A Low Temperature Coolant Conditioning Cart for Testing DEF Thawing Systems 2021-01-0612

Diesel Exhaust Fluid (DEF) systems are required to function in cold ambient temperatures below the freezing point of DEF. Manufacturers may demonstrate compliance by following an EPA guidance procedure described below [2], using whole vehicles at winter test sites at −18 deg C or lower. However, commercial trucks may have multiple variants with different DEF system layouts, so it is impractical to test every possible configuration. A climatic chassis dynamometer (CCD) can also be used for this test, but this is still expensive and time consuming, and does not address the problem of complexity. Instead, much time and expense can be saved by using simulation methods to identify worst case configurations, and to demonstrate with confidence that a limited number of tests will cover the whole possible range. This methodology can further be used to show that a range of vehicles can be represented with selected rig tests in a cold chamber. Such a methodology depends on the ability to generate repeatable test data in a cold room environment. Previously published work [1] has shown that it is difficult to achieve a repeatable test. In particular, it is challenging to provide coolant with repeatable and accurate temperature and flow profiles, between −40 deg C and +95 deg C. A coolant cart has been developed to provide a stream of conditioned coolant, starting at −40 deg C or higher, utilizing user-specified profiles of temperature and flow rate versus time. The desired profiles were designed to match test data logged from truck engines during warmup from a typical cold overnight temperature of −22 deg C. Surprisingly, no suitable test equipment was found to be commercially available, and the task of designing and building such equipment was found to be challenging. The need to function at −40 deg C restricted the choice of components. The requirement to follow user-defined profiles for both flow and temperature, within tight error bands and following sudden changes, also required unusual care in design. A dedicated coolant cart was therefore commissioned and built. This paper documents the design and operation of the cart. Major component descriptions are provided, with circuit and input/output detail, recharge time and operator interface and processing. The end result is a cart that provides for repeatable cold room testing of tank thaw performance to support a simulation-based verification method, thereby reducing the need for whole-vehicle testing by 75%.