Research on the characteristics of the exhaust energy splitting method for the two-stroke low speed marine diesel engine

Efficient waste heat recovery (WHR) is the key to improve the thermal efficiency of the marine diesel engine and reduce the cost. According to the characteristics of long stroke of low-speed marine diesel engine, the exhaust energy splitting (EES) method based on exhaust energy distribution is proposed in this paper. EES is a new method of improving waste heat grade by separating high temperature exhaust gas and low temperature scavenging air. Compared with other studies on increasing exhaust temperature, EES significantly increases exhaust temperature and improves waste heat recovery efficiency without negatively affecting engine performance. Moreover, due to the adjustable EES valve, the optimal performance of engine and WHR system can be achieved under various operating conditions by adjusting the exhaust splitting phase (ESP). The One-Dimension and Three-Dimension simulation models for a two-stroke low speed marine diesel engine with waste heat recovery system are established. The exhaust energy distribution and the splitting phase to be optimized are also explored synchronously. The results show that by using the exhaust energy splitting method, temperature after turbine can be increased by more than 100 K compared with the baseline of the original engine system. Using Organic Rankine cycle (ORC) as WHR system, the waste heat recovery efficiency can reach over 17 %. Compared with the original engine, the total output power of the optimized EES low-speed engine and ORC system Increase by 100.90 kW under 75 % load and 154.72 kW under 100 % load, and the NOx emissions can be reduced by 5 %.