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Removal of NOx from a light-duty diesel automotive exhaust system can be achieved by SCR reactions using aqueous urea spray as the reductant. Measurements of emissions from such a system are necessary to provide data for CFD model validation. A test exhaust system was designed that featured an expansion can, nozzle and diffuser arrangement to give a controlled flow profile to define an inlet boundary for a CFD model and to approximate to one-dimensional flow. Experiments were carried out on the test exhaust using injection of either ammonia gas in nitrogen or aqueous urea spray. Measurements were made of NO, NO₂ and NH₃ at inlet to and exit from the SCR using a CLD analyzer. The NO and NO₂ profiles within the bricks were found by measuring at the exit from different length bricks. The spray and gas measurements were compared, and insights into the behavior of the droplets upstream and within the bricks were obtained.

Modeling of SCR in diesel exhaust systems with injection of urea spray is complex and challenging but many models use only the conversion observed at the brick exit as a test of the model. In this study, the case modeled is simplified by injecting ammonia gas in nitrogen in place of urea, but the spatial conversion profiles along the SCR brick length at steady state are investigated. This is a more rigorous way of assessing the ability of the model to simulate observations made on a test exhaust system. The data have been collected by repeated engine tests on eight different brick lengths, all which were shorter than a standard-sized SCR. The tests have been carried out for supplied NH₃ /NOx ratios of a 1.5, excess ammonia, a 1.0, balanced ammonia, and a 0.5, deficient ammonia. Levels of NO, NO₂ and NH₃ have been measured both upstream and downstream of the SCR using a gas analyzer fitted with ammonia scrubbers to give reliable NOx measurements.

Use of selective catalytic reduction technology is the most popular strategy for removing NOx from lean diesel exhaust. The reductant is essentially ammonia and this has been supplied as a spray of urea droplets, but more recently alternative technology where ammonia gas is released from a storage medium has become a viable alternative. Experiments have been carried out on an engine test rig run to steady state conditions using NOx composed of either 25% or 50% of NO₂, with ammonia gas as the reductant. This was a 1D study where a long 10 degree diffuser provided uniform temperature and velocity profiles to the SCR catalyst brick. Under the transient conditions that occur during drive cycles, the dosing of the ammonia can deviate from the optimum. In this study, the dosage rate of ammonia was held at a fixed value, while the engine load was varied.

Removal of NOx from lean diesel exhaust can be achieved by the use of selective catalytic reduction technology. The supplied reductant is often ammonia, either as urea or as ammonia gas released from a storage medium. Experiments have been carried out on an engine test rig run to steady state conditions using NOx composed mainly of NO, with ammonia gas as the reductant. This was essentially a 1D study because a long 10 degree diffuser was used to provide uniform temperature and velocity profile to the SCR catalyst brick in the test exhaust system. Tuning of the standard reaction, the NO SCR reaction, in a kinetic scheme from the literature and adjustment of the ammonia adsorption kinetics achieved improved agreement between the measurements and CFD simulations. This was carried out for studies at exhaust gas temperatures between 200 and 300°C.