Charge-Air Cooling of High Performance Engines in an Ejector Refrigeration Cycle

Continuous reductions of the CO2 emission targets in Europe demand further efforts to improve fuel consumption. Downsizing of engines proved to be a powerful concept to help achieving current targets. It has though limitations regarding engine knocking and thermal stress of the components. Low temperature charge air cooling can be a solution to overcome these limitations. This study presents a new concept for a stand-alone charge air cooling system in an ejector refrigeration cycle. A high performance engine was measured for different load cases as benchmark for simulations of the new concept. The measured charge air conditions were used as an input in the simulation model. First simulations varied the ejector nozzle diameter and refrigerant filling mass to determine the optimal design for the maximum thermal load condition. Then, a fixed nozzle diameter and filling mass were chosen to simulate other load cases. In comparison to the benchmark, the charge air temperature for knocking sensitive conditions reduces by 5.6 K. Almost no backpressure builds up by the ejector, allowing energy demands to drive the system of less than 50 W. For high thermal stress regions, the charge air temperature is lower by 11.5 K and the energy demand increases up to 460 W. The higher the heat input, the better is the relative cooling performance of the ejector cooling system. Therefore, the system seems a promising approach to enable further downsizing without adding a high system complexity or cost to the engine.