Performance Analysis of Organic Rankine Cycle (ORC) for Recovering Waste Heat from a Heavy Duty Diesel Engine

The heat losses through exhaust gases and the engine coolant contribute significantly towards reduction in thermal efficiency of an Internal Combustion (IC) engine. This largely impacts the fuel economy and power output. Waste Heat Recovery (WHR) has proven to be an effective method of overcoming these challenges. A Rankine cycle is a reverse refrigeration cycle that circulates a working fluid through the four basic components namely the pump, evaporator, turbine and condenser. It is a popular WHR approach in automotive applications with varying levels of success in the past. As the heat transfer capability in organic working fluids is greater than the conventionally used inorganic fluids, the former is used to capture maximum waste heat from low grade heat sources such as the automobile engine.

A dual-loop Organic Rankine Cycle (ORC) is proposed for a heavy duty IC Engine with working fluids R245fa and R236fa for the High Temperature (HT) and Low Temperature (LT) loops respectively. The HT loop utilizes heat from exhaust and the LT loop recovers heat from the engine block and the residual heat from the HT loop. The cycle design also helps in reducing the cooling system load by recovering the otherwise wasted heat from the engine block. A mathematical model is generated using engine data from the ESC cycle and the improvement in overall thermal efficiency and power output is thereby obtained. The study shows an overall cycle efficiency of 5-10% which translates to improvement in engine overall thermal efficiency.