific components, based on the amount of the specific components; a fuel determination unit that determines that the alternative fuel is being used when the ignition timing determination unit determines that the pre-ignition has occurred and the exhaust determination unit determines that the exhaust deterioration has not occurred during a predetermined fuel determination period; and The present invention is characterized by comprising:

[0008] In a compression-ignition internal combustion engine, when diesel fuel is used, pre-ignition can result in an increase in NOx and PM in the exhaust. On the other hand, when a fuel with a higher cetane number and lower calorific value than diesel is used as an alternative fuel to diesel, pre-ignition occurs, but NOx and PM in the exhaust do not increase. Focusing on this difference, the system determines whether pre-ignition has occurred in the internal combustion engine during a predetermined fuel determination period, and also determines whether exhaust deterioration, resulting in excessive amounts of specific components including at least one of NOx and PM, has occurred. If pre-ignition is determined to have occurred but exhaust deterioration has not occurred, it is determined that an alternative fuel is being used. This makes it possible to accurately determine that an alternative fuel is being used when a fuel with a higher cetane number and lower calorific value than diesel is used as an alternative fuel. [Brief explanation of the drawings]

[0009] [Figure 1] Overall schematic diagram of the engine. [Figure 2] 4 is a flowchart showing a procedure for fuel determination. [Figure 3] 4 is a flowchart showing a processing procedure for determining pre-ignition. [Figure 4] 4 is a flowchart showing a processing procedure for determining exhaust deterioration. [Figure 5] 4 is a flowchart showing a processing procedure for fuel injection control. [Figure 6] 10 is a flowchart showing a processing procedure for determining pre-ignition in another example. [Figure 7] 10 is a flowchart showing a processing procedure for determining exhaust deterioration in another example. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment in which a fuel property determination device according to the present invention is applied to a multi-cylinder diesel engine equipped with a common rail fuel injection system will be described below with reference to the drawings. The multi-cylinder diesel engine in this embodiment uses diesel as the standard fuel, but is also capable of using hydrogenated biodiesel fuel (HVO) or GTL fuel as an alternative fuel. The following describes the determination of fuel properties and fuel injection control when alternative fuels are used. An overall schematic diagram of the engine is shown in FIG.

[0011] In engine 10, a piston 11 is housed in a cylinder so as to be able to reciprocate. A combustion chamber 12 is connected to an intake passage 14 via an intake valve 13 and to an exhaust passage 16 via an exhaust valve 15. Engine 10 is provided with a fuel injection valve 17 that directly injects fuel into combustion chamber 12. Engine 10 is also provided with a rotation sensor 18 that detects the rotation of the crankshaft. Rotation sensor 18 is a crank sensor that outputs a rectangular crank pulse for each predetermined crank angle of engine 10. In this embodiment, rotation sensor 18 outputs a crank pulse every 6° CA during rotation of the crankshaft.

[0012] The exhaust passage 16 is provided with exhaust purification devices such as a diesel oxidation catalyst 21 that oxidizes and purifies hydrocarbons, carbon monoxide, and the like contained in the exhaust, a diesel particulate filter 22 that captures particulate components such as PM in the exhaust, and a selective reduction catalyst 23 that reduces nitrogen oxides (NOx) in the exhaust with ammonia. The exhaust passage 16 is also provided with a NOx sensor 24 that detects the amount of NOx in the exhaust emitted from the combustion chamber 12.

[0013] A fuel pump 33 is connected to the fuel tank 31 via a fuel pipe. Fuel introduced from the fuel tank 31 to the fuel pump 33 is pressurized by the operation of the fuel pump 33, and the pressurized fuel is supplied to a common rail 34. A fuel filter 32 that filters the fuel is disposed in the fuel pipe downstream of the fuel tank 31 and upstream of the fuel pump 33.

[0014] As is well known, the ECU 50 is an electronic control device mainly configured with a microcomputer including a CPU, ROM, RAM, etc., and executes various control programs stored in the ROM to perform various controls of the engine 10 according to the engine operating state at each time. Specifically, the ECU 50 calculates the fuel injection amount based on various detection signals input from the rotation sensor 18, accelerator sensor, etc., and controls fuel injection from the fuel injection valve 17 based on the fuel injection amount.

