JPH0658058B2 - Diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention can reduce the concentration of nitrogen oxides in the exhaust gas, which increases or decreases with the dryness or humidity of the supply air due to seasonal changes in the absolute humidity of the atmosphere, to a certain low level. Regarding diesel engine.

<Prior Art> As a device for reducing the concentration of nitrogen oxides in exhaust gas,
For example, there is a selective reduction ammonia denitration device applied to exhaust gas from a boiler or the like. This denitrification device allows an exhaust gas containing air of about 320 to 450 ° C. to pass through a container filled with a catalyst, and injects a sufficient amount of ammonia gas necessary for the reaction, and reduces the exhaust gas in the exhaust gas by the following reduction reaction. NO
Is to reduce.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O <Problems to be solved by the invention> However, the conventional denitration device has applicability and merit to a diesel engine with a large output, but has a relatively large structure. Due to its large scale and cost, it has a drawback that it is practically difficult to apply to small and medium-sized diesel engines. Further, the concentration of nitrogen oxides in the exhaust gas has a characteristic of increasing and decreasing with the dryness and humidity of the supply air. Therefore, in order to reduce NO in the exhaust gas to a certain level, the amount of NH ₃ injection should be adjusted as shown in FIG. It must be controlled so that it increases during winter, and this control is not easy. Furthermore, when the denitration device is installed in the exhaust pipe downstream of the supercharger, it is necessary to install an exhaust gas heating device or raise the exhaust gas temperature by matching, which substantially increases fuel consumption and There is a problem in that the reliability of

Furthermore, the national standard for NOx emissions in exhaust gas is 950 ppm, which is the current O ₂ : 13% conversion when the cylinder diameter is less than 400 mm, but local governments will strictly regulate it to 114 ppm. Exhaust as it is in the organization
There is an urgent need to further reduce the NOx concentration from the NOx level.

Therefore, an object of the present invention is to combine a NOx reduction means capable of reducing the denitration load of this device with the selective reduction ammonia denitration device and facilitating the control of ammonia injection, and devising the arrangement of the denitration device. The purpose of the present invention is to provide a diesel engine capable of greatly reducing the NOx concentration in the exhaust gas, which varies depending on the season, to a certain level close to the above regulated value.

<Means for Solving the Problems> In order to achieve the above object, the inventors have recently proposed a NOx reduction method by humidifying air supply (Japanese Patent Application No. 63-3.
As a result of repeated studies focusing on No. 31985), the above method was found to be optimal for reducing the denitration load of the selective reduction ammonia denitration device and facilitating the ammonia injection control,
The present invention has been completed.

That is, the diesel engine according to the present invention can reduce the nitrogen oxide concentration in the exhaust gas, which increases or decreases with the dryness or humidity of the supply air due to the seasonal change in the absolute humidity of the installation environment, to a certain low level. The humidifier installed in the air supply piping system to add a predetermined amount of water to the sucked air to humidify it, and the exhaust piping system of the diesel engine, which reduces nitrogen oxides in the exhaust with ammonia and a catalyst. Reducing device, the absolute humidity of the supply air, the supply air temperature that is uniquely determined by the operating conditions of the engine, the specific gravity of the fuel used, and the governing equation for the NOx concentration defined by the function of the nitrogen content. Initial function value calculating means for substituting the above-mentioned variable values to obtain a function value, and the obtained function value is multiplied by the NOx regulation value at the time of shipment adjustment and divided by the NOx first regulation value at the time of operation Function of Substituting the operating air temperature and the specific gravity of the fuel used and the nitrogen content into the above governing equation, the function value becomes the above operating function value, and Reference absolute humidity calculating means for calculating the absolute humidity of the supply air so that the nitrogen oxide concentration becomes the NOx first regulation value, and the calculated reference absolute humidity and the atmospheric air at the time of operation given as actual measurement or meteorological data. A first controller having a humidification amount calculating means for calculating a humidification amount proportional to a difference from the absolute humidity and an output of the diesel engine, and outputting a signal representing the calculated humidification amount to the humidifier,
NOx concentration in the exhaust is less than the above NOx first regulation value
Calculate the amount of ammonia to be added to the exhaust gas to reach the second regulation value based on the output of the diesel engine and the humidification amount,
A second control device for outputting a signal representing the amount of ammonia to the reduction device is provided.

