Low-Cost Open-Source Data Acquisition for High-Speed Cylinder Pressure Measurement with Arduino

In-cylinder pressure measurement is an important tool in internal combustion (IC) engine research and development for combustion analysis, cycle performance analysis, and knock analysis in spark-ignition engines. In a typical laboratory setup, a sub crank angle resolved (typically between 0.1 o and 0.5 o ) optical encoder is installed on the engine crankshaft, and a piezoelectric pressure transducer is installed in the engine cylinder. The charge signal produced by the transducer due to changes in cylinder pressure during the engine cycle is converted to voltage by a charge amplifier, and this analog voltage is read by a high-speed data acquisition (DAQ) system at each encoder trigger pulse. The high speed of engine operation and the need to collect hundreds of engine cycles for appropriate cycle-averaging requires significant processor speed and memory, making typical data acquisition systems very expensive. The objective of this work was to develop an affordable, open-source DAQ system capable of measuring in-cylinder pressure in an IC engine with Arduino. Such a system could then be applied to any engine where there is space to install an encoder on the crankshaft, and could be particularly valuable for Formula SAE teams, hobbyists, and engine builders. To this end, an absolute crankshaft encoder was installed on an Armfield CM11- MKII engine test stand, providing an absolute reference (Z) pulse once per revolution, and an incremental (B) pulse every 0.5 o CA, enabling synchronisation of pressure measurements with the engine rotation. In-cylinder pressure was measured by a Kistler piezoelectric sparkplug pressure transducer installed in the first cylinder. The transducer signal was then amplified by a Kistler charge amplifier, and the output sent to the analog input of an Arduino DUE microcontroller, while the encoder Z and B pulse signals were connected to digital input pins. Analog to Digital (ADC) readings from the Arduino are then streamed to an external SD card, enabling storage of hundreds of engine cycles worth of data. Finally, we demonstrate the range of operation, capabilities, and limitations of the Arduino DAQ system.