KR100309143B1 - Method for controlling temperature of exhaust gas for diesel engine - Google Patents

Abstract

PURPOSE: A method for controlling temperature of an exhaust gas for a diesel engine is provided to control the temperature of the exhaust gas not with any additional external heat source but with a thermodynamic cycle. CONSTITUTION: A control method of exhaust gas temperature includes steps of: raising the temperature of an air supplied to a front intake pipe of a throttle valve(TV) by passing an exhaust gas of high temperature purified by a ceramic filter(SF) through a heat exchanger(HE) by diverging a rear exhaust pipe of the ceramic filter communicated with a diesel engine(DE); measuring the temperature of the exhaust gas discharged on starting the diesel engine by installing a temperature sensor(TS) at the front of the ceramic filter; calculating a control data of the heat exchanger with an ECU(electronic control unit) which is electrically connected to the temperature sensor and operation-controls the data of the exhaust gas measured by the temperature sensor; and stopping the heat exchanger by a heat exchanger control data of the ECU in case that the data of the exhaust gas gives a bad effect to the ceramic filter or is over the optimal activated temperature of a catalyst and a fuel additives.

Description

How to control exhaust gas temperature of diesel engine

The present invention relates to a method for controlling the exhaust gas temperature of a diesel engine, and more particularly, to burn and burn unburned fine particles adsorbed to the exhaust gas purifying filter of a diesel engine, thereby repeatedly regenerating and using the filter. To reduce the amount of intake air supplied to the diesel engine or to heat the high temperature of the exhaust gas emitted from the diesel engine to the diesel engine to improve the purifying ability of the exhaust gas by the filter by implementing the proper activation temperature of the fuel additive. The present invention relates to a method of controlling the temperature of a thermodynamic cyclobuty exhaust gas without a separate external heat source by raising the temperature of the supplied suction air to raise the exhaust gas temperature.

In general, exhaust gases emitted from automobiles include carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter and toxic compounds. In order to reduce such harmful substances, gasoline automobiles are equipped with a catalytic device to filter out exhaust gas components such as carbon monoxide and hydrocarbons from the engine with water and carbon dioxide, and nitrogen oxides with nitrogen and oxygen.

In addition, in order to reduce harmful components emitted from diesel cars, the intake resistance is reduced by changing the shape of the intake manifold, improving the intake hole, and changing the valve opening / closing time so as to secure sufficient air for combustion and intake air into the cylinder. Vortex flows to promote mixing with the fuel to provide good combustion conditions.In addition, the injection timing, injection amount, injection pressure, degree of atomization and distribution of fuel particles of the fuel injection device are properly adjusted. It is reducing harmful substances.

However, each engine has a different discharge rate, compression ratio, shape of the combustion chamber, valve opening, closing time, fuel injection timing and fuel injection amount, so that the emission tendency is not only different. It is difficult to control, which makes it difficult to reduce nitrogen oxide and particulate matter at the same time.

In view of these problems, the diesel engine is fitted with a ceramic microporous filtration plate-shaped filter between the exhaust pipe and the silencer to pass the sulfur dioxide and soot gas contained in the exhaust gas through the micropores of the filter plate. This gas was filtered to collect. The various unburned particulates collected are easily attached to the main wall of the micro-pores to close the micro-pores, thereby reducing the filtration function of the filter and causing a back pressure increase due to the accumulation of the collected unburned particulates.

In order to solve the above problems, a catalyst method, an electric heater heating method, and an incineration method by a diesel fuel burner have been proposed. In this case, the use of a catalyst has a disadvantage in that the catalyst is not activated in the exhaust gas so that nitrogen oxides are increased, and in the case of the use of an electric heater, there is a disadvantage in that a load is placed on the vehicle electrical system. In this case, the control of the burner heating temperature is particularly difficult, and there are disadvantages in that the price is high.

