Particle size distribution and number concentration were measured in the dilute exhaust of a heavy-duty diesel engine for steady-state and transient engine operation using two different dilution systems that included a full flow CVS that was coupled to an ejector pump (CVS-EP), and a double-ejector micro-dilution tunnel (DEMDT) that was connected to engine exhaust close to turbocharger outlet. Measurements were performed using a scanning mobility particle sizer (SMPS), an electrical low pressure impactor (ELPI), and a parallel flow diffusion battery (PFDB). Fuels with sulfur content of about 385 ppm and 1 ppm were used for this work.
The PFDB performed well in measuring nanoparticles in the size range below 56 nm when compared with the SMPS. This was especially valid when a distinct log-normal size distribution in the size range below 56 nm in diameter, the upper size limit of the PFDB, was present.
The dilution method and the sulfur content in the fuel influenced the characteristics of the size distributions significantly under both steady-state and the FTP hot-start transient cycle. The CVS-EP resulted in more particle growth and higher number of nanoparticles compared to the DEMDT.
Harmonizing the measurement method of total particle number and size emissions from engines by providing a reference condition to variables such as dilution temperature, dilution rate, dilution ratio, relative humidity, dilution and transfer line residence time, will be a key next step in developing a protocol and a standard operating procedure for such measurement. Until then, different researchers will continue to produce different results in measuring total particle size and number, depending on the sampling and dilution system selected.