In this technical article, EnginSoft and Prometech explain how they executed a highly complex computational simulation on the fluid-structure interaction of the oil flow inside a reciprocating engine, on behalf of Honda R&D. Since such simulation usually involves high computational and time costs, the engineers opted to use the more sophisticated technology of Moving Particle Simulation (MPS) to approach the challenge because of its semi-implicit scheme for time integration in incompressible flow.
Predicting and optimizing the oil flow in a reciprocating engine is an important design task. The engineers explain how they simulated the oil separation process in two different breather chamber structures using Particleworks to investigate their efficiency in separating the oil from the blow-by gas. In a two-phase process, they first computed the drag force using grid-based Computational Fluid Dynamics (CFD) software, after which the defined it as a spatial function of the external force in the breather chamber in the Particleworks simulation.
Image source: www.honda.co.uk/cars/new/civic-type-r-2015/overview.html
One of the particle methods for fluid dynamics simulations, Moving Particle Simulation (MPS) has begun to be used as an innovative and effective computational simulation technique for design and development. In contrast to one of the major particle methods Smoothed Particle Hydrodynamics (SPH), which is mainly used to model compressible flow and adopts an explicit scheme for time integration, MPS is formulated to treat incompressible flow and uses a semi-implicit scheme for time integration. In general, since most engineering problems concerning fluid-like materials in the manufacturing industries can be treated as incompressible, it is thought that MPS is suitable to treat these problems. In addition, the semi-implicit time integration scheme in MPS has an advantage in computational cost for longer manufacturing process. For these reasons, MPS is used in various industries including automotive, power transmission, chemical and pharmaceutical, food and beverage, medical, and civil and environmental engineering. In this article, we introduce a real application from one of the leading automotive companies in Japan which is using the MPS-based simulation software, Particleworks.
It is important to predict oil flow in a reciprocating engine in a design task. In this article the design of the structure of the breather chamber was investigated using Particleworks. The engine and the breather system are shown in Fig.1. The breather chamber is used to separate oil from blow-by gas. Oil separation in the breather chamber must be efficient.
Air-resistance (drag force of the air) in the breather chamber was considered by adding the drag term to Eq.(2). In addition, the drag term was defined considering the size of the particles as in Eq.(3). Since the size of the real oil mist found in the blow-by gas is very small (1 mm to 10 mm), the coarse graining model technique was used to reduce computational cost. The MPS particles representing the oil mist were defined using the coarse graining model with a size of approximately 250 mm to 500 mm. The drag force was computed using grid-based Computational Fluid Dynamics (CFD) software prior to the Particleworks simulation and defined as a spatial function of the external force in the breather chamber in the Particleworks simulation.
The governing equations for incompressible flow are the continuity and the Navier-Stokes equations:
where, r is density, u is velocity, P is pressure, n is the diffusion coefficient, and g is gravity.
where, CD is coefficient of drag, rair is mass density of air, ul is liquid velocity, ug is gas velocity, S is liquid body surface area, Dl is particle size of MPS, dl is particle size of oil mist, and ml is oil mist mass. Two types of the breather chambers, type 1 and type 2, shown in Fig.2 were examined.
The differences between these two chambers are 1) the distance between the inlet hole and the collision plate of 30 mm for type 1 and 15 mm for type 2; and 2) the diameter of the inlet of 15 mm for type 1 and 6 mm for type 2.
The results of the simulations and the experiments on breather chamber type 1 and type 2 are shown in Fig.3 and 4 respectively. Type 1 can capture more oil mist on the collision plate and the oil flow towards the oil drainage holes at the bottom of the chamber can be seen clearly in Fig.3. While in chamber type 2, the oil mist scatters under the collision plate and the oil flow to the oil drainage holes is not formed (see Fig.4). According to the results, breather chamber type 1 showed a superior ability to separate the oil mist from the blow-by gas than breather chamber type 2, and the use of MPS in the experiments was able to reproduce the tendency of the real oil flow in these chamber types.
MPS-based numerical computational technology has already been used in front-line design and development processes, as stated in the introduction to this article. MPS represents a more sophisticated technology that will supplement the more conventional numerical methods, ie. Finite Element Method (FEM) and Multi Body Dynamics for complex flow problems and fluid-structure interaction problems in the near future.
Acknowledgements: The author and Prometech Software wish to thank Mr. Haga of Honda R&D Co., Ltd. for the permission and opportunity to introduce their important research projects using Particleworks.
Source of Image at the top of the article: www.honda.co.uk/cars/new/civic-type-r-2015/overview.html
More detail can be obtained from “Honda R&D Technical Review Vol.26 No.2, 2014” if you have interest in this topic. Sunao Tokura, Prometech Software Inc.,
Engine and breather system
Degree of constant volume vs heat loss
Oil flow in breather chamber type 1
Oil flow in breather chamber type 2
Particleworks is an advanced CFD Software solution, based on the Moving Particle Simulation (MPS) method.
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