Hazardous particles during diesel engine cold-start and warm-up: Characterisation of particulate mass and number under the impact of biofuel and lubricating oil
Ali Zare, Meisam Babaie, Alireza Shirneshan, Puneet Verma, Liping Yang, Zoran Ristovski, Richard J. Brown, Timothy A. Bodisco, Svetlana Stevanović
Abstract
The increasing share of using biofuels in vehicles (mandated by current regulations) leads to a reduction in particle size, resulting in increased particle toxicity. However, existing regulations disregarded small particles (sub-23 nm) that are more toxic. This impact is more significant during vehicle cold-start operation, which is an inevitable frequent daily driving norm where after-treatment systems prove ineffective. This study investigates the impact of biofuel and lubricating oil (as a source of nanoparticles) on the concentration, size distribution, median diameter of PN and PM, and their proportion at size ranges within accumulation and nucleation modes during four phases of cold-start and warm-up engine operation (diesel-trucks/busses application). The fuels used were 10 and 15% biofuel and with the addition of 5% lubricating oil to the fuel. Results show that as the engine warms up, PN for all the fuels increases and the size of particles decreases. PN concentration with a fully warmed-up engine was up to 132% higher than the cold-start. Sub-23 nm particles accounted for a significant proportion of PN (9%) but a smaller proportion of PM (0.1%). The fuel blend with 5% lubricating oil showed a significant increase in PN concentration and a decrease in particle size during cold-start. This study focuses on unregulated hazardous fine particles emitted from vehicles, particularly highlighting the impact of increasing the share of biofuel (as mandated by current regulations), which leads to a reduction in particle size, resulting in increased particle toxicity. However, existing emissions regulations and standards disregarded small particles (diameter < 23 nm) that are more toxic. The particle size reduction, therefore increased toxicity, escalates significantly during vehicle cold start operation, which is an inevitable frequent daily driving norm where after-treatment systems prove ineffective. Thus, urgent attention is required to include smaller particles in regulations to safeguard public health.