Development and test of regenerative exhaust particulate filter for electric heating diesel engine

A diesel exhaust particulate filter with electric heating regeneration device was developed and its characteristics were tested. The results show that the district electric heating regeneration technology adopted by the system is reliable and effective, and the regeneration efficiency of the filter body is about 70%. The regeneration device is controlled according to the change of exhaust back pressure, and the regeneration device has the expected effect.

Diesel engine; particulate filter; regeneration 1 随着 With the rapid development of China's economy, the number of automobiles and various agricultural machinery is rapidly increasing. The particulate emissions of diesel engines are increasingly polluting the atmosphere and affecting people's health. In particular, since the implementation of the new Law of the People's Republic of China on Air Pollution Prevention and Control since September 1, 2000, the issue of motor vehicle emission control has been placed in an important position. Therefore, it is necessary to speed up the research and raise the vehicle emission control technology to a new level.

The control of diesel particulate emissions is an important part of vehicle emission control. The particulate filter with regenerative device is one of the hot issues at home and abroad. At present, the research and use of regeneration methods can be divided into two categories: First, the use of diesel engine energy for regeneration, such as throttling regeneration (strong regeneration), heavy load regeneration, catalytic regeneration; second, the use of external energy for regeneration, such as electric heating Regeneration, fuel injection combustion regeneration, filter reverse jet evolution regeneration, microwave regeneration and other technologies. The use of electric heating regeneration is a new concept put forward in recent years, and a large number of studies have proved the feasibility and effectiveness of electric heating filter regeneration.

This paper introduces a self-developed diesel exhaust particulate post-processing system with electric energy as external renewable energy, and discusses the technical problems of the selection, winding and zoning of the electric heating components of the micro-particle post-processing system. The diesel engine bench test of the filter systematically studied the perfection and regeneration ability of the filter electric heating regeneration, which provided a basis for further improving the emission performance.

2 The overall structure and working principle of the system The system is mainly composed of diesel exhaust particulate post-treatment collector (filter), filter regenerative electric heater, vehicle power supply and control system. The system diagram is as shown.

1. Discharge port 2. Smoke meter 3. Valve 4.6110B diesel engine 5. Thermometer 6. Exhaust pipe 7. Valve 8. Filter 9.24V battery Diesel engine exhaust particulate filter regeneration system overall layout diagram Diesel engine exhaust gas through the filter After the filter element, part of the particles in the exhaust gas are trapped by the filter body, and the purified exhaust gas is discharged into the atmosphere from the exhaust pipe tail pipe. However, as time goes by, the particles accumulated on the filter element gradually increase, which increases the resistance of the diesel exhaust system, increases the exhaust back pressure, and degrades the engine performance. Therefore, it is necessary to periodically remove the particles that have been deposited in the filter body to restore the exhaust back pressure to a normal level, that is, to achieve regeneration of the filter body.

The diesel engine exhaust particulate post-treatment system filter body developed in this paper uses a ceramic filter. The wire wound on the filter body is heated by electric heating to heat, ignite and burn the particles deposited on the filter body, so that the exhaust back pressure returns to normal. During regeneration, the valve 1 is closed and the valve 2 is opened to avoid direct impact of the gas flow on the filter body during regeneration to ensure stable and efficient regeneration of the filter body.

3 filter and regeneration device development Diesel exhaust particle capture device is mainly from the filter body, glass Yan Jiang (1973-), male, Hunan Yueyang people, Zhejiang University Power Machinery and Vehicle Engineering Research Institute, mainly engaged in internal combustion engines The exhaust purification technology is composed of working fibers, and the filter carrier used in the device is a honeycomb ceramic.

Because the power of the vehicle battery is low, it is necessary to adopt district electric heating, that is, the filter body is divided into several zones and heated and regenerated separately.

The defect of district electric heating regeneration is that the regeneration time is long, the internal temperature of the filter element is high, and the temperature gradient is large. Due to the large thermal stress, it is easy to cause the filter element to burn off and the thermal shock rupture accident. In order to solve this problem, an accelerator is applied to the filter element to increase the regeneration temperature and shorten the regeneration time, thereby achieving a good regeneration effect at a large regeneration rate.

The filter material used in the test is high silica glass fiber, which has good high temperature resistance and ablation resistance. It can be used at 900*C for a long time and used at 1200*C for a short period of time. In order to improve the filtration efficiency, it is wound into a rope by a special process, and then impregnated with paraffin in a ceramic. The exhaust temperature of the diesel engine is about 2000*500*C, and the high silica glass fiber as a filter material can work safely for a long time at this temperature.

A more ideal solution. However, in practical applications, it is necessary to solve problems such as limited power supply, more partitions, and complicated leads.

