Soot emission characteristic evaluation method and soot emission characteristic evaluation system

Abstract

To allow for appropriately estimating the amount of soot generated when a fuel is injected and burned.SOLUTION: A soot discharge characteristics evaluation method disclosed herein comprises injecting and burning a fuel under predetermined injection conditions, and estimating the amount of soot generated by the fuel on the basis of a spatio-temporal luminescence intensity distribution of self-luminescence of C2 radicals and OH radicals, which are active chemical species that differs depending on the composition of the fuel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a soot emission characteristic evaluation method and a soot emission characteristic evaluation system. [Background technology]

[0002] Starting in January 2020, regulations on the sulfur content of marine fuel oil in general sea areas will become stricter, and in response to these regulations, the use of light cycle oil (LCO), which is considered to have a high aromatic content, is expected to increase. It is known that soot emitted by the combustion of fuel oil is affected by the fuel composition. The amount of soot produced is generally said to increase in the following order: normal paraffins, isoparaffins, and aromatics.

[0003] Cracked diesel contains a lot of aromatic components, and the amount of aromatics in the cracked diesel is determined by the amount of aromatics contained in the crude oil. Therefore, there are various types of cracked diesel depending on the country of crude oil production. As a result, the emission characteristics of soot in exhaust gas are greatly influenced by the type of cracked diesel mixed with it. In addition, the injection characteristics of the fuel are important in reducing the amount of soot generated, and the effects of high-pressure fuel injection and multi-stage injection have been shown.

[0004] On the other hand, it is known that C2 radicals, which are intermediate products of combustion, contribute to the generation of soot emitted from internal combustion engines, and OH radicals, which are also intermediate products, contribute to the oxidation of soot.

[0005] As a method for measuring soot particles resulting from fuel combustion, a laser induced incandescence method is known in which soot particles are irradiated with high-intensity laser light and the signal from the red-hot soot particles is measured to determine the soot particle concentration (Non-Patent Document 1). In addition, a technology has been disclosed for determining the temperature of particles or droplets based on the principle of a two-color pyrometer using two laser beams (Patent Document 1). In the two-color method, the blackbody radiation intensity of two wavelengths is captured as the brightness of an image, and the soot temperature can be determined by utilizing the fact that the blackbody radiation intensity is expressed as a function of the soot concentration and flame temperature.

[0006] Also disclosed is a method for diagnosing combustion from combustion products such as OH, C3, CH, CHO, CHO, C2, soot, H2O, and CO2 by measuring the emission spectrum of the flame when fuel is burned (Patent Document 2). Also disclosed is a combustion state diagnosis device that measures the emission intensity of CH radicals, C2 radicals, etc. from the emission spectrum of the flame to diagnose the combustion state of the fuel (Patent Document 3). Also disclosed is a combustion analysis device that images a combustion field and analyzes the combustion state in the combustion field using hyperspectral data that shows the spectrum for each pixel of the captured image (Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 61-138002 [Patent Document 2] JP 2012-13580 A [Patent Document 3] JP 2013-72574 A [Patent Document 4] JP 2015-218699 A [Non-patent literature]

[0008] [Non-Patent Document 1] "Soot Measurement by LII Method and Its Application to Diesel Exhaust Gas", Kazuhiro Yamamoto et al., Transactions of the Japan Society of Mechanical Engineers (Series B), Vol. 74, No. 738 (2008-2) Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the method of evaluating the amount of soot generated from a fuel by conducting a combustion test using an actual internal combustion engine, the soot contained in the exhaust gas is collected and evaluated, which has the problem that the equipment required for the combustion evaluation becomes large-scale.

[0010] In addition, the conventional two-color method is suitable for analyzing the combustion of fuels with good ignition properties, such as diesel, but is not suitable for analyzing the combustion of fuels with low ignition properties, such as marine fuels and some alternative fuels. In addition, depending on the combustion conditions, there are cases where a luminous flame is not observed but there is a large amount of soot generated, and there are limitations to the evaluation of soot using the two-color method.

[0011] In addition, in conventional soot evaluation using image analysis, the spontaneous emission distribution of C2 radicals, which are one of the intermediate combustion products that are thought to contribute to soot generation, and the spatial distribution of blackbody radiation of soot generated during combustion are measured. However, these are merely measurements of the emission intensity of substances involved in soot generation. In other words, the soot generation process begins with the thermal decomposition of fuel and involves time-dependent changes such as the generation of aromatic compounds, soot nucleation, coagulation, and oxidation, and there are limitations to the method of evaluating the amount of soot generation only based on the emission intensity of substances related to soot generation. In particular, there are no known cases in which the generation of soot emitted from intermittent combustion, such as diesel engines, has been evaluated.

[0012] An object of the present invention is to provide a soot emission characteristic evaluation method and a soot emission characteristic evaluation system for appropriately estimating the amount of soot generated relative to the fuel composition and fuel injection characteristics. [Means for solving the problem]

[0013] A method for optically evaluating the soot emission characteristics of a fuel corresponding to claim 1 is a soot emission characteristics evaluation method characterized by injecting and combusting the fuel under specified injection conditions, and estimating the amount of soot generated from the fuel based on the spatiotemporal emission intensity distribution due to the spontaneous emission of active chemical species, C2 radicals and OH radicals, which differ depending on the composition of the fuel.

[0014] Here, it is preferable to estimate the amount of soot generated based on the maximum value of the integrated brightness value of each of the C2 radicals and the OH radicals as the emission intensity distribution and the emission time.

[0015] The amount of soot generated is estimated by the following formula (1):

number

[0016] It is also preferable that the coefficients α, β, γ, and δ in the estimation formula are set using actually measured soot values.

[0017] In addition, it is preferable that the coefficients α, β, γ, and δ are set by selecting multiple types of hydrocarbon fuel as the fuel, burning them with uniform injection amounts as the injection condition, and using the least squares method based on the spatiotemporal emission intensity distribution and the actually measured soot value.

