An Integrated System for Energy-efficient Exhaust Aftertreatment for Heavy-duty Vehicles

Abstract

This chapter presents a unique system approach applied in a joint academic–industrial research programme, E4 Mistra, to attain the goals of high energy efficiency and low emissions in an exhaust aftertreatment system for heavy-duty vehicles. The high energy efficiency is achieved by heat recuperation, onboard hydrogen production for NO _x reduction, and by finding new solutions for making the aftertreatment system active at low exhaust temperatures. To reach low particulate emissions, a mechanical filter using a sintered metal powder is developed and coated with catalytic material to improve the soot oxidation efficiency. Low NO _x emissions are achieved by an efficient NO _x reduction catalyst.

The integrated E4 Mistra system comprises four technological advances: thermoelectric (TE) materials for heat recuperation, catalytic reduction of NO _x over innovative catalyst substrates using either the onboard diesel or biodiesel, H₂ from a high-efficiency fuel reformer, and particulate filtration over a porous metal filter. The TE materials are used in a TE generator (TEG) which converts thermal energy into electricity. The TEG is used to recuperate heat from the exhaust-gas recirculation (EGR) circuit of heavy-duty trucks and is expected to generate ~1 kW electric power from 20 kW heat in the exhaust gas. The TEG is integrated in a plate heat exchanger (HEX) designed particularly for this application. Apart from the knowledge and experiences in TEG and heat exchange technologies, a thorough fluid dynamics and TE analysis are performed in this project to understand the governing processes and optimize the system accordingly.

The components of the E4 Mistra system are explained in the chapter in addition to test results, which show the system’s capacity for H₂ production, NO _x conversion, particulate matter filtration and soot oxidation, and finally electric power generation via heat recuperation from the exhaust gas using the developed TEG–HEX system.