A comparison between cylinder charge composition of common rail diesel engine

Abstract

Using a diesel passenger-car, we measured charge composition and emissions of nitrogen oxide and soot, on the European extra-urban drive cycle (EUDC), and also on isolated transients, representative of the EUDC. Our objective was to compare emissions and charge composition, between a transient, and engine operation at specific points on the transient locus ('quasi-steadystate'). On the EUDC, we measured two nitrogen oxide spikes. The first, fast-response nitrogen oxide spike, could be ascribed to the pedal demand step input: this is small, compared to the second nitrogen oxide spike resulting from the remainder of the transient (adjustments in speed and load). The estimated charge composition, in a transient, agreed closely with the measurement, both qualitatively and quantitatively. The burned-gas fraction (BGF), estimated from a transient, revealed that the period of largest discrepancy from that demanded, is short (≈1 sec). This indicates that the use of BGF, rather than the customary mass air-flow, may be more apposite during transients encountered in real driving. However, since this discrepancy is short-lived, the realisable reduction in overall NOx emissions, using BGF as a controlled variable, at least during the EUDC, is likely to be small. BGF-based control is nevertheless attractive, insofar as boundary conditions bearing direct relationships to combustion are easily imposed.