[0018] In addition, it is preferable that the coefficients α, β, γ, and δ are set by using a soot emission characteristic evaluation system used for evaluating the soot emission characteristics.

[0019] In addition, it is preferable that the spatiotemporal emission intensity distribution of the C2 radicals and the OH radicals is obtained by integrating the brightness values ​​for each pixel of image data obtained by spectroscopically capturing the spontaneous emission of the C2 radicals and the OH radicals in the fuel using a high-speed camera, and converting the data into time-series data.

[0020] It is also preferable that the injection conditions include at least the pressure in the injection space and the injection pressure of the fuel.

[0021] It is also preferable that the injection conditions include a condition for changing the injection pressure of the fuel, or a condition for injecting the fuel a plurality of times.

[0022] A system for optically evaluating the soot emission characteristics of a fuel corresponding to claim 10 is a soot emission characteristics evaluation system characterized by comprising: a combustion means for injecting and combusting the fuel under predetermined injection conditions; an emission measurement means for measuring the spontaneous emission of active chemical species, C2 radicals and OH radicals, which differ depending on the composition of the fuel; an emission intensity distribution analysis means for analyzing the spatiotemporal emission intensity distribution of the measured spontaneous emission; and a soot generation amount estimation means for estimating the amount of soot generation of the fuel based on the emission intensity distribution.

[0023] Here, it is preferable that the soot generation amount estimating means estimates the amount of soot generation based on a maximum value of an integrated luminance value of each of the C2 radicals and the OH radicals as the emission intensity distribution and an emission time.

[0024] The soot generation amount estimating means estimates the amount of soot generated according to the following estimation formula (2):

number

[0025] It is also preferable that the luminescence measuring means has a two-branch optical system for separately measuring the spontaneous luminescence of the C2 radical and the OH radical, or has a plurality of imaging means for respectively imaging the C2 radical and the OH radical.

[0026] It is also preferable that the light emission measuring means has a high-speed camera, and the high-speed camera captures images of the spontaneous light emission of the C2 radicals and the OH radicals in the fuel.

[0027] It is also preferable that the luminescence intensity distribution analysis means obtains the spatiotemporal luminescence intensity distribution of the C2 radical and the OH radical as time-series data by integrating the brightness values ​​of each pixel of image data captured by the high-speed camera.

[0028] In addition, it is preferable that the combustion means uses a rapid compression device capable of simulating one cycle of combustion in a diesel engine, and that in the rapid compression device, at least the pressure of the injection space and the injection pressure of the fuel are changeable as the injection conditions. Effect of the Invention

[0029] The method for optically evaluating the soot emission characteristics of a fuel corresponding to claim 1 comprises injecting and combusting the fuel under specified injection conditions, and estimating the amount of soot generated from the fuel based on the spatiotemporal distribution of emission intensity due to the spontaneous emission of active chemical species, C2 radicals and OH radicals, which differ depending on the fuel composition, thereby making it possible to appropriately estimate the amount of soot generated by the combustion of the fuel under specified injection conditions.

[0030] Here, by estimating the amount of soot generated from the maximum integrated brightness values ​​of C2 radicals and OH radicals as the emission intensity distribution and the emission time, it is possible to appropriately estimate the amount of soot generated, taking into account intermediate combustion products that contribute to the generation and oxidation of soot due to the combustion of hydrocarbon fuels such as diesel fuel.

[0031] The amount of soot generated is estimated by the following formula (3):

number

[0032] Furthermore, by setting the coefficients α, β, γ, and δ in the estimation equation using the actually measured soot values, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion based on an estimation equation that uses coefficients optimized based on the actually measured soot values.

[0033] In addition, by selecting multiple types of hydrocarbon fuels as the fuel, burning them with the same injection amount as the injection condition, and setting the coefficients α, β, γ, and δ using the least squares method based on the spatiotemporal emission intensity distribution and the actually measured soot value, it becomes possible to appropriately set the coefficients related to the amount of soot generated by the combustion of multiple types of hydrocarbon fuels.

[0034] Furthermore, by setting the coefficients α, β, γ, and δ using a soot emission characteristics evaluation system used to evaluate soot emission characteristics, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion based on the coefficients optimized using the same soot emission characteristics evaluation system.

[0035] In addition, the spatiotemporal emission intensity distribution of C2 radicals and OH radicals was obtained by integrating the brightness values ​​for each pixel of image data obtained by spectroscopically capturing the spontaneous emission of C2 radicals and OH radicals in the fuel using a high-speed camera, and converting it into time-series data.This makes it possible to appropriately estimate the amount of soot generated by fuel combustion using the highly accurate time-series data obtained by the high-speed camera.

[0036] In addition, by including at least the pressure of the injection space and the fuel injection pressure in the injection conditions, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion, for example, based on the pressure difference between the pressure of the injection space and the fuel injection pressure, i.e., the fuel injection pressure.

[0037] In addition, by including a condition for changing the fuel injection pressure or a condition for injecting fuel multiple times, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion based on the condition for changing the fuel injection pressure or the condition for injecting fuel multiple times.

[0038] A system for optically evaluating the soot emission characteristics of a fuel corresponding to claim 10 comprises a combustion means for injecting and combusting the fuel under predetermined injection conditions, an emission measurement means for measuring the spontaneous emission of active chemical species, C2 radicals and OH radicals, which differ depending on the composition of the fuel, an emission intensity distribution analysis means for analyzing the spatiotemporal emission intensity distribution of the measured spontaneous emission, and a soot generation amount estimation means for estimating the amount of soot generated from the fuel based on the emission intensity distribution, thereby making it possible to appropriately estimate the amount of soot generated by fuel combustion.

