The impact of a magnesium zirconate thermal barrier coating on homogeneous charge compression ignition operational variability and the formation of combustion chamber deposits

Abstract

The accumulation and burn-off of combustion chamber deposits create uncontrolled shifting of the homogeneous charge compression ignition operability range. This combustion chamber deposit–created operational variability places increased control burden on a multi-mode engine. However, the operational variability can be mitigated by manipulating combustion chamber deposit accumulation. A magnesium zirconate thermal barrier coating was applied to the piston of a homogeneous charge compression ignition engine in an effort to reduce combustion chamber deposit accumulation through elevated piston surface temperatures. While reduced combustion chamber deposit thicknesses were observed on the magnesium zirconate piston periphery, combustion chamber deposit accumulation in the bowl region increased relative to aluminum piston operation. Additionally, combustion chamber deposit thicknesses on the aluminum cylinder head were reduced during operation with the magnesium zirconate coated piston. Chamber-wide alterations to combustion chamber deposit accumulation taken together with the increased burn duration and hydrocarbon emissions measured during operation with the magnesium zirconate piston indicate significant interaction between the directly injected fuel spray and thermal barrier coating porosity. The porosity and surface roughness of the magnesium zirconate thermal barrier coating are speculated to create fuel pooling/absorption within the piston bowl, increasing combustion chamber deposit accumulation in the bowl and leaning the remaining fuel–air charge. The charge leaning lengthens the magnesium zirconate burn duration and reduces cylinder head combustion chamber deposit accumulation. Furthermore, hydrocarbon emissions were increased during magnesium zirconate operation due to late desorption and subsequent incomplete burning of fuel from piston bowl and the presence of incombustibly lean areas in the remaining cylinder charge.

Assessing the capability of conventional in-cylinder insulation materials in achieving temperature swing engine performance benefits

“…There has been considerable recent activity to minimize heat losses and improve engine performance through in-cylinder insulation. [1][2][3][4][5][6] Historically, many authors have attempted to use incylinder insulation for engine performance benefits. Some of the pioneering works were performed by TACOM for military vehicles, emphasizing the elimination of the engine cooling system, and the tactical benefits provided by improved efficiency.…”

Analysis of the effects of wall temperature swing on reciprocating internal combustion engine processes

“…There has been considerable recent activity to minimize heat losses and improve engine performance through in-cylinder insulation. [1][2][3][4][5] In-cylinder insulation has been investigated in earnest beginning with the efforts of Cummins and TACOM to improve military diesel engine performance, smoke levels, flexible fuel capability, and to reduce cooling requirements. 6 Many of the early attempts used monolithic ceramics 7,8 such as silicon carbide, 9 partially stabilized zirconia, 10 and silicon nitride, 11 as well as the removal of coolant 12 and plasma-sprayed zirconia.…”

Analytical and Experimental Investigation of Temperature-Swing Insulation on Engine Performance

“…There has been considerable recent activity to minimize heat losses and improve engine efficiency through in-cylinder temperature-swing insulation (Kosaka, et al, 2013) (Kogo, et al, 2016) (Kumar & Nagarajan, 2012) (Hoffman, Lawler, Guralp, Najt, & Filipi, 2015). The capability for surface temperature swing is dictated in part by the intrinsic material properties of the material in contact with the gas.…”

“…The engine's coolant temperature, and by extension the combustion chamber wall and inlet port temperatures, have a large impact the in-cylinder thermal stratification that affects HCCI combustion phasing (Sjoberg, Dec, Babajimopoulos, & Assanis, 2004) (Chang, Lavoie, Babajimopoulos, Filipi, & Assanis, 2007). By extension, the combustion chamber surface temperature, including deposits and thermal history, also play a large, variable role in HCCI combustion, since their effects will change based on the operating history of the engine and the wall's thermal inertia and deposit formation or erosion (Guralp, et al, 2006) (Hoffman, Lawler, Guralp, Najt, & Filipi, 2015). In-cylinder insulation with low thermal inertia and high surface temperature during combustion and expansion could potentially help to mitigate these effects by quickly responding to changes in engine speed and load, masking the underlying metal's thermal inertia, as well as preventing deposit formation on the insulated surfaces.…”

“…The use of thermal barrier materials to promote wall temperature swing in an HCCI engine environment have been investigated by (Hoffman, 2012) (Hoffman, Lawler, Guralp, Najt, & Filipi, 2015) ) (O'Donnell, Powell, Hoffman, Jordan, & Filipi, 2016. Application of a magnesium zirconate (MGZ) or yttria-stabilized zirconia (YSZ) coating to the piston top surface advanced the HCCI combustion phasing, which increased combustion efficiency and lowered unburned hydrocarbon and CO levels, resulting in a benefit to gross indicated thermal efficiency.…”