Thermo-swing insulation to reduce heat loss from the combustion chamber wall of a diesel engine

Abstract

Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue, because it deteriorates charging efficiency, increases the emissions of soot and NOx in diesel engines, and promotes the knock occurrence tendency in gasoline engines. A new concept heat insulation methodology which can reduce cooling heat loss without heating the charging air has been developed. Surface temperature of insulation coating on the combustion chamber wall changes rapidly, according to the quickly changing in-cylinder gas temperature in each engine stroke. During the compression and expansion stroke, the surface temperature of the insulation coating goes up rapidly, and consequently, the heat transfer becomes lower by the reduced temperature difference between the surface and the gas. During the intake stroke, the surface temperature goes down rapidly, and it prevents intake air heating from the wall. To realize the above-mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement in thermal efficiency. It also showed a reduction of unburnt fuel emission in low temperature engine starting condition. The energy balance analysis showed reduction of cooling heat loss and, on the contrary, increase in the brake power and the exhaust loss.

A study of suspension plasma-sprayed insulated pistons evaluated in a heavy-duty diesel engine

“…Higher exhaust temperatures have been observed in experiments, as well as in simulations, with TBC on combustion chamber components. 3–5 The higher exhaust energy may partly be recovered by waste heat recovery (WHR) systems. 3 Improved work on the piston seems to be more difficult to accomplish.…”

Evaluation of thermal barrier coatings and surface roughness in a single-cylinder light-duty diesel engine

“…For the motored energy balance, the terms in equation (2) were scaled with the engine swept volume and expressed in terms of mean effective pressure, resulting in equation (9). These terms for indicated work, wall heat transfer, and exhaust loss add-up to zero as there was no input of fuel energy for the motored case…”

“…The purpose of the differentiation of the pistons with the top coating was to evaluate the findings of Kawaguchi et al 9 that the TBC applied in the bowl had an adverse effect on the combustion process, whereas the coating on the top reduced heat losses and improved indicated efficiency. The difference in the coated surface area between the alumina and zirconia coated pistons was related to the limitations in the used plasma-spraying process.…”

Special Issue on COMODIA 2017

“…They observe higher heat-flux values in the peripheral region around the stagnation point due to the higher temperature and thinner boundary layer. Kawaguchi et al 11 developed a novel approach to reduce heat loss at the piston top surfaces in a diesel engine. The technique named ''Thermo-swing wall insulation technique'' features a thin thermal layer that follows quickly the transient in-cylinder gas temperature, thus reducing the temperature difference between the piston surface and the in-cylinder gas.…”