[0039] Here, the soot generation amount estimation means estimates the amount of soot generation based on the maximum integrated brightness values ​​of C2 radicals and OH radicals as the emission intensity distribution and the emission time, thereby making it possible to appropriately estimate the amount of soot generation taking into account intermediate combustion products that contribute to the generation and oxidation of soot due to the combustion of hydrocarbon fuels such as diesel fuel.

[0040] The soot generation amount estimation means estimates the amount of soot generated by the following estimation formula (4):

number

[0041] In addition, the light emission measuring means may have a two-branch optical system for separately measuring the spontaneous emission of C2 radicals and OH radicals, or may have multiple imaging means for imaging C2 radicals and OH radicals, respectively, making it possible to divide a single subject into two or more parts and appropriately estimate the amount of soot generated based on the spontaneous emission of C2 radicals and OH radicals.

[0042] In addition, the light emission measurement means has a high-speed camera which captures images of the spontaneous emission of C2 radicals and OH radicals in the fuel, making it possible to appropriately estimate the amount of soot generated by fuel combustion using highly accurate time series data obtained by the high-speed camera.

[0043] In addition, the emission intensity distribution analysis means calculates the spatiotemporal emission intensity distribution of C2 radicals and OH radicals by integrating the brightness values ​​of each pixel of image data captured by a high-speed camera to generate time-series data, thereby making it possible to appropriately estimate the amount of soot generated by fuel combustion using time-series data based on the brightness values ​​of each pixel contained in the image data obtained by the high-speed camera.

[0044] In addition, the combustion means uses a rapid compression device that can simulate one cycle of combustion in a diesel engine, and the rapid compression device allows the injection conditions, namely, at least the pressure of the injection space and the fuel injection pressure, to be changed, making it possible to appropriately estimate the amount of soot generated by fuel combustion without using large-scale equipment or large amounts of test fuel. [Brief description of the drawings]

[0045] [Figure 1] 1 is a diagram showing a configuration of a soot emission characteristic evaluation system according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing a configuration of an optical system device according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing an example of components contained in a fuel according to an embodiment of the present invention. [Figure 4] FIG. 4 is a graph showing the relationship between the aromatic content and the ignition delay time of fuel. [Diagram 5] FIG. 13 is a graph showing changes in spontaneous emission of C2 radicals and OH radicals with respect to the elapsed time from the start of fuel injection. [Figure 6] FIG. 4 is a graph showing a change in heat release rate with respect to the elapsed time from the start of fuel injection. [Figure 7] FIG. 13 is a graph showing changes in spontaneous emission of C2 radicals and OH radicals with respect to the elapsed time from the start of fuel injection. [Figure 8] FIG. 4 is a graph showing a change in heat release rate with respect to the elapsed time from the start of fuel injection. [Figure 9] FIG. 13 is a graph showing the change in integrated luminance value for C2 radicals versus the elapsed time from the start of fuel injection. [Figure 10] FIG. 13 is a graph showing the change in integrated luminance value for OH radicals versus the elapsed time from the start of fuel injection. [Figure 11] FIG. 13 is a graph showing the change in integrated luminance value for C2 radicals versus the elapsed time from the start of fuel injection. [Figure 12] FIG. 13 is a graph showing the change in integrated luminance value for OH radicals versus the elapsed time from the start of fuel injection. [Figure 13]FIG. 11 is a graph showing the relationship between the maximum value of the C2 radical integrated brightness value per fuel injection amount and the amount of soot generated. [Figure 14] FIG. 11 is a graph showing the relationship between the maximum value of the OH radical integrated brightness value per fuel injection amount and the amount of soot generated. [Figure 15] FIG. 1 is a graph showing the relationship between the emission time of C2 radicals and the amount of soot generated per fuel injection amount. [Figure 16] FIG. 11 is a graph showing the relationship between the light emission time of OH radicals and the amount of soot generated per fuel injection amount. [Figure 17] FIG. 4 is a diagram showing the relationship of the effect of each parameter on the amount of soot generated. [Figure 18] FIG. 4 is a diagram showing the relationship between the estimated amount of soot generated and the actually measured amount of soot generated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] As shown in Figure 1, the soot emission characteristic evaluation system 100 in an embodiment of the present invention is configured to include a rapid compression device 10, which is a combustion means, a dry air cylinder 12, a dry air tank 14, a heating and pressurizing means 16, a fuel supply means 18, an exhaust means 20, a collection filter 22, and an observation window 24.

[0047] The rapid compression device 10 has a configuration in which a piston is arranged in a cylinder. The rapid compression device 10 can combust a mixture of fuel and air supplied into the cylinder under predetermined injection conditions by hydraulically driving the piston, by rapidly compressing the mixture. The rapid compression device 10 can simulate one cycle of combustion in a diesel engine. Note that instead of the rapid compression device 10, a constant volume combustion vessel or a visualization engine that can visualize the overall picture of combustion can also be used.

[0048] The dry air cylinder 12 is a cylinder that stores the dry air to be supplied to the rapid compression device 10. The dry air tank 14 is a tank that temporarily stores the dry air to be supplied from the dry air cylinder 12 to the rapid compression device 10. The dry air is supplied from the dry air cylinder 12 to the heating and pressurizing means 16 via the dry air tank 14.

[0049] The heating and pressurizing means 16 is a means for heating and pressurizing the dry air and supplying it to the rapid compression device 10. The heating and pressurizing means 16 adjusts the intake air temperature by heating the dry air with a heater. The heating and pressurizing means 16 also pressurizes the dry air to a desired pressure using a compressor, and introduces the dry air into the rapid compression device 10 by opening the intake valve at a desired timing. Since at least the pressure of the injection space and the fuel injection pressure can be changed as fuel injection conditions, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion without using large-scale equipment or a large amount of test fuel.

