FAQ

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4. Is it sensitive enough for post-DPF measurements?

6. What kind of dilution ratio is required?

7. What is the correlation between gravimetric measurement and DMM obtained data?

8. After DPF the DMM shows almost zero result while the gravimetric measurement shows much higher emission.

9. How much difference is caused by different sampling system?

10. How do we convert the concentration [mg/m3] to emission rate [mg/km] or [mg/s]?

DMM stands for Dekati® Mass Monitor, a unique device for real-time automotive PM (particulate matter) mass emission measurements.

DMM is based on well-known ELPI™ technology, where a diffusion charger is used to give precisely designed charge to particles, and after that particles are size-classified a 6-stage inertial impactor. Sensitive electrometers are connected to impactor collection sensors and the measured current is proportional to the amount of particles in the corresponding size range.

Yes. Even though the concentration levels are much lower than what gravimetric filter can measure we can still measure engine PM mass emissions in second-by-second basis.

4. Is it sensitive enough for post-DPF measurements?

Yes. Even with 99.99% efficient diesel particulate filters we can see the mass emission signal. DMM measures particle mass concentrations down to 1 mg/m³ levels, so it is well suitable for post-DPF measurements, both for steady state and transient tests.

DMM is used either with a a CVS tunnel with some extra dilution (DI-1000) or a tailpipe sampling system (Dekati® FPS or 2 ejector diluters).

6. What kind of dilution ratio is required?

Usually the total dilution ratio is about 1:70 for conventional diesel vehicles and about 1:20 for DPF (Diesel Particle Filter) equipped vehicles. 

7. What is the correlation between gravimetric measurement and DMM obtained data?

DMM result is usually within 10% when compared to gravimetric measurement. Sampling system and presence of volatile/semi-volatile particles might increase the difference (see next 2 questions).

8. After DPF the DMM shows almost zero result while the gravimetric measurement shows much higher emission.

A typical filter paper collects particles with high efficiency, but they also adsorb gas-phase volatile material (e.g. hydrocarbons). DMM does not measure any gas-phase material.

With conventional diesel engines this filter artefact is almost negligible, but after DPF most of the solid particles are removed and filter artefact becomes more significant.

See article SAE2004-01-0967 for more information.

9. How much difference is caused by different sampling system?

Sampling system plays important role especially in volatile material behavior. E.g. heated dilution or a Thermodenuder removes most of the volatile material, and the amount of this can be 10-15% with conventional diesels and up to 90% with DPF-equipped vehicles.

10. How do we convert the concentration [mg/m³] to emission rate [mg/km] or [mg/s]?

In tailpipe measurements we must know the exhaust flow rate – which is usually difficult, but it can be calculated for example from the intake air flow.

[m³/s] is the flow rate – either CVS tunnel flow or tailpipe exhaust flow.