Study On The Control Oriented Modeling Of Diesel Oxidation Catalyst(DOC)

As environmental issues have attracted more and more attention, engine control has become a hot topic. Traditional interior purification can hardly meet the increasingly strict emission regulations of the engine. So only extra aftertreatment devices can be used to reduce harmful exhaust emissions. Diesel Oxidation Catalyst(DOC) is a very important part in aftertreatment system of heavy-duty diesel engine, it is not only to eliminate engine exhaust CO, NO and HC by oxidation, is also to control the internal exothermic oxidation reactions by adjusting controlling fuel injection, so it can control downstream temperature to create conditions for initiative regeneration of diesel particulate filter. Through the control of the fuel post-injection, achieving precise control of downstream temperature of the DOC is a typical closed-loop control problems. The basis of high-performance control strategy design is the control oriented modeling of DOC. On the one hand,the control oriented modeling requires that the model can accurately reflect the transient characteristics of the controlled object, on the other hand, it requires that the model can be solved in real time,so the traditional Computational Fluid Dynamics(CFD) model and static laboratory characteristics of DOC are unavailable for control oriented modeling. This paper is exactly for above control-oriented requirements, taking DOC of aftertreatment systems for diesel engines as the research object, did a more in-depth research DOC modeling work, concrete works such as:First, summed up the main approach for control oriented modeling of DOC and derived in sufficient detail for the main control oriented modeling of one-dimensional model of DOC. Based on sufficient abroad research about the modeling study for DOC, in-depth analysing the working mechanism of DOC and dominant physical and chemical processes influencing internal temperature field distribution. Established one-dimensional distributed parameter model to describe DOC internal temperature field by taking advantaging of the basic principles of fluid mechanics, heat transfer, chemical reaction kinetics. Using finite volume method, spatial discretization for the partial differential equation, derived discrete one-dimensional axial model of DOC and take the model as the main study object.Using the software to build different models of DOC. With Simulink software, set up discrete one-dimensional model of the above derivation, at the same time, set up another common control oriented "first order + delay" model. In order to verify the reasonableness and simulation performance of one-dimensional model and zero-dimensional model, building a three-dimensional temperature field model with Fire software.Compared the performance of different simulation model under two simulation conditions, one is ideal step condition of upstream temperature and another ETC condition. The simulation results of steady state performance, transient response process and spatial temperature field distribution were compared and analyzed. Generally speaking simulation results of derived one-dimensional discrete model and CFD models are close. Both can reflect well the changing process in the transient temperature field and temperature field distribution. Zero-dimensional "first order + delay" model error is slightly larger compared to results of one-dimensional discrete model and CFD models and can not calculate the spatial distribution of the temperature field.Proposed and designed the one-dimensional DOC model based on the circuit. Although discrete one-dimensional model can achieve a certain degree compromise in DOC temperature field distribution and calculations, but its calculation is still affected by the number of the finite volume element and consumes large computing resources of controller. Therefore, this paper proposes a DOC model based on circuit and imitating the output characteristics of one-dimensional DOC model by transient characteristics of the circuit itself. Thus, this model needs not take up computing resources and can apply more limited numbers of units to increase accuracy of the simulation model without affecting real-time response characteristics of the model, it is very suitable for HIL test of the DOC controller. Completed circuit model prototypes by designing and debugging of software and hardware, The model was initially verified by experimental testing.