Characteristics of ultrafine particles emitted from a dimethyl ether (DME) engine
Characteristics of ultrafine particles emitted from a dimethyl ether （DME） engine

Measurements of exhaust particle number concentration and size distribution from a dimethyl ether (DME) engine at different engine loads and speeds were carried out by using a two-stage dilution sys- tem and an SMPS. The results of the DME engine were compared with those of the original diesel en- gine. The fuel composition had significant effects on the exhaust particle size distribution, the total exhaust particle number and mass concentrations. Compared with those of the DME engine, the parti- cle mass emissions of the diesel engine increased 5.7-17.7 times. At high engine speed (n=2200 r/min), compared with those of the DME engine, the total particle number emissions of the diesel engine in- creased 0.75-2.2 times, while the total particle number emissions of the diesel engine decreased by about 50%-80% for middle and high loads at middle engine speed (n=1400 r/min). Compared with those of the DME engine, the total exhaust particle number concentrations in the accumulation mode of the diesel engine increased 4.2-62.6 times and the exhaust particle geometric number mean diameters in the accumulation mode increased by about 10-30 nm. This correlated with higher oxygen level and lack of C-C bonds in DME. A lot of nucleation mode particles were emitted from the DME engine, this correlated with the processes of nucleation and condensation of the volatile and semi-volatile com- pounds in the exhaust gas.