JP2002242661A - Combustor for exhaust emission control of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical, practical temperature rising system having one DPF system as a means for raising the temperature of exhaust gas to the specified temperature by burning fuel with remaining oxygen in the exhaust gas to keep the effectiveness of a catalytic action in an oxidation catalyst used for the regeneration of a DPF and the oxidation combustion of DP used for catching the DP in diesel exhaust gas, preventing the stop of an engine, ensuring temperature rising action, having a simple, compact, and inexpensive system, easily being installed to an engine exhaust system, and minimizing a running cost such as fuel consumption. SOLUTION: The ignition and combustion timing of a combustor is controlled by using oxygen concentration, exhaust gas temperature, and exhaust gas flow rate or a signal replaceable to the exhaust gas flow rate of three elements for keeping sure ignition and a stable combustion state of fuel, according to the operation state of the engine, in order to raise the temperature of exhaust gas to the specified temperature during the operation of the engine by surely burning fuel with the remaining oxygen in the exhaust gas. The exhaust gas temperature of the DPF or an oxidation catalyst inlet is monitored so as not to exceed the allowable temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the regeneration of a DPF provided to prevent the emission of the DP contained in the exhaust gas of a diesel engine from being released to the atmosphere or the securing of the catalytic effect of an oxidation catalyst. The present invention relates to a combustor for raising the temperature of exhaust gas.

[0002]

2. Description of the Related Art DPF used for trapping soot and SOF, which are harmful components in exhaust gas of a diesel engine, becomes a filter when the DPF is used alone due to the trapped DP along with the operation time of the engine. The filter is gradually clogged, and the pressure loss in the filter portion is increased, thereby not only lowering the engine output but also increasing the fuel consumption of the engine, which is uneconomical. Further, when the clogging proceeds extremely, the operation of the engine itself becomes impossible.

However, since most of the components of the DP trapped in the filter portion are combustible, the DP is trapped in the DPF by heating with an electric heater or raising the temperature of exhaust gas with a burner device using a burner. Various methods for regenerating the filter portion by burning the DP and SOF are considered.

[0004] The electric heater system is an intermittent regeneration system in which the electric power is forcibly heated to incinerate the DP to regenerate the filter function, and the filter function is alternately switched at regular time intervals to alternately repeat capture and regeneration. Is common. Also, recently, it has been studied to use an oxidation catalyst for simultaneous treatment of DP and SOF, and to increase the temperature of exhaust gas for incineration of DP and SOF trapped by DPF.

[0005] The outline and problems will be described below. FIG. 5 shows a backwash regenerating system in which a backflow air (26) and an electric heater (27) are used in combination with a cross flow DPF (7). The amount of DP trapped in the filter is detected by a separately installed filter differential pressure gauge, and if necessary, compressed air is fed in the opposite direction of the normal exhaust gas flow to blow the DP down to the hopper below the DPF (7). Then, the DP is incinerated with an electric heater in the hopper.

The interior of the DPF (7) is divided into two chambers, each having a filter element (28) and a hopper (19). The filter element (28) is formed by integrating plate-like fired ceramics in a multilayer arrangement. DPF
Since (7) has two chambers, there is a disadvantage that the outer shape is large and the weight is heavy. Further, since the electric heater is used, the power consumption is large and the capacity of the generator and the battery (11) needs to be increased to 1.5 times or more of the conventional one. Therefore, when applied to a vehicle, the DPF (7) as a whole becomes large, so that space restrictions and control become complicated, so that application to ordinary vehicles is difficult.

FIG. 6 shows a pair of wall flow type DPFs.
(A) (5) and DPF (B) (6).
(B) While capturing the DP through the exhaust gas in (5), the exhaust gas switching valve (17) of the system of the other DPF (A) (6) (clogging progressed in the DP) is closed and the control valve is closed. (1
6) Open, and at the same time energize the electric heater (27) to
Play F (A).

[0008] Since the DPF has two systems, the apparatus becomes complicated and has the same problem as that shown in FIG. Fig. 7 shows a pair of DPF (A) (5) and DPF (B) using a bellows type filter element in which the entire filter is covered with a reticulated electric heater.
(6) is provided. Exhaust gas flow is controlled by an exhaust gas switching valve (1
Although switching is alternately performed in 7), there is the same problem as in FIG.

