GB2184669A - Control system for regenerating a diesel engine exhaust filter - Google Patents

Abstract

A system for controlling regenerative burning in a diesel engine exhaust particulate filter (20) comprises a first temperature sensor (30), a burner (32 to 38) and a second temperature sensor (42) mounted in that order upstream of the filter (20) in the exhaust system.The temperature sensors feed signals to a control device (50), which also receives signals representing pressure drop across the filter, engine speed and vehicle brake pressure. Device (50) initiates supply of fuel and air to the burner and actuates igniter (40) in response to predetermined conditions, for example when the engine is idling and the vehicle stationary with brakes on. A third temperature sensor inside filter (20) signals device (50) to stop the burner when all particulates have been burned. Device (50) may abort the regeneration if the engine speed rises. <IMAGE>

Description

SPECIFICATION Particulate emission control for diesel engines This invention relates generally to a system forcollecting and eliminating particulate emissionsfrom diesel engines, and more particularly concerns a system for positively assisting the regenerative burning of particulate emissions collected on a ceramic filter in a diesel engine exhaust system.

Diesel engines are widely used in trucks and other transport equipment. Under some operating conditions, these diesel engines can produce unacceptably great amounts of particulate emissions. But in accordance with known practice, this particulate matter can be collected on a particulate filter installed in the engine exhaust system. In fact, some ceramic filters can collect as much as 90% of diesel exhaust particulate emissions.

As particulate material collects on thefiltersurfaces, a gradual increase in engine exhaust back pressure occurs. Over a relatively short period of time, this increased back pressure can result in a loss of engine power and increased fuel consumption.

Over a relatively long period, excessive exhaust back pressure can lead to failure of engine components.

It has been discovered that both soluble and insoluble particulates trapped on the ceramicfilterwalls can be ignited, and the gaseous products of emission can be permitted to travel through the filter and out the downstream portions of the exhaust system.

This process of igniting and burning the particulates fromthefilterwalls is commonly referred to as regeneration, and it results in a reduction of particulates in the filter and the consequent reduction of exhaust back pressure acting on the engine. Systems ofthis general type are disclosed in U. S. Patent 4,541,239 and in European patent application No.

84100667.9 published on August 1, 1984 as Publication No.0114696.

It is an object of the present invention to provide a diesel engine particulate trap regeneration system in which the regeneration is actively assisted undercertain conditions so as to maintain a controlled ex haust back pressure in the engine exhaust system. A related object is to provide an assisted regeneration system which will operate even when the hostvehicle is parked with the engine running at idle speed.

Another object is to provide an assisted regeneration system which is reliable and effective at an attractive price.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.

Summary ofthe invention To accomplish these objectives, the invention includes a first temperature sensor mounted in an engine exhaust system, and a burner assembly moun- ted in the exhaust system downstream ofthe first temperature sensor. A second temperature sensor is mounted in the exhaust system downstream ofthe burnerassembly,anda particulatetrap is mounted downstream ofthe second temperature sensor. A programmable controller operates the burner assembly in response to sensed temperatures and other conditions to positively initiate and assist regenerative burning in the particulate trap.

Brief description ofthe drawings: Figure 1 is a schematic illustration of a diesel engine and its exhaust system which includes a cer amic particulatefilterand the novel regenerationassisting system ofthe present invention; and Figure2 is a schematic illustration showing in further detail the regeneration-assisting system.

Detailed description: While the invention will be described in connec tionwitha preferred embodiment, twill be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope ofthe invention as defined by the appended claims.

Turning more specifically to the drawing, there is shown a diesel engine 10 having an exhaust system 12. This exhaust system 12 includes an exhaust manif old 14 of the usual sort, which leads to an exhaust pipe 16. In the pipe 16 is a burner assembly 18, and downstream of the assembly 18 is located a ceramic particulate exhaust filter 20. Exhaust piping 22 leads from the filter 20 to an exhaust pipe end. Itwill be understood that exhaust traveling through the exhaustsystem 12 bears particulate matter, which col lects on the surface orwalls ofthe ceramic filter 20.

Particulate matter ordinarily collects on the filter 20 when the engine 10 is operating at a loworidle speed. When the engine 10 operates under other conditions --forexample, when the engine 10 operates at close to its maximum load --the exhaust gas temperatures can increase considerably. If sufficient oxygen is present, this increase in exhaust gas tem perature can causethe particulates collected on the filter to ignite and burn.The products ofthis particulate combustion are mostly gases, and these gases mingle with the engine exhaust gases to pass through the downstream portions of the fiiter 20 and out the downstream portions 22 of the exhaust system. This self-ignition and combustion has been referred to as spontaneous filter regeneration.

However, when the engine 10 is operated at idle speeds for a long period oftime,considerable amounts of particulate matter can collect on the filter without spontaneous regeneration occurring.As ex- plained above, this excessive particulate collection can lead to increased fuel consumption or even engine damage.

