Potential of Exhaust Heat Recovery by Turbocompounding 2012-01-1603
Energy recovery of internal combustion engines has proved to be of primary interest to increase engine global efficiency. The motivation behind is to meet future fuel economy requirements and more stringent emissions regulations. Among all engine waste, research has shown that exhaust energy is the most promising solution due to its high availability. In this context, this paper deals with the analysis of the potential of exhaust heat recovery, especially by a turbocompound system. Turbo-compounding is already established in heavy-duty engines, in which an additional stage of expansion is made through an exhaust recovery turbine. This technique is now being studied for small displacement engines. In the first part of this document, a short history on turbocompounding is presented. Then we present a simulation study conducted on AMESim software, using a 0D 2L diesel engine model, calibrated to fit real engine test bench results. In order to investigate the sensitivity of the engine to a turbocompound system, the existing exhaust line has been modified. Back pressure is analysed by exhaust throttling using a simple converging nozzle for multiple section ratios. The effect of the increase of the exhaust back pressure on the engine is revealed by the increase of residual gases, the delay of combustion, the increase in heat transfer in the cylinder, the variation of global engine thermodynamic balance, and the effect on LP loop (negative pumping work). The equivalent isentropic power of the pressure drop across the nozzle is evaluated and the global gain of engine and exhaust power is assessed on the overall engine map. The comparison of the throttled engine and the original one is done at steady state speed and load points, by maintaining constant the quantity of fuel injected for both engines. The potential of this system is evaluated to determine the practicality of installing such a system on a small displacement engine.