Exhaust Phases in a DI Diesel Engine Based on Instantaneous Cyclic Heat Transfer Experimental Data 2013-01-1646
In the present paper a new method is proposed for the analysis of the two main phases of the engine exhaust stroke blowdown and displacement. The method is based on the processing of fast-response experimental temperatures obtained from the exhaust manifold wall during the engine cycle. A novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the long- and the short- term response ones. This has been achieved by processing the respective signals acquired from 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. For the experimental procedure a direct injection (DI), air-cooled diesel engine is used. One-dimensional heat conduction theory with Fourier analyses techniques are implemented to calculate the instantaneous local heat flux in the exhaust manifold wall surfaces. To estimate the duration of the different phases of exhaust stroke a numerical method is developed which makes use of first and second temporal derivatives of exhaust manifold wall temperature. The analysis reveals the effect of engine speed and load on the initiation (engine crank angle) and duration of both blowdown and displacement exhaust phases. In addition, the distribution of instantaneous wall temperatures and heat fluxes between the different exhaust phases is analyzed indicating several important characteristics. The results reveal that duration of blowdown phase is correlated adequately with cylinder pressure at the point of Exhaust Valve Opening.