GB2245692A

GB2245692A - Heating particles in a gas stream

Info

Publication number: GB2245692A
Application number: GB9014820A
Authority: GB
Inventors: Peter Stanley Robertson
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1990-07-04
Filing date: 1990-07-04
Publication date: 1992-01-08
Also published as: GB9014820D0

Abstract

Particles can be heated in a gas stream by making the gas flow through an intense beam of radiant energy. The particles absorb energy from the beam and their temperature rises. By selecting the correct conditions, it is possible to raise the temperature of soot particles in an exhaust gas stream from a vehicle engine to a temperature at which the soot will oxidise to gaseous products in the oxygen available in the exhaust gases. <IMAGE>

Description

HEATING PARTICLES IN A GAS STREAM This invention relates to apparatus for and a method of heating particles in a gas stream. The invention is particularly applicable to the oxidation of soot particles in vehicle exhaust gasses, particularly diesel engine exhaust gasses. These particles can be oxidised by being heated in the presence of oxygen, whereupon the particle is oxidised into gaseous components.

It is known from European Patent 0 191 437 to pass exhaust gasses containing soot particles through a chamber in which an electro magnetic microwave field is established, with the result being that the microwaves excite the conductive soot particles and raise the temperature of the soot particles to a level at which oxidation of the soot particles to carbon dioxide and other gaseous components can be achieved.

According to the present invention, there is provided apparatus for heating particles in a gas stream, the apparatus comprising an elongate enclosure for directing the gas stream, a source of radiant energy, and means for directing the energy in a beam across the enclosure and transverse to the direction of flow of the gas stream.

In contrast to the use of microwaves, where moving magnetic fields are set up in the particles being heated, the present invention relies upon the absorption of the radiant energy by the particles to heat the particles.

If the particles are soot particles and the gas stream includes oxygen, then the soot particles will be oxidised in the stream and converted to gaseous products.

The radiant energy is preferably in the ultra-violet /visible/infra-red spectrum, with wave lengths predominantly between 1,500 and 80,000 . The energy level of the radiation emitted by the source is preferably between 100 and 1000 watts and is preferably adjustable depending on engine speed and load. These figures are considered to be appropriate for heating soot particles in the exhaust gas stream of a medium van. engine. Higher energy levels may be appropriate for larger engines. In particular the energy level which could be satisfactorily used on a stationary engine may be higher than that for a vehicle engine. On a vehicle, the energy supplied to excite the radiation source will all have to be supplied by the output from the vehicle engine, whereas with a stationary engine, an external energy supply can be used.

A focusing arrangement may be provided to direct the beam across the gas stream, and this focusing arrangement may include a reflective collector and a set of lenses.

In a preferred embodiment, the elongate enclosure is rectangular (preferably square) in cross-section and the walls of the enclosure are able to reflect the beam in the plane of the beam.

The apparatus may be incorporated in a motor vehicle engine installation and may include means responsive to the speed and load of the engine for varying the energy output of the energy source in accordance with the operating state of the engine. In certain circumstances the energy output may be varied to zero.

The invention also provides a method of heating particles as they flow in a gas stream, wherein a beam of radiant energy is directed across the gas stream, so that as the particles pass through the beam, they are heated by absorbing energy from the beam.

The invention will now be further described, by way of example, with reference to the accompanying drawing which is a perspective view of apparatus in accordance with the invention, with a top wall of an enclosure omitted in order to assist explanation.

The drawing shows an elongate enclosure 10, the top of which has been removed so that the interior space can be seen. The enclosure has side walls 12 and 14 and open ends at 16 and 18. The exhaust gas will flow through the enclosure in the direction indicated by yarrows 20, 22.

In use, the enclosure 10 will be connected into the run of an exhaust pipe from an engine to an outlet. It is preferred if the enclosure is mounted as close to the engine as possible so that the exhaust gas is hot at the time that it passes through the enclosure. The centre part of the enclosure is wider than the two ends so that the gas stream will be decelerated as it passes through the centre of the enclosure.