In order to overcome the problems caused by this method, Korean Patent Application No. 91-15982 (Publication No. 93-5660) provides a method and apparatus for burning unburned particulates contained in exhaust gas of a diesel filter during operation of a diesel engine. Specifically, the actual temperature is detected upstream and downstream of the exhaust gas of the diesel filter, and the regeneration operation is automatically started when the first set value exhaust temperature reaches the upstream of the diesel filter during operation of the diesel engine. The operation is automatically turned off when the upstream outside the second setpoint exhaust temperature of the diesel filter is exceeded, and the regeneration of the diesel filter when the predetermined exhaust temperature downstream of the diesel filter is exceeded, By passing the exhaust through a bypass passage bypassing the diesel filter, the diesel filter is temporarily disconnected from the exhaust stream. The enemy was achieved.

However, these methods and apparatus have a reduction in output of 25 to 100% and a range of temperature increase of up to 119 ° C because they use a forced regeneration method that requires an increase in temperature during compression and expansion, that is, specific operating conditions. As a result, there were disadvantages in that temperature control was impossible at low power.

Accordingly, the present invention has been made in consideration of the above problems, and an object thereof is to provide an exhaust gas temperature control method of a diesel engine which can adjust the temperature of the exhaust gas discharged during operation of the diesel engine from a thermodynamic cycle without a separate external heat source. In providing.

Another object of the present invention is to provide a method of controlling the temperature of the exhaust gas so that the unburned fine particles adsorbed to the exhaust gas purification filter of the diesel engine can be burned and incinerated so that the filter can be repeatedly used.

Still another object of the present invention is to provide a method of controlling the temperature of exhaust gas so as to realize an optimum activation temperature of the filter catalyst and fuel additive for exhaust gas purification of a diesel engine.

Here, the temperature of the exhaust gas is controlled at a temperature that prevents thermal damage of the filter, and the temperature of the exhaust gas should be controlled within a temperature range capable of burning and burning unburned particulates adsorbed on the filter, while achieving an optimum activation temperature of the catalyst.

Figure 1 (a) is a P-V diagram of a diesel air standard cycle.

Figure 1 (b) is a T-S diagram of a diesel air standard cycle.

2 is a diagram showing the change in exhaust temperature according to the change in air fuel ratio.

3 is a diagram showing a change in exhaust temperature according to an initial temperature change.

Figure 4 is a schematic diagram of adjusting the temperature of the exhaust gas by adjusting the air fuel ratio of the diesel engine according to an embodiment of the present invention.

Figure 5 is a schematic diagram of controlling the temperature of the exhaust gas using an exhaust gas heat exchanger according to another embodiment of the present invention.

Figure 6 is a schematic diagram of adjusting the air fuel ratio of the diesel engine according to another embodiment of the present invention and the temperature of the exhaust gas using the exhaust gas heat exchanger.

Figure 7 is a schematic diagram showing the exhaust gas temperature change according to the fuel supply amount generated in the diesel engine and the exhaust gas temperature change according to the air supply amount controlled in the present invention.

* Explanation of symbols for main parts of the drawings

DE: Diesel engine SF: Ceramic filter

TS: Temperature Sensor ECU: Electronic Control Unit

TV: Throttle Valve FI: Fuel Injection

HE: Heat Exchanger

The object of the present invention, by installing a temperature sensor in front of the ceramic filter (SF) in communication with the diesel engine (DE) to measure the exhaust gas temperature generated when driving the diesel engine (DE), the temperature sensor (TS) And an electronic control unit (ECU) electrically connected to each other to generate output control data by calculating and controlling the exhaust temperature data measured by the temperature sensing sensor TS, and each of the throttle valves controlled by the electronic control unit (ECU). TV) by controlling the exhaust gas temperature by an iterative process of adjusting the air supply amount by controlling based on the output control data.

In addition, another object of the present invention is to branch the rear exhaust pipe of the ceramic filter (SF) in communication with the diesel engine (DE) to throttle the high-temperature exhaust gas purified by the ceramic filter (SF) through the heat exchanger (HE) Increase the temperature of the air supplied to the front intake pipe of the valve (TV) and install a temperature sensor in front of the ceramic filter (SF) in communication with the diesel engine (DE) to exhaust the exhaust gas generated when driving the diesel engine (DE) Measuring the gas temperature, the electronic control unit (ECU) electrically connected to the temperature sensor (TS) generates heat exchanger control data by calculating and controlling the exhaust temperature data measured by the temperature sensor (TS), electronic control Adjusting the temperature of the exhaust gas by an iterative process of adjusting the temperature of the air supplied to the diesel engine DE by controlling the heat exchanger HE controlled by the unit ECU based on the heat exchanger control data. Characterized It is achieved by the exhaust gas temperature control method of the diesel engine.

