Sensitivity Analysis of Injection Duration on Combustion Characteristics and Exhaust Emissions in a Marine Diesel Engine

This study investigates the role of injection duration in marine diesel engine combustion within an optimised operating framework. While injection parameters are typically analysed in isolation, their interaction within a coupled engine system remains insufficiently understood, particularly under realistic operating conditions. To address this gap, a structured methodology integrating one-dimensional (1D) engine simulation and optimisation is applied to evaluate the sensitivity of injection duration around optimised operating points across multiple engine loads. The approach is based on a calibrated engine model developed in WAVE, coupled with an optimisation framework to determine load-dependent optimal control parameters. Injection duration is then systematically varied around its optimised values to assess its influence on engine performance, emissions, and heat release rate (HRR). This enables the evaluation of the robustness of the optimised solution under realistic deviations. The results demonstrate that injection duration governs the transition between premixed and diffusion-controlled combustion, directly influencing heat release structure, combustion stability, and emissions formation. Longer injection durations promote mixing-limited combustion, leading to reduced peak temperatures and lower nitrogen oxide (NOx) emissions, but increased incomplete combustion products, including carbon monoxide (CO) and unburned hydrocarbons (HCs), due to reduced oxidation efficiency. These effects are strongly load-dependent, with part-load operation showing higher sensitivity. The study provides a system-level interpretation of injection duration as a control variable rather than an isolated parameter, offering new insight into its role in combustion regime transitions and engine response. The proposed framework enables a more physically consistent understanding of injection control in modern electronically controlled marine diesel engines and supports the development of robust optimisation and calibration strategies.