In the middle of the enclosure a radiant beam 24 is directed across the enclosure in such a way that all the gas flowing into the enclosure has to pass through the beam. The beam will be a high intensity beam so that when soot particles entrained in the gas stream enter the beam they are very rapidly heated to a temperature sufficiently high for them to be oxidised by the oxygen in the gas stream, to form gaseous products. It will be noted in the drawing that the gas on the left hand side of the beam 24 includes small soot particles, but that the gas on the right hand side of the beam contains no such particles.

The beam is produced by an energy source 26 in the form of a generally elongate light emitter. A first curved mirror 28 is positioned on one side of this source and a second, larger curved mirror 30 is positioned at the other side of the source. These mirrors have the effect of focusing the light from the source 26 on a lens system 32 which collimates the light to produce the narrow beam 24 which lies in one plane. The beam can for example be approximately lmm wide. The surfaces of the enclosure on which the beam is incident are arranged so that light is reflected from them back into the plane of the beam.

In use, the whole of the exhaust gas flow passes through the enclosure 10 and the beam 24 operates continuously.

There may however be certain engine operating conditions under which the intensity can be lowered or even possibly the beam switched off and a control device may be used to control the current fed to the electrically excited radiation source 26 to control the intensity.

The actual radiation intensity, the best wavelengths to use and the mirror and lens design will be determined by experiment.

It is considered that the beam should be as narrow as possible. A narrow beam will reduce the opportunities for convected and radiant heat loss from the particles whilst oxidation is under way because the temperature gradient whilst the particle is being heated will be very steep; the particle will remain in the beam for a very short time and will be rapidly heated to its oxidation temperature.

As the size of the particles varies so the input energy will need to be increased for larger particles and decreased for smaller particles.

The apparatus described can provide a simple but effective means of oxidising soot particles in an engine exhaust, particularly a diesel exhaust. The apparatus operates continuously and does not obstruct or hold up the flow of gas. As a result, there is no increase in back pressure as results from the use of a filter. In the present invention, the stream of exhaust gasses is treated continually and continuously as it passes from the engine to atmosphere.

Claims

1. Apparatus for heating particles in a gas stream, the apparatus comprising an elongate enclosure for directing the gas stream, a source of radiant energy, and means for directing the energy in a beam across the enclosure and transverse to the direction of flow of the gas stream.

2. Apparatus as claimed in Claim 1, wherein the radiant energy is in the ultra violet/visible/infra-red spectrum.

3. Apparatus as claimed in Claim 1 or Claim 2, wherein the radiant energy has wavelengths predominantly between 1,500 and 80,000 .

4. Apparatus as claimed in any preceding claim, wherein the energy level of the source is between 100 and 1000 watts and is adjustable depending on engine loading.

5. Apparatus as claimed in any preceding claim, wherein a focusing arrangement is provided to direct the beam across the gas stream.

6. Apparatus as claimed in Claim 5, wherein the focusing arrangement includes a parabolic collector and a set of lenses.

7. Apparatus as claimed in any preceding claim, wherein the elongate enclosure is rectangular in cross-section and the walls of the enclosure are able to reflect the beam in the plane of the beam.

8. Apparatus as claimed in any preceding claim and incorporated in a motor vehicle engine installation the apparatus including means responsive to the speed and load of the engine for varying the energy output of the energy source in accordance with the operating state of the engine.

9. A method of heating particles as they flow in a gas stream, wherein a beam of radiant energy is directed across the gas stream, so that as the particles pass through the beam, they are heated by absorbing energy from the beam.

10. A method as claimed in Claim 9, wherein the particles are soot particles and the gas stream includes oxygen, then the soot particles will be oxidised in the stream and converted to gaseous products.

11. Apparatus for heating particles in a gas stream, substantially as herein described with reference to the accompanying drawing.