In addition, another object of the present invention is to install a temperature sensor in front of the ceramic filter (SF) in communication with the diesel engine (DE) to measure the exhaust gas temperature generated when driving the diesel engine (DE), the temperature sensor An electronic control unit (ECU) electrically connected to the TS generates and outputs the output control data and the heat exchanger control data by calculating and controlling the exhaust temperature data measured by the temperature sensor TS. The air supply amount is controlled by controlling the throttle valves TV respectively controlled based on the output control data, and branching the rear exhaust pipe of the ceramic filler SF in communication with the diesel engine DE to the ceramic filter SF. The exhaust gas of the high temperature purified by passing through the heat exchanger (HE) increases the temperature of the air supplied to the front intake pipe of the throttle valve (TV), and the heat exchanger (HE) controlled by the electronic control unit (ECU). Heat up Basis, control the ventilation control data to be achieved by the exhaust gas temperature control method of a diesel engine, characterized in that for adjusting the temperature of the exhaust gas by an iterative process of adjusting the temperature of the air supplied to the diesel engine (DE).

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the exhaust gas temperature T ₄ is calculated by analyzing the thermodynamic cycle of the diesel engine, which is the theoretical basis of the present invention.

The diesel cycle is an ideal cycle corresponding to the compression ignition internal combustion engine, and as shown in FIG. 1, each process is as follows.

로 등엔트로피 압축1-2: compression ratio

Isentropic compression

2-3: Temperature rise by heat transfer to gas at constant pressure

3-4: Isotropic expansion up to the first volume V ₁ = V ₄

4-1: heat release at a constant volume

In this cycle, the heat supply and the heat release are assumed as follows, assuming that the specific heat is constant.

Supply calories:

Emitted calories:

Therefore, the theoretical thermal efficiency η _th is

Is calculated.

On the other hand, since processes 1-2 and 3-4 are isentropic processes, and V ₂ = V ₃ , V ₁ = V ₄

Where ε is the compression ratio.

Therefore, the exhaust gas temperature T _{4 to be obtained} is given by Equation (1),

Obtained as

From the equation (2), the factors influencing the exhaust gas temperature T ₄ are expressed in a functional relationship as in the equation (3).

Here, the specific heat Cp the specific heat ratio k is handled from the home to the air cycle, a constant compression ratio ε is handling as it is a constant engine design parameters and, as a result, the temperature of the exhaust gas is supplied to the initial intake air temperature T ₁ and the working fluid is a function only the heat quantity ₂ q _3.

The assumption of the above-described air cycle is

(a) The working fluid is a constant mass of air that constitutes a closed system or cycles through steady state flow.

(b) Air is an ideal gas, and in most cases the specific heat is considered to be constant

(c) The combustion process is replaced by heat transfer from the high temperature heat source and the exhaust process by heat transfer to the low temperature heat source.

(d) Each process of the cycle is internally ideal, ie reversible, ignoring kinetic and potential energy, so that the constant pressure specific heat Cp and specific heat ratio k become constant by being considered constant by the assumption of (b). .

As a result, T ₄ is

It is represented by

Therefore, the inventors have found that the exhaust gas temperature T ₄ can be increased as desired by appropriately adjusting the initial intake temperature T ₁ and the amount of heat ₂ q ₃ supplied to the working fluid without a separate heat source.

In addition, the inventors were in the diesel engine that the amount of heat supplied to the working fluid _{3 2} q analysis whether or have any relationship with other factors, the result is as follows.

Where m'a is the mass flow rate of the working fluid (air),

Actually, the heat supply Q in a diesel engine is

Therefore, as a result, the amount of heat ₂ q ₃ supplied to the working fluid is summarized in equations (4) and (5),

Becomes Where (A / F) is the air fuel ratio.

Therefore, the amount of heat ₂ q ₃ supplied to the working fluid is proportional to the low calorific value Hl of the fuel and inversely proportional to the air fuel ratio A / F.

