GB2245506A

GB2245506A - Particulate filter for diesel engine

Info

Publication number: GB2245506A
Application number: GB9014602A
Authority: GB
Inventors: Derek Graham Parker
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1990-06-30
Filing date: 1990-06-30
Publication date: 1992-01-08
Also published as: GB9014602D0; EP0591180A1; WO1992000443A1

Abstract

The invention relates to a diesel engine fitted with a filter trap. The filter trap comprises a filter material (12) having embedded in it particles of a catalyst and disposed within the exhaust manifold (10) of the diesel engine immediately downstream of the exhaust ports. By-pass channels (34) are included in the filter material (12) to permit part of the gases to be directed for recirculation through the engine without passing through the filter material.

Description

Title Particulate Filter Trap for a Diesel Engine Field of the invention The present invention relates to a particulate filter trap for a diesel engine.

Description of Prior Art It is known to place a filter trap in the exhaust of a diesel engine. Particles are trapped in a filter formed for example of a ceramic foam to prevent them from being discharged into the atmosphere. The build up of trapped particles in the filter results in the filter being choked after a period of time and steps must be taken to dispose of the collected particles in order to regenerate the filter.

Various approaches have been adopted for regenerating a filter trap by burning the particles within the trap. To this end, there have been suggested filter traps with different types of built in electrical heaters to burn off the particles, these being chassis filters connected to the exhaust pipe at some distance from the engine.

Aside from the fact that power is consumed to burn off the particles, these filter traps have the disadvantage that they are only regenerated periodically and during the intervening periods the filter is allowed to block.

Object of the invention The present invention seeks to provide a particulate filter trap in which particles trapped in the filter are continuously burned off without requiring an external energy source.

Summarv of the invention The present invention provides a diesel engine fitted with a filter trap comprising a filter material having embedded therein particles of a catalyst, which filter material is disposed within the exhaust manifold of the diesel engine immediately downstream of the exhaust ports.

The invention takes advantage of the fact that the particles will burn in the presence of a catalyst without applying any more heat than is already present in the exhaust gases, provided that the trap is positioned in the path of the gases before they have had the opportunity of cooling down in the exhaust pipe of the engine.

Preferred features of the invention At high engine speeds, the exhaust gas pressure will be sufficient to overcome the resistance to flow presented by the filter material, which may for example be a ceramic foam, and the temperature of the gases will be sufficient to enable the trapped particles to be burned in the presence of the catalyst.

However, a difficulty presented by placing the filter material near to the exhaust ports is that there is greater risk at low engine speeds of the filter being blocked. At low engine speeds, the back pressure of the filter material may present a problem even when the filter is not blocked and this problem is aggravated, at low engine speeds, in that there is more tendency for particles to be trapped and in that such particles are burnt off less efficiently. This process forms a cycle in which increased back pressure increases filter blockage and increased filter blockage results in increased back pressure, and the effect of this positive feedback is that the filter may be blocked very rapidly.

To avoid this problem, it is preferred to incluae n the filter material by-pass channels of relatively small cross section to permit part of the gases to be directed for recirculation through the engine without passing through the filter material.

Because of the presence of the by-pass channels, a large proportion of the gases under low speed conditions will not pass through the filter and will carry the particles back to the engine for combustion. Under higher speed the proportion of exhaust gas recirculation (EGR) is automatically reduced as the pressure increases and overcomes the back pressure in the filter trap.

It is preferred that the filter trap should comprise sections located with the individual manifold branches leading to the exhaust port. Such a configuration, apart from catching the exhaust gases at their hottest, has the advantage that the pressure pulses from individual cylinders will be sensed. Thus between pulses, particles will have more time to settle in the trap and their combustion will be improved.

Though heat is required to start the burning of the particles in a conventional filter trap, once the process has begun heat is given off during the exothermic reaction which results in the trap heating to such an extent as to become in some cases a fire hazard.

