introduction

In recent years, with the development of high-speed railway and heavy-duty railway, in order to meet the needs of speed, safety and smooth traction of railway locomotives, the oil-injected screw air compressor (referred to as “screw air compressor”) has less wearing parts. High reliability, good dynamic balance, strong adaptability, stable exhaust pressure, etc., are widely used on locomotives, such as SS 7D, SS 7E, SS 9, high-speed EMU, "Tissot", Qingzang online locomotive A screw air compressor is used. The screw air compressor is a system that integrates multiple components with different functions. In addition to the main engine, there are important components such as motors, fans, coolers, oil separators, air filters, and oil filters. This paper analyzes the performance requirements and energy-saving conditions of air filters, and provides reference for the design, selection and maintenance of screw air compressors for locomotives.

1 The effect and influence of air filter on screw compressor

The air filter is the first protective barrier in the open system of "intake D exhaust" for the screw air compressor of the locomotive. Screw air compressor Under any working condition, the air filter must filter out harmful dust, particles, impurities and foreign matter in the air sucked by the air compressor to prevent it from entering the compressor, resulting in the main engine, oil and gas separation filter, The performance and life of the oil filter, lubricating oil (coolant) are damaged, so the air filter plays a vital role in protecting the compressor.

During the use of the screw air compressor, the compressor's compression ratio, displacement, shaft power, and specific power are changed due to the presence of the air cleaner. The air filter creates a resistance to the flowing air, and the air must lose a certain static pressure to overcome the gas flow resistance in the filter (hereinafter referred to as the air filter differential pressure), and the air can pass through the air filtration at a certain flow rate. Device. During the use of the air filter, due to the air flow filter, dust in the air accumulates on the air filter element, which reduces the air flow passage of the filter element, thereby gradually increasing the air filter pressure difference. The initial pressure difference, the ash content of the air filter, the pressure difference during use, and the maximum pressure difference at the end of the life, the displacement of the compressor, the specific power, the operating cost of the compressor, and whether the compressor is energy-saving Other aspects have important implications.

2 Air filter control parameters

At present, the screw air compressor uses a two-stage air filter with a "tangential swirl tube prefilter" in addition to a single-stage air filter with a solid outer casing. The control parameters (or characteristic parameters, performance requirements) of the air filter are as follows: 1 Operating temperature: -4080 °C.

2 Sealed reliably, anti-vibration fatigue performance meets the requirements.

3 air filter intake resistance recovery rate is greater than 85%.

4 The initial intake resistance is not more than 3.0 kPa.

5 initial filtration efficiency requirements are shown in Table 1.

6 Under the rated air flow conditions, the pre-filter efficiency requirements of the air filter are shown in Table 2.

7 filter ash storage capacity (capacity): Under the rated air volume flow, when the filter resistance increase reaches 2.5 kPa or the filtration efficiency drops to the specified value, the ash storage capacity is calculated according to the following formula: C ≥ AF, where : CDD ash storage capacity, g; where: ADD unit area of ​​the specified ash storage capacity, g / cm 2; where: FDD filter effective filtration area, cm 2.

The filter ash storage capacity (capacity) can be converted to the use time of the air filter under a certain flow rate and ambient dust concentration.

8 Air filter differential pressure increase: During the use of screw air compressor, the air filter pressure difference should be controlled within 5.0 kPa (that is, the differential pressure increase should be controlled within 2.0 kPa) .

9 Filtration efficiency and filtration accuracy: During the use of the screw machine, the filtration accuracy of the air filter should be below 4.0μm. The current screw air compressor air filter accuracy index, that is: the particle equivalent diameter of 1.0μm is greater than or equal to 1.0μm, the filtration efficiency is 98.5%; the particle equivalent diameter is greater than or equal to 4.0μm, the filtration efficiency is 99.99%. Here, the industry standard TB /T 2710.2 "Air filter for locomotives and motor vehicles, Part 2: Screw air compressors", Section 3.13 of the "Air filter can filter out solid particles larger than 25μm in air" has been combined with screw air The actual requirements of the compressor are out of line.

3 Analysis of the influence of air filter pressure difference on compressor parameters

As the air filter usage time increases, the air filter differential pressure gradually increases from the initial differential pressure difference. The rate of increase of this differential pressure is mainly determined by the dust concentration of the ambient air. After the air filter differential pressure changes, the compressor's compression ratio, displacement, shaft power, and specific power change. For further analysis of the problem, Table 3 lists the parameter symbols and the location of the measurement points.

