Research On Characteristics Of Diesel Particulate Filter And Its Performance Optimization Based On Ash Deposition

With the worsening hazy weather in a wide range of our country, research about control diesel particulate emission has become a hotspot issue for urgent attention. Diesel particulate filter(DPF) as the most effective post-processing device for diesel particulate emissions has become a research focus for a long time. As the particulate trapping and regeneration technology become road-ready in recent years, DPF was gradually widely used in diesel passenger car and commercial vehicles in the domestic and overseas. Due to the presence of a small amount of non-combustible ash in exhaust particulate matter at real-time applicion, which can not be cleared by the regeneration, the ash accumulated in the filter pores can deteriorate the performance and durability of DPF after hundreds of times of regeneration, and restricts development and application of DPF. Therefore, it has important practical significance to study ash deposited and its effects in DPF.Ash in the diesel exhaust particles is derived from lubricating oil additives, fuel additives, engine wear, and the exhaust system corrosion, its main components are sulfates, phosphates, and oxides of inorganic metal elements. Ash accumulated in the filter can increase the flow resistance of post-processing apparatus, enhance exhaust back pressure, deteriorate engine power and economy, and hinder post-processing apparatus work properly. In addition, the fuel quality of our country is not high, especially with high sulfur conten, resulting in an increase in the proportion of ash in exhaust particles, and easier to worsen the performance of DPF. This paper is supported by the project of Ntional Natural Science Foundation of China “Failure recognition & analysis and anti failure mechanism on porous medium filter from the diesel particulate filter in the diesel engine(51276056)”, “Research on Compostite Regeneration and Multi-Field Synergy Mechanism of Diesel Particulate Filter Medium(51176045)” and the project of Production and Research of Guangdong Province “Research and Development on Diesel Emission Key Technologies of Industrialization(2011B090400112)”. This paper has mainly researched on ash deposition characteristics and its impact on the exhaust flow and regeneration characteristics of DPF, and based on these, DPF structure design and regeneration control strategies were optimized to reduce the impact of ash deposition on operating characteristics of DPF and engine performance, and extend the life of DPF. The main research work of this article is summaried as follow:1. Based on deposition mechanism of ash particles, the effect of the exhaust flow rate, temperature and particle size of ash on the ash deposition was analyzed, the variation of ash layer permeability with the exhaust flow rate, temperatur e and particle size was obtained, it provides a good theoretical basis for study the flow and regeneration model of DPF under the ash deposited condition.2. A flow model of DPF was established based on the characteristic of ash deposition, the DPF pressure drop model was modified according to ash deposition, and then the flow and pressure drop models were validated by using e ngine testing. The effect of deposited ash within the filter pores on the flow velocity was studied, the variation of the filter wall microstructure with ash deposition at deep bed ash deposition was obtained, also the pressure drop of DPF during ash deposition was well describled by the pressure drop model.3. A model of soot regeneration is established in this paper to describe the effects of ash deposit on exhaust condition and heat transfer. Mass, momentum, and energy balances are considered for the multiphase system of gas, soot, and wall. The good agreement with experimental data confirms that the model is able to describe the processes. The axial patterns of flow characteristic and temperature field during DPF regeneration are investigated by numerical simulation, the variation of flow velocity in inler channel and filter, soot oxidation rate of regeneration, wall temperature with the ash deposition and its distribution was revealed. Thus, the maximum amount of the soot carrying under different ash deposition can calculated.4. According to the ash deposition characteristics within DPF a variable cross-section channel was designed, the aperture ratio of inlet and outlet channel was inceasing to enhance the volume of inlet channels, and achieve an increase in ash carrying capacity of DPF, and then extend the life of DPF. At the same time, the effect of the variable cross-section channel on the flow and regeneration characteristics of DPF was investigated by using thermal regeneration model, and the effect of the variable cross-section channel on the ash deposition was studied.5. A new regeneration control system was proposed to real-time update the judging MAP of regeneration and termination timing and regeneration control program due to the flow and regeneration characteristics changing with deposited ash. DPF regeneration control process was optimized to determine regeneration timing accurately, control regeneration process fine, and predict termination timing timely. Consequently, uncontrolled regeneration was prevented which can cause DPF failure and unnecessary energy consumption.This paper mainly studies on the impact of ash deposition on the operating characteristics of DPF, and based on this, DPF structure design and regeneration control strategies were optimized. The research work in this paper can not only provide a theoretical basis for the accurate prediction of DPF flow resistance and regeneration performance, but also provide an important theoretical guidance for the optimization of DPF structure and active regeneration control strategy, it has an important theoretical and practical significance to promote the application of DPF.