FIG. 8 shows an oxidation catalyst and a wall flow type DP.
5 shows a DPF system combining F. DPF (4)
Fuel such as light oil is injected from a nozzle (25) into an exhaust gas pipe (20) as a heat source for incinerating the DP trapped in the fuel tank, and the fuel is supplied to an oxidation catalyst (10) provided upstream of the DPF (4). Oxidizes and heats the exhaust gas. Here, the oxidation action of the oxidation catalyst on DP in diesel exhaust gas generally does not work effectively unless the exhaust gas temperature is 350 ° C. or higher. On the other hand, diesel engine exhaust gas temperature is usually 30
Since it is operated at 0 ° C. or less, a sufficient oxidizing effect of the fuel supplied from the fuel oil pump cannot be expected much.

Further, the current oxidation catalyst has a remarkable deterioration in performance due to the sulfur content in the fuel such as light oil which is widely used at present, so that not only the sulfur content in the fuel needs to be 50 ppm or less but also platinum or palladium. Precious metal-based oxidation catalysts are expensive and use in large quantities is problematic in terms of cost and resources. Figure 9 shows a DP using a burner (37) that uses combustion air (3) taken from the atmosphere.
1 shows the F system.

[0011] The pressure sensor (42) installed before and after the DPF (4) detects the capturing state of the DP, and if necessary, ignites and burns the fuel by the burner (37) to reduce the exhaust gas temperature for the above purpose. It is intended to raise the temperature. This system requires a system of combustion air to be supplied by an air fan (15), so that not only is the entire system including these controls complicated and maintenance is troublesome, but also the size of the burner body is increased. It is difficult to arrange in the exhaust system.

Furthermore, since the amount of exhaust gas to be treated increases,
It is necessary to increase the size of the PF (4) and the exhaust gas pipe (20), and it is necessary to heat the combustion air (3). It is uneconomical because the amount of fuel consumption is increased because the amount of heat is increased with respect to the net calorific value for raising the temperature of itself.

[0013]

SUMMARY OF THE INVENTION Regeneration of DPF used for trapping DP in diesel exhaust gas and DP
As means for burning fuel using residual oxygen in exhaust gas and raising the temperature of exhaust gas to a predetermined temperature, in order to ensure the effectiveness of catalytic action in an oxidation catalyst used to oxidize and combust gas, a DPF system is used. It is a single system, and it does not stop the engine. It has a reliable heating function, the system is simple, compact and inexpensive. It is easy to arrange in the engine exhaust system, and running costs such as fuel consumption are minimized and economical. Provide a highly practical heating system.

[0014]

In order to reliably burn fuel using residual oxygen in exhaust gas and to raise the temperature of the exhaust gas itself to a required temperature during operation of the engine, the temperature of the exhaust gas depends on the operating condition of the engine. The ignition and combustion timing of the combustor is controlled using the oxygen concentration and the exhaust gas temperature and the exhaust gas flow rate or the signals that can be changed, which are the three factors to ensure the ignition of the fuel in the combustor and the stable combustion state I do.

Also, the temperature of the exhaust gas at the inlet of the DPF or the oxidation catalyst is monitored so that these do not rise above the allowable temperature.

First, the exhaust gas characteristics of a general diesel engine will be described with reference to FIG. From this figure, the residual oxygen in the exhaust gas is usually 13% or more of the engine output, which is relatively high at low load and rises to about 18% at idling. Further, it can be seen that the exhaust gas temperature and the exhaust gas flow rate at the engine outlet increase as the engine output increases.

FIG. 11 shows the combustion characteristics of fuel with respect to the temperature of the exhaust gas with the residual oxygen in the engine exhaust gas in the combustor. It can be seen from the figure that when the exhaust gas temperature decreases, the oxygen concentration in the stable combustion limit exhaust gas is required to be high. still,
The upper part of the curve in the graph indicates the ignition / stable combustion range.

FIG. 12 shows the relationship between the exhaust gas flow rate in the combustor and the ratio of the fuel flow rate to the exhaust gas flow rate (hereinafter referred to as fuel-air ratio). From this figure, it can be seen that the stable combustion range is limited to a range where the exhaust gas flow rate is somewhat small and the fuel-air ratio is constant. The left side of the curve in the graph indicates the ignition / stable combustion range.

