Ammonia Storage and Delivery Systems for Automotive NOx Aftertreatment

It is well-known that ammonia is the active molecule for the selective catalytic reduction of NOx in diesel exhaust. However, the use of liquid ammonia for on-board storage in a pressure vessel has been excluded due to safety issues. The industry has thus far chosen urea dissolved in distilled water (AdBlue®) for storage in order to overcome the safety issues, but critical challenges must be overcome for efficient vehicle integration when indirect ammonia storage in the form of urea is applied. These challenges are related to the handling of the liquid in the tank as well as the conversion of urea to ammonia and CO₂ inside the exhaust line.

This paper presents a technology for safe, on-board ammonia storage. It is a technology that enables direct ammonia dosing for NOx abatement using a simple, high-density storage and delivery system.

The storage concept, which is based on metal ammine complexes, will be presented along with system design and performance data. The implications for vehicle integration are discussed, and a comparison is made with urea-based systems.