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A rapid urea and byproduct deposit experimental platform was built and an integrated after-treatment device model of the nonroad agricultural diesel engine was established based on CONVERGE software. The effects of exhaust temperature, exhaust flow rate, and urea injection mass on urea and byproduct deposits were studied by both experiments and simulation. The model was validated using the back pressures of catalysts, mixer wall temperature, and distribution of urea and byproduct deposits. The performance of the mixer was evaluated using the concentration, mass, and uniformity of NH 3 at the front-end cross-section of its selective catalytic reduction catalyst. Wall temperature is the key influence factor on the composition of the liquid film and is affected by the urea injection mass and exhaust flow rate. When the wall temperature is low, the liquid film is mainly composed of urea solids, but when it is above 423 K, urea solids begin to decompose into biuret, cyanuric acid, ammelide, and other byproducts. As for mixer performance, the uniformities of NH 3 , temperature, and velocity are above 0.9, 0.975, and 0.965, respectively, under all working conditions.

Hydrodynamic and structural stability directly affect the efficiency and safety of pump units operation. In this paper, we simulated inner flow field of a shaft tubular pump unit through Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) for exploring the blade pressure and dynamic stress characteristics, where first part focus on the hydrodynamic pressure fluctuation on inlet and outlet of impeller and second part focus on dynamic stress distribution in time and frequency domain on pump impeller. Monitoring points are set at the inlet and outlet of impeller to obtain the dynamic pressure, then mapping the time domain data to frequency domain through Fast Fourier Transform (FFT) method. The results show that the pressure fluctuation has strong periodicity, and the fundamental frequency of the pressure fluctuation on the inlet and outlet surfaces is the blade passing frequency and the blade passing frequency respectively, which means the rotation of impeller and rotor stator interaction (RSI) phenomenon between impeller blades and guide vanes are the origin of hydrodynamic pressure fluctuation. Hydrodynamic pressure on impeller blade is applied to the impeller structure to obtain structural responses, results show that maximum dynamic stress appears in the root of impeller blade, the dynamic stress fluctuate in the nearby of static stress concentration and maximum dynamic stress appear in the permissible stress range. In frequency domain, the basic frequency and secondary basic frequency are impeller blade passing frequency and guide vane passing frequency, which indicated that the major reason of impeller dynamic stress fluctuation is water excitation pressure.

Diesel particulate filter (DPF), as part of aftertreatment system of internal combustion engine, is considered to be the only feasible way to prominently lessen particle emissions under the requirement of today’s strict regulations such as Euro Ⅵ, US Tier 3 and China Ⅵ. This paper gives a brief introduction of the mechanism and regeneration approaches of DPF, with emphasis on soot load estimation inside the filters, which plays a vital role in formulating regeneration control strategy and ensuring exhaust systemic dependability. Various methods are covered according to different principles, including differential-pressure based methods, which are mostly used nowadays, novel model-based methods and also several newfangled soot sensors, which are progressively developed to meet the increasingly stringent on-board diagnosis (OBD) requirements. The focus of future soot detection and quantitative prediction is to improve accuracy, reliability and robustness, which may necessitate consideration of soot distribution, ash effect, failure identification and fault tolerance handling.