As discussed above, ₂ q ₃ is based on equation (6),

There is a functional relationship as above. Therefore, when the exhaust gas temperature T ₄ finally substitutes Equation (7) into Equation (3-1),

It can be seen that there is a function relation as

Figure 2 shows the theoretical calculation of the change in exhaust temperature (T ₄ ) according to the change in the air fuel ratio (A / F) based on the above formula (2), wherein the initial temperature (T ₁ ) is 15 ℃ Fixed.

As shown in the figure, the exhaust temperature is about 220 ° C. in a very sparse region where the air fuel ratio is about 100, but when the air fuel ratio is about 40, a temperature of 580 ° C. or more is obtained. That is, the lower the air fuel ratio, the higher the temperature of the exhaust temperature.

Figure 3 shows the theoretical calculation of the change in the exhaust temperature (T ₄ ) according to the change in the initial temperature (T ₁ ) based on the above equation (2), wherein the air fuel ratio was fixed at 80.

Although the rise of exhaust gas temperature is slightly slower than the increase of the intake air temperature in the calculation section, the result is almost linearly proportional and the exhaust gas temperature increases by 290 ° C as the intake air temperature increases by 300 ° C.

Figure 4 is a schematic diagram of controlling the temperature of the exhaust gas by adjusting the air fuel ratio of the diesel engine according to an embodiment of the present invention.

The present invention measures the exhaust gas temperature generated when driving the diesel engine (DE) by installing a temperature sensor in front of the ceramic filter (SF) communicated with the diesel engine (DE), and electrically connected to the temperature sensor (TS) The connected electronic control unit ECU controls the exhaust temperature data measured by the temperature sensing sensor TS to generate output control data, and the throttle valve TV controlled by the electronic control unit ECU is controlled. By controlling based on the output control data, the process of adjusting the air supply amount was repeatedly performed.

Here, the regulated air supply amount is maintained by the exhaust gas temperature in a range that does not adversely affect the ceramic filter (SF) by the repetitive action of incineration of unburned fine particles with the additives adsorbed to the ceramic filter (SF) ceramic filter ( By repeatedly regenerating SF), the original function of the ceramic filter SF can be maintained at all times.

At this time, the exhaust temperature of the exhaust gas was most suitable in the range of 300 ° C. to 600 ° C., but below 300 ° C., the incineration of the additive and the unburned fine particles adsorbed to the ceramic filter SF does not occur, so the regeneration efficiency of the ceramic filter SF While extremely low, the ceramic filter SF was incinerated or broken at 600 ° C. or more.

In order to maintain the temperature range of the exhaust gas, by adjusting the control degree of the air supply amount, that is, the air fuel ratio to be in the range of 20 to 60, the exhaust gas temperature is maintained in the range of 300 ° C. to 600 ° C. as described above. It was possible to achieve the original purpose intended to obtain (see Fig. 7).

The present invention in turn controls the throttle valve (TV) to be supplied to the diesel engine (DE) at the air fuel ratio described above to burn the additives and unburned fine particles adsorbed on the ceramic filter (SF) of the ceramic filter (SF) Regeneration was achieved, and the activation temperature of the catalyst and fuel additive coated on the ceramic filter (SF) could be optimally realized.

In the case of adjusting the fuel supply amount, as in a conventional engine, the amount of intake air is controlled to the maximum regardless of the amount of intake air, and the amount of fuel discharged from the fuel pump is adjusted. In the case of adjusting the air supply amount, the intake amount is gradually reduced by the throttle valve TV in the idle state, that is, the fuel supply amount is extremely low. The exhaust gas temperature is lower than the calculated value due to thermal dissociation, heat loss, etc., but the trend is inversely proportional to the air fuel ratio, indicating that the desired exhaust gas temperature can be controlled under any operating conditions. .

Here, the exhaust gas temperature rises in inverse proportion to the air fuel ratio. That is, since the exhaust gas temperature is proportional to the amount of fuel and inversely proportional to the amount of air, the exhaust gas temperature can be increased by controlling only the intake air amount without additional supply of the fuel amount. This can be realized by controlling only the throttle valve TV by the control of the electronic control unit ECU while the fuel injection injection FI is stopped.

