Testing pressure pulsations in automotive air conditioning systems

Testing pressure pulsations in automotive air conditioning systems

Pressure pulsation, also known as dynamic pressure or pulsating pressure, refers to pressure that is not uniformly distributed across the object it acts upon, with concentrated or higher pressure at certain points. The duration of each pressure pulse is short, and it may exhibit a certain degree of periodicity. It is a dynamic pressure, i.e., a varying pressure, as illustrated in the diagram below.

Pressure pulsations, a common phenomenon in fluid systems, are widely present across multiple fields. In the aerospace industry, the complex flow conditions inside engines generate pressure pulsations that affect engine performance and operational status assessment. In the hydropower sector, changes in turbine operating conditions—such as variations in the circumferential velocity of water flow in the tailrace pipe when deviating from optimal operating conditions—can trigger pressure pulsations, posing challenges to the stable operation of the unit. In petrochemical processes, the fluctuating flow states of fluids within pipelines, as well as the operation of pumps and valves, can also induce pressure pulsations.

Pressure pulsation in automotive air conditioning systems

The pipes and compressor in a car's air conditioning system are typical examples. The operating mode of a car air conditioning compressor is intermittent suction and exhaust, which causes the flow and pressure of the refrigerant in the system to fluctuate periodically. Taking a swash plate compressor as an example, the reciprocating motion of the internal piston causes the working chamber to cycle through the processes of intake, compression, exhaust, and expansion. By solving the pressure fluctuation equation constructed using plane wave theory combined with phase interface effects, it is found that the pressure pulsations in the exhaust pipe section of the automotive air conditioning system exhibit periodicity, and the peak-to-peak values of the pulsations increase with rising compressor speed. At different speeds, the peak-to-peak values of pressure pulsations at the compressor outlet show significant changes, while those at the condenser inlet remain relatively stable.

In automotive air conditioning systems, pressure pulsations are the primary source of vibration and noise in the piping system. Under the influence of refrigerant pressure pulsations, the rubber hoses near the compressor in the low-pressure piping exhibit periodic vibrations, and the stress on the piping is directly proportional to the operating frequency of the compressor. When the pressure pulsation frequency approaches the natural frequency of the piping, resonance occurs, leading to increased piping vibrations, wear or even rupture at connection points, reduced system reliability and service life, and potential refrigerant leaks that impair cooling performance and cause environmental pollution.

Pressure pulsation testing and sensor selection

In the research, development, and production of automotive air conditioning systems, testing pressure pulsations provides critical data for system optimization design. By analyzing the patterns of pressure pulsations, it is possible to improve compressor structure, optimize pipe layout and dimensions, reduce system vibration and noise, and enhance in-cabin comfort and air conditioning system performance. But how do you measure the magnitude of these pressure pulsations?

In the actual operation of automotive air conditioning system equipment, in addition to pressure pulsations, the system typically also experiences a relatively large static pressure. The two pressures are superimposed, as illustrated in the diagram below.

Dynamic pressure sensors can withstand a certain amount of static pressure while only responding to dynamic pressure changes. Therefore, dynamic pressure sensors are typically used for testing pressure pulsations. If static pressure sensors (typically piezoresistive pressure sensors) are used, their resolution is significantly lower compared to dynamic pressure sensors because they also respond to static pressure. Therefore, static pressure sensors with a relatively larger measurement range must be used. In contrast, dynamic pressure sensors do not have this issue; the measurement range can be selected based on the magnitude of the pressure pulsations, thereby significantly improving resolution.

Xiyuan Electronics' dynamic pressure sensor Y1004E is suitable for pressure pulsation testing and can measure pressure pulsations in automotive air conditioning pipes or compressors.

Y1004E Series Pressure Sensors：

Yangzhou Xiyuan Electronic Technology Co.,Ltd.

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