GB2214449A

GB2214449A - Exhaust gas particulate measurement

Info

Publication number: GB2214449A
Application number: GB8801342A
Authority: GB
Inventors: David Haydn Blunt
Original assignee: Perkins Engines Group Ltd
Current assignee: Perkins Engines Group Ltd
Priority date: 1988-01-21
Filing date: 1988-01-21
Publication date: 1989-09-06
Anticipated expiration: 2008-01-21
Also published as: GB2214449B; GB8801342D0

Abstract

A sample of I.C. engine exhaust gas is drawn into duct 2 at inlet 1 and mixed with cold air, and some of the mixture is drawn from duct 2 through a particle-collecting filter 14 and returned to duct 2 through a gas meter 18, the filter 14 subsequently being examined. To determine the proportions of air and exhaust gas in the mixture, respective pumps 3 and 4 driven by a common motor draw a given volume flow of air into duct 2 and expel a given, greater volume flow of air and gas from its downstream end. Venturis 5 and temperature and pressure sensors 7, 8 enable the two volume flows to be measured, and the mixture proportions may then be calculated. <IMAGE>

Description

EXHAUST GAS PARTICULATE MEASUREMENT This invention relates to the measurement of particulate matter in engine exhaust gas.

It is known to measure particulate matter in engine exhaust gas by diluting a portion of the gas in a stream of air through a mixing duct and then filtering a sample of the diluted exhaust gas for the measurement of particulates.

The purpose of the dilution is to reduce the gas temperature to an acceptable standard for particulate measurement by filtering, for example, below 52 degrees C. The particulate measurement taken is then scaled in accordance with the dilution ratio of the exhaust gas and air. This ratio has been calculated by mitering the carbon dioxide content of the exhaust gas and the diluted exhaust gas that flow through the mixing duct.

An object of the present invention is to provide an improved arrangement for the measurement of particulates in engine exhaust gas.

This is achieved according to the invention by providing a mixing duct for the dilution of exhaust gas, a first gas pump to draw air into the duct at a first constant volume flow rate, a second gas pump to extract air from the mixing duct at a second constant volume flow rate higher than the first flow rate, means to remove a sample of the diluted exhaust gas from the mixing duct for particulate measurement, means for returning said sample of the diluted exhaust gas to the mixing duct after said particulate measurement, and means for determining the ratio of said first and second flow rates to produce a factor that is used to scale said particulate measurement.

The invention will now be described by way of example with referent to the accompanying drawings showing a schematic diagram of measuring apparatus according to the invention.

A sampling probe removes gas from an engine exhaust and feeds this via a heated line 1 into a mixing duct 2. A first positive displacement pump 3 draws air into the duct 2 at a point upstream of the exhaust sampling line 1, and a second positive displacement type pump 4 extracts the air/exhaust mixture from the duct 2 downstream of tne line 1, and a venturi 5 and silencer 6 is provided at the inlet of pump 3 and the outlet of pump 4 together with temperature and pressure sensors 7,8. Both pumps 3, 4 are driven by the same motor 9 via belt drives 10, 11 which determine a drive ratio such that the constant volume flow rate of the second pump 4 exceeds that of the first pump 3, thereby drawing exhaust gas into the duct from the sampling line 1.

A sample of diluted exhaust gas is removed from the duct 2 through a probe 12 that is located downstream of the sampling line 1. The probe 12 is connected via an isolating valve 13, a particulate filter 14, a second filter 15 and a flow regulator 16 to a pump 17 which removes the diluted gas sample from the duct 2 and returns it via a dry gas meter 18 and a second isolating valve 19 to the duct at a point 20 just upstream of the second pump 4. Particulates in the diluted gas sample are removed in the filter 14 and measured once the filter is isolated by closing the valves 13, 19.

The measured weight of particulates can then be related to the exhaust gas sample drawn in at line 1 during the measurement period using the ratio of the flow rates of pumps 3 and 4.

The venturi 5 and temperature and pressure sensors 7, 8 allow the respective flow rates to be measured as V1 and V2 for the pumps 3 and 4, respectively, the exhaust to air dilution ratio then being V2 - V1 . It will be appreciated V2 that the accuracy of this relationship is unaffected by the measurement sampling process because the sample is returned to the duct at 20 for removal by pump 4.

Claims

1. A method of measuring particulate matter in engine exhaust gas in which a portion of the exhaust gas is diluted in a stream of air tnrough a mixing duct, a sample of the diluted exhaust is removed from the mixing duct for measurement of particulate matter therein, and said particulate measurement is scaled in accordance with the dilution ratio of the exhaust and air, characterised in that a first gas pump draws air into the mixing duct at a first constant volume flow rate, a second gas pump extracts air from the mixing duct at a second constant volume flow rate which is higher than the first flow rate, the sample of diluted exhaust is returned to the mixing duct after said particulate measurement, and the ratio of said first and second flow rates is used to scale said particulate measurement.

2. Apparatus for measuring particulate matter in engine exhaust gas comprising a mixing duct for the dilution of exhaust gas, means to remove a sample of the diluted exhaust gas from the mixing duct, and means for measuring particulate matter in said sample, characterised in that said apparatus further comprises a first gas pump to draw air into the duct at a first constant volume flow rate, a second gas pump to extract air from the mixing duct at a second constant volume flow rate higher than the first flow rate, means for returning said sample to the mixing duct after said particulate measurement and means for determining the ratio of said first and second flow rates to produce a factor that is used to scale said particulate measurement.

3. Apparatus as claimed in claim 2 which includes drive means common to both said first and second pumps and which has a predetermined drive ratio in accordance with the required ratio of the first and second flow rates produced by the pumps.

4. Apparatus as claimed in claim 2 or 3 in which said means for determining the ratio of said first and second flow rates comprises gas flow measuring means located upstream of the first pump and gas flow measuring means located downstream of the second pump.

5. A method of measuring particulate matter in engine exhaust gases substantially as herein described with reference to the accompanying drawings.

6. Apparatus for measuring particulate matter in engine exhaust gases substantially as herein described with reference to the accompanying drawings.