Concept of rapid and controllable combustion for high power-density diesel engines

•A concept of rapid and controllable combustion for diesel engine is proposed.•The Sabathe-Miller cycle is suggested and related with the combustion process.•The inflection point of heat release rate corresponds to the spray impingement.•The fuel mass for pre-inflection combustion is a function of injection parameters.•The proposed theoretical method can be applied to other kind of diesel-like engines. Over recent years, the demand to abate global carbon emissions has attracted significant interest and resulted in more stringent policies and regulations. For diesel engines, the fundamental solution to addressing carbon emissions entails optimizing the thermal efficiency. However, for high power-density marine diesel engines, large amount of injection mass companied with little intake swirl makes further optimization of fuel consumption quite difficult. To address this issue, a concept for rapid and controllable combustion is proposed herein. The concept is a theory-based method to design and optimize the combustion system in a forward direction from theory to control method. The concept of rapid combustion relies on the optimization of the combustion process based on ideal Sabathe-Miller cycle to get the optimal heat release rate. The concept of controllable combustion was conducted by theoretically relating the in-cylinder spray evolution with heat release rate so as to determine the controllable parameters of combustion system. The concept proposed was validated by the computational fluid dynamics simulation as well as a high power-density diesel engine with a cylinder power of 450 kW and displacement of 18.9L which has been optimized by traditional benchmark and design of experiments method. The results showed that, the optimization method suggested is reliable to define the combustion system to achieve thermal efficiency as high as possible under the boundary constrains. Moreover, without excessive requirement for turbocharger capacity and injection system, both the fuel consumption and NOx emission decrease under all tested loads by using the proposed method, when compared to the results of traditional optimization method. For the commonly-used 100 % and 75 % load, the fuel consumption respectively drops from 199.02 to 196.5 and 199.75 to 197.15 g/kWh, and NOx emission is reduced by 22 % and 12.6 %, which is relatively remarkable for high power-density marine diesel engines. Therefore, it offers the advantage of significantly reducing the workload whe