Analysis of a Novel Method for Low-Temperature Ammonia Production Using DEF for Mobile Selective Catalytic Reduction Systems

Abstract

The worldwide introduction of new emission standards and new, more encompassing, legislating cycles have led to a need to increase both a selective catalytic reduction (SCR) system's capacity and conversion efficiency. To this end, it is important for an SCR system to operate to the extremes of its temperature range which in many systems is currently limited by the temperature at which diesel exhaust fluid (DEF) can easily decompose without the formation of deposits. This paper analyses a new system for low-temperature ammonia provision to the SCR reaction. Ammonia Creation and Conversion Technology (ACCT) uses pressure controlled thermal decomposition of DEF followed by reformation to form a fluid with greater volatility and the same ammonia density as DEF. A dosing strategy can be employed with any combination of DEF and ACCT solution to provide ammonia as a reductant over the entire temperature range of the catalyst. High-speed shadowgraphy data identifies ammonia production below 100°C with rapid decomposition and full water vaporisation above 100 °C. This study has also equipped an optically accessible hot flow, diesel exhaust simulation rig with a prototype ACCT device. The optical components allow rapid visual verification of deposit growth for bench-marking urea-based system. At a variety of exhaust temperature and mass flow conditions, the study identified a minimum deposit limited working temperature for DEF of approximately 200 °C whereas ACCT solution was shown not to form any deposits and readily generate ammonia as low as 100 °C. Further to this, gaseous species quantification using FTIR techniques has shown ammonia release in an 800 mm flow path for ACCT solution to be in excess of 80 %. The study has demonstrated the effectiveness of ACCT at extending low temperature operating limits of DEF based SCR systems thereby increasing the total possible NOx conversion.

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

“…In order to solve some of the above-mentioned issues, different alternatives are currently under investigation. They include solid urea [37,38], ammonium formate [38][39][40], ammonium carbamate [38,41,42], guanidinium salts, and metal ammine chlorides [38,43]. Although they might overcome some of the issues typical of urea-based solutions, these methods also present some new challenges.…”

“…The ammonium carbamate can store up to 0.436 kg NH3 /kg [38]. Moreover, in certain applications [42] allow early dosing of NH 3 at temperatures as low as 50 • C, in principle well before the light-off temperature of conventional metal exchanged zeolite catalysts normally used in SCR. Despite the interesting developments, there are no technological solutions commercially available at the time being.…”

Impacts of De‐NOx system layouts of a diesel passenger car on exhaust emission factors and monetary penalty

“…The operation theory of the ACCT system was reported in the reference. 37 The ACCT system was consist of an AdBlue tank, an AdBlue pump, an ACCT reactor, an ACCT fluid tank, and an ACCT fluid injector (see Figure 2). AdBlue was injected into the ACCT rector under high exhaust temperature conditions; then, AdBlue was hydrolyzed into CO 2 , gaseous water, and gaseous ammonia under the assistance of exhaust energy; furthermore, the gaseous hydrolyzed products were cooled down in the ACCT tank, being converted into ACCT fluid (a new product).…”

“…The impacts of cold-start emissions by driving behaviors were also discussed in Gao et al's study. 30 Many technologies are investigated to drop cold-start emissions such as burners, 31 reformers, 32 thermal insulations, 33,34 heat storage materials, 35 electric catalytic converters (eHC), 36 Ammonia Creation and Conversion Technology (ACCT), 37 Ammonia Storage and Delivery systems (ASDS) 38 ; meantime, some of these measures are helpful for diesel particulate filter (DPF) regeneration. The main purposes of these technologies are to increase exhaust temperature or provide an easier way to supply reactants (eg, gaseous ammonia), ensuring high efficiency of after-treatment systems.…”

“…ACCT system as a new technique aiming to drop cold-start NO x emissions has excellent performance and no energy penalty. 37 It used exhaust energy to hydrolyze AdBlue into gaseous CO 2 , water (H 2 O), and ammonia (NH 3 ) under high exhaust temperature conditions; then, they were formed as a new product (ACCT fluid) after cooling down. ACCT fluid was much easier than AdBlue to provide gaseous NH 3 under relative low-temperature conditions.…”