<Operation> The initial function value calculation means of the first control device is shipped by substituting the values of absolute humidity of supply air, supply temperature, specific gravity of fuel used, and nitrogen content into the governing equation of NOx concentration during shipping adjustment. Find the function value during adjustment.

Next, the operating-time function value calculating means multiplies the obtained function value by the NOx regulation value at the time of shipment adjustment and divides by the NOx first regulation value at the time of operation to obtain the function value at the time of operation. Furthermore, the reference absolute humidity calculating means substitutes the supply air temperature during operation, the specific gravity of the fuel used, and the nitrogen content into the governing equation, and the function value becomes the function value during operation, and the nitrogen in the exhaust gas The absolute humidity is calculated so that the oxide concentration becomes the NOx first regulation value during the above operation. Finally, the humidification calculation means of the control device
A humidification amount proportional to the difference between the calculated reference absolute humidity and the absolute humidity of the atmosphere during operation and the output of the diesel engine is calculated, and a signal representing the calculated humidification amount is output to the humidifier.

The humidifier humidifies the supply air by adding the amount of water corresponding to the signal to the atmosphere sucked into the supply pipe system of the diesel engine.

In this way, when the absolute humidity of the atmosphere during operation falls below the reference absolute humidity, moisture proportional to the difference and engine output is added to the air supply, so the NOx concentration in the exhaust is always below the minimum seasonal fluctuation value. NOx 1st regulation value is reduced.

On the other hand, the second control device for controlling the amount of ammonia determines the amount of ammonia to be added to the exhaust in order to bring the concentration of nitrogen oxides in the exhaust to the NOx second regulation value which is equal to or lower than the NOx first regulation value, the engine output or the humidification. It is calculated based on the amount, and a signal representing this amount of ammonia is output to the reduction device.

Although the above-mentioned ammonia amount slightly increases as the engine output increases, it is a constant value that does not change seasonally, and the exhaust gas to which this amount of ammonia has been added by the reducing device further exceeds the NOx first regulation value and the NOx second regulation value. Reduce to the regulation value. Thus,
The NOx concentration in the exhaust gas discharged to the atmosphere will meet the strict NOx emission standard value.

<Examples> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

FIG. 1 is a schematic view showing an embodiment of a diesel engine of the present invention, 1 is an engine body having an air supply pipe 2 and an exhaust pipe 3, and 4 is an output for detecting a displacement of a fuel rack of the engine body 1. A rack scale sensor 5 serving as a sensor is a supercharger in which a compressor 5a is arranged at the inlet of the air supply pipe 2 and a turbine 5b connected to the compressor is arranged at the outlet of the exhaust pipe 3, 6
Is an air cooler provided in the air supply pipe 2 on the downstream side of the supercharger 5, 7 is a built-in first control device for controlling the flow control valve 7a, and the air supply pipe 2 is on the upstream side of the air cooler 6. It is a humidifier that humidifies the supply air by supplying water vapor or atomized water droplets to.

Further, 8 is a cylinder for supplying ammonia gas to the exhaust pipe 3 via the flow control valve 8a, 9 is a second control device for controlling the flow control valve 8a, and 10 is the exhaust pipe 3 on the upstream side of the supercharger 5. Is connected in parallel to a bypass pipe 3a forming a part of the exhaust gas, and a reducing device for reducing nitrogen oxides (NOx) from the exhaust gas containing ammonia by a catalyst filled therein, 11 is a reducing device 10
And a bypass valve 3a for controlling the flow rate ratio of the exhaust gas that is branched.

The first controller composed of a computer in the humidifier 7 has an initial function value calculation means, an operation time function value calculation means, a reference absolute humidity calculation means, and a humidification amount calculation means, which will be described later.
FIG. 3 shows the nitrogen oxide concentration in the exhaust gas based on the absolute humidity X of the atmosphere detected by an absolute humidity sensor (not shown) or given in advance as meteorological data and the engine output L detected by the rack scale sensor 4. Minimum seasonal fluctuation Cmin
The humidification amount Y to be added to the supply air to calculate the NOx first regulation value C ₁ ^* , which is a constant level below, is calculated, and a signal representing this humidification amount Y is output to the flow control valve 7a. .
The calculation procedure of the humidification amount Y will be described below.

