Direct heat loss to combustion chamber walls in a direct-injection diesel engine: Evaluation of direct heat loss to piston and cylinder head

Abstract

The purpose of this study is to clarify the state of the heat loss in a direct-injection diesel engine. Originally developed thin-film thermocouples (TFTs) are embedded into the combustion chamber walls for accurate measurement of instantaneous surface temperature from which instantaneous heat flux is evaluated through the heat conduction equation. Measured points are arrayed on the cavity bottom, the cavity side wall, the piston top, and the cylinder head. The TFTs are designed and fabricated so that disturbance of the temperature field is minimized when they are embedded into the combustion chamber walls. As a result, it is observed that the behaviour of instantaneous temperature and heat flux depends on the radius of the measured point. Measured points located radially inwards seem to be influenced by the combustion flame considerably more than those located outwards because the flame is presumed to stay in and around the cavity which occupies a region around the central axis of the piston. On the other hand, the heat loss ratio, namely the ratio of lost heat to the heat supplied by the fuel, is larger than in a gasoline engine.

Heat transfer coefficient on the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine

“…High q values were also registered at the measured points on the inner side of the piston top where the influence of squish was strong. 18,24 We infer that at the piston top land combustion flame cannot penetrate easily, and because of that q shows negative values after a crank angle of approximately 25°ATDC. As a result, heat transfer from piston top land through the crevice to the cylinder liner was registered.…”

“…The temperature scales of the vertical axis differ for the piston, cylinder liner, cylinder head and the intake/exhaust valves because the temperature ranges of these combustion chamber wall surfaces are all different. [18][19][20][21] For the piston, high temperatures were measured at the points around the inner circumference of the top surface and the upper part of the cavity side wall. 18 This was as a result of the contact with the hot combustion flame.…”

“…[18][19][20][21] For the piston, high temperatures were measured at the points around the inner circumference of the top surface and the upper part of the cavity side wall. 18 This was as a result of the contact with the hot combustion flame. In comparison, the temperature range for the entire piston top land was lower and the temperature amplitude was also smaller.…”

“…21 For the cylinder liner, 20 an observed tendency for each side is summarized as follows. The range of the temperature on the rear side is smaller than that on any of the other sides.…”

“…In this study, the new TFTs were used to obtain T w and q from 100 points on all the combustion chamber wall surfaces of a naturally aspirated, direct-injection (DI) diesel engine. [18][19][20][21] This article describes the process of deriving a g and a gm for all the combustion chamber wall surfaces of the DI diesel engine based on the measured data and the results thus obtained. In addition, a comparison was made of the experimentally measured a gm values and the values of a E and a W calculated, respectively, with Eichelberg's and Woschni's empirical equations for different engine speeds and ignition timings.…”