Air supply system design of a Diesel-Brayton combined cycle engine

The Diesel-Brayton combined cycle engine was proposed previously to achieve the goal of lower fuel consumption, higher power density and good startup performance under low-temperature conditions. The prototype engine was designed and tested based on an off-the-shelf gas turbine and a diesel engine. To achieve a more compact and lighter design, the air supply system was designed based on the centrifugal compressor of the gas turbine. In the coupling operation mode aiming to generate the maximum power, a large amount of compressed air must be extracted into the diesel engine. The present paper presents the design methodology of the compact air supply system. The bleeding slot configuration was selected based on a parametric study and proven by systematic experiments. Three-dimensional simulations were conducted to investigate the performance and flow field of the compressor. Backflow appeared in several passages of the axial diffuser caused by air bleeding, which further distorted the air flow in the combustion chamber. Such distortion may cause compressor and combustion instabilities. In the future, the combustion chamber and the axial diffuser must be designed in combination with an air bleeding system to improve the engine performance.