[0050] The fuel supply means 18 is a means for supplying fuel to the rapid compression device 10. The fuel supply means 18 includes a compressor, an electromagnetic fuel injection valve, and the like, and pressurizes fuel supplied from the outside and injects the fuel into the rapid compression device 10 at a desired timing and in a desired injection amount. The fuel supply means 18 may include, for example, a common rail injector (manufactured by Denso).

[0051] The fuel to be evaluated by the emission characteristic evaluation system 100 may be diesel fuel, but hydrocarbon fuels other than diesel fuel may also be evaluated.

[0052] The exhaust means 20 is a means for exhausting the exhaust gas of the air-fuel mixture combusted in the rapid compression device 10 from the rapid compression device 10. The exhaust means 20 exhausts the exhaust gas in the rapid compression device 10 to the outside by opening an exhaust valve at a desired timing.

[0053] The trapping filter 22 is a filter that traps particulate matter in the exhaust gas. The trapping filter 22 is provided midway through the exhaust pipe of the exhaust means 20. The trapping filter 22 allows the degree of pollution, such as the amount of soot generated, to be measured by a filter smoke meter based on the particulate matter.

[0054] The observation window 24 is a window for observing the inside of the rapid compression device 10. The observation window 24 may be a quartz glass window fitted into a flange provided in front of the combustion chamber of the rapid compression device 10. The state of fuel combustion in the combustion chamber of the rapid compression device 10 can be observed through the observation window 24. It is important that the observation window 24 can provide an overall view of the combustion. This is because the emission characteristic evaluation system 100 estimates the total amount of each radical related to the soot emission characteristics by integrating the luminance values, and utilizes the fact that the maximum value of the total amount (maximum value of the integrated luminance value) and the emission time are correlated with the amount of soot emission. Therefore, for example, if the observation window 24 is small, part of the overall image of the combustion may be cut off, which may result in poor accuracy in estimating the emission amount.

[0055] In the exhaust emission evaluation test of this embodiment, the intake temperature of dry air was adjusted by a heater, and the dry air was introduced into the rapid compression device 10, and then compressed by the hydraulic piston of the rapid compression device 10. During fuel injection and combustion, the piston was fixed at the top dead center position, and the volume of the combustion chamber in the rapid compression device 10 was kept constant. In addition, by setting the intake pressure and temperature by the heating and pressurizing means 16, the atmospheric pressure in the combustion chamber of the rapid compression device 10 at the start of fuel injection was 4.8 MPa and the temperature was 915 K. The fuel injection hole was a single hole, and the diameter of the hole was 0.2 mm. The fuel injection period was 3.0 ms, regardless of the pressure difference with the fuel injection pressure, i.e., the fuel injection pressure. In addition, the fuel injection pressure (P inj ) was set in increments of 30 MPa from 40 MPa to 130 MPa. The process from fuel injection to combustion was photographed through an observation window 24.

[0056] FIG. 2 shows the configuration of an optical system device 200 for observing combustion. In this study, the spatial distribution of C2 radicals present in the reaction region of hydrocarbons and OH radicals present in the oxidation region is the subject of observation. In order to simultaneously capture these two phenomena, a two-branch optical system was created and images were taken with a high-speed video camera (HX-3, manufactured by NAC Image Technology) equipped with an image intensifier (UVi, manufactured by Invisible Vision). C2 radicals emit light in the visible light range (520 nm wavelength for imaging), whereas OH radicals emit light in the ultraviolet range (310 nm wavelength for imaging). Therefore, all optical elements compatible with ultraviolet light were used in the optical path for imaging OH radicals.

[0057] As shown in FIG. 2, the optical system device 200 includes an ultraviolet half mirror 30, a mirror 32, a mirror 34, an ND filter 36, a bandpass filter 38, a mirror 40, a mirror 42, an ultraviolet mirror 44, an ND filter 46, a bandpass filter 48, an ultraviolet mirror 50, an ultraviolet mirror 52, an ultraviolet lens 54, an image intensifier 56, and a camera 58.

[0058] The ultraviolet half mirror 30 receives light observed through the observation window 24 of the emission characteristic evaluation system 100, and separates light in the visible light range, including light (520 nm) caused by C2 radicals, to the mirror 32 side, and separates light in the ultraviolet light range, including light (310 nm) caused by OH radicals, to the ultraviolet mirror 44 side.

[0059] The mirror 32, the mirror 34, the ND filter 36, the bandpass filter 38, the mirror 40, and the mirror 42 constitute an optical system for light in the visible light range including light caused by C2 radicals. The mirror 32 and the mirror 34 reflect the light in the visible light range separated by the ultraviolet half mirror 30 so that it passes through the ND filter 36 and the bandpass filter 38. The ND filter 36 is a filter for reducing the amount of light passing through. The ND filter 36 is provided to balance the amount of light caused by C2 radicals and the amount of light caused by OH radicals. Therefore, when the amount of light caused by C2 radicals and the amount of light caused by OH radicals are balanced, the ND filter 36 does not need to be provided. The bandpass filter 38 is a filter that transmits only the visible light range close to the light caused by C2 radicals (520 nm) from the light separated by the ultraviolet half mirror 30. The light that passes through the ND filter 36 and the bandpass filter 38 is incident on the mirror 40 and the mirror 42. Mirrors 40 and 42 reflect the light that passes through ND filter 36 and bandpass filter 38 through UV lens 54 and image intensifier 56 toward camera 58 .