[0015] Furthermore, the ECU 50 variably sets the pressure of the fuel injected from the fuel injection valve 17 based on the operating state of the engine 10. In this case, the ECU 50 sets the fuel pressure to a higher pressure as the load of the engine 10 increases.

[0016] When diesel fuel is used, if the diesel fuel has a high cetane number, pre-ignition occurs, in which the fuel ignites early after injection from the fuel injection valve 17. When pre-ignition occurs, the fuel burns under conditions of high in-cylinder temperature and pressure, which may result in an increase in NOx and PM. Therefore, the ECU 50 detects pre-ignition and, if pre-ignition is detected, performs control to correct the injection timing to the retard side in order to retard the ignition timing. This suppresses an increase in NOx and PM.

[0017] On the other hand, the use of paraffin fuels such as hydrogenated biodiesel (HVO) and GTL fuels is being considered as an alternative fuel to diesel. These paraffin fuels have a higher cetane number and a lower calorific value than diesel.

[0018] According to the findings of the inventors, when paraffin fuel is used, pre-ignition occurs but NOx and PM in the exhaust do not increase. However, unless it is known whether the fuel being used is paraffin fuel or diesel, it becomes impossible to appropriately control the engine according to the fuel properties. In other words, when paraffin fuel is used, NOx and PM do not increase even if pre-ignition occurs, so retarding the injection timing is unnecessary. However, there is a concern that unnecessary retarding of the injection timing may result in a decrease in output and a deterioration in fuel efficiency.

[0019] Therefore, in this embodiment, a fuel determination is performed within a predetermined fuel determination period after refueling (after refueling the fuel tank 31) to determine whether or not paraffin fuel is being used as the fuel, and if it is determined that paraffin fuel is being used, the injection timing is not retarded. Furthermore, as the fuel determination, a determination is made as to whether or not pre-ignition has occurred and whether or not deterioration in exhaust emissions resulting in an excessive amount of NOx has occurred, and if it is determined that pre-ignition has occurred and that deterioration in exhaust emissions has not occurred, it is determined that paraffin fuel is being used.

[0020] 2 is a flowchart showing the fuel determination process according to this embodiment, which is executed by the ECU 50 at predetermined intervals after the IG is turned on.

[0021] In step S11, it is determined whether or not the fuel determination flag F1 is 0. The fuel determination flag F1 is a flag that indicates whether or not the fuel determination has been completed, and is reset to 0 when refueling and is set to 1 when the fuel determination is completed after refueling. Therefore, if the fuel determination is incomplete after refueling, the fuel determination flag F1 is 0, and if the fuel determination is completed, the fuel determination flag F1 is 1. The period during which the fuel determination flag F1 is 0, that is, the period until the fuel determination flag F1 is set to 1 after refueling, corresponds to the fuel determination period. The determination of whether or not refueling has been performed may be made based on detection information from a fuel amount sensor in the fuel tank 31, information on whether the fuel filler opening is open, etc.

[0022] If the fuel determination flag F1 is 0, the process proceeds to step S12. If the fuel determination flag F1 is 1, the process concludes that the fuel determination has been completed. In step S12, it is determined whether pre-ignition has occurred in the engine 10. The process procedure for determining pre-ignition will be described with reference to the flowchart in FIG. 3.

[0023] In step S21, it is determined whether the engine 10 is in a predetermined low-load operating state (e.g., an idling state). At this time, it is determined that the engine 10 is in a low-load operating state based on, for example, whether the fuel injection amount is equal to or less than a predetermined value, or whether the required torque or accelerator opening is equal to or less than a predetermined value. If the engine 10 is in a low-load operating state, the process proceeds to step S22. If the engine 10 is not in a low-load operating state, the pre-ignition determination is terminated.