From these facts, in order to raise the temperature of the exhaust gas itself by using the residual oxygen in the exhaust gas, it is desirable to confirm the three elements of the oxygen concentration in the exhaust gas, the exhaust gas temperature and the exhaust gas flow rate to ensure the fuel. Igniting and stable combustion can be performed, and the DPF and the oxidation catalyst can be regenerated during operation of the engine. Here, the exhaust gas amount of the engine is not only a signal that is not normally used, but also requires a considerable cost to directly detect it, so that it is not practical to use the exhaust gas amount itself.

Accordingly, as a substitute value, the exhaust gas pressure downstream of the DPF or the exhaust gas pressure downstream or upstream of the oxidation catalyst, the engine speed or the vehicle speed, or the signal of both the engine speed and the vehicle speed or the engine speed if no DPF is installed downstream. It can be approximately obtained by a calculator as a value obtained by multiplying the output by a predetermined function.

FIG. 13 shows D versus exhaust gas flow rate.
It indicates the exhaust gas pressure at the PF outlet, and since the two values are correctly correlated, the exhaust gas pressure at the DPF outlet can be used as an index of the substitute value of the exhaust gas flow rate. The same applies to the exhaust gas pressure downstream or upstream of the oxidation catalyst.

Similarly, the engine speed or the vehicle speed or the engine speed and the vehicle speed or the engine output can be used in the same manner as the index. Note that these index values are converted into exhaust gas flow values inside the ECU.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 shows an embodiment of the present invention for DPF regeneration. Exhaust gas (2) from the engine (1) is sequentially purified by the DPF (4) via the combustor (34) and the DPF (4) and discharged to the atmosphere from the exhaust gas tail pipe (22).

An oxygen sensor (40) and a temperature sensor (41) are installed upstream of the combustor, a temperature sensor and a pressure sensor (42) are installed upstream of the DPF (4), and a pressure sensor is installed downstream of the DPF (4). I have. The pressure sensors (42) at the inlet and outlet of the DPF are also used for monitoring the DPF differential pressure for monitoring the DP capturing state of the DPF (4). In this case, signals from a differential pressure gauge separately installed may be used.

The combustor (39) has a fuel oil tank (31)
The fuel oil (45) is supplied from the fuel oil pump (14), injected from the nozzle (25) into the combustor (39), and ignited and burned by the glow plug (35). Electric power to the fuel oil pump (14) and the glow plug (35) is supplied from the battery (11).

If necessary, depending on the DP capture state of the DPF, the rise of the exhaust gas is determined by an oxygen sensor (40) signal and a temperature sensor (42) signal upstream of the combustor and a pressure sensor (42) signal downstream of the DPF (4). After confirming that the conditions for igniting and stable combustion for the temperature are secured, the fuel oil is introduced to raise the temperature of the exhaust gas.

The temperature of the DPF (4) is monitored by a temperature sensor (41) at the inlet of the DPF so as not to exceed the allowable value, and the fuel flow rate is adjusted by a fuel oil pump or the fuel is cut off as required. I do.

FIG. 2 shows another embodiment of the present invention for DPF regeneration, in which fuel gas is used instead of fuel oil in FIG. The use of the fuel gas cylinder (32) filled with liquefied gas eliminates the need for a fuel oil pump and simplifies the apparatus. The ignition source is ignited by a spark plug (34) using a spark generator (36). Others are the same as FIG.

FIG. 3 shows another embodiment of the present invention for securing the effectiveness of the catalytic action of the oxidation catalyst. This is a case where an oxidation catalyst (10) is used instead of the DPF (4) in FIG. 1, and the other is the same as FIG.

FIG. 4 shows another embodiment of the present invention for ensuring the catalytic activity of the oxidation catalyst and regenerating the DPF.
The case where an oxidation catalyst is added upstream of the DPF (4) in FIG. 1 is shown. Oxidation catalyst (10) and DPF (4)
Temperature sensor (41) for protection of the oxidation catalyst (10)
It is installed upstream of. Others are the same as FIG.

[0031]

The embodiments are as described in the "embodiment of the invention". However, an adsorbent for adsorbing the SOF component may be provided instead of the oxidation catalyst of FIG.

