Influence of Yttria-Stabilized Zirconium Oxide Thermal Swing Coating on the Flame-Wall Interaction in Spark Ignition Engines

Abstract

Future vehicle powertrain systems with internal combustion engines must achieve higher efficiencies and further reduced pollutant emissions. This will require the application of new advanced technologies. Against this background, this paper presents a holistic approach to reduce temporally the wall heat losses, and hydrocarbon and carbon monoxide emissions with thermal coatings on the combustion chamber walls. For this purpose, an yttria-stabilized zirconia (YSZ) coating is applied and evaluated by different methods. The thin layer in combination with the low thermal effusivity of the material allows the wall temperature to follow the gas temperature and perform a so-called thermal swing. The interaction between an uncoated and a YSZ-coated wall with the flame front as well as partially burned gas was investigated. First, in terms of the coating’s potential to reduce the flame quenching distance using an optical method in a constant volume combustion chamber. Second, regarding its influence on the near-wall gas composition, which was analyzed with in-situ diffuse reflectance infrared Fourier transform spectroscopy measurements and a fast gas sampling technique on a single-cylinder engine. From this, it could be derived that the quenching distance can be reduced by 10% at ambient conditions and by 5% at an elevated temperature of 200 °C by using the coating. These findings also support the results that have been obtained by the near-wall gas composition measurements, where a reduced total hydrocarbon emission was found with the applied coating.

Impact of thermal swing piston top land coatings on gasoline engine performance and raw emissions

“…The THC emissions are increased by 46.4% for the YSZ coating. The absolute change in the wall quenching distance is reduced as described in Fischer et al 53 toward higher engine speeds, but still observable, and loads due to higher peak cylinder pressure, see Figure 1, and therefore also higher cylinder temperatures. This results in higher laminar burning velocity 54 and therefore a reduced quenching distance.…”

“…These effects overcompensate the effect of the partly reduced quenching distance of the thermal coating. 53 With the increase of the piston wall temperature during compression and finally combustion the trapped hydrocarbons inside the piston coating are evaporated and oxidized during the expansion stroke. Consequently, the fuel hydrocarbons (Isopentane and Ethanol) and partially oxidized hydrocarbons (Methane, Formaldehyde, Acetylene) increase notable.…”

“…55 Consequently, the effect of an increased surface temperature on the quenching distance is reduced leading to significant reduced effect on the wall-near hydrocarbon concentration. 53 Accordingly, the effect of the coated piston on the quenching distance is relatively lower and cannot compensate the discussed effects as at lower engine speeds and loads, see section 3.3. This is further displayed by the notable increase in fuel hydrocarbons, Isopentane by 75% and Ethanol by 89% for the YSZ coating due to the increased crevice volume by the porous coating and insufficient time and temperature for post-combustion oxidation.…”