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The urea-water-solution based selective catalyst reduction (SCR) system is one of the effective devices for reduction of NOx from diesel engines. In an effort to understand the various levels of oscillation observed in the NOx measurement downstream of a SCR in which the urea dosage is controlled by a crankshaft-link pump, a zero-dimensional dynamic SCR model is developed in this paper based on conservation of mass. The model contains three states including the concentrations of NOx and ammonia in the SCR and the surface coverage rate of the catalyst. The temperature-dependent reactions considered in the model include the adsorption, desorption and oxidation of ammonia and the NOx reduction with the reaction constants provided by the catalyst company. The dynamic SCR model is validated both at steady state and during transient under various engine operating conditions and urea dosing rates.

Homogeneous charge compression ignition (HCCI) engines create a more efficient power source for either stationary power generators or automotive applications. Control of HCCI engines, however, is difficult since the ignition cannot be actuated directly. For the purpose of model-based analysis and control design, a crank-angle based HCCI engine model is developed in this paper based on experimental data from a single-cylinder engine. The zero-dimensional dynamic engine model is constructed based on conservation of mass and energy, and ideal gas law. Subsystems in this model included valve lift profile, cylinder volume, mass flow rate, intake and exhaust runner dynamics, cylinder dynamics, combustion model and heat-transfer model. Inputs to the model include engine speed, intake temperature, fueling rate, intake throttle and exhaust throttle positions.