[0060] The ultraviolet mirror 44, the ND filter 46, the bandpass filter 48, the ultraviolet mirror 50, and the ultraviolet mirror 52 constitute an optical system for ultraviolet light including light caused by OH radicals. The ultraviolet mirror 44 reflects the ultraviolet light separated by the ultraviolet half mirror 30 so that it passes through the ND filter 46 and the bandpass filter 48. The ND filter 46 is a filter for reducing the amount of light passing through. The ND filter 46 is provided to balance the amount of light caused by C2 radicals and the amount of light caused by OH radicals. Therefore, when the amount of light caused by C2 radicals and the amount of light caused by OH radicals are balanced, the ND filter 46 does not need to be provided. The bandpass filter 48 is a filter that transmits only the ultraviolet light area close to the light caused by OH radicals (310 nm) from the light separated by the ultraviolet half mirror 30. The light that passes through the ND filter 46 and the bandpass filter 48 enters the ultraviolet mirror 50 and the ultraviolet mirror 52. UV mirror 50 and UV mirror 52 reflect the light that passes through ND filter 46 and bandpass filter 48 through UV lens 54 and image intensifier 56 toward camera 58 .

[0061] The ultraviolet lens 54 converges light in the visible light region near the light (520 nm) caused by C2 radicals and light in the ultraviolet light region near the light (310 nm) caused by OH radicals to a desired focal position. In this embodiment, the f-number of the ultraviolet lens 54 is set to 105 mm. The image intensifier 56 is configured to include an element for detecting and multiplying weak light. The image intensifier 56 is used for observing high-speed phenomena, etc. Specifically, the image intensifier 56 includes a combination of a photomultiplier tube, a photoelectric conversion element, and a microchannel plate (MCP) that amplifies electrons. The camera 58 captures the image multiplied by the image intensifier 56. The camera 58 is preferably a high-speed camera that can capture the state of fuel combustion in the emission characteristic evaluation system 100 at high speed. Image intensifier 56 and camera 58 may be, for example, a high speed video camera (HX-3, manufactured by NAC Image Technology) with an image intensifier (UVi, manufactured by Invisible Vision).

[0062] In this embodiment, the optical system device 200 is configured to have a two-branch optical system for measuring the spontaneous emission of active chemical species that are intermediate products when fuel is burned. That is, the optical system device 200 is configured to have a two-branch optical system for separately measuring the spontaneous emission of C2 radicals and OH radicals when fuel containing aromatic components is burned. However, the optical system device 200 is not limited to this, and may be configured to have a plurality of imaging means for measuring the spontaneous emission of intermediate products when fuel is burned. For example, the optical system device 200 may be configured to have a plurality of cameras 58 for respectively capturing the spontaneous emission of C2 radicals and OH radicals when fuel containing aromatic components is burned. This makes it possible to divide one subject into two or more parts and appropriately estimate the amount of soot generated based on the spontaneous emission of C2 radicals and OH radicals.

[0063] FIG. 3 shows the base material of the fuel used in the combustion test in this embodiment. In order to observe the effect of the number of aromatic rings on the generation of soot, it is preferable to use fuels with ignition delay times as close as possible. 16 H 34 ) as the base fuel, and the aromatic monocyclic toluene (C7H8) and bicyclic α-methylnaphthalene (C 11 H 10 ) as the base n-hexadecane (C 16 H 34 The test fuel was a mixture of 50, 60, and 70 vol% aromatics.

[0064] Figure 4 shows the ignition delay time versus aromatics content of the test fuel. The ignition delay time was measured under the conditions of an ambient pressure of 4.8 MPa, a temperature of 915 K, a fuel injection period of 3.0 ms, and an injection pressure of 130 MPa. Figure 4 plots the average value of six tests.

[0065] The ignition delay increased with increasing aromatic content for all aromatics. 11 H 10 The ignition delay time was longer when C7H8 was used than when toluene (C7H8) was used, the maximum difference being approximately 0.2 ms.

[0066] 5 and 6 show n-hexadecane (C 16 H 34 5 shows the time variation of the spontaneous emission of C2 radicals and OH radicals and the heat generation rate during combustion when fuels prepared by mixing toluene (C7H8) at 50, 60, and 70 vol% with C2 radicals (C7H8) as the base fuel. In FIG. 5, the upper part shows the spontaneous emission image of C2 radicals, and the lower part shows the spontaneous emission image of OH radicals. In FIG. 5, the shape of the combustion chamber of the rapid compression device 10 is indicated by a white dashed line. The test conditions were an ambient pressure of 4.8 MPa, a temperature of 915 K, a fuel injection period of 3.0 ms, and an injection pressure of 130 MPa.

[0067] The heat release rate and the spontaneous emission of each radical at each concentration of toluene (C7H8) when 2.0 ms has elapsed since the start of fuel injection are compared. In the heat release rate shown in Figure 6, the fuel burned at toluene (C7H8) concentrations of 50% and 60%, and the heat release rate reached its peak at a toluene (C7H8) concentration of 50%. However, in the spontaneous emission images of each radical shown in Figure 5, the spontaneous emission distribution of both C2 radicals and OH radicals was confirmed at a toluene (C7H8) concentration of 50%, but the spontaneous emission intensity was weak. In addition, at a toluene (C7H8) concentration of 60%, the spontaneous emission distribution of OH radicals could be observed, but the spontaneous emission distribution of C2 radicals was hardly confirmed. After that, from 3.0 ms to 4.0 ms from the start of fuel injection, the heat release rate at toluene (C7H8) concentrations of 50% and 60% passed its peak and a gradual change was observed. The spontaneous emission intensity of the C2 radical was strong, especially when the concentration of toluene (C7H8) was 50%. In addition, the OH radical showed a distribution that was roughly one size larger than the emission region of the C2 radical. When the concentration of toluene (C7H8) was 70% at the same time, the heat release rate reached a peak in Figure 6. At this time, as shown in Figure 5, the spontaneous emission of the C2 radical was only faintly visible, and the combustion region was confirmed only in the intensity distribution of the spontaneous emission of the OH radical. After that, the heat release rate began to decrease around 4.5 ms from the start of fuel injection for all toluene (C7H8) concentrations, and the slope of the decrease was almost the same. After 5.0 ms from the start of fuel injection, the emission region of the C2 radical narrowed rapidly, and it almost disappeared, especially under conditions where the concentration of toluene (C7H8) was high. On the other hand, as with the decreasing tendency of the heat release rate, no significant difference in the spontaneous emission region of the OH radical due to the difference in the concentration of toluene (C7H8) was observed.

