A Simulation Study to Understand the Efficiency Analysis of Multiple Injectors for the Double Compression Expansion Engine (DCEE) Concept

Heavy-duty vehicles face increasing demands of emission regulations. Reduced carbon-dioxide (CO2) emission targets motivate decreased fuel consumption for fossil fuel engines. Increased engine efficiency contributes to lower fuel consumption and can be achieved by lower heat transfer, friction and exhaust losses. The double compression expansion engine (DCEE) concept achieves higher efficiency, as it utilizes a split-cycle approach to increase the in-cylinder pressure and recover the normally wasted exhaust energy. However, the DCEE concept suffers heat losses from the high-pressure approach. This study utilizes up to three injectors to reduce the wall-gas temperature gradient rendering lower convective heat losses. The injector configuration consists of a standard central injector and two side-injectors placed at the rim of the bowl. An increased distance from side-injector to the wall delivered lower heat losses by centralizing hot gases in the combustion chamber. Computational fluid dynamics (CFD) simulations investigated two different piston bowls, in a heavy-duty diesel engine, to obtain in-cylinder conditions for one, two and three-injector concepts. One-dimensional (1D) simulations then used the CFD data to obtain the complete efficiency analysis of the DCEE concept. The results showed that the three-injector case improved the brake thermal efficiency and reduced the heat transfer losses, compared to the two-injector and single-injector cases. In particular, the three-injector case resulted in a high indicated and brake thermal efficiency of 58.5 % and 54.2 %, respectively.