Real-Time Measuring System for Engine Exhaust Solid Particle Number Emission - Performance and Vehicle Tests

The prototype solid particle counting system (SPCS) has been used to study solid particle emission from gasoline and diesel vehicles. As recommended by the PMP draft proposal, exhaust is diluted by a Constant Volume Sampler (CVS). The SPCS takes the sample from the CVS tunnel.

Transient test cycles such as EPA FTP 75, EPA HWFET (EPA Highway Fuel Economy Cycle), and NEDC (New European Driving Cycle) were tested. The repeatability of the instrument was evaluated on the diesel vehicle for three continuous days. The instrument exhibits good repeatability. The differences for the EPA ftp 75, the EPA HWFET, and the NEDC in three continuous tests are ± 3.5%. The instrument is very sensitive as well and detects the driving differences.

A large number of solid particles are found during the hard acceleration from both the gasoline and the diesel vehicles. Solid particle emissions decrease quickly at deceleration and when vehicles approach constant speed. High concentrations of solid particle emissions are observed during cold and hot starts with the gasoline vehicle. This is due to the gasoline engine running rich at the start. The solid particle emission, in unit particles/km, strongly depends on the driving cycles and pre-condition for the gasoline vehicle, but not for the diesel vehicle.