Measurement of the instantaneous in-cylinder pressure of reciprocating compressors using the connecting rod strain

The measurement of in-cylinder pressure during operation in reciprocating compressors is usually done in a destructive test in which a small bore is machined in the side of the cylinder. This instrumentation process not only impacts the real clearance volume of the compressor but also adds undesired dynamics to the measured value. This paper proposes a novel method for pressure measurement based on the connecting rod strain which solves most of the limitations of traditional methods. Experimental results obtained with a refrigeration compressor indicate that the proposed method presents errors smaller than ±0.2 bar for a coverage probability of 95% when compared with the values measured by a reference piezoelectric pressure transducer. The results are at least equivalent to the ones presented by traditional in-cylinder pressure measurement methods, but the proposed method uses a simpler setup and does not affect the compressor working condition.