The glow plug (35) in FIGS. 1, 3, and 4 and the spark plug (34) in FIG. 2 are all ignition sources for the fuel injected into the combustor (39). It is not intended to be a particular application.

Although the description mainly assumes a diesel engine for vehicles, the present invention can be applied not only to vehicles but also to stationary diesel engines such as land generators and marine diesel engines.

Although the structure of the filter element of the DPF is mainly described as a wall flow type, a bellows type or a granular (granular layer) using a nonwoven fabric is used.
It can be applied to all types such as a mold or a ceramic foam type or a multi-pipe type in which DPF can be regenerated by heating exhaust gas.

The electric power to the electric equipment may be directly supplied from a generator other than the battery.

[0036]

According to the present invention, since there is only one DPF system, there is no need to stop the engine, and reliable ignition of fuel in the combustor and a stable combustion state are maintained, so that the effect of increasing the temperature of exhaust gas is ensured. In addition, the system is simple, compact, inexpensive, easy to arrange in the engine exhaust system, running costs such as fuel consumption are minimized, and it is possible to provide an economical and practical exhaust gas temperature raising system with high practicality .

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention for DPF regeneration.

FIG. 2 shows another embodiment of the present invention for DPF regeneration.

FIG. 3 shows another embodiment of the present invention for ensuring the catalytic activity of the oxidation catalyst.

FIG. 4 shows another embodiment of the present invention for ensuring the catalytic activity of the oxidation catalyst and regenerating the DPF.

FIG. 5 is a cross-flow DPF system using an electric heater.

FIG. 6 is a switchable DPF system using an electric heater.

FIG. 7 is a bellows type DPF system using an electric heater.

FIG. 8 is an exhaust gas purification system combining an oxidation catalyst and a DPF.

FIG. 9 is a DPF system using a burner that uses combustion air.

FIG. 10 Exhaust gas characteristics of a diesel engine

FIG. 11 Ignition / stable combustion characteristics of a combustor (1)

FIG. 12: Ignition / stable combustion characteristics of a combustor (2)

FIG. 13: Change in exhaust gas pressure at DPF outlet

[Explanation of symbols]

 Reference Signs List 1 engine 2 exhaust gas 3 combustion air 4 DPF 5 DPF (A) 6 DPF (B) 7 DPF (cross-flow type) 8 DPF (wall flow type) 9 DPF (bellows type) 10 oxidation catalyst 11 battery 12 generator 13 regulator 14 Fuel oil pump 15 Air fan 16 Control valve 17 Exhaust gas switching valve 18 Exhaust gas valve 19 Hopper 20 Exhaust gas pipe 21 Regeneration exhaust gas pipe 22 Exhaust gas tail pipe 23 Diffuser 24 Reflector 25 Nozzle 26 Backwash air 27 Electric heater 28 Filter Element 31 Fuel oil tank 32 Fuel gas cylinder 33 Air tank 34 Spark plug 35 Glow plug 36 Spark generator 37 Burner 38 Vaporization mixer 39 Combustor 40 Oxygen sensor 41 Temperature sensor 42 Pressure sensor 43 Engine load 44 ECU (control device) 5 fuel oil 46 fuel gas 47 solenoid valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/36 B 3/36 9/00 Z 9/00 B01D 46/42 B // B01D 46/42 53/36 103C F-term (reference) 3G090 AA02 CA01 CA02 CA04 CB01 CB02 CB03 CB04 CB11 CB12 CB13 CB15 DA02 DA03 DA04 DA09 DA10 DA12 DA18 DA19 DA20 EA02 3G091 AA02 AA04 AA06 AA18 CA15 DB10 EA17 EA32 EA34 FB10 FC02 GA05 GA06 GA20 HA11 HA15 HA22 HA36 HA37 HA42 HA45 HA47 HB02 HB03 4D048 AA14 AA17 AB01 BB02 CC51 CD05 DA01 DA02 DA13 4D058 JA32 MA41 MA51 SA08 TA06

Claims (6)