Figure 5 is a schematic diagram of controlling the temperature of the exhaust gas using an exhaust gas heat exchanger according to another embodiment of the present invention.

The present invention, by branching the rear exhaust pipe of the ceramic filler (SF) in communication with the diesel engine (DE) through the heat exchanger (HE) through the high-temperature exhaust gas purified by the ceramic filter (SF) throttle valve (TV) Increase the temperature of the air supplied to the front intake pipe of the engine, and install the temperature sensor in front of the ceramic filter (SF) in communication with the diesel engine (DE) to measure the exhaust gas temperature generated when driving the diesel engine (DE) The electronic control unit (ECU) electrically connected to the temperature sensor (TS) generates heat exchanger control data by calculating and controlling the exhaust temperature data measured by the temperature sensor (TS), and the electronic control unit (ECU). By controlling the heat exchanger (HE) controlled by the heat exchanger control data, it is to repeatedly perform the process of adjusting the temperature of the air supplied to the diesel engine (DE).

Here, the temperature of the suction air raised by the heat exchanger (HE) maintains the exhaust gas temperature in a range that does not adversely affect the ceramic filter (SF) to collect unburned fine particles together with the additives adsorbed on the ceramic filter (SF). By repeatedly regenerating the ceramic filter (SF) by the repeated action of incineration, it is possible to always maintain the original function of the ceramic filter (SF) and to maintain the optimum activation temperature of the catalyst and fuel additives coated on the ceramic filter (SF) It can be implemented.

At this time, since the exhaust gas temperature is the same as described above, a detailed description thereof will be omitted.

In this method, high heat of exhaust gas discharged from an engine is transferred to intake air by using a heat exchanger so that the intake air whose temperature rises is sucked into the engine to raise the exhaust gas temperature.

The temperature rise of the intake air is proportional to the amount of heat delivered to the intake air, and the heat transfer amount is expressed by the following equation.

Therefore, when the temperature of the intake air is increased by the high heat of the exhaust gas, the temperature of the exhaust gas is increased by Equation (2), and when the exhaust gas temperature is increased, the intake air temperature is further increased by Equation (9). As a result, the temperature increases cyclically every time the engine cycle is repeated.

Here, since the temperature is further increased cyclically every cycle of the engine is repeated, the electronic control unit (ECU) by the exhaust temperature data measured by the temperature sensor (TS) is a ceramic by the generated heat exchanger control data The heat exchanger HE is stopped when the temperature is higher than the temperature adversely affecting the filter SF or the optimum activation temperature of the catalyst. That is, the electronic control unit ECU cuts off heat transfer between the exhaust gas and the air supplied to the diesel engine DE.

Figure 6 is a schematic diagram of adjusting the air fuel ratio of the diesel engine according to another embodiment of the present invention and the temperature of the exhaust gas using the exhaust gas heat exchanger.

The present invention measures the exhaust gas temperature generated when driving the diesel engine (DE) by installing a temperature sensor in front of the ceramic filter (SF) communicated with the diesel engine (DE), and electrically connected to the temperature sensor (TS) The connected electronic control unit (ECU) generates and outputs the output control data and the heat exchanger control data by calculating and controlling the exhaust temperature data measured by the temperature sensing sensor TS, and the throttle valves respectively controlled by the electronic control unit (ECU). By controlling the TV on the basis of the output control data, the air supply is regulated, and the exhaust pipe of the high heat purified by the ceramic filter SF is branched by branching the rear exhaust pipe of the ceramic filter SF in communication with the diesel engine DE. By passing the gas through the heat exchanger (HE), the temperature of the air supplied to the front intake pipe of the throttle valve (TV) is increased, and the heat exchanger (HE) controlled by the electronic control unit (ECU) is controlled by the heat exchanger control data. On of Then, the process of adjusting the temperature of the air supplied to the diesel engine (DE) by adjusting it was to be carried out repeatedly.

The embodiment shown in FIG. 6 is a method of adjusting the air supply amount as in the embodiment described in FIG. 4 and a method of raising the initial air temperature by heat-exchanging high heat of the exhaust gas as in the embodiment described in FIG. It is to be done selectively or at the same time.

