In-cylinder pressure measurement is an important tool in internal combustion engine research and development for combustion, cycle performance, and knock analysis in spark-ignition engines. In a typical laboratory setup, a sub crank angle resolved (typically between 0.1o and 0.5o) 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 engine in-cylinder pressure 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 educators, Formula SAE teams, hobbyists, and engine builders. The DAQ system developed in this work utilized an Arduino DUE microcontroller and was tested on an Armfield CM11-MKII engine test stand with a 0.5o CA resolution absolute crankshaft encoder and Kistler piezoelectric sparkplug transducer and charge amplifier. Analog to Digital (ADC) readings from the Arduino were streamed to an external SD card, enabling storage of hundreds of engine cycles worth of data. The DAQ was found to be capable of acquisition speeds of 100 kHz, and was tested on engine at speeds up to 4000 rev/min, collecting 1000 consecutive engine cycles with low noise and no loss of signal.