Measurements of the mass allocation for multiple injection strategies using the rate of injection and momentum flux signals

Abstract

As legislations set very stringent environmental and fuel economy standards, researchers have pushed into a continuous development in all areas of the diesel engine. The recent evolution of the injection technologies has permitted to modify the fuel-delivery strategies. From what was a single pulse per injection event, modern systems allow to inject up to eight different times precisely per combustion cycle. In such sense, experimental results of the rate of injection and momentum flux could be useful for validation and improvement of computational models. Moreover, accurately quantifying the injected mass per pulse in a fuel–gas interface can provide data with more realistic engine-like conditions. To this end, this research presents measurements of the rate of injection and momentum flux for two simple multiple injection strategies: a pilot-main and a main-post. Boundary conditions included two rail and discharge pressures, two different pilot/post quantities and four dwell times. A new approach was employed to estimate the mass allocation with the momentum flux data, and results were compared to the rate of injection traces to verify the distribution calculated. On the results, signals for each pulse were successfully decoupled using its rising and falling edge. The shot-to-shot variability of the pilot/post injection was highly dependent on its transitory characteristics, and on the dwell time for post injections due to internal pressure waves. The injected mass per pulse was successfully measured as well in the momentum flux test rig, and the energizing time changed slightly to account for the different operation interfaces. Signals from both measurement campaigns showed a remarkable agreement when compared, ascertain the possibility of measuring the injected mass, and its allocation for multiple injection strategies, in the momentum flux test rig.