1 Condition: The resistance loss of the intake valve is not considered, the exhaust pressure of the main engine is constant, the exhaust temperature of the main engine is constant, and the suction state of the filter is set to the standard state, that is, the temperature is 20 ° C, the atmospheric pressure is 1.0 Bar, and the relative humidity is 0. %.

2 Compressor inlet pressure: P 1 =P a -(ΔP+ v 2 /2), where v is the velocity of the airflow from the air filter to the inlet valve of the main engine intake valve. When the airflow speed is omitted, then P 1 =P a -ΔP.

3 When ΔP=0, and excluding the airflow velocity in the takeover, the corresponding shaft power is N 0, the compression ratio is 0, the exhaust volume is Q 0, and the specific power is N r0 (this state point is used as the reference point), then: Percentage of compression ratio increase: K 1 = Δ / 0 = ( - 0) / 0 = / 0 -1 % of shaft power reduction: K 2 = ΔN / N 0 = (N - N 0) / N 0 = N / N 0 -1 percentage of exhaust gas reduction: K 3 = ΔQ / Q 0 = (QQ 0) / Q 0 = Q / Q 0 - 1 percentage of specific power increase: K 4 = ΔN r / N r0 = (N r - N r0 ) /N r0 =N r /N r0 -1 K 1,K 2,K 3,K 4 are functions of pressure, temperature, specific volume, multivariate index, and variable efficiency, which can be calculated according to the formula recommended by the professional books. However, there is a big difference between the calculated results and the measured values. Here, according to the measurability of the reference point, combined with the existing widely used screw air compressor calculation program, the power used on the locomotive is 22 kW, the displacement is 2.4 m 3 /min, and the exhaust pressure is 800 kPa. It can be seen from the K 1 , K 2 , K 3 , and K 4 curves of the 900 kPa and 1 000 kPa sample machines that as the air filter differential pressure ΔP increases, the displacement Q and the shaft power N decrease, while compression The ratio and specific power N r rise. Here we should pay attention to the growth of K 1 , K 2 , K 3 and K 4 under different pressure differences. When the pressure difference ΔP increases, the exhaust pressure is arranged at 800 kPa, 900 kPa, and 1 000 kPa. The reduction of the displacement of the three is basically the same, the reduction of the shaft power is smaller, and the increase of the specific power is changed. Big. This is because the compression ratio is increased and the compression work is increased. Table 4 lists the growth ratios for several typical differential pressures for reference during actual selection.

The decrease in the 1-axis power N and the increase in the compression ratio have no adverse effects on the use, and are rarely paid attention to during the use of the unit.

2 The air filter differential pressure ΔP has a significant effect on the displacement. When the pressure difference reaches 8.0 kPa, the displacement decreases by nearly 8.0%, even when the air filter recommends a pressure difference of 5.0 kPa. The amount is reduced by nearly 5.0%.

Excessive reduction in exhaust volume may affect the locomotive's air volume requirements. Therefore: a) The effect of the initial pressure difference must be taken into account when selecting compressors for compressor manufacturing and locomotives; b) to ensure locomotive air volume requirements, Consider using an air filter under low differential pressure conditions.

High flame retardant performance, less toxic substances released when the vehicle material is burned, and less smoke generated when the material is burned. These characteristics reduce the chance of fire caused by the train and improve the living conditions of the passenger under fire.

4 Conclusion

The large parts selected for the Beijing Metro Line 4 vehicles have passed the vibration, EMC and other routine tests according to the relevant standards; after the preparation, they have passed various train-level tests; the test results are better than the owner's contract requirements. All trains were put into trial operation in September 2009 and are in good condition. Among them, the battery traction function carried out the AW3 load operation test on the positive line. Under the battery traction condition, the train ran smoothly in an interval. Currently, this function is widely used in the segmental shunting operation. The new type of externally sealed door shows good sound and noise reduction effect, and the reliability is high, which is well received by the owners.

Mini-Prism Striped Acrylic Sheet

Jiangmen Kunxin new Material Technology Co.,Ltd , https://www.plasticskunxinjm.com