Investigation of exhaust flow and exergy fluctuations in a diesel engine

Abstract

In the present study, we investigated cyclic fluctuations of exhaust flow through measured variations in instantaneous pressure of the exhaust manifold and its implications on the exergy (the useful available energy) of exhaust flow of a single cylinder representation of a heavy-duty diesel engine over a range of operating conditions. The engine was operated at a speed of 1500 rpm and at loads of 2.5 bar and 5 bar brake mean effective pressure (BMEP) and different boost pressures (1.2 bar to 2.4 bar). Instantaneous exhaust pressures were measured over 1000 consecutive engine cycles by a piezoresistive exhaust sensor and instantaneous exhaust temperatures as well as mass flow rates were obtained by constructing GT-SUITE models. Cycle to cycle variations in magnitudes of maximum measured exhaust pressure, calculated exhaust temperature and phasing of the blowdown to displacement transition were analyzed. Additionally, cyclic variability in exhaust exergy components, i.e., thermal and mechanical exergies were estimated. The results show that the magnitude of the maximum exhaust pressure increased at higher engine load (i.e., from the average values of 1.63 bar to 2.00 bar at 2.5 bar BMEP to the average values of 1.78 bar to 2.16 bar at 5 bar BMEP). Also, the crank-resolved ensemble exergy rate in the exhaust process was higher at higher engine load and the return maps of the cumulative exergy at both engine loads exhibited a stochastic pattern. Furthermore, the mechanical component of exergy in the exhaust process had lower variations in comparison to the thermal component of exergy at both engine loads.