A combined air cycle used for IC engine supercharging based on waste heat recovery

• A combined air cycle is proposed for IC engine supercharging based on WHR.
• Cycle efficiency and energy recovery efficiency depend largely on working pressure.
• Exhaust gas pressure of IC engine with combined air cycle is reduced largely.
• IC engine fuel efficiency can be increased by 4.1% points at most.

A combined air cycle is designed for internal combustion (IC) engine supercharging, which consists of IC engine working cycle and bottom cycle of waste heat recovery (WHR). The bottom cycle uses IC engine exhaust gas as cycle heat source, and its output power is used to drive the gas compressor. Both the heat transfer and thermodynamic processes of combined air cycle were investigated by numerical calculation under various cycle parameters and IC engine operating conditions. On this basis, the performances of combined air cycle and the improvement to IC engine performances were analyzed. Results show that, the cycle efficiency and exhaust gas energy recovery efficiency depend largely on the working pressure, and their maximum values appear at the working pressure of 0.35 MPa and 0.2 MPa, respectively. Compared with the naturally aspirated (NA) engine and turbocharging engine, this approach can make the fuel utilization efficiency of IC engine increase by 8.9% points and 4.1% points at most, respectively, due to the reduction of exhaust gas pressure. All these demonstrate that the proposed concept is a potentially useful approach for IC engine energy saving.