[0068] 7 and 8 show n-hexadecane (C 16 H 34 ) as the base fuel, toluene (C7H8) and α-methylnaphthalene (C 11 H 10 ) was mixed with 50 vol% of fuel, and the fuel injection pressure (P inj7 shows the time variation of the spontaneous emission of C2 radicals and OH radicals and the heat generation rate during combustion when the pressure is set to 130 MPa and 40 MPa. In FIG. 7, the upper part shows the spontaneous emission image of C2 radicals, and the lower part shows the spontaneous emission image of OH radicals. In FIG. 7, the shape of the combustion chamber of the rapid compression device 10 is indicated by a white dashed line. Even under these conditions, the spontaneous emission images of C2 radicals and OH radicals during combustion could be clearly captured.

[0069] Comparing the heat release rate shown in Figure 8 with the spontaneous emission images of each radical shown in Figure 7, the start of the rise in the heat release rate was within the range of the ignition delay time shown in Figure 4. In other words, it is presumed that the difference in the initial radical spontaneous emission images due to differences in each test condition is due to the difference in ignition delay. On the other hand, focusing on the vicinity of the end of combustion, the decay in the heat release rate was more gradual when the fuel injection pressure was 40 MPa compared to 130 MPa. Furthermore, the decay in the heat release rate was more gradual when the fuel injection pressure was 40 MPa compared to toluene (C7H8). 11 H 10 ) showed a slower decay in the heat release rate.

[0070] In the spontaneous emission images of C2 radicals and OH radicals shown in Fig. 7, the fuel injection pressure (P inj The spontaneous emission region of the C2 radical was wider at 40 MPa than at 130 MPa. Furthermore, when comparing the types of aromatics, α-methylnaphthalene (C 11 H 10 ) the spontaneous emission region of the C2 radical extended to the vicinity of the nozzle.

[0071] Under conditions where the time from the start of fuel injection to the rise of the heat release rate, i.e., the ignition delay time, is long, or the fuel injection pressure is high, promoting the mixing of air and fuel, the intensity of the spontaneous emission of C2 radicals is weak and the range is narrow. In addition, under conditions where the fuel injection pressure is low, the time until the spontaneous emission of OH radicals disappears is long. Regarding the difference in the type of aromatic, both C2 and OH radicals are more likely to emit α-methylnaphthalene (C 11 H 10 ) took longer for the spontaneous emission of radicals to disappear.

[0072] [Method for evaluating soot emission characteristics] A method for evaluating soot emission characteristics in this embodiment will be described below. The brightness value per pixel obtained from a spontaneous emission image of intermediate products (radicals, etc.) during combustion indicates the product of the emission intensity of the intermediate products themselves, their density, and their distribution in the depth direction. Therefore, a method for estimating the amount of soot emission using the parameters of the maximum spatial integrated emission intensity and emission time of intermediate products during combustion that contribute to the generation and oxidation of soot was devised.

[0073] By integrating the brightness values ​​of each pixel in the spontaneous emission image of intermediate products (radicals, etc.) during combustion over the entire image, an integrated brightness value (R) equivalent to the total number of intermediate products present in the image is calculated. By applying this process to the image at each time, it is possible to obtain the time-series data of the integrated brightness value (R) of the intermediate products, i.e., the total number of intermediate products.

[0074] When analyzing the combustion of fuels containing aromatic components, it is preferable to use C2 radicals and OH radicals as intermediate products during combustion. C2 ,R OH ) time series data, the fuel injection characteristics and the types of aromatics contained in the fuel can be calculated by the integrated brightness value (R C2 ,R OH ) can be quantitatively evaluated.

[0075] 9 and 10 show the fuel injection pressure (P inj ) when changing the integrated brightness value R for C2 radical C2 and the integrated brightness value R for OH radicals OH The change over time is shown.

[0076] Fuel injection pressure (P inj ) is 40MPa and 130MPa is 40MPa, and the cumulative brightness value R C2and the integrated brightness value R for OH radicals OH The rate of increase in both is fast, and the integrated brightness value R C2 and the integrated brightness value R for OH radicals OH In both cases, the decline began earlier.

[0077] In addition, the fuel injection pressure (P inj ), the aromatic compounds contained in the fuel are α-methylnaphthalene (C 11 H 10 ) has a higher integrated brightness value R C2 and the integrated brightness value R for OH radicals OH The decrease in both was slow. C2 Maximum value of (Rmax C2 ), the fuel injection pressure (P inj ) and the type of aromatics. In contrast, the integrated brightness value R OH Maximum value of (Rmax OH ), the fuel injection pressure (P inj ) is low under low conditions, and the aromatic species is α-methylnaphthalene (C 11 H 10 ) was lower.

[0078] 11 and 12 show the fuel injection pressure (P inj ) when changing the integrated brightness value R for C2 radical C2 and the integrated brightness value R for OH radicals OH The change over time is shown.

[0079] Fuel injection pressure (P inj ) is 40MPa and 130MPa is 40MPa, and the cumulative brightness value R C2 The aromatic compounds in the fuel were α-methylnaphthalene (C 11 H 10 ) has a higher integrated brightness value R C2is high, and the time from the onset of light emission to its extinction (T RC2 ) has become longer. On the other hand, the fuel injection pressure (P inj ) is high, the integrated brightness value R OH The fuel injection pressure (P inj Under low conditions, the time it takes for OH radicals to disappear (T ROH ) became longer. Furthermore, α-methylnaphthalene (C 11 H 10 ) is the time it takes for OH radicals to disappear (T ROH ) has become longer.