As described above, according to the method of the present invention, by controlling the temperature of the exhaust gas discharged during operation of the diesel engine from a mechanical cycle without a separate external heat source, unburned fine particles adsorbed to the exhaust gas purification filter are burned and incinerated. The filter can be repeatedly regenerated and at the same time achieve the optimum activation temperature of the catalyst and fuel additive.

In addition, in implementing the method, the structure is implemented by an electronic control unit and a heat exchanger, and thus, the structure is very simple and the unit cost is low.

Claims (2)

The ceramic filter (SF) is regenerated by burning the additives and unburned particulates contained in the exhaust gas discharged when the diesel engine (DE) is driven and adsorbed to the ceramic filter (SF), thereby regenerating the ceramic filter (SF). In the exhaust gas temperature control method of the diesel engine to realize the optimum activation temperature of the catalyst and the fuel additive coated on the), the ceramic filter by branching the rear exhaust pipe of the ceramic filter (SF) in communication with the diesel engine (DE) Passing the high-temperature exhaust gas purified by SF) through a heat exchanger (HE) to raise the temperature of the air supplied to the front intake pipe of the throttle valve (TV); Installing a temperature sensor TS in front of the ceramic filter SF in communication with the diesel engine DE to measure the exhaust gas temperature discharged when the diesel engine DE is driven; Calculating heat exchanger control data by calculating and controlling the exhaust temperature data measured by the temperature sensing sensor TS by an electronic control unit ECU electrically connected to the temperature sensing sensor TS; When the exhaust temperature data adversely affects the ceramic filter SF or exceeds the optimum activation temperature of the catalyst and the fuel additive, the heat exchanger HE is controlled by the heat exchanger control data of the electronic control unit ECU. Comprising the step of controlling the temperature of the exhaust gas by adjusting the temperature of the air supplied to the diesel engine (DE) comprising the step of controlling the exhaust gas temperature of the diesel engine. The ceramic filter is burned by burning the unburned particulates and additives such as metal additives and selenium added to the diesel fuel adsorbed to the conventional ceramic filter SF while being discharged in the exhaust gas generated when the diesel engine DE is driven. A temperature sensing sensor is installed in front of the ceramic filter SF to regenerate the SF and to realize an optimum activation temperature of the catalyst and the fuel additive coated on the ceramic filter SF. In the exhaust gas temperature control apparatus of a diesel engine, in which a heat exchanger HE is installed at a branched exhaust pipe at the rear, exhaust gas generated when the diesel engine DE is driven by the temperature sensor in communication with the diesel engine DE. Measuring temperature, and an electronic control unit (ECU) electrically connected to the temperature sensor TS calculates and outputs the output control data by calculating and controlling the exhaust temperature data measured by the temperature sensor TS. And a first exhaust gas temperature adjusting step of controlling an air supply amount by controlling a throttle valve TV respectively controlled by an electronic control unit ECU based on the output control data; The step of raising the temperature of the air supplied to the front intake pipe of the throttle valve (TV) by passing the high heat exhaust gas purified by the ceramic filter (SF) in communication with the diesel engine (DE) through the heat exchanger (HE); Measuring exhaust gas temperature generated when driving the diesel engine DE, calculating and controlling heat exchanger control data by calculating and controlling the exhaust temperature data measured by the electronic control unit ECU; A second exhaust gas temperature including controlling the temperature of the exhaust gas by controlling the temperature of the air supplied to the diesel engine DE by controlling the heat exchanger HE by the electronic control unit ECU based on the control data; A second exhaust gas temperature adjusting step of controlling the temperature of the exhaust gas by adjusting the temperature of the air supplied to the diesel engine DE by controlling the heat exchanger HE by the regulating fish unit ECU; Third exhaust gas temperature control for controlling the temperature of the exhaust gas by controlling the air supply amount by operating the fuel injection injection (FI) installed in the diesel engine (DE) according to the data calculated in the first and second exhaust gas temperature adjustment step step; A method of controlling the exhaust gas temperature of a diesel engine, characterized in that the step of selectively performing one or two or more steps simultaneously.

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