Accelerometer Location Study for Non-Intrusive Start of Combustion (SOC) Detection in Compression-Ignition Engines

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 with variations in engine load, speed, injection timing, and injection strategy. Start of combustion (SOC) was identified from the filtered acceleration signal using a previously developed approach. Each location was assessed using both signal-based metrics, including magnitude squared coherence (MSC) between block surface acceleration and in-cylinder pressure, as well as SOC outcome-based metrics, such as detection success rate. Results demonstrate that the mounting location has a significant impact on the ability to extract 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, side-mounted locations delivered the most reliable performance, with SOC detection success above 98 percent, defined as correctly identifying the acceleration peak most closely aligned with the corresponding pressure-derived SOC for each cycle. 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.