The rated voltage of the vehicle battery is generally 24V, but after working for a period of time, the voltage is often reduced to only 20V or even lower. At the same time, its maximum operating current is generally around 20A. This requires partitioning the heating elements to limit the power during heating. It can be seen from the above discussion that the heating power at the same time cannot exceed 480 W. In order to facilitate the winding into a specific shape of the resistance wire, the resistance wire material selected is softer than the iron chromium silicon. The filter carrier used in the apparatus is a cylinder having a cross-sectional diameter of 150 mm and a thickness of 50 mm, and the filter micro-holes are squares having a side length of 1.3 mm, and a total of about 6,000 holes. In order to reasonably select the diameter of the resistance wire, the electric wires of various diameters are energized, and the current required to be heated to redness is observed (the temperature of the resistance wire is red, and the temperature causes the soot particles to ignite), of course, this current is of course The smaller the better. after.

From the filter, the filter was thoroughly regenerated before the experiment.

Diesel engine external characteristics, smoke and filtration efficiency Diesel engine external characteristics, power (1) When the load is full, the smoke is generally higher. The reason is that the combustion temperature is high, and the oxygen concentration is low, which is caused by fuel cracking. When the maximum speed of the diesel engine is 2900r/min, due to the low inflation coefficient, it is difficult to organize a good mixture and combustion process in a short period of time, and the combustion is not complete, so the smoke is large. When working at a low speed of 1200r/min, the smoke is also high due to the low temperature in the cylinder, the low injection speed, and poor atomization. The smoke value is stable at other speeds, and is about 2Rb after filtration.

(2) After the filter is installed, the power loss increases with the increase of the rotational speed. This is because the rotational speed increases, the exhaust flow rate increases, the filter back pressure rises, and the influence on the power increases.

4.3 Other experiments In order to explain the necessity of installing a regenerative device, the change of the exhaust back pressure of the diesel engine equipped with the filter without regenerator is measured with time under fixed working conditions. The experiment found that the exhaust back pressure increased rapidly with time. After about 3 m, the exhaust back pressure rises to a very high level and then decreases. Upon analysis, this drop was due to damage to certain pores in the filter. Experiments have shown that it is necessary to add a regenerative device to the filter.

In addition, in the aforementioned load characteristic test, engine noise was also measured when the throttle was fully opened. It can be seen from the experiment that at 1800r/min, the noise is 110.5dB when no filter is added; after adding 108dB, the filter is decreased by 2.5dB, and the power is decreased by 0.2%. At 2400r/min, no filter is added. The noise is 113dB; after adding the filter, it is 108dB, which is reduced by 5dB, and the power is reduced by about 1%. Therefore, it can be considered that it is desirable to obtain higher purification and noise reduction functions with less power loss, indicating that the developed The aftertreatment system was successful.

5 Conclusions This paper proves the feasibility and effectiveness of using the district electric heating to regenerate the diesel exhaust particulate filter by experimental analysis. The district electric heating regeneration technology is simple, reliable and effective.

Filters equipped with electric heating devices generally have a filtration efficiency of about 70%. In order to achieve safe and effective regeneration of the filter body, it is necessary to select the heating power and the electric heating zone in the regeneration chamber according to the nature of the filter body, and select the appropriate regeneration cavity structure and filter body size.

The regeneration time of the filter body is generally about 2min, and the regeneration duration is moderate. It can avoid the high temperature peak of the filter during regeneration and improve the service life of the filter.

During regeneration, the amount of particulate deposition in the filter has no significant effect on the electrical heating regeneration effect, and the effective regeneration range of the system is wide.

Electric heating regeneration is a simple and reliable diesel particulate filter regeneration technology. This method can largely overcome some of the shortcomings and deficiencies of other prior regeneration methods. If the automatic regeneration control device is added, the pressure difference in the filter is used to control the regeneration time. Although the cost is improved, the accuracy can be improved and the inconvenience of operation can be reduced.

Seasonal rain. Development of exhaust particulate filters for heavy-duty diesel engines. Foreign internal combustion engine, 1994, (1): Shi Zhaoxi. Research on diesel particulate characteristics and honeycomb ceramic particulate filter regeneration technology. Journal of Internal Combustion Engines, 1990, (4): 73-74. Zhang Bidong. Continuous glass fiber foundation. Beijing: China Building Industry Press, 1988.40-50. (Continued from page 141) He Yuezhen, Yang Xiaowen, Zhang Yucun. Agricultural machinery test design. Beijing: Mechanical Industry Press, 1986.24-26. Tian Qingyi. Agricultural machinery and equipment technical transformation and selection. Xinjiang: Shihezi University, 2001.35-37.

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