Solid Particle Counting System


Able to take raw sample from engine tailpipe, as well as diluted sample from tunnel-CVS. Applicable to after-treatment system evaluation, by taking sample gas from upstream and downstream of catalyst to check efficiency.


Two-stage dilution by Wide Range Continuous Diluter (WRCD); Developed by HORIBA - Patent applied. Dilution ratio:

  • Primary diluter: 10 to 1000
  • Secondary diluter: 10 to 50
  • Dilution accuracy: typically within ±5% (confirmed standard gas)
  • Removal efficiency of volatile particle: 99% or higher (at CPC inlet)
  • Penetration of solid particle: 95% or higher at CPC (based on poly-disperse)
  • High repeatability of measurement


Daily check functions for dilution factor, particle penetration, and zero level of CPC. Optional NaCI particles generation unit for checking CPC linearity.

Based on PMP New Standard (Draft)

The configuration of HORIBA solid particle counting system conforms to the recommendation by the Particle Measurement Program (PMP) in Working Party on Pollution and Energy (GRPE) under the auspices of United Nations Economic Commission for Europe (UN ECE).

The system performance also meets with the requirements of the PMP draft standard, which has a high possibility to affect future regulations in other countries. The reliability of the system has been demonstrated by cross-checking with the PMP standard system, so-called "golden system" that participates in the Inter-Laboratory Correlation Exercise arranged by PMP.

Technical article from:  Mr. Qiang Wei, HORIBA Instruments Incorporated, United States

Particle Measurement Program of EU (PMP) has proposed a draft regulation for light-duty diesel (LDD) vehicle exhaust particle number measurement. It is recommended that soluble organic fraction (SOF) and sulfate particles should be removed from the exhaust and only solid particles should be measured within limited size range. The draft regulation recommends the particle measurement system should consist of pre-classifier, heated diluter, evaporation unit, cold diluter, and particle counter.

A solid particle counting system (SPCS) to measure engine exhaust solid particle number emission in real time has been developed. The instrument is designed to follow the recommendation in PMP draft regulation for number emission measurement on light-duty diesel vehicles. The SPCS consists of hot dilution and thermal conditioning of exhaust gas followed by cold dilution according to the PMP recommendation. Two wide range continuous diluters developed in this project have been used as cold diluter and hot diluter in the instrument. An evaporation unit has been used for thermal conditioning of exhaust gas. A condensation particle counter (CPC) has been used for counting particles after cold dilution. Many functions, some of which are recommended by PMP such as particle measurement, such as zero checks for CPC and the system, flow check for CPC, daily linearity check, and data saving, etc., were automated in the SPCS.

The performance of the instrument has been evaluated according to PMP recommendations. All of them have achieved the required levels or better than those in the PMP recommendation. The accuracy of overall dilution ratio in the SPCS is normally within ±4% in the designed range. The instrument has very low particle losses, and exhibits over 95% penetration for solid particles larger than 20 nm. The evaporation unit shows more than 99% removal efficiency of volatile fractions. The system has very good linearity, larger than 0.95 as R2 value, in measurement.

The SPCS has been used to study solid particle emission from gasoline and diesel vehicles. As recommended by PMP draft regulation, exhaust is diluted by a constant volume sampler (CVS). The SPCS takes sample from the CVS tunnel. Transient test cycles such as EPA FTP 75, EPA HWFET, NEDC, and Japanese JE05 mode, have been tested. The repeatability of the instrument has been evaluated on the diesel vehicle for three continuous days.

The instrument exhibits good repeatability, is very sensitive as well, and can detect the driving differences. Solid particle emission increases during hard acceleration and decreases quickly at deceleration. High concentration of solid particle emission has been observed during cold and hot start with the gasoline vehicle, due to gasoline engine running rich at the start. The SPCS can respond very well against any after-treatment devices fitted with gasoline and diesel vehicles.

Conforming to standardsGRPE-PMP draft regulation
ApplicationMeasurement of solid particles in engine exhaust with and without after-treatment systems
PrinciplesLaser Based Condensation Particle Counting (CPC)
Lower particle size limit23 nm scattering (±1), 50% counting efficiency)
Measuring ranges0-10,000 up to 50,000 particles/m3
Sample handling temperatureControlled at 47°C ± 5°C (for CVS sampling)
191°C or 350°C (for direct sampling)
Dilution ratio in primary diluter (PND1)10 to 700
Dilution ratio in secondary diluter (PND2)10 to 50
Evaporation unit temperature300°C to 400°C
Pre-classifier temperature47°± 5°C
Environment for operationAmbient temperature: from 5°C to 30°C
Ambient relative humidity: under 80% RH

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