Experimental investigation of a spray from a multi-jet common rail injection system for small engines

This paper illustrates the results of an experimental investigation on the liquid fuel spray from a multi-jet, common-rail injection system both under non-evaporative and evaporative conditions. Tests have been taken using a 5-hole, 0.13 mm diameter, 150\mD spray angle, micro-sac nozzle having a flow rate of 270 cm3/30 sec@10 MPa exploring different injection strategies. Experiments have been taken, under non-evaporative conditions, injecting the fuel within stagnant inert gas, at different densities, in a high-pressure optically-accessible cylindrical vessel with three large quartz windows. Under evaporative conditions, the experiments have been taken within a crank-case scavenged single-cylinder, 2-stroke direct injection diesel engine provided of optical accesses to the combustion chamber. It allows to study the fuel injection process under thermodynamic conditions similar to those currently reached in modern direct injection diesel engines. The air velocity field within the combustion chamber is low enough to assume that the fuel is injected at quiescent conditions, guaranteeing the same fluid flow conditions as those reproduced for tests within the vessel for non-evaporative spray conditions. The investigation has allowed to assess the management of timing and quantity up to 3 consecutive injections on the accuracy and stability of the delivered fuel as well the effect of the gas density on the liquid spray penetration. The exploration has also been focused on the effect of short dwell time on the stability of the mass flow rate injected during the pre-injection matching measurements of the amount of delivered fuel to images of the spray.