Experimental investigation of combustion engine with novel jacket and flue gas heat recovery

Abstract

Internal combustion engines (ICE) are utilized in a number of energy and transportation systems and with the prospect of synthetic green fuels have also secured a place in the future low emission systems. Still, aiming at the effective utilization of the fuel suggests an addition of waste heat recovery systems such as organic Rankine cycle (ORC) to boost electric efficiency. Greater widespread of the ORC integration into the ICE systems is however limited from multiple aspects. Furthermore, when these systems are employed, they are typically applied only for flue gas waste heat utilization, while the large amounts of lower temperature jacket cooling heat remain unutilized, or at the cost of high system complexity. Direct cooling of the ICE jacket by the ORC working fluid has been previously theoretically proposed to tackle some of them. Complexity of the system can be reduced while more waste heat can be effectively transferred from the ICE jacket cooling to the ORC. Here we propose further configuration of ICE waste heat sources integration into a biomass fired ORC unit, creating a multi-fuel system. Such system offers the possibility to increase the electricity demand while reducing biomass consumption. This system has been experimentally explored on a case of a 3 kWe/50 kWth micro-cogeneration ORC and an 8 kWeICE. The experimental data are evaluated in comparison to the theoretically predicted operation. A specific control system has been developed for this system to be easily operated. The results, experience and operation verification from the ICE jacket cooling with the ORC fluid can be also utilized in the construction for waste heat recovery ORC integrated to ICE for higher electrical efficiency. Integration of combined direct jacket and flue gas heat recovery increased the overall electrical efficiency of the system from about 5% for operation of standalone ORC to over 20% for full ICE power.