In an advantageous development of the present invention, a water jacket connected in the engine cooling circuit is arranged to cool the section of the exhaust manifold containing the filter trap. Such an arrangement offers two major advantages in that (i) it avoids excessive under bonnet temperatures and (ii) it heats the water in the cooling system. It is normally a problem with a diesel engine that its thermal efficiency is so high that the temperature of the cooling circuit is sometimes not sufficient to achieve effective warming of the cab or passenger compartment. In the preferred embodiment of the invention, the heat emitted during the exothermic reaction occurring within the filter trap is used to supplement the heat rejection from the engine to achieve better heater performance and more rapid engine warm up.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section taken along the line I-I in Figure 2 through a manifold incorporating a filter trap of the invention, and Figure 2 is a section taken along the line II-II in Figure 1.

Description of the preferred embodiment An exhaust manifold 10 for a four cylinder diesel engine includes a water jacket 22 connected through feed holes 14 and 16 to a coolant passage 18 in the cylinder head 20.

The manifold 10 is mounted by bolts 24 passing through holes 26 onto the side of the engine and mates with the four exhaust ports, of which one is shown in section in Figure 2. The manifold has two output connections, as shown in Figure 1, one leading to the down pipe of the exhaust system and the other to the EGR system which recycles the exhaust gases by supplying them through an EGR valve to the intake manifold.

Within the exhaust manifold, there is disposed a ceramic foam filter 12 in the form of a large rectangular block 12a with four projecting cylindrical cores 12b which extend into the individual exhaust ports of the cylinder head. The cores 12b have an axial passage 30 intersectea by cross bores 32 which lead the exhaust gases into the rectangular block 12a. Additionally, a low gas flow bypass channel 34 leads from each axial passage 30 directly to the EGR outlet, without the exhaust gases passing through the filter trap.

The material of the filter trap has embedded on its surfaces particles of a suitable catalyst, such as platinum, applied by techniques known from the manufacture of catalytic converters. The presence of the catalyst enables carbon monoxide to react with excess oxygen in the exhaust gases to produce less environmentally harmful carbon dioxide. This exothermic reaction also gives off heat which helps to burn off the soot particles collected in the trap. The latter reaction is itself exothermic and gives off still more heat. The heat from the various chemical reactions taking place in the filter trap is transferred to the water jacket, the coolant in which is circulated by way of a further outlet of the manifold through the heat exchanger of the vehicle heater.

During high engine speed operation, the exhaust gases pass through the filter material which traps soot particles and burns them off continuously using the heat generated by the reaction of carbon monoxide with excess air in the presence of the catalyst. Because the gases from the different ports are not combined before reaching the filter trap, the latter will experience the individual pressure pulses at the exhaust ports. As a result, higher pressure is available at the peaks of the pressure pulses to overcome to back pressure created by the presence of the filter and in the period between pulses, more time is allowed for the particles to settle and be trapped for combustion in a subsequent cycle. The exhaust gases cleaned of particles and with a reduced carbon monoxide content are passed to the exhaust pipe for discharge into the atmosphere.

At engine idle speed, some forty per cent of the exhaust gases pass to the exhaust pipe in the same manner as described above but the remaining sixty per cent flows along the passages 30 and the by-pass channels 34 to the EGR system for recirculation. This is done to avoid the filter being blocked at low engine speeds.

The heat transferred to the water jacket of the manifold is not only the heat of the exhaust gases themselves, which in an engine with a conventional manifold would be wasted by being discharged to atmosphere, but also the heat generated by the catalytically initiated exothermic reactions within the filter trap. The heat rejected from the engine is therefore increased and used to reduce warm up time and improve comfort within the passenger compartment.

Claims

1. A diesel engine fitted with a filter trap comprising a filter material having embedded therein particles of a catalyst, which filter material is disposed within the exhaust manifold of the diesel engine immediately downstream of the exhaust ports.

2. A diesel engine as claimed in claim 1, wherein bypass channels are included in the filter material to permit part of the gases to be directed for recirculation through the engine without passing through the filter material.

3. A diesel engine as claimed in claim 2, wherein the by-pass passages are dimensioned such that sixty per cent of the exhaust gases are recirculated at engine idling speed.

4. A diesel engine as claimed in any preceding claim, wherein the filter trap comprises sections located with the individual manifold branches leading to the exhaust port.

5. A diesel engine as claimed in any preceding claim, wherein a water jacket connected in the engine cooling circuit is arranged to cool the section of the exhaust manifold containing the filter trap.

6. A diesel engine fitted with a filter trap constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.