CFD driven design and optimization of a natural gas engine inlet manifold using overset mesh

Abstract

With a constant strive towards sustainability, especially for vehicles, Volvo Penta has committed towards research and development of using renewable fuels to power their engine platforms. One example of a renewable fuel is biogas (bio-methane) which can be used in spark ignition Otto-cycle engines. This is a substitution to one of the most widely used fossil fuels today, which is petrol. For an engine to work properly with high efficiency and minimized environmental impact, the flow of air and fuel entering the engine is of paramount importance. It is crucial to ensure that the air-fuel mixture is delivered to each cylinder with minimal pressure losses and that the distribution of the mixture between the cylinders is equal. One key component affecting this is the intake manifold which is responsible for distributing air from the turbocharger to the six cylinders, and this component was the main focus of the analysis conducted throughout this project. After a thorough background study mapping out which parameters affect intake performance, existing concepts and patents, a design-build-test cycle (DBT) was used including generation of concepts and several evaluations and design-phases. A comprehensive requirements specification was created to use during the development process. Concepts were then designed in Creo Parametric and pre-processed in ANSA. Evaluation of concepts was carried out in STARCCM+ with 3D CFD simulations, both with steady state conditions and with fully transient boundary conditions imported from 1D simulations. A new method for simulating transient valve behaviour was developed using an overset mesh approach, allowing accurate replication of the pulsating gas dynamics within the manifold. The simulation results were used to refine and optimize the secondary duct of the inlet manifold, focusing on minimizing the pressure drop and guaranteeing an equal distribution to all cylinders. The used CFD-evaluation method agrees well with 1D simulation results, showcasing that the more data-efficient overset mesh simulation process is a viable option for future design work. The results also showed promising potential for increasing engine performance through incremental design changes that can be implemented with minimal modifications to the existing manifold-design.