Conjugate heat transfer study of the impact of ‘thermo-swing’ coatings on internal combustion engines heat losses

Abstract

To comply with the very strict emissions regulation the automotive industry is succeeding in developing ever more efficient engines, and there is scope for more improvements. In this regard, some investigations have suggested that insulating the combustion chamber walls of an internal combustion engine (ICE) yield low thermal losses. Most of the literature available on this topic presents simplified models that do not allow studying in detail the coating impact on engine efficiency. A more precise approach that consists in the combination of Computational Fluid Dynamics (CFD) and Conjugate Heat Transfer (CHT) simulations is used in this paper to predict the heat losses through the combustion chamber walls of a spark ignition (SI) engine. Two configurations are considered for the single cylinder engine: the metallic case and the same engine with coated piston and cylinder head. The insulation material has a low thermal conductivity ( k[Formula: see text]1.0 W/( mK)). The numerical results are validated by comparison with the results of a 1D heat transfer model and with experimental data for a medium load operation point (3000 rpm −7 bar IMEP). The solutions obtained are analysed in detail in terms of wall temperature distribution and heat transfer. The impact of the coating on the engine efficiency is thus assessed. The CFD-CHT calculations yields very good results in terms of heat transfer prediction during the whole engine cycle.

Development of a Novel Numerical Methodology for the Assessment of Insulating Coating Performance in Internal Combustion Engines

“…Insulating coating layers in recent engine applications are characterized by a very small thickness (~100 µm) which, from the computational point of view, leads to a significant increase of the modelling effort and computing time in 3D CHT simulations, due to the necessity of extremely refined grids. In this regard, a methodology to numerically assess the heat losses through coated combustion chamber walls with reduced computational effort has been developed [20], which is briefly summarized in Figs. 1 and 2 and described in the following sections.…”

“…These values were calculated with a combustion diagnosis tool [16] using the experimental data available for the Diesel engine under study at a low speed -high load operating point, Experimental working conditions were considered compatible with the engine working point 10/19/2016 under study in terms of heat rejection.. For the discretization of the coating and adjacent aluminum layer 500 nodes were used for the 1D mesh, 400 nodes of which were placed in the thin coating. As discussed in [20], the number of nodes used to describe the equivalent thick coating layer in the 1D-HTM should match the one used in 3D-CFD-CHT simulations, since there is a tight coupling between the number of nodes and the physical properties of the equivalent coating layer material. In particular, if the number of nodes used to describe the thick coating layer changes, then also the properties of the equivalent coating material will change ( [20]).…”

Experimental investigation of wall heat transfer due to spray combustion in a high-pressure/high-temperature vessel

“…More recently, the potential of TBCs has however been firmly recognised and also put to use: notably, the Toyota metal-based silica-reinforced porous anodised aluminium (SiRPA Ò ) coating 2 was developed within the last decade. Recent computational studies [7][8][9] have attempted to estimate the efficiency potential of coating solutions in diesel engines. Moreover, more extreme TSMs continue to be investigated: Andrie et al 10 recently report marked efficiency gains with a thin layer of a material that possesses a conductivity and heat capacity nearly an order of magnitude smaller than plasma-sprayed partially stabilised zirconia (PSZ), a conventional TBC material.…”

Modelling of Heat Losses through Coated Cylinder Walls and their Impact on Engine Performance

“…However, generating a mesh to solve adequately such thin layers leads to prohibitive mesh size. The thick 'equivalent' material with few nodes (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) has to reproduce the behavior of the real coating with fine mesh. Then, in the developed approach, the properties of the thick coating layer are adjusted to match the properties of the real thin coating meshed with a finer discretization.…”

“…Conjugate Heat Transfer study of the impact of "thermo-swing" coatings on Internal Combustion Engines heat losses [4] faces calculated with CHT were compared to that predicted by the CMT-1D HTM lumped model described in Chapter 4, since they cannot be measured experimentally.…”