[0080] As described above, the integrated brightness value R C2 Maximum value of (Rmax C2 ) and the integrated brightness value R for OH radicals OH Maximum value of (Rmax OH ) and the emission time of C2 radicals and OH radicals (T RC2 ,T ROH ) differences were observed.

[0081] 13 to 16 show the fuel injection pressure (P inj ), and the integrated brightness value R for C2 radicals for the types and concentrations of aromatics contained in the fuel. C2 Maximum value of (Rmax C2 ) and the integrated brightness value R for OH radicals OH Maximum value of (Rmax OH ) and the emission time of C2 radicals and OH radicals (T RC2 ,T ROH 13 to 16, in order to avoid the influence of different fuel injection amounts, the integrated brightness value R C2 Maximum value of (Rmax C2 ) and the integrated brightness value R for OH radicals OH Maximum value of (Rmax OH The results are shown in Table 1. The amount of soot generated was calculated by dividing the amount of fuel injected by the amount of fuel used.

[0082] Figure 17 shows the relationship between the amount of soot generated and each parameter derived from the results shown in Figures 13 to 16. Under conditions such as low fuel injection pressure and short ignition delay, the amount of soot generated increased because of insufficient mixing of air and fuel due to a decrease in the amount of entrainment caused by a deterioration in atomization of the fuel spray and a decrease in the momentum of the fuel. In other words, under such conditions, the integrated brightness value R C2 Maximum value of (Rmax C2 On the other hand, because the amount of air is small, the amount of OH radicals generated is small, and the integrated brightness value R OH Maximum value of (Rmax OH ) is expected to be lower. In addition, the emission time of C2 radicals (T RC2 ) and the emission time of OH radicals (T ROH Conversely, under conditions of high fuel injection pressure and long ignition delay, the amount of soot generated was small. C2 Maximum value of (Rmax C2 ) is low, and the integrated brightness value R OH Maximum value of (Rmax OH ) is expected to be higher. In addition, the emission time of C2 radicals (T RC2 ) and the emission time of OH radicals (T ROH ) was shortened.

[0083] Based on these relationships, the maximum integrated brightness value of C2 radicals and OH radicals (Rmax C2 ,Rmax OH ) and light emission time (T RC2 ,T ROH In other words, the amount of soot generated per one injection amount Sest can be estimated by the estimation formula shown in Equation (5). Here, the coefficients α, β, γ, δ, and the maximum integrated brightness value Rmax of C2 radicals per one injection amount are C2 , the emission time of C2 radical T RC2, the maximum integrated brightness value of OH radicals per injection amount Rmax OH , the emission time of OH radicals T ROH Let us assume that.

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[0084] The coefficients α, β, γ, and δ can be determined by applying Equation (5) to the measured amount of soot generated and performing multiple regression analysis by the least squares method. That is, the coefficients α, β, γ, and δ can be determined by selecting multiple types of hydrocarbon fuel as the fuel, burning them with the same injection amount as the injection condition, and applying multiple regression analysis such as the least squares method based on the spatiotemporal emission intensity distribution and the measured soot value. In this case, it is preferable that the injection condition includes at least the pressure of the injection space and the injection pressure of the fuel. It is also preferable that the injection condition includes a condition for changing the injection pressure of the fuel or a condition for injecting the fuel multiple times.

[0085] When the coefficients α, β, γ, and δ are determined based on the actual measurement example in Fig. 17, the formula (5) showing the amount of soot generation Sest can be expressed as an estimation formula shown in formula (6). Note that since the coefficients α, β, γ, and δ in formula (5) may vary depending on the specifications of the optical system device 200 applied to the emission characteristic evaluation system 100, it is preferable to redo the multiple regression analysis for the coefficients α, β, γ, and δ when the configuration of the optical system device 200 is changed.

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[0086] Figure 18 shows the correlation between the amount of soot generation calculated using formula (6) and the amount of soot generation that was actually measured. In Figure 18, the horizontal axis shows the amount of soot generation calculated using formula (6), and the vertical axis shows the amount of soot generation that was actually measured. In Figure 18, the amount of soot generation calculated using formula (6) and the amount of soot generation that was actually measured are roughly consistent, and the amount of soot generation was able to be appropriately estimated by using formula (6).

[0087] In this way, by setting the coefficients α, β, γ, and δ in estimation equation (5) using the actually measured soot values, it becomes possible to appropriately estimate the amount of soot generated by fuel combustion based on estimation equation (6) using the coefficients α, β, γ, and δ optimized based on the actually measured soot values.

[0088] As described above, according to the emission characteristic evaluation system 100 of the present embodiment, it is possible to appropriately estimate the amount of soot generated, taking into consideration the intermediate combustion products that contribute to the generation and oxidation of soot. C2 ,Rmax OH ) and light emission time (T RC2 ,T ROH ) it is possible to appropriately estimate the amount of soot generated by taking into account intermediate combustion products that contribute to the generation and oxidation of soot caused by the combustion of hydrocarbon fuels such as diesel fuel. [Industrial Applicability]

[0089] The present invention can be applied to estimate the amount of soot generated in an internal combustion engine with intermittent combustion, such as a marine diesel engine, etc. For example, the soot emission characteristic evaluation method and soot emission characteristic evaluation system of the present invention can be applied to the evaluation of soot emission characteristics for fuel combustion by internal combustion engine manufacturers, oil companies, etc. [Explanation of symbols]

[0090] 10 rapid compression device, 12 dry air cylinder, 14 dry air tank, 16 heating and pressurizing means, 18 fuel supply means, 20 exhaust means, 22 collection filter, 24 observation window, 30 ultraviolet half mirror, 32 mirror, 34 mirror, 36 ND filter, 38 band pass filter, 40 mirror, 42 mirror, 44 ultraviolet mirror, 46 ND filter, 48 band pass filter, 50 ultraviolet mirror, 52 ultraviolet mirror, 54 ultraviolet lens, 56 image intensifier, 58 camera, 100 emission characteristic evaluation system, 200 optical system device.