[0024] In step S22, the ignition timing T of the fuel after fuel injection from the fuel injection valve 17 is detected. Specifically, the ignition timing T is detected by calculating the interval time ΔTCA between crank pulses output from the rotation sensor 18, and detecting the timing at which the interval time ΔTCA becomes equal to or shorter than a predetermined time as the ignition timing T. Alternatively, instead of the rotation sensor 18, a cylinder pressure sensor or a torque sensor may be used to detect the ignition timing T based on pressure fluctuations in the combustion chamber 12 detected by the cylinder pressure sensor or engine torque fluctuations detected by the torque sensor.

[0025] In step S23, the ignition delay Di is calculated, which is the elapsed time from fuel injection by the fuel injection valve 17 to ignition of the fuel. At this time, the ignition delay Di is calculated as the time from the injection timing to the ignition timing T. If pre-ignition occurs, that is, if the ignition timing T is excessively advanced, the ignition delay Di is calculated as a short time.

[0026] In step S24, 1 is added to the number m of times the ignition timing T is detected. In step S25, it is determined whether the number m of times the ignition timing T is detected is equal to or greater than a predetermined number Th1. If the number m of times the ignition timing T is detected is not equal to or greater than the predetermined number Th1, the process returns to step S21, and the detection of the ignition timing T and the calculation of the ignition delay Di are performed again (steps S21 to S24). In step S25, if the number m of times the detection is equal to or greater than the predetermined number Th1, the process proceeds to step S26, and an average value Dave of the ignition delay Di for m times is calculated.

[0027] In step S27, a reference value Dth is set as a reference for ignition delay Di. Specifically, the reference value Dth is set to an adapted value for ignition delay in an engine low load state (idling state) when diesel fuel with a predetermined cetane number (standard cetane number) obtained by a bench test or the like. Alternatively, the reference value Dth is set to a learned value for ignition delay in an engine low load state (idling state) when diesel fuel with a predetermined cetane number obtained by an inspection after vehicle assembly (End Of Line).

[0028] In step S28, it is determined whether the average value Dave is smaller than a reference value Dth, which is a threshold value for determining pre-ignition. If the average value Dave is smaller than the reference value Dth, the process proceeds to step S29, where it is determined that the ignition timing is excessively advanced, that is, pre-ignition has occurred. If the average value Dave is not smaller than the reference value Dth, step S29 is skipped, and the process for determining pre-ignition is terminated.

[0029] 2, after determining whether pre-ignition has occurred in step S12, the process proceeds to step S13, where it is determined whether exhaust deterioration has occurred. The processing procedure for determining whether exhaust deterioration has occurred will be described with reference to the flowchart in FIG.

[0030] In step S31, it is determined whether the engine 10 is in a predetermined medium-to-high load operating state. At this time, it is determined whether the engine 10 is in a medium-to-high load operating state based on, for example, whether the fuel injection amount is equal to or greater than a predetermined value, or whether the required torque or accelerator opening is equal to or greater than a predetermined value. If the engine 10 is in a medium-to-high load operating state, the process proceeds to step S32. If the engine 10 is not in a medium-to-high load operating state, the determination of exhaust gas deterioration is terminated.

[0031] In step S32, the amount E of NOx in the exhaust gas is acquired. The amount E of NOx is acquired from the detection value of the NOx sensor 24. The amount E of NOx generated by combustion may be estimated based on the engine operating state. In this case, for example, an in-cylinder pressure sensor provided in the combustion chamber 12 may detect the in-cylinder pressure during combustion, and the amount of NOx may be estimated based on the in-cylinder pressure.

[0032] In step S33, 1 is added to the number of times n the NOx amount E has been acquired. In step S34, it is determined whether the number of times n is acquired is equal to or greater than a predetermined number of times Th2. If the number of times n is not equal to or greater than the predetermined number of times Th2, the process returns to step S31, and the NOx amount E is acquired again (steps S31 to S33). In step S34, if the number of times n is acquired is equal to or greater than the predetermined number of times Th2, the process proceeds to step S35, and the average value Eave of the NOx amount E for n acquisitions is calculated.

