Assessing the Impact of Thermal Barrier Coatings on Charge Temperature Stratification Within a Homogeneous Charge Compression Ignition Engine

2018 ◽  
Author(s):  
Ryan O’Donnell ◽  
Tommy Powell ◽  
Zoran Filipi ◽  
Mark Hoffman
Keyword(s):  
Thermal Barrier Coatings ◽  
Homogeneous Charge Compression Ignition ◽  
Thermal Barrier ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Barrier Coatings ◽  
Charge Mass ◽  
The Impact ◽  
Charge Temperature ◽  
Homogeneous Charge

The application of a Thermal Barrier Coating (TBC) to combustion chamber surfaces within a Low Temperature Combustion (LTC) engine alters conditions at the gas-wall boundary and affects the temperature field of the interior charge. Thin, low-conductivity, TBCs (∼150μm) exhibit elevated surface temperatures during late compression and expansion processes. This temperature ‘swing’ reduces gas-to-wall heat transfer during combustion and expansion, alters reaction rates in the wall affected zones, and improves thermal efficiency. In this paper, Thermal Stratification Analysis (TSA) is employed to quantify the impact of Thermal Barrier Coatings on the charge temperature distribution within a gasoline-fueled Homogeneous Charge Compression Ignition (HCCI) engine. Using an empirically derived ignition delay correlation for HCCI-relevant air-to-fuel ratios, an autoignition integral is tracked across multiple temperature ‘zones’. Charge mass is assigned to each zone by referencing the Mass Fraction Burn (MFB) profile from the corresponding heat release analysis. Closed-cycle temperature distributions are generated for baseline (i.e., ‘metal’) and TBC-treated engine configurations. In general, the TBC-treated engine configurations are shown to maintain a higher percentage of charge mass at temperatures approximating the isentropic limit.

scholarly journals Enhancing the efficiency benefit of thermal barrier coatings for homogeneous charge compression ignition engines through application of a low-k oxide

2020 ◽  
pp. 146808742091840
Author(s):  
Zoran Filipi ◽  
Mark Hoffman ◽  
Ryan O’Donnell ◽  
Tommy Powell ◽  
Eric Jordan ◽  
...  
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Combustion Efficiency ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Compression Ignition ◽  
Stabilized Zirconia ◽  
Compression Ignition Engine ◽  
Temperature Swing ◽  
Low K ◽  
Homogeneous Charge

Prior experiments reported by the authors have proven the hypothesis that achieving a dynamic temperature swing on the combustion chamber surface will lead to improved thermal and combustion efficiencies of the homogeneous charge compression ignition engine. A thin layer of yttria-stabilized zirconia, roughly 150 μm, was plasma sprayed on the piston top. It led to markedly advanced ignition and heat release in the gasoline homogeneous charge compression ignition engine, accompanied with reduced unburnt hydrocarbon and carbon monoxide emissions, improved combustion efficiency, and a higher thermal efficiency. A related computational study highlighted the critical role of coating thermal conductivity in achieving a desired dynamic response; hence, the second phase of experimental investigations focused on introducing structured porosity in the yttria-stabilized zirconia coating, as a means of reducing effective conductivity. Indeed, additional incremental improvements were observed, as well as limitations related to adverse effects of the surface roughness and the fuel interactions with the surface roughness and open pores. Erosion can also be a problem in a direct injection engine. Therefore, the third round of investigations focused on a material with a natively low conductivity (low-k), sprayed on the top of an Al piston in a relatively dense form, and in a way that yields a smooth surface. The objective was to capitalize on the low conductivity, while avoiding the pitfalls accompanying high-porosity formulations. The heat-storage capacity was limited by keeping the thickness relatively low. The results verify the paramount importance of thermal conductivity in the context of high “temperature swing” behavior and indicate a potential to improve the homogeneous charge compression ignition engine’s combustion efficiency roughly 1.5%, with the overall indicated efficiency improvement on the order of 5%, on a relative basis. In addition, the low-k oxide thermal barrier applied to the piston extended significantly the low-load homogeneous charge compression ignition operability limit.

scholarly journals Experimental investigation of the relationship between thermal barrier coating structured porosity and homogeneous charge compression ignition engine combustion

