Sensor Location Study for Non-Intrusive Start of Combustion (SOC) Detection Using Engine Block Vibration

This study investigates the impact of sensor location on accelerometer-based sensing of combustion phasing for compression-ignition engines. Ten accelerometer locations were studied on a light-duty compression-ignition engine for a set of conditions varied in engine load, speed, injection timing and injection strategy. Start of combustion (SOC) was identified from filtered acceleration signals. Each location was assessed using both signal quality metrics, including magnitude squared coherence (MSC) with in-cylinder pressure, passband intensity, signal to noise ratio, and spectrogram shape, as well as SOC outcome metrics such as detection success rate. Results demonstrate that the mounting location has a significant impact on the ability to extract relevant combustion phasing information from the accelerometer signal. Sensors mounted on the front face of the engine produced the strongest signals for an individual cylinder. For multi-cylinder sensing, a side mounted location delivered the most reliable performance, with SOC detection exceeding 98 percent across all conditions and cylinders. This work outlines a practical framework for selecting and evaluating accelerometer mounting locations, enabling broader use of accelerometers in engine platforms operating on a range of combustion approaches