[0033] In step S36, a reference value Eth is set as a reference for the NOx amount E. Specifically, the reference value Eth is set to an adapted value for the NOx amount in a medium-to-high load operating state when diesel fuel with a predetermined cetane number (standard cetane number) is used, obtained through a bench test. Alternatively, the reference value Eth is set to a learned value for the NOx amount in a medium-to-high load operating state when diesel fuel with a predetermined cetane number is used, obtained through an inspection after vehicle assembly (End Of Line).

[0034] In step S37, it is determined whether the average value Eave is smaller than a reference value Eth, which is a threshold value for determining whether exhaust gas has deteriorated. If the average value Eave is smaller than the reference value Eth, the process proceeds to step S38, where it is determined that no deterioration in exhaust gas has occurred. If the average value Eave is not smaller than the reference value Eth, step S38 is skipped, and the process for determining whether exhaust gas has deteriorated is terminated.

[0035] Returning to FIG. 2, in step S14, it is determined whether the pre-ignition determination and the exhaust gas deterioration determination have both been completed. If the pre-ignition determination and the exhaust gas deterioration determination have both been completed, the process proceeds to step S15. If either the pre-ignition determination or the exhaust gas deterioration determination has not been completed, the process is temporarily terminated.

[0036] In step S15, it is determined whether or not pre-ignition has occurred and exhaust gas deterioration has not occurred. If it is determined that pre-ignition has occurred and exhaust gas deterioration has not occurred, it is determined that paraffin fuel is being used as the fuel, and the process proceeds to step S16, where a paraffin fuel flag F2 indicating that paraffin fuel is being used as the fuel is set to 1. If the result in step S15 is negative, it is determined that diesel, which is the reference fuel, is being used as the fuel, and the process proceeds to step S17, where the paraffin fuel flag F2 is set to 0.

[0037] Thereafter, in step S18, the fuel determination flag F1 is set to 1, and the fuel determination process ends.

[0038] 5 is a flowchart showing the procedure for fuel injection control in this embodiment. This process is executed by the ECU 50.

[0039] 5, when it is detected that the ignition timing is advanced, retard control is performed to correct the injection timing of the fuel injection valve 17 to the retard side. The amount of retard of the injection timing when retard control is performed is set according to the degree of advance of the ignition timing, and the greater the degree of advance of the ignition timing, the greater the retard amount is set.

[0040] 5, when paraffin fuel is used as the fuel, in order to avoid unnecessary retardation of the injection timing, even if the ignition timing is advanced, retard correction of the injection timing is prohibited if paraffin fuel is used. Also, in order to avoid being unable to determine pre-ignition, retard correction of the injection timing is prohibited until fuel determination is completed.

[0041] 5, in step S41, an injection amount map is used to determine the fuel injection amount based on the engine rotation speed and required torque. In step S42, an injection period (a period during which the fuel injection valve 17 is energized) is calculated based on the fuel injection amount and fuel pressure, and the injection timing is determined based on the injection period and the engine rotation speed.

[0042] In step S43, it is determined whether the ignition timing of fuel has been advanced after the immediately preceding fuel injection. In this case, the ECU 50 detects the ignition timing for each combustion cycle based on, for example, the crank pulse interval time ΔTCA, and determines whether the ignition timing has been advanced based on whether the ignition timing is more advanced than a predetermined timing. Note that the ignition timing can also be detected based on fluctuations in pressure within the combustion chamber 12 or fluctuations in engine torque. It can also be determined whether the ignition timing has been advanced based on the ignition delay Di calculated by the process of FIG. 3.

[0043] If the ignition timing is not advanced, steps S44 to S46 are skipped and the process proceeds to step S47. In step S47, fuel injection is performed without correcting the injection timing to be retarded.

[0044] On the other hand, if the ignition timing has been advanced, the process proceeds to step S44. In step S44, it is determined whether or not the fuel determination flag F1 is set to 1, that is, whether or not the fuel determination has been completed. In this case, if the fuel determination has not been completed after refueling (if F1=0), the result of step S44 is negative and the process proceeds to step S47 to prohibit retarding of the injection timing. As a result, even if the ignition timing has been advanced during the period from refueling until the fuel determination is completed, fuel injection is performed without retarding the injection timing.

