Composition and toxicity of particulate matter emitted from turbocharged common rail DME-biodiesel engine

Both ultrafine particle and toxicity emissions originating from diesel engine gain an increasing concern. In this study, size distribution and toxicity of particles from a turbocharged common rail engine fueled with clean fuels-dimethyl ether (DME) and biodiesel blends-were investigated. Effects of different DME-biodiesel blends (B0, B5, B10, and B15) and different engine loads were considered. The results demonstrate that particles emitted from DME-biodiesel engine are mainly in form of nucleation mode. Engine running at intermediate load exhausts the maximum number of accumulation mode particles owing to local hypoxia and not high enough combustion temperature. The addition of biodiesel slightly increases the total particle number, peak of particle number concentration, and particle size corresponding to the peak. Effect of biodiesel proportion on particle size distribution gets weaker with the increase of engine load. Engine fueled with B5, B10, and B15 mainly exhausts low molecular weight polycyclic aromatic hydrocarbons (PAHs) (ring number ≤ 4) which are closely related to unburned fuel, and the total PAH emissions are linear versus the fuel consumption. Toxicity equivalent (TE) of particles at low load is lower than that at intermediate load. DME-biodiesel blends with biodiesel mass proportion ≤ 15% can release the DME engine from abrasion and leakage, but no obvious increase in both particle emissions and the risk of particle toxicity.