That is, the computer has a program for calculating the value K that governs the NOx concentration in the exhaust gas, which is defined by the following function.

K = K (X, Tb, γ, y) (1) where X: absolute humidity of supply air Tb: supply air temperature uniquely determined by standard operating conditions of engine γ: specific gravity or ignitability of fuel used Indicating y: variable indicating the nitrogen content in the fuel The computer, as an initial function value calculating means,
The above variables X ₀ , Tb ₀ , γ ₀ , y ₀ at the time of engine shipment adjustment are substituted into the equation (1) to calculate the initial setting value K ₀ , and this K ₀ value is used as the operation time function value calculating means. The target value during operation is divided by the product of the NOx concentration regulation value C ₀ ^* at the time of shipment adjustment without the NOx reduction device and the above-mentioned NOx first regulation value C ₁ ^* which is the operation target value.
Calculate Ks. Next, the computer serves as a reference absolute humidity calculating means, the condition value Tb, which is input prior to the operation,
By substituting γ, y into the equation (1), the reference absolute humidity X ^* is calculated so that K (X, Tb, γ, y) becomes the target value Ks.
Further, as a humidification amount calculating means, after subtracting the absolute humidity X of the atmosphere detected by the absolute humidity sensor during operation (or given in advance as meteorological data) from the reference absolute humidity X ^* , the rack scale sensor 4 detects it. When the engine output L is equal to or less than the set value L ₀ (see FIG. 4), and when L ≧ L ₀ , it is proportional to the subtraction result (X ^* −X) and the engine output L. The humidification amount Y is calculated as (Y = f (L, X)), and a signal representing the calculated humidification amount Y is output.
It is output to a.

In this way, the calculated humidification amount Y is obtained as a straight line having a constant slope proportional to the engine output L between the maximum value in winter indicated by the straight line A in FIG. 4 and the minimum value in the summer indicated by the straight line B. Humidification is started when L becomes L ₀ or more. And
When the humidification amount Y of water vapor or the like is added to the air supply pipe 2, the NOx concentration in the exhaust gas is a constant level, which is a target value from the curve C showing the seasonal variation in FIG. C ₁ ^*
Will be reduced to.

On the other hand, the second controller 9 that controls the amount of ammonia gas is
Based on the engine output L detected by the rack scale sensor 4,
The NOx concentration in the exhaust gas is the NOx second regulation value below the NOx first regulation value C ₁ ^* .
Ammonia amount Z to be added to the exhaust gas to reach the regulation value C ₂ ^*
(Z = g (Y, L)) is calculated and a signal representing this ammonia amount Z is output to the flow rate control valve 8a. Although the ammonia amount Z slightly increases as the engine output L increases, it is a constant value without seasonal fluctuations, and the exhaust pipe 3
When this amount Z of ammonia is added to the exhaust gas inside and passes through the reduction device 10, the NOx concentration in the exhaust gas is the straight line C in FIG.
It will be further reduced from ₁ ^* to a certain allowable level C ₂ ^* .

FIG. 2 shows the basic concept of compounding NOx reduction technology in the above embodiment. NOx concentration in exhaust gas and fuel consumption rate b
The relationship of e decreases as the injection timing is delayed in the direction of arrow E, that is, as be increases, as indicated by the curve D in the figure. Therefore, a point P ₁ with an appropriately low NOx concentration that does not deteriorate the fuel consumption rate be is selected, and combustion is improved in the engine by adopting combustion matching or a high compression ratio to increase be to the point P ₂ . Next, the humidifier 7 humidifies the supply air as described above to obtain NO.
The NOx concentration is reduced to a certain allowable level point C ₂ ^* by reducing the x concentration to a certain level point C ₁ ^* , further supplying ammonia to the exhaust by the control device 9, and performing selective reduction ammonia denitration by the reducing device 10. We will try to reduce it and achieve the strict NOx emission standard value.

The denitration operation of the diesel engine having the above configuration will be described below with reference to the flowchart of FIG.

