New Dekati Sensor Provides Detailed Data About Vehicle Particulate Emissions
22 March 2006
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| An early prototype of the AutoTest system, with Dekati Mass Monitor and Fine Particle Sampler. Click to enlarge. |
Smoke opacity testing (smoke darkness) currently is widely used in motor vehicle inspections to assess particulate emissions from diesel engines. There are more than 100,000 vehicle inspection stations in Europe using smoke darkness to measure particulate emissions.
Testing is performed on a vehicle at rest and in neutral, while the engine is accelerated without any external load to the maximum governed speed. A smoke meter placed at the end of the exhaust pipe measures the opacity of the smoke, expressed in percent of light reduction—the degree to which the exhaust obscures a beam of light shining through it.
Other shortcomings aside, this method is particularly unsuitable for measurement of the smallest particles, which are considered to be the most dangerous.
Finnish company Dekati Oy has developed a new sensor-based instrument to measure particulate emissions from vehicles that will address those issues at a reasonable cost.
Dekati is a designer and manufacturer of fine particle measuring and sampling devices. One of its key innovations has been the Electrical Low Pressure Impactor (ELPI), developed in co-operation with Tampere University of Technology. ELPI is capable of measuring fine particle concentrations and size distribution in real time.
Dekati’s new AutoTest instrument will feature a sensor to enable the measurement of vehicle particulate emissions during vehicle inspections. Dekati has signed an R&D contract to develop AutoTest with a US company.
It will be possible to develop the sensor into a vehicle-specific sensor that could be fitted in every diesel-driven vehicle.
Demand for such measuring instruments is expected to increase rapidly with the measurement of vehicle particulate emissions in vehicle inspections beginning in 2007 in the USA, in 2008 in Japan and possibly in the EU in 2012. Dekati estimates the potential demand in just those markets from 80,000 to 200,000 measuring instruments.
Tekes, the Finnish Funding Agency for Technology and Innovation, has partly funded Dekati’s research into particle measurement technology for a number of years.
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While I like the idea of being able to measure particulate matter, the real test in my experience with diesels is under load conditions, especially accelleration. Without that load, the test misses the large pollution source/mode.
Posted by: Richard Burton | 22 March 2006 at 06:11 PM
Richard -
diesel smoke tests are conducted using so-called free acceleration tests, in which the engine is rapidly revved up and down in a prescribed pattern with the transmission in neutral. To get a repeatable reading, any soot that has accumulated in the exhaust pipes is first flushed.
This applies to the field testing of all diesels in Europe and e.g. diesel trucks in California.
Posted by: Rafael Seidl | 23 March 2006 at 12:30 AM
Rafael; I appreciate the info re how tests are actually run.But I still question whether they very realisticly measure reality-I can see heavy smoke pour out of some diesels while they are pulling heavy load,especially at lower rpm-and I don't see this other test as measuring what appears to be the most gross pollution time.But then of course, many cars super-pollute while they are warming up,especially older with carberators, and we have chosen to not measure that phase....
Posted by: Richard Burton | 23 March 2006 at 09:49 AM
Richard -
diesels do not have carburetors.
The visible smoke is due partly to flushing of soot that has accumulated in the exhaust and partly to the fact that the drivetrain response lags the driver request. If the engine displacement is small relative to torque demand, as is the case in many trucks, the air ratio lambda will fall close to or even slightly below 1. This substantially increases engine-out particulate emissions.
Note that while visible diesel smoke is dirty and a respiratory irritant if inhaled, the greater problem is posed by particles below ~7 microns in diameter. These penetrate deep into the lungs and can accumulate there or enter the bloodstream. This can exacerbate respiratory ailments such as asthma, especially in vulnerable persons such as children and senior citizens. This is particularly true if the particles also contain sulphuric acid, which is why Europe and soon the US have required refineries to remove virtually all sulphur from diesel fuel.
On the other hand, concerns about carcinogenic effects are no longer as strong after it was discovered that they only occur in extremely high doses and then only in rats, not other test animals.
Diesel particulate filters will hold back about 99% of the engine-out emissions, eliminating visible smoke and sharply reducing health effects. However, carmakers have only recently achieved the control strategy breakthroughs that keep these filters from being destroyed when the accumulated soot is finally burnt off. They are now available standard or as an option on many diesel cars in Europe, even though the present regulations (Euro 4) can be met without them.
Posted by: Rafael Seidl | 23 March 2006 at 01:47 PM