2019 ◽  
Vol 22 (1) ◽  
pp. 88-108 ◽  
Author(s):  
Tommy Powell ◽  
Ryan O’Donnell ◽  
Mark Hoffman ◽  
Zoran Filipi ◽  
Eric H Jordan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Plasma Spray ◽  
Homogeneous Charge Compression Ignition ◽  
Thermal Barrier ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Spray Process ◽  
Plasma Spray Process ◽  
Temperature Swing ◽  
Homogeneous Charge

Heat transfer has a profound influence on homogeneous charge compression ignition combustion. When a thermal barrier coating is applied to the combustion chamber, the insulating effect magnifies the wall temperature swing, decreasing heat transfer during combustion. This enables improvements in both thermal and combustion efficiency without the detrimental impacts of intake charge heating. Increasing the temperature swing requires coatings with lower thermal conductivity and heat capacity. A promising avenue for simultaneously decreasing both thermal conductivity and capacity is to increase the porosity fraction. A proprietary solution precursor plasma spray process enables discrete organization of the porosity structure, called inter-pass boundaries, which in turn produces a step-reduction in thermal conductivity for a given porosity level. In this investigation, yttria-stabilized zirconia is used to create four different thermal barrier coatings to study the potential of structured porosity as means of improving the “temperature swing” behavior in a homogeneous charge compression ignition engine. The baseline coating is “dense YSZ,” applied using a standard air-plasma spray process. Next, significant reductions of the thermal conductivity are achieved by utilizing the solution precursor plasma spray process to create inter-pass boundaries with a moderate overall porosity. Performance, efficiency, and emissions are compared against both a baseline configuration with a metal piston and an air-plasma spray “dense YSZ” coating. Experiments are carried out in a single-cylinder gasoline homogeneous charge compression ignition engine with exhaust re-induction. Experiments indicate that incorporating structured porosity into thermal barrier coatings produces tangible gains in combustion and thermal efficiencies. However, there is an upper limit to porosity levels acceptable for homogeneous charge compression ignition engine application because an elevated porosity fraction leads to excessive surface roughness and undesirable fuel interactions. Comparison of the coatings showed the best results with coating thickness of up to 150  µm. Thicker coatings led to slower surface temperature response and attenuated swing temperature magnitude.

scholarly journals Inverse Analysis of In-Cylinder Gas-Wall Boundary Conditions: Investigation of a Yttria-Stabilized Zirconia Thermal Barrier Coating for Homogeneous Charge Compression Ignition

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Ryan O'Donnell ◽  
Tommy Powell ◽  
Mark Hoffman ◽  
Eric Jordan ◽  
Zoran Filipi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Homogeneous Charge Compression Ignition ◽  
Engine Performance ◽  
Ex Situ ◽  
Thermal Barrier ◽  
Compression Ignition ◽  
The Impact ◽  
Homogeneous Charge

Thermal barrier coatings (TBCs) applied to in-cylinder surfaces of a low temperature combustion (LTC) engine provide an opportunity for enhanced efficiency via two mechanisms: (i) positive impact on thermodynamic cycle efficiency due to combustion/expansion heat loss reduction, and (ii) enhanced combustion efficiency. Heat released during combustion increases the temperature gradient within the TBC layer, elevating surface temperature over combustion-relevant crank angles. Thorough characterization of this dynamic temperature “swing” at the TBC–gas interface is required to ensure accurate determination of heat transfer and the associated impact(s) on engine performance, emissions, and efficiencies. This paper employs an inverse heat conduction solver based on the sequential function specification method (SFSM) to estimate TBC surface temperature and heat flux profiles using sub-TBC temperature measurements. The authors first assess the robustness of the solution methodology ex situ, utilizing an inert, quiescent environment and a known heat flux boundary condition. The inverse solver is extended in situ to evaluate surface thermal phenomena within a TBC-treated single-cylinder, gasoline-fueled, homogeneous charge compression ignition (HCCI) engine. The resultant analysis provides crank angle resolved TBC surface temperature and heat flux profiles over a host of operational conditions. Insight derived from this work may be correlated with TBC thermophysical properties to determine the impact(s) of material selection on engine performance, emissions, heat transfer, and efficiencies. These efforts will guide next-generation TBC design.

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