The performance improvement of direct injection engines in cold start conditions integrating with phase change material: Energy and exergy analysis

摘要

The cold start problem is still one of the most significant drawbacks of diesel engines, especially in cold climates despite all technological improvements of fuel injection and control systems. Starting diesel engines becomes more difficult at low ambient air and engine block temperatures. Moreover, the production of pollutant exhaust emissions increases during the cold start and warm-up period of the engine. In this study, the thermal energy storage system (TES) with phase change materials (PCMs) has been proposed to improve the cold start and warm-up performance and exhaust emission characteristics of diesel engines. The waste heat from the engine main coolant using as the heat source is transferred to TES with integrated PCM after the warm-up period of the engine for heat storage. Then, the latent and sensible heat stored in PCM is transferred to the engine manifold to increase the temperature of intake air during cold start. The experiments have been conducted under low dead state temperature (approximate to 6 degrees C) conditions of the engine block and ambient. The experimental and energy-exergy comparison analysis results show that the cold start cranking period, CO and HC exhaust emission performances have improved by approximately 68.2%, 27.5% and 44% compared to classical engine system with the use of a designed TES, respectively. The efficiency of the strategy of increasing the intake air temperature by designing a PCM-based TES is supported by energy and exergy comparison analysis. Thermal efficiency and exergy efficiency improved in the range of 1.02%-7.45% and 0.9%-9.63%, respectively. These improvements show that the performance of a diesel engine under cold start conditions can be improved with a PCM-supported TES system.