Numerical study of the waste heat recovery potential of the exhaust gases from a tractor engine

The paper presents an analysis of the possibilities of exhaust gas heat recovery for a tractor engine with an output power of 110 kW. On the basis of a literature review, the Rankine cycle seems to be the most effective way to recover the exhaust gas energy. This approach reduces the fuel consumption and allows engines to meet future restrictions on carbon dioxide emissions. A simulation model of the engine by means of a one-dimensional approach and a zero-dimensional approach was built into the simulation code AVL BOOST, and a model of the Rankine cycle was implemented. The experimental values of the effective power of the engine, the mass flow and the exhaust gas temperature were used to validate the engine model. The energy balance of the engine shows that more than 28.9% of the fuel energy is rejected by exhaust gases. Using the engine model, the energy and the exergy of the exhaust gases were studied. An experimental study of the real working cycle of a tractor engine revealed that the engine operates most of the time at a constant speed (n = 1650 r/min) and a constant load (brake mean effective pressure, 10 bar). Finally, Rankine cycle simulations with four working fluids were carried out at the most typical operating point of the engine. The simulation results reveal that the output power of the engine and the efficiency of the engine increase within the range 3.9–7.5%. The highest value was achieved with water as the working fluid while the lowest value was obtained with the organic fluid R134a. The power obtained with water as the working fluid was 6.69 kW, which corresponds to a Rankine cycle efficiency of 15.8%. The results show good prospects for further development of the Rankine cycle.