To provide positively assisted regeneration,the burner assembly arrangement 18 is provided upstream of the filter 20. In accordance with the inven tin, this regeneration burner system is inexpensive yet effective in operation. To this end, a firsttemperature sensor 30 is provided at an appropriate place in the exhaust system. Just downstream ofthe firsttemperaturesensor30 is provided a burner nozzle mechanism 32 of known arrangement.Afuel supply from a remote source passes through a con trol valve34,and a supplyofcompressed airfrom a remote source passes through solenoid valve 36, to the burner assembly 32. The burner assembly is provided with a nozzle 38 adapted to atomizethefuel and airmixturesso asto provide good pilotorinitial ignition.

Downstream ofthe nozzle assembly 38 is an igni ter4O of known design. Thefuel-airmixturefromthe nozzle 38 is caused to move downstream by the ex haust flow E and past the igniter 40 where ignition occurs.

Downstream ofthe igniter 40 and burner assembly 38 is a second temperature sensor 42, and downstream ofthe second temperature sensor 42 is the filter 20 as shown in Figures 1 and 2. Within the filter 20 is located a third temperature sensor 44.

Connected to the temperature sensors 30,42 and 44is an electronic control unit 50 which can include a programmable microprocessor section 51 and suitable memories 52. Programs to control the system of the present invention can be prepared using known programming techniques.A program for controlling an exhaust emission regeneration system is generally described and illustrated in published European PatentApplication 0114696, for example.

The electronic control unit 50 receives input signalsfrom the temperature sensors 30,42 and 44 on lines 60,62 and 64. Lines 66,68 and 70 receive signals related to engine speed, exhaust system back pressure and vehicle air brake line pressure, respectively. Control signals from the electronic control unit 50 are routed to a burnerfuel pump 74along a line 76; to the igniter40 along a line 78, and to the burnerair solenoid valve 36 along a line80.

In normal operations, excess oxygen in the spent but hot exhaust gases is used to initiate and promote proper regenerative combustion and the filter 20. A continous supply of compressed air from storage tanks or an air pump located aboard the vehicle purges the burner nozzle of residual diesel fuel so as to prevent "coking" aatthe burner nozzle 38. The compressed air routed through the nozzle 38 also servesto assist in atomization ofthedieselfuel droplets.

An exhaust back-pressure signal delivered on line 68 from a sensor 82 located at a convenient place in the exhaust system signals the electronic control unit 50 when a preselected backpressurevaluehas been reached If desired, the electronic control unit 50 can be programmed to provide fuel from the burner assembly 32 and ignition from the igniter 40 only when the engine vehicle is operating at an idle speed and condition, and when the air brake line pressure sensor 60 indicates thatthe vehicle pneu mastic parking brake has been set.

When pressure in the particulate filter 20 has risen above a preselected value as indicated by the pressure sensor 82 over the line 68, an output signal is delivered to the fuel pump 74so as to suppiy diesel fuel through the line 34to the burner assembly 32.

Simultaneously, the igniter 40 is activated so asto ignite the atomized fuel. The temperature sensor42 located downstream of the ignitor 40 senses the tem- peraturn rise so asto insure positive burneroperation.

The burner 40 is operated for a period of time while the controller 50 monitors internal filtertemperaturves through the temperature sensor 44. When a maximum selected temperature is reached in thefilter,the controller 50 shuts off the burner operation.

The electronic control unit 50 continuesto scan or monitor the trap internal temperature through the third temperature probe orsensor44.

It is contemplated that, if the engine speed rises above its minimum idle speed at any time, the regeneration positive assistance cycle will be aborted by the controller halting delivery of fuel and air to the burner assembly 32. Once filter regeneration is complete, as indicated by a drop in the internal temperature ofthe filter, the controller 50 begins to mon itorengine operating parameters in its normal operating mode.

Claims (4)

1. A particulate control regeneration system comprising, in combination a first temperature sensor mounted at a given location in an engine exhaust system; a burner assembly mounted in the engine exhaust system downstream of the firsttemperature sensor; a second temperature sensor mounted in the engine exhaust system downstream of the burner assembly; a particulate trap mounted downstream ofthe second temperature sensor; and control means connected to the sensors and the burner assembly for operating the burner assembly so asto ignite and positively assist theregenerative burning of particulate matter in the trap when predetermined conditions are present.

2. Asystem according to claim 1 wherein said control means controls the operation of said burner assembly in response to temperatures sensed by the first temperature sensor.

3. A system according to claim 1 or 2 further including means for sensing engine speed,the control means being adapted to halt burner operation when the engine speed exceeds the preset minimum value.

4. A system according to claim 1 substantially as hereinbefore described with reference to the drawings.