Experimental Assessment of Instantaneous Heat Transfer in the Combustion Chamber and Exhaust Manifold Walls of Air-Cooled Direct Injection Diesel Engine

Abstract

An experimental analysis is carried out to investigate several heat transfer characteristics during the engine cycle, in the combustion chamber and exhaust manifold walls of a direct injection (DI), air-cooled, diesel engine. For this purpose, a novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the longand the short-term response ones, processing the respective signals in two independent data acquisition systems. Furthermore, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object-oriented, control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams together with semi-empirical equations for instantaneous heat transfer were used as basis for the calculation of overall heat transfer coefficient. On the other hand, one-dimensional heat conduction theory with Fourier analysis techniques combined with an iterative procedure between calculated and measured temperature data are implemented, in order to calculate the instantaneous local engine cylinder heat transfer coefficients in the cylinder head surfaces. For the exhaust manifold, the local gas temperature was calculated based on a thermal-zone model approach developed. Analysis of experimental results revealed significant differences between the overall and local peak heat transfer coefficient values in the cylinder head surface. The effect of engine speed and load as well as the effect of air-swirling motion on cylinder head heat transfer coefficient variation are presented and quantified, revealing the significant influence of turbulence on local heat transfer conditions. The effect of valve motion on instantaneous heat transfer is also depicted and quantified. Analysis of the results for the instantaneous wall temperatures and heat transfer coefficient on the exhaust manifold reveals interesting details regarding the flow of exhaust gases, both in the blowdown and displacement phases of the engine exhaust stroke. From the results it is concluded that the instantaneous heat transfer coefficient variation for engine combustion chamber is highly non-uniform, unlike its values calculated from standard correlations that assume spatial uniformity. This is very important, since especially for air-cooled diesel engines limited relevant information seems to exist in the literature.

Effect of combustion regime on in-cylinder heat transfer in internal combustion engines

“…For the CDC mode, the location of the flame front determines the local heat transfer loss. 41 As can be seen in Figure 6(a), the heat flux is relatively small prior to the arrival of the flame, and the wall heat flux sharply increases when the diesel flame front impinges on the wall with the maximum in-cylinder temperature exceeding 2200 K. The heat flux distribution in CDC combustion is highly non-uniform. Since the combustion mostly takes place within the piston bowl with higher gas temperature and turbulence kinetic energy (see Figures 4(a) and 5(a)), the heat flux within the piston bowl is much higher than at other locations.…”

Analysis and evaluation of the thermal shock phenomena in the in-cylinder surfaces of a DI diesel engine during its transient operation

“…The reasons for this failure are described in detail in reference [49]. Therefore, in this work the results for the cylinder head will be presented only from sensor HT#1 together with results for the exhaust manifold from sensor HT#4.…”

Effects of transient diesel engine operation on its cyclic heat transfer: an experimental assessment

“…The model for the processing and analysis of experimental data has been developed by the authors. It is an adaptation for the case of transient engine operation of a similar model presented already in previous publications [32,46,49,50]. The procedure consists of the following submodels:…”

“…The last of the above submodels concerning the estimation of heat transfer coefficient will not be used in the present paper due to space limitations: it will be the subject of a future communication. Details on this submodel concerning analysis and calculation of heat transfer coefficient (HTC) variation both for the combustion chamber and exhaust manifold surfaces during steady state can be found in reference [50].…”

“…Within this framework, they have already reported detailed structural and thermodynamic analysis models [31,45,46], which are also capable of taking into account the heat transfer behaviour of the insulated engine [47]. They also reported in detail the short-term variations of instantaneous diesel engine heat flux and temperature during an engine cycle [32,[48][49][50]. Recently, they have also published the first results of their research work [51] aiming to explore the changes occurring in the mechanism of instantaneous cyclic heat transfer during transient engine operation.…”