[0045] Furthermore, if the fuel determination is completed after refueling (if F1 = 1), the process proceeds to step S45. In step S45, it is determined whether or not the paraffin fuel flag F2 is set to 0, that is, whether or not paraffin fuel is being used as the fuel. In this case, if diesel is being used as the fuel (if F2 = 0), the injection timing is retarded in step S46, and then fuel injection is performed in step S47.

[0046] If paraffin fuel is used as the fuel (F2=1), step S46 is skipped and fuel injection is performed in step S47. As a result, in a situation where paraffin fuel is used, even if the ignition timing is advanced, fuel injection is performed without correcting the injection timing to be retarded.

[0047] According to the present embodiment described above in detail, the following excellent effects can be obtained.

[0048] During a predetermined period after refueling, the system determines whether pre-ignition has occurred in the engine 10 and whether exhaust gas deterioration, resulting in an excessive amount of NOx in the exhaust, has occurred. If it is determined that pre-ignition has occurred but exhaust gas deterioration has not occurred, it is determined that an alternative fuel is being used. This makes it possible to properly determine that an alternative fuel is being used when paraffin fuel, which has a higher cetane number and a lower calorific value than diesel, is being used as an alternative fuel.

[0049] When paraffin fuel is used as the alternative fuel, there is no need to retard the injection timing even if pre-ignition occurs, and unnecessary retardation of the injection timing can cause a decrease in output and lead to a deterioration in fuel economy. In this regard, by prohibiting the retard correction of the injection timing when it is determined that paraffin fuel is being used, it is possible to suppress the deterioration in fuel economy caused by unnecessary retardation of the injection timing.

[0050] The fuel used is determined each time refueling is performed, but if the fuel injection timing is retarded immediately after refueling due to the occurrence of pre-ignition, it may be difficult to determine whether pre-ignition occurs when paraffin fuel is used. In this regard, the system prohibits the retardation of the fuel injection timing until the fuel determination is completed after refueling. This makes it possible to properly determine whether paraffin fuel is being used as an alternative fuel.

[0051] The ignition timing of fuel varies depending on the volatility of the fuel immediately after injection from the fuel injection valve 17. Furthermore, the volatility of fuel varies depending on the fuel pressure. Focusing on these facts, the occurrence of pre-ignition is determined based on the ignition timing T calculated when the engine 10 is operating at low load. In other words, when the engine 10 is operating at low load, the fuel pressure is low and therefore the volatility of the fuel in the combustion chamber 12 is low, making it possible to properly determine pre-ignition when using paraffin fuel. This enables improved accuracy in fuel determination.

[0052] Furthermore, when the engine 10 is in a medium to high load operating state, the amount of exhaust gas increases, and it is possible to properly determine the increase or decrease in the amount of NOx E in the exhaust gas. This makes it possible to improve the accuracy of fuel determination.

[0053] (Other embodiments) The above embodiment may be modified as follows, for example.

[0054] When paraffin fuel is used, the degree of variation in ignition timing T increases compared to when diesel is used due to the improved ignition characteristics of the fuel. Taking this into consideration, the method of determining pre-ignition using the average value of ignition timing T in Figure 3 may be changed to determine pre-ignition based on the degree of variation in ignition timing T.

[0055] Fig. 6 is a flowchart showing the processing steps when determining pre-ignition based on the degree of variation in ignition timing T. The processing in Fig. 6 is performed in place of the processing in Fig. 3. In steps S51 to S55 in Fig. 6, the same processing as in steps S21 to S25 in Fig. 3 is performed.

[0056] In step S56, a standard deviation Dσ indicating the degree of variation in the ignition timing T is calculated based on m ignition timings T. Note that what is calculated here is not limited to the standard deviation as long as it indicates the degree of variation in the ignition timing T.