[Claims] An exhaust gas particulate filter (hereinafter, referred to as DPF) used for trapping soot and soluble organic substances (hereinafter, referred to as SOF), which are suspended particulate matter (hereinafter, referred to as DP), which is a harmful component in diesel engine exhaust gas. Combustion for burning the fuel and raising the temperature of the exhaust gas to a required value in order to ensure the catalytic action of the oxidation catalyst used to incinerate or regenerate the trapped DP or to oxidize and combust the harmful substances in the step (1). An oxygen concentration signal and an exhaust gas temperature signal and an exhaust gas flow signal or DP in the exhaust gas to be heated which are detected by an oxygen sensor and a temperature sensor installed upstream of the combustor burner.
Using one or more of the following: an exhaust gas pressure signal downstream of F, an exhaust gas pressure signal upstream or downstream of the oxidation catalyst, an engine speed signal, a vehicle speed signal, a signal of both engine speed and vehicle speed, or an engine output.
The fuel is injected under the condition that one or more of these signals satisfies at least one of the stable combustion conditions of the fuel injected to raise the temperature of the exhaust gas, and the residual oxygen contained in the exhaust gas itself is used for the fuel. A combustor that is controlled to stably ignite and burn. 2. An exhaust gas particulate filter (hereinafter, referred to as DPF) used for trapping soot and soluble organic substances (hereinafter, referred to as SOF) as suspended particulate matter (hereinafter, referred to as DP), which is a harmful component in exhaust gas of a diesel engine. Combustion for burning the fuel and raising the temperature of the exhaust gas to a required value in order to ensure the catalytic action of the oxidation catalyst used to incinerate or regenerate the trapped DP or to oxidize and combust the harmful substances in the step (1). An oxygen concentration signal and an exhaust gas temperature signal and an exhaust gas flow signal or DP in the exhaust gas to be heated which are detected by an oxygen sensor and a temperature sensor installed upstream of the combustor burner.
Using at least two of the following: an exhaust gas pressure signal downstream of the F, an exhaust gas pressure signal upstream or downstream of the oxidation catalyst, an engine speed signal or a vehicle speed signal, a signal of both the engine speed and the vehicle speed, or an engine output.
The fuel is injected under the condition that two or more of these signals satisfy the stable combustion condition of the fuel injected to raise the temperature of the exhaust gas, and the residual oxygen contained in the exhaust gas itself is used for the fuel. A combustor that is controlled to stably ignite and burn. 3. An exhaust gas particulate filter (hereinafter referred to as DPF) used for trapping soot and soluble organic substances (hereinafter referred to as SOF), which are suspended particulate matter (hereinafter referred to as DP), which is a harmful component in diesel engine exhaust gas. Combustion for burning the fuel and raising the temperature of the exhaust gas to a required value in order to ensure the catalytic action of the oxidation catalyst used to incinerate or regenerate the trapped DP or to oxidize and combust the harmful substances in the step (1). An oxygen concentration signal and an exhaust gas temperature signal and an exhaust gas flow signal or DP in the exhaust gas to be heated which are detected by an oxygen sensor and a temperature sensor installed upstream of the combustor burner.
These signals raise the exhaust gas using the exhaust gas pressure signal downstream of the F, the exhaust gas pressure signal upstream or downstream of the oxidation catalyst, the engine speed signal, the vehicle speed signal, the signal of both the engine speed and the vehicle speed, or the signal of the engine output. Combustion controlled so that fuel is injected under conditions that satisfy the stable combustion conditions of the fuel injected for warming, and the fuel is stably ignited and burned using the residual oxygen contained in the exhaust gas itself. vessel. 4. The combustor according to claim 1, wherein the temperature of the DPF inlet or the inlet of the oxidation catalyst is monitored by a temperature sensor so as not to be an abnormally high temperature exceeding an allowable temperature set for the DPF or the oxidation catalyst. A combustor controlled to regulate or shut off the flow rate of the input fuel. 5. The combustor according to claim 2, wherein the temperature of the DPF inlet or the inlet of the oxidation catalyst is monitored by a temperature sensor so as not to be an abnormally high temperature exceeding an allowable temperature defined for the DPF or the oxidation catalyst, and if necessary. A combustor controlled to regulate or shut off the flow rate of the input fuel. 6. The combustor according to claim 3, wherein the temperature of the DPF inlet or the inlet of the oxidation catalyst is monitored by a temperature sensor so as not to be an abnormally high temperature exceeding an allowable temperature set for the DPF or the oxidation catalyst, and if necessary. A combustor controlled to regulate or shut off the flow rate of the input fuel.