Modeling and Simulation of Urea Dosing System

To protect our health and environment from pollution, among others regulatory agencies in the European Union (EU) and legislation from the U.S. Environmental Protection Agency (EPA) has required that pollutants produced by diesel engines - such as nitrogen oxides (NOx), hydrocarbons (HC) and particulate matter (PM) - be reduced. The key emission reduction and control technologies available for NOx control on Diesel engines are combination of Exhaust Gas Recirculation (EGR) and Selective Catalytic Reduction (SCR). SCR addresses emission reduction through the use of Diesel Exhuast Fluid (DEF), which has a trade-name AdBlue. Which is 32.5% high purity urea and 67.5% deionized water, Adblue in the hot exhaust gas decomposes into ammonia (NH3) which then reacts with surface of the catalyst to produce harmless nitrogen(N2) and water (H20). Highest NOx conversion ratios while avoiding ammonia slip is achieved by Efficient SCR and accurate Urea Dosing System it’s therefore critical we model and simulate the UDS in order to analyze and gain holistic understanding of the UDS dynamic behavior. The process of Modeling and Simulating of Urea Dosing System is a result of a compromise between two opposing trends. Firstly, one needs to use as much mathematical models as it takes to correctly describe the fundamental principles of fluid dynamics such as, (1) mass is conserved (2), Newton’s second law and (3) energy is conserved, secondly the model needs to be as simple as possible, in order to express a simple and useful picture of real systems. Numerical model for the simulation of Urea Dosing System is implemented in GT Suite® environment, it is complete UDS Model (Hydraulic circuit and Dosing Unit) and it stands out for its ease of use and simulation fastness, The UDS model has been developed and validated using as reference Hilite Airless Dosing System at the ATC Lab, results provided by the model allow to analyze the UDS pump operation, as well the complete system, showing the trend of some important parameters which are difficult to measure such as viscosity, density, Reynolds number and giving plenty of useful information to understand the influence of the main design parameters of the pump, such as volumetric efficiency, speed and flow relations.Conclusions In the theory section, we have shown two fundamental principles of fluid flow, conservation of mass (continuity equation) and conservation of momentum (the Cauchy equation) of fluid motion. To get to Euler equations we employed the Navier-Stokes equations for incompressible flow, by neglecting fluid viscosity making μ=0 [21], with this assumption Navier-Stokes equations take the form of Euler equations, detailed discussions and derivations might be found at Atil’s lecture notes[21][23] The second last step is derivation of exact solutions to the Navier-Stokes quations, the Hagen–Poiseuille eqautions, by applying basic physics with the assumptions of laminar flow, constant viscosity and straight pipe with circular cross-section, we derived Hagen–Poiseuille eqautions, this led to a relationship between pressure changes over a length L of pipe, and a friction factor associated with viscous effects We then applied Euler equations to derive well known Bernoulli equation, which signifies that when the velocity increases in a fluid stream, the pressure decreases and when velocity decreases the pressure increases [31] [15] We must highlight that all of these equations have their roots in the Navier– Stokes equations, once again underscoring the universality of these equations in the context of describing the motion of fluids [10] Why did we have to derive all these equations? It is important when applying any equation that we are aware of the restrictions on its use, the restrictions are normally seen in the derivation of the equation when certain simplifying assumptions about the nature of the problem are made. If we ignore the restrictions, we may get inaccurate results from the equation. e.g. an equation was derived while assuming that the flow was incompressible, which means that the speed of the flow is much less than the speed of sound. If you use this form for a supersonic flow, the answer will be wrong [32] In the Modeling and simulations section, the following steps have been completed as given on the goal statement: To broaden our level of understanding and interactions of different components we shown simplified model of the UDS To ensure model meets requirements and fulfills its intended use we have verified (e.g. Right flow, pressure, and mass flow rate) To gain confidence in the model we have validated by comparing model with the real system data and found acceptable agreement We have also shown Effects of various parameters of the system, such as Volumetric Efficiency of the pump, return restriction diameter variations, relationship between flow rate and speed Finally we have demonstrated Adblue density as function of pressure and temperature, and effects of the temperature on Dynamic and Kinematic viscosity of the Adblue, more Adblue fluid properties is also given on Appendix