[0057] In step S57, a reference value Dσth of the standard deviation Dσ is set. This reference value Dσth is preferably determined based on the standard deviation of the ignition timing T when diesel fuel is used. In step S58, it is determined whether the standard deviation Dσ is greater than the reference value Dσth. If the standard deviation Dσ is greater than the reference value Dσth, the process proceeds to step S59, where it is determined that pre-ignition has occurred. If the standard deviation Dσ is not greater than the reference value Dσth, it is determined that pre-ignition has not occurred, step S59 is skipped, and the pre-ignition determination ends.

[0058] Pre-ignition may also be determined based on the average value of the ignition timing and the degree of variation in the ignition timing. In this case, it is preferable to determine that pre-ignition has occurred when the average value Dave is shorter than the reference value Dth and the standard deviation Dσ is larger than the reference value Dσth.

[0059] When paraffin fuel is used, the degree of variation in ignition timing is greater than when diesel fuel is used, which causes greater variations in in-cylinder pressure and in-cylinder temperature during fuel combustion, resulting in greater variations in the amount of NOx. Taking this into consideration, while Figure 4 shows that exhaust gas deterioration is determined based on the average value of the amount of NOx, this may be changed to determine exhaust gas deterioration based on the degree of variation in the amount of NOx.

[0060] Fig. 7 is a flowchart showing the processing procedure when determining exhaust deterioration based on the degree of variation in the NOx amount. The processing in Fig. 7 is performed in place of the processing in Fig. 4. In steps S61 to S64 in Fig. 7, the same processing as in steps S31 to S34 in Fig. 3 is performed.

[0061] In step S65, a standard deviation Eσ indicating the degree of variation in the NOx amount is calculated based on the n-times NOx amount E. Note that what is calculated here is not limited to the standard deviation as long as it indicates the degree of variation in the NOx amount.

[0062] In step S66, a reference value Eσth of the standard deviation Eσ is set. This reference value Eσth is preferably determined based on the standard deviation of the NOx amount E when diesel fuel is used. In step S67, it is determined whether the standard deviation Eσ is greater than the reference value Eσth. If the standard deviation Eσ is greater than the reference value Eσth, the process proceeds to step S68, where it is determined that no deterioration in exhaust emissions has occurred. If the standard deviation Eσ is not greater than the reference value Eσth, it is determined that deterioration in exhaust emissions has occurred, and step S68 is skipped, and the determination of exhaust emissions deterioration is terminated.

[0063] Furthermore, exhaust deterioration may be determined based on the average value of the NOx amount and the degree of variation in the NOx amount. In this case, it may be determined that exhaust deterioration is not occurring when the average value Eave is smaller than the reference value Eth and the standard deviation Eσ is larger than the reference value Eσth.

[0064] In the determination of exhaust gas deterioration in FIG. 4 , the amount of NOx is acquired as the amount of a specific component in the exhaust, and whether exhaust gas deterioration is occurring is determined based on the amount of NOx. However, this may be modified. Specifically, a PM sensor that detects the amount of PM in the exhaust may be provided in the exhaust passage 16, and the amount of PM in the exhaust may be acquired and used to determine whether exhaust gas deterioration is occurring. Alternatively, the amount of PM may be calculated from the detection value of an air-fuel ratio sensor provided in the exhaust passage 16. For example, a correlation between the air-fuel ratio and the amount of PM per unit volume of exhaust gas may be used to calculate the unit amount of PM based on the air-fuel ratio detected by the air-fuel ratio sensor, and the PM amount may be calculated based on the unit amount of PM and the exhaust flow rate calculated based on the engine speed, etc.

[0065] When determining whether exhaust gas is deteriorating based on the amount of PM, as when determining whether exhaust gas is deteriorating based on the amount of NOx, the average amount of PM is calculated, a reference value that is the standard for the amount of PM is set, and if the average amount of PM is less than the reference value, it is determined that exhaust gas is not deteriorating, and if the average amount of PM is not less than the reference value, i.e., if the average amount of PM is equal to or greater than the reference value, it is determined that exhaust gas is deteriorating.

