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With introductions of stringent diesel engine emission regulations, the DOC and DPF systems have become the mainstream technology to eliminate soot particles through diesel combustion under various operation conditions. Urea-based SCR has been the mainstream technical direction to reduce NOx emissions. For both technologies, low-temperature conditions or cold start conditions pose challenges to activate DOC or SCR emission-reduction performance. To address this issue, mini or full flow burner systems may be used to increase exhaust temperature to reach DOC light-off or SCR initiation temperature by combustion of diesel fuel. In essence, the burner systems incorporate a fuel injector, spray atomization, proper fuel / air mixing mechanisms, and combustion control as independent heat sources.

Selective Catalytic Reduction (SCR) has become a mainstream approach to reduce diesel engine NOx emissions. Urea Water Solution (UWS) injection and interactions with mixers and exhaust gases affect the homogeneity of ammonia distribution at catalyst inlet and solid deposits formation on walls / mixer surfaces, therefore influencing SCR performance and durability. Computational Fluid Dynamics (CFD) is used to simulate an EU V compliant SCR system with a dual baffle mixer for heavy duty diesel engines. The modeling procedure is carried out by a multi-dimensional CFD code CONVERGE that includes transient urea transport processes in an exhaust flow configuration, detailed spray break-up, evaporation, wall-film, turbulence, and Conjugate Heat Transfer (CHT) models as well as an automated mesh generation approach. Locations of urea deposits and system pressure drop are predicted and validated against measurements, providing uniformity index (UI) predictions at the catalyst inlet.

To meet EPA Tier IV large diesel engine emission targets, intensive development efforts are necessary to achieve NOx reduction and Particulate Matter (PM) reduction targets [1]. With respect to NOx reduction, liquid urea is typically used as the reagent to react with NOx via SCR catalyst [2]. Regarding to PM reduction, additional heat is required to raise exhaust temperature to reach DPF active / passive regeneration performance window [3]. Typically the heat can be generated by external diesel burners which allow diesel liquid droplets to react directly with oxygen in the exhaust gas [4]. Alternatively the heat can be generated by catalytic burners which enable diesel vapor to react with oxygen via DOC catalyst mostly through surface reactions [5].

To meet the 2010 diesel engine emission regulations, an aftertreatment system was developed to reduce HC, CO, NOx and soot. In NOx reduction, a baseline SCR module was designed to include urea injector, mixing decomposition tube and SCR catalysts. However, it was found that the baseline decomposition tube had unacceptable urea mixing performance and severe deposit issues largely because of poor hardware design. The purpose of this article is to describe necessary development work to improve the baseline system to achieve desired mixing targets. To this end, an emissions Flow Lab and computational fluid dynamics were used as the main tools to evaluate urea mixing solutions. Given the complicated urea spray transport and limited packaging space, intensive efforts were taken to develop pre-injector pipe geometry, post-injector cone geometry, single mixer design modifications, and dual mixer design options.

Selective Catalytic Reduction (SCR) based on urea water solution (UWS) has become a promising technology to reduce Nitrogen Oxides (NOx) emissions for mobile applications. However, urea may undergo incomplete evaporations, resulting in formation of solid deposits on the inner surfaces including walls and mixers, limiting the transformation of urea to ammonia and chemical reaction between NOx and ammonia. Numerous design parameters of SCR system affect the formation of urea deposits [1] ; they are: exhaust condition, injector type, injector mounting angle, geometrical configurations of mixer, injection rate and etc. Research has been available in urea deposits, mixers, urea injection rates and others [2,4,5,6]. In this paper, focus is placed on improving mixing structure design from baseline design of EU IV to EU V. On-road tests indicate that deposits are highly likely to occur near locations where spray and exhaust gas interact most.

In order to satisfy China IV emissions regulations, a unique design concept was proposed with injector closely coupled with Selective Catalytic Reduction (SCR) system outer body. The benefit of this design is significant in cost reduction and installation convenience. One paper was published to describe the vertical inlet layout [1]; this work is the second part describing applications of this concept to horizontal inlet configurations. For horizontal inlet pipe, two mixing pipe designs were proposed to avoid urea deposit and meet EU IV emission regulations. Computational Fluid Dynamics (CFD) technique was used to evaluate two design concepts; experiments were performed to validate both designs. CFD computations and experiments give the same direction on ranking of the two decomposition tubes. With the straight decomposition pipe design and unique perforated baffle design, no urea deposits were found; in addition, the emission level satisfied EU IV regulations.

Hybrid bulldozers use less fuel by providing better efficiency and fewer emissions, which was confirmed by one Caterpillar application of D7E in the market in 2010. To take advantages of the series hybrid bulldozer system, Chinese government launched similar hybrid bulldozer with independent double motor design. The Hybrid Bulldozer Power-Train system includes 14 components including motor, motor control system, engine, super capacitor to BMS and etc. This specific hybrid architecture, compared with D7E, removes the complicated hydraulic steering system. Instead, the steering function was developed by running both traction motors, further simplifying the power-train system. A Diesel engine is used to propel the attached generator to produce AC power which is then converted to DC power and connected with the main power link (super capacitor). DC power is finally converted back to AC to propel those two independent traction motors. CAN network is applied for communication.