The emission of nanoparticles from combustion engines has been shown to have a poorly understood impact on the atmospheric environment and human health, and legislation tends to err on the side of caution. Researchers have shown that Gasoline Direct Injection (GDI) engines tend to emit large amounts of small-sized particles compared to diesel engines fitted with Diesel Particulate Filters (DPFs). As a result, the particulate number emission level of GDI engines means that they could face some challenges in meeting the likely EU6 emissions requirement. This paper presents size-resolved particle number emissions measurements from a spray-guided GDI engine and evaluates the performance of an Evaporation Tube (ET). The performance of an Evaporation Tube and hot air dilution system with a 7:1 dilution ratio has been studied, as the EU legislation uses these to exclude volatile particles.
The Evaporation Tube was tested over a range of engine operating conditions with a Spray-Guided Direct Injection engine. The results show that at a temperature of 450°C, the Evaporation Tube had a significantly greater reduction effect on nucleation mode particles compared with accumulation mode particles. With a rich mixture and without dilution air, the transmission efficiency of large size particles was reduced compared to the performance with a stoichiometric mixture. With hot air dilution, the concentration of nucleation mode particles also reduced to a very low level, and at these conditions, the Evaporation Tube had a much smaller effect on the remaining nucleation mode particles. There was also a slight reduction in HC emissions post Evaporation Tube even with rich combustion, especially with the addition of dilution air.
The evaporation tube and hot air dilution were both found to be effective in removing the nucleation mode. Unlike a thermo-denuder there was no active charcoal for removing vaporized hydrocarbons, but with dilution of the sample after the evaporation tube or hot air dilution, there was no evidence of the nucleation mode reforming. In addition it was found that using the accumulation mode defined by the Cambustion DMS500 was also effective at excluding nucleation mode particles, as was a digital filter.