Abstract
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•Linear motor implementation enhances cylinder pressure stability and piston motion adjustability in RCMs.•Optimized adjustable structural parameters of the bench improve cylinder pressure stability.•Enhanced weighted KNN control strategy targeting cylinder pressure eliminates environmental disturbances.
Advanced combustion technologies are crucial for enhancing the overall performance of internal combustion engines. Rapid compression machine (RCM), which closely replicate the thermodynamic conditions of engine operation, serve as platforms for these advanced combustion technologies. However, the current gas/liquid-driven rapid compression machine, due to the limitations of the driving medium’s properties, experiences variations in the in-cylinder thermodynamic state between compression cycles. This increases the uncertainty of the in-cylinder environment before ignition, thereby impacting the research on combustion technologies based on this platform. To enhance the stability of compression pressure, this study employs a fast-response and highly controllable linear motor as the driving source and develops a piston-type RCM. Through experimental and simulation analyses, the effects of key compressor design parameters on in-cylinder compression pressure are investigated. A novel control method is proposed, which stabilizes and regulates the in-cylinder pressure at top dead center (TDC) by adjusting the piston motion profile, based on the principle of managing heat loss and leakage during compression. Furthermore, an advanced pressure control strategy at TDC is developed, leveraging an improved k-nearest neighbors (KNN) algorithm. The experimental results indicate that the piston speed deviation is limited to 2.5 %, and the standard deviation of in-cylinder pressure does not exceed 0.42 bar, under the same target trajectory. Furthermore, validation experiments of the improved weighted K-nearest neighbors algorithm demonstrate that, even with wall friction coefficient variations not exceeding 26.2 %, the maximum cylinder pressure deviation can be kept within 1.0 % through adjustments from this control strategy.