Design and characteristic research of ultra-low-temperature cold-start system based on small SI diesel engine

To address the difficulty of starting diesel engines under ultra-low ambient temperatures, this paper proposes and designs a cold-start system based on a small spark-ignition diesel engine. The small SI diesel engine serves as a unified energy hub, simultaneously providing exhaust waste heat, coolant sensible heat, and electrical power converted from crankshaft output. This enables multi-objective coordinated preheating for oil, coolant, and the power battery. We have established a one-dimensional thermal flow network model comprising the cooling circuit, oil preheating circuit, and engine block, and constructed a power battery preheating model. At −60 °C, under conditions of an optimized energy allocation strategy (35 % electrical energy for engine oil, 65 % for the battery) and a small SI diesel engine operating at 3500 r/min, the oil, coolant and battery can be simultaneously heated to 20 °C, 60 °C and 10 °C respectively within 10 min, thereby meeting the requirements for reliable cold starting of the diesel engine. Compared to a 60 kW fuel-operated auxiliary heating scheme, the preheating time is reduced by approximately 50 %. 76.8 % of the energy input to the system is effectively utilized for synergistic preheating, demonstrating the high energy efficiency and reliability advantages of this cold-start system based on a small SI diesel engine when deployed in extremely cold regions.