In step S1, the engine output signal L of the engine body 1 detected by the rack scale sensor 4 is input to the computer and the second control device 9 which are the first control device in the humidifier 7, and the absolute humidity sensor or the weather condition is measured. The absolute humidity signal X of the atmosphere at that time (season) based on the data is input to the computer. The computer is based on the engine output signal L and the absolute humidity signal X at step S2, to the NOx concentration in the exhaust gas to the seasonal variation minimum value Cmin following NOx first regulating value C ₁ ^* (see FIG. 3) The humidification amount Y to be added to the intake air is calculated, and the flow control valve 7a is controlled so that the humidification amount Y calculated when the engine output exceeds L ₀ is obtained.
The supply air in the supply pipe 2 is humidified. Next, the second control device 9
Calculates the NH ₃ amount Z to be added to the exhaust in order to set the NOx concentration in the exhaust to the NOx second regulation value C ₂ ^* (see FIG. 3) based on the engine output signal L in step S3. When the output exceeds L ₀ , the flow rate control valve 8a is controlled so that the calculated NH ₃ amount Z is obtained, and NH ₃ is supplied to the exhaust gas in the exhaust pipe 3. By passing through the reduction device 10, NOx in the exhaust gas is reduced to N ₂ according to the supplied NH ₃ amount, and the NOx concentration in the exhaust gas is reduced to a certain level C ₁ ^* by the humidification in step S2. Is a more constant tolerance level C ₂ ^*
Can be reduced to Thus, the turbine of the supercharger 5
The NOx concentration in the exhaust gas discharged to the atmosphere via 5b will meet the strict NOx emission standard value C ₂ ^* .

In the present invention, the humidifier 7 is used to reduce the NOx concentration to the minimum seasonal fluctuation value C.
Since it is reduced to a constant level C ₁ ^* of min or less, the reducing device 10 can be miniaturized and installed upstream of the supercharger 5, and the NH ₃ injection amount can be made constant over the year. There is an advantage that the control can be simplified and the regulation to the strict emission standard can be performed accurately and easily. Further, in the above-described embodiment, since the reducing device 10 is provided on the upstream side of the supercharger 5, the catalyst reaction can be activated by the high temperature exhaust gas even when there is no preheating device at the time of medium and low load of the engine, and the denitration can be performed. The efficiency is greatly improved and the operating load range can be expanded. When the engine has a low load and the NOx concentration in the exhaust is low or there is a large amount of medium, the flow control valve 8a is stopped to stop the injection of NH ₃ , and the shunt valve 11 is adjusted to exhaust gas bypass pipe.
By leading to 3a, the useful life of the catalyst in the reduction device 10 can be extended.

FIG. 6 shows another embodiment of the diesel engine of the present invention. In this embodiment, the reducing device 10 of the first embodiment is moved to the downstream side of the supercharger 5, NH ₃ is directly injected into the reducing device 10 from the cylinder 8 through the flow rate control valve 8a, and the humidifier 7 is also used. Control device 9 for receiving a signal indicating the humidification amount Y of
Except that the flow control valve 8a is controlled by
This is the same as the embodiment of FIG. 1, and the same members are given the same numbers.

In this embodiment, the humidifier 7 is used as a main means for reducing NOx, whereby the NOx concentration is lowered to a certain level below the level C ₁ ^{* in} FIG. 3, and the denitration efficiency is lower than that in FIG. 1 because of the downstream side. Using the inferior reducing device 10 as an auxiliary means,
In order to achieve the constant allowable level C ₂ ^* in the figure, the operation of each member is basically the same as that of the above-described embodiment. Therefore, although the denitrification efficiency of the reduction device 10 is not significantly improved, the efficiency of the supercharger 5 is improved by that amount, and the reduction device 10 is downsized and the NH ₃ injection amount control is simplified and accurate, as described above. Therefore, the operating load range can be expanded by sharing the denitration load by the humidifier 7 and the reducing device 10.

Needless to say, the present invention is not limited to the embodiments.