Claims

1. 1. A method for optically characterizing soot emission characteristics of a fuel, comprising the steps of: The fuel is injected under a predetermined injection condition and burned, and the activated chemical species C, which differs depending on the composition of the fuel, is generated. ２ A method for evaluating soot emission characteristics, comprising estimating the amount of soot generated from the fuel based on the spatial and temporal distribution of luminescence intensity due to spontaneous luminescence of radicals and OH radicals.

2. The soot emission characteristic evaluation method according to claim 1, The emission intensity distribution is ２ a maximum integrated brightness value of each of the radicals and the OH radicals and a light emission time are used to estimate the amount of soot generated.

3. The soot emission characteristic evaluation method according to claim 2, The amount of soot generated is estimated by the following formula: [0010] where Sest is the amount of soot generated per injection, α, β, γ, and δ are coefficients, and Rmax Ｃ２ is the amount of C per injection ２ The maximum integrated brightness value of the radical, T ＲＣ２ is the above C ２ Radical emission time, Rmax ＯＨ is the maximum integrated brightness value of the OH radical per one injection, T ＲＯＨ is the emission time of the OH radical, A method for evaluating soot emission characteristics, comprising: estimating the soot emission characteristics based on the above-mentioned

4. The soot emission characteristic evaluation method according to claim 3, A method for evaluating soot emission characteristics, characterized in that the coefficients α, β, γ, and δ in the estimation formula are set using actually measured soot values.

5. The soot emission characteristic evaluation method according to claim 4, A method for evaluating soot emission characteristics, characterized in that the coefficients α, β, γ, and δ are set by using a least squares method based on the spatiotemporal emission intensity distribution and the actually measured soot value, by selecting multiple types of hydrocarbon fuel as the fuel, burning them with the same injection amount as the injection condition.

6. The soot emission characteristic evaluation method according to claim 5, A soot emission characteristic evaluation method, characterized in that the coefficients α, β, γ, and δ are set using a soot emission characteristic evaluation system used for evaluating the soot emission characteristics.

7. The soot emission characteristic evaluation method according to any one of claims 1 to 6, Said C ２ The spatial and temporal emission intensity distribution of the radicals and the OH radicals is ２ The method for evaluating soot emission characteristics is characterized in that the spontaneous emission of the radicals and the OH radicals is spectrally imaged using a high-speed camera, the brightness values ​​of each pixel of the image data being integrated to obtain time-series data.

8. The soot emission characteristic evaluation method according to any one of claims 1 to 7, The soot emission characteristic evaluation method, wherein the injection conditions include at least the pressure in an injection space and the injection pressure of the fuel.

9. The soot emission characteristic evaluation method according to claim 8, The soot emission characteristic evaluation method, wherein the injection conditions include a condition for changing the injection pressure of the fuel or a condition for injecting the fuel a plurality of times.

10. 1. A system for optically assessing soot emission characteristics of a fuel, comprising: a combustion means for injecting and combusting the fuel under predetermined injection conditions; The active species C varies depending on the composition of the fuel. ２ A luminescence measuring means for measuring spontaneous luminescence of radicals and OH radicals; an emission intensity distribution analysis means for analyzing a spatiotemporal emission intensity distribution of the measured spontaneous emission; and a soot generation amount estimation means for estimating an amount of soot generated from the fuel based on the emission intensity distribution.

11. The soot emission characteristic evaluation system according to claim 10, The soot generation amount estimation means estimates the amount of soot generated by the soot generation amount estimation means based on the emission intensity distribution C ２ and estimating the amount of soot generated based on the maximum integrated brightness values ​​of the radicals and the OH radicals and the emission time.

12. The soot emission characteristic evaluation system according to claim 11, The soot generation amount estimating means estimates the soot generation amount by the following estimation formula: [0025] where Sest is the amount of soot generated per injection, α, β, γ, and δ are coefficients, and Rmax Ｃ２ is the amount of C per injection ２ The maximum integrated brightness value of the radical, T ＲＣ２ is the above C ２ Radical emission time, Rmax ＯＨ is the maximum integrated brightness value of the OH radical per one injection, T ＲＯＨ is the emission time of the OH radical, A soot emission characteristic evaluation system characterized by estimating soot emission characteristics based on the above.

13. The soot emission characteristic evaluation system according to any one of claims 10 to 12, The luminescence measuring means is ２ A two-branch optical system for separately measuring the spontaneous emission of the radical and the spontaneous emission of the OH radical, or ２ A soot emission characteristic evaluation system comprising a plurality of imaging means for respectively imaging the radicals and the OH radicals.

14. The soot emission characteristic evaluation system according to any one of claims 10 to 13, The luminescence measuring means includes a high-speed camera, The high-speed camera detects the C of the fuel. ２ A soot emission characteristic evaluation system, comprising: an imaging unit that images the spontaneous emission of radicals and the OH radicals.

15. The soot emission characteristic evaluation system according to claim 14, The emission intensity distribution analysis means ２ The soot emission characteristic evaluation system is characterized in that the spatial and temporal emission intensity distribution of the radicals and the OH radicals is obtained as time-series data by integrating the brightness values ​​for each pixel of the image data captured by the high-speed camera.

16. The soot emission characteristic evaluation system according to any one of claims 10 to 15, The soot emission characteristic evaluation system is characterized in that the combustion means uses a rapid compression device that can simulate one cycle of combustion in a diesel engine, and in the rapid compression device, at least the pressure of the injection space and the injection pressure of the fuel are changeable as the injection conditions.

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