Particle Characterization in the Exhaust Devices of Direct Injection Engines
Time: Fri 2021-05-28 10.00
Subject area: Machine Design
Doctoral student: Arun Prasath Karuppasamy , Förbränningsmotorteknik
Opponent: Univ.-Prof. Mag. Alexander Bergmann, University of Technology Graz
Supervisor: Prof. Anders Christiansen Erlandsson, Förbränningsmotorteknik; Dr. Hanna Bernemyr, Förbränningsmotorteknik
Minimizing pollutants are of utmost importance to ensure sustainability in transportation. Particle emissions from internal combustion engines are especially harmful to human health, while also contributing to global warming. In an effort to counteract climate change and enhance air quality, various technological solutions are currently being scrutinized with the objective to abate transport emissions. Increasing focus has been directed towards electric powertrain solutions, prompting the development of battery technology, charging systems and power grid infrastructure. However, given the present uncertainty around the time and resources required for the electrification of heavy-duty transport, it would be worth investigating advanced solutions for reducing tailpipe emissions from internal combustion engine vehicles.
This current research work investigates the evolution of exhaust particles along the exhaust and after-treatment system of a heavy-duty engine. The findings presented in this thesis can be used for devising effective particle emission mitigation techniques. The impact on particle number (PN) and distribution was evaluated for individual exhaust system devices, namely: a periodic particle grouping pipe, a turbocharger turbine, and a selective reduction catalyst (SCR).
A specially designed periodic particle grouping pipe, intended to increase particle grouping did not prompt particulate grouping and the reduction of non-volatile particle number in the exhaust system. Particles smaller than 50 nm were observed to be predominant in the exhaust stream and showed no relevant response to induced periodic grouping.
Exhaust conditions such as temperature, flow-rate and initial particle concentration influence the number and distribution of particles entering the turbine of the turbocharger. At low loads, the turbine caused particle fragmentation due to impingement, increasing the PN in size range 30 to 200 nm. On the other hand, temperatures above 400°C at the turbine inlet promoted soot oxidation, enabling the reduction of the PN at high loads.
When operating the engine at high loads with increased NOx emissions and high exhaust temperatures, excess urea injection upstream of the SCR catalyst triggered the formation of ammonium salts in the exhaust stream. Subsequently, a surge in particles less than 23 nm was observed across the SCR catalyst, leading to a NOx-PN trade off.
As the nature of particle emissions changes along the after-treatment system, sample conditioning may affect PN readings. To this purpose, the impact of sample conditioning procedure and of the adopted diluter type on PN measurements was also investigated. PN measurements were carried out using two different dilutions systems: a two-stage rotating disk diluter with an evaporation tube and a two-stage ejector diluter with hot air dilution. Motoring tests outlined that volatile particle removal is enhanced using the rotating disk diluter.
In conclusion, it is not only the DPF which impacts tailpipe emissions, but also the turbocharger turbine and the SCR under certain conditions. A comprehensive method has been devised and presented to select a suitable dilution and conditioning system while evaluating PN measurements in the exhaust devices.