<Effects of the Invention> As is clear from the above description, the diesel engine of the present invention is a humidifier that humidifies the supply air to the air supply pipe system that inhales the atmosphere that dries and humidifies with the seasonal changes in the absolute humidity of the installation environment. On the other hand, the exhaust pipe system is provided with a reducing device for reducing the nitrogen oxides in the exhaust gas with ammonia and a catalyst, and the absolute humidity of the supply air, the supply air temperature uniquely determined by the operating conditions of the engine, and the fuel used. The initial function value calculating means for calculating the function value by substituting the above-mentioned various variable values at the time of shipping adjustment into the governing equation of the NOx concentration defined by the function of the specific gravity and the nitrogen content, and the calculated function value at the time of shipping adjustment. NOx regulation value of, and operating time function value calculating means for obtaining the function value at the time of operation by dividing by the NOx first regulation value at the time of operation, and the specific gravity of the supply air temperature at the time of operation and the fuel used in the above governing equation. And the nitrogen content is substituted and the function value is The reference absolute humidity calculating means for calculating the absolute humidity of the supply air that becomes the function value at the time of operation and that makes the concentration of nitrogen oxides in the exhaust the NOx first regulation value, and the calculated reference absolute humidity. A humidification amount calculation means for calculating a humidification amount proportional to the difference between the absolute humidity of the atmosphere during operation given as actual measurement or meteorological data and the output of the diesel engine, and outputting a signal representing the calculated humidification amount to the humidifier. And a NOx concentration in the exhaust gas above the NO.
x NOx that is less than or equal to the first regulation value Calculates the amount of ammonia to be added to the exhaust gas based on the output of the diesel engine and the humidification amount, and outputs a signal representing this ammonia amount to the reduction device. 2 Since it is equipped with an explanation device, the humidifier eliminates seasonal fluctuations in the nitrogen oxide concentration in the exhaust gas to a certain low level, thereby realizing downsizing of the reduction device and simple and accurate denitration control. The operating load range can be expanded, and it becomes possible to meet the severe nitrogen oxide emission standards in the future.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the diesel engine of the present invention, FIG. 2 is a diagram showing the basic concept of compounding NOx reduction technology in the above embodiment, and FIG. 3 is a graph showing NOx concentration in exhaust gas. FIG. 4 is a diagram showing a seasonal change, FIG. 4 is a diagram showing a relationship between an engine output and a humidification amount, FIG. 5 is a flow chart showing a denitration operation of the above embodiment, and FIG. 6 is a schematic diagram showing another embodiment of the present invention. FIG. 7 is a diagram showing seasonal variation of the NH ₃ injection amount into the conventional denitration device. 1 ... Engine main body, 2 ... Air supply pipe, 3 ... Exhaust pipe, 4 ... Rack scale sensor, 5 ... Supercharger, 7 ... Humidifier, 7a, 8a ... Flow control valve, 8 ... Tank, 9 ... Control device, 10 ... return device.

Claims (1)

[Claims] 1. A diesel engine capable of reducing the concentration of nitrogen oxides in the exhaust gas, which increases and decreases with the dryness of the supply air due to seasonal changes in the absolute humidity of the installation environment, to a certain low level. A humidifier installed in the piping system to add a predetermined amount of moisture to the sucked air to humidify it, and a reducing device installed in the exhaust piping system of the diesel engine to reduce nitrogen oxides in the exhaust with ammonia and a catalyst. , The absolute humidity of the supply air, the supply air temperature that is uniquely determined by the operating conditions of the engine, the specific gravity of the fuel used, and the NOx concentration defined by the functions of the nitrogen content. An initial function value calculating means for substituting a value to obtain a function value, and the calculated function value is multiplied by the NOx regulation value at the time of shipment adjustment, and divided by the NOx first regulation value at the time of operation, and the function value at the time of operation Seeking luck Substituting the operating temperature supply air temperature, the specific gravity of the fuel used and the nitrogen content into the above governing equation, the function value becomes the above operating function value, and the nitrogen oxides in the exhaust gas Reference absolute humidity calculating means for calculating the absolute humidity of the supply air so that the concentration becomes the NOx first regulation value, and the calculated reference absolute humidity and the absolute humidity of the atmosphere at the time of operation given as actual measurement or meteorological data. Difference and a humidification amount proportional to the output of the diesel engine, and a first controller having a humidification amount calculation means for outputting a signal representing the calculated humidification amount to the humidifier, and a nitrogen oxide concentration in the exhaust gas. NOx below the above NOx first regulation value
Calculate the amount of ammonia to be added to the exhaust gas to reach the second regulation value based on the output of the diesel engine and the humidification amount,
A diesel engine comprising a second control device for outputting a signal representing the amount of ammonia to the reduction device.