Effects of EGR Addition onto Combustion Stability and Alternator Performance Variability of a Small, Single-Cylinder Diesel Generator 2016-32-0063

The aim of this investigation was to improve understanding and quantify the impact of exhaust gas recirculation (EGR) as an emissions control measure onto cyclic variability of a small-bore, single-cylinder, diesel-fueled compression-ignition (CI) power generation unit. Of special interest were how cycle-to-cycle variations of the CI engine affect steady-state voltage deviations and frequency bandwidths. Furthermore, the study strived to elucidate the impact of EGR addition onto combustion parameters, as well as gaseous and particle phase emissions along with fuel consumption. The power generation unit was operated over five discrete steady-state test modes, representative of nominal 0, 25, 50, 75, and 100% engine load (i.e. 0-484kPa BMEP), by absorbing electrical power via a resistive load bank. The engine was equipped with a passive EGR system that directly connected the exhaust and intake runners through a small passage.

Analysis of combustion parameters indicated no distinct increase in cycle-to-cycle variability observed during EGR addition to the intake charge. Moreover, absolute combustion parameters proved conclusive to published literature. COV_IMEP was observed to slightly increase for low load modes, however, reduce for higher load modes with the addition of EGR, whereas COV_Pmax indicated the cyclic variability to decrease as a function of EGR addition which was hypothesized to be due to an increase in equivalence ratio towards a less lean combustion. COV for other parameters showed a distinct change around 50% engine load with variability being lower for tests with EGR during low load modes. In comparison, variability in engine parameters was higher as load increased compared to tests without EGR.

Alteration in combustion due to the addition of EGR to the intake was observed to influence the magnitude of the AC frequency. This was primarily caused by the changing in-cylinder pressure that affected engine speed, and thus, frequency of the AC voltage. A similar impact was also noticed for the AC voltage; however, changes in electrical load were the dominating factor affecting the voltage. In general, the addition of EGR appeared to have a stronger impact on increasing variability in alternator performance parameters for higher load operation, which was in agreement with variability in combustion parameters that were observed to increase more predominantly for higher load modes when EGR was added.