[0066] Alternatively, the amount of NOx and the amount of PM may be acquired, and it may be determined whether or not exhaust gas deterioration has occurred based on the amount of NOx and the amount of PM. When determining whether or not exhaust gas deterioration has occurred based on the amount of NOx and the amount of PM, it may be determined that exhaust gas deterioration has not occurred if the average value of the NOx amount is less than a reference value and the average value of the PM amount is also less than a reference value.

[0067] When determining pre-ignition in FIG. 3 (step S28), the pre-ignition determination threshold may be set by correcting the reference value Dth, which is set by adaptation, learning, or the like, in accordance with the refueling amount. Specifically, the ECU 50 calculates a refueling ratio R, which indicates the ratio of the additional fuel amount added to the fuel amount after refueling (R = additional fuel amount / fuel amount after refueling), and calculates a reference change amount ΔD based on the refueling ratio R. The pre-ignition determination threshold may be variably set based on the reference value Dth and the reference change amount ΔD. In this case, the smaller the refueling ratio R, the higher the value of the determination threshold is preferably set. As a result, the smaller the refueling ratio R, the more likely it is that pre-ignition has occurred. Note that the determination threshold may be set to a higher value as the refueling ratio R increases.

[0068] When determining whether exhaust gas has deteriorated (step S37) in FIG. 4, the determination threshold for exhaust gas deterioration may be set by correcting the reference value Eth, which is set by adaptation, learning, or the like, in accordance with the refueling amount. Specifically, the ECU 50 calculates a refueling ratio R, which indicates the ratio of the additional fuel amount added to the fuel amount after refueling (R = additional fuel amount / fuel amount after refueling), and calculates a reference change amount ΔE based on the refueling ratio R. The determination threshold for exhaust gas deterioration is variably set based on the reference value Eth and the reference change amount ΔE. In this case, the smaller the refueling ratio R, the higher the determination threshold value should be set. As a result, the smaller the refueling ratio R, the more easily it becomes possible to determine that no deterioration in exhaust gas has occurred. Note that the determination threshold value may be set to a higher value as the refueling ratio R increases.

[0069] In the above embodiment, the pre-ignition determination is performed when the engine 10 is operating at a low load, and the exhaust gas deterioration determination is performed when the engine 10 is operating at a medium to high load. However, this may be modified. For example, the pre-ignition determination and the exhaust gas deterioration determination may be performed under the same engine operating conditions. Alternatively, the pre-ignition determination may be performed during combustion in which the pre-ignition occurs, and if the pre-ignition occurs but the NOx deterioration does not occur, the determination may be made that paraffin fuel is being used.

[0070] The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium.

[0071] The technical ideas extracted from the above-described embodiments will be described below. [Configuration 1] The present invention is applied to a compression ignition internal combustion engine (10) that uses diesel as a standard fuel but allows the use of alternative fuels that have a higher cetane number and a lower heating value than diesel, an ignition timing determination unit that calculates an ignition timing at which fuel injected from a fuel injection valve (17) in a combustion chamber (12) of the internal combustion engine ignites, and determines whether or not pre-ignition, in which the ignition timing is advanced, occurs based on the calculated ignition timing; an exhaust determination unit that acquires the amount of specific components including at least one of NOx and PM in the exhaust gas discharged from the combustion chamber, and determines whether or not exhaust gas deterioration has occurred, resulting in an excessive amount of the specific components, based on the amount of the specific components; a fuel determination unit that determines that the alternative fuel is being used when the ignition timing determination unit determines that the pre-ignition has occurred and the exhaust determination unit determines that the exhaust deterioration has not occurred during a predetermined fuel determination period; and A fuel property determination device (50) comprising: [Configuration 2] a retard control unit that corrects the injection timing of the fuel injection valve to a retard side based on the occurrence of an advance in the ignition timing of fuel in the internal combustion engine, 2. The fuel property determination device according to claim 1, further comprising a correction prohibition unit that prohibits the retardation control unit from correcting the injection timing in a retarded state when the fuel determination unit determines that the alternative fuel is being used. [Configuration 3] 3. The fuel property determining device according to claim 2, wherein the correction prohibition unit prohibits the retard control unit from making a retard correction of the injection timing after refueling until the fuel determination unit completes the fuel determination. [Configuration 4] The present invention is applied to a fuel injection system in which the pressure of fuel injected from the fuel injection valve is variable, and the higher the load of the internal combustion engine, the higher the fuel pressure is, The fuel property determination device according to any one of configurations 1 to 3, wherein the ignition timing determination unit determines that the pre-ignition has occurred based on the ignition timing calculated under a predetermined low-load operating condition of the internal combustion engine. [Configuration 5] 5. The fuel property determination device according to any one of configurations 1 to 4, wherein the exhaust determination unit determines that the exhaust deterioration is not occurring based on the amount of the specific component acquired during medium to high load operation of the internal combustion engine. [Configuration 6] 6. The fuel property determination device according to any one of configurations 1 to 5, wherein the ignition timing determination unit calculates a degree of variation in the ignition timing during the fuel determination period, and determines that the pre-ignition has occurred based on the degree of variation in the ignition timing being equal to or greater than a reference value. [Configuration 7] The fuel property determination device according to any one of configurations 1 to 6, wherein the exhaust determination unit calculates a degree of variation in the amount of the specific component during the fuel determination period, and determines that the exhaust deterioration has not occurred based on the degree of variation in the amount of the specific component being equal to or greater than a reference value. [Explanation of symbols]

[0072] 10...engine, 12...combustion chamber, 17...fuel injector, 50...ECU.

Claims

1. The present invention is applied to a compression ignition internal combustion engine (10) that uses diesel as a standard fuel, but allows the use of alternative fuels that have a higher cetane number and a lower calorific value than diesel, an ignition timing determination unit that calculates an ignition timing at which fuel injected from a fuel injection valve (17) in a combustion chamber (12) of the internal combustion engine ignites, and determines whether or not pre-ignition, in which the ignition timing is advanced, has occurred based on the ignition timing; an exhaust determination unit that acquires the amount of specific components including at least one of NOx and PM in the exhaust gas discharged from the combustion chamber, and determines whether or not exhaust gas deterioration has occurred, resulting in an excessive amount of the specific components, based on the amount of the specific components; a fuel determination unit that determines that the alternative fuel is being used when the ignition timing determination unit determines that the pre-ignition has occurred and the exhaust determination unit determines that the exhaust deterioration has not occurred during a predetermined fuel determination period; and A fuel property determination device (50) comprising:

2. a retard control unit that corrects the injection timing of the fuel injection valve to a retard side based on the occurrence of an advance in the ignition timing of fuel in the internal combustion engine, 2. The fuel property determining device according to claim 1, further comprising a correction prohibition unit that prohibits the retardation control unit from retarding the injection timing when the fuel determining unit determines that the alternative fuel is being used.

3. 3. The fuel property determining device according to claim 2, wherein the correction prohibition unit prohibits the retard control unit from retarding the injection timing after refueling until the fuel determination unit completes the fuel determination.

4. The present invention is applied to a fuel injection system in which the pressure of fuel injected from the fuel injection valve is variable, and the higher the load of the internal combustion engine, the higher the fuel pressure is, 2. The fuel property determining device according to claim 1, wherein the ignition timing determining unit determines whether the pre-ignition has occurred based on the ignition timing calculated under a predetermined low-load operating condition of the internal combustion engine.

5. 2. The fuel property determining device according to claim 1, wherein the exhaust determining unit determines that the deterioration of exhaust gas is not occurring based on the amount of the specific component acquired during medium to high load operation of the internal combustion engine.

6. 6. The fuel property determination device according to claim 1, wherein the ignition timing determination unit calculates a degree of variation in the ignition timing during the fuel determination period, and determines that the pre-ignition has occurred based on the degree of variation in the ignition timing being equal to or greater than a reference value.

7. 6. The fuel property determination device according to claim 1, wherein the exhaust determination unit calculates a degree of variation in the amount of the specific component during the fuel determination period, and determines that the exhaust deterioration has not occurred based on the degree of variation in the amount of the specific component being equal to or greater than a reference value.

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