Delivery-Valve Effects on the Performance of an Automotive Diesel Fuel-Injection System

An integrated theoretical and experimental investigation was carried out in order to evaluate the effects that the pump delivery-valve assembly can produce on the performance of a pump-line-nozzle fuel-injection system with a distributor-type pump for automotive diesel engines.

Four distinct delivery valves, one constant-pressure valve, one reflux-hole and two relief-volume valves, were separately fitted to the pump and for each configuration of the delivery assembly the system behavior was analyzed under full-load steady-state operations in a wide pump angular-speed range. Fuel injection-rate as well as local pressure time-histories were investigated, paying specific attention to the occurrence and temporal evolution of cavitation phenomena in the pressure pipe and injector nozzle, after the valve closure. The flow across the delivery-valve assembly was theoretically examined in order to ascertain any instability sources as possible causes of cyclic fluctuations.

The previously developed NAIS code, based on a novel implicit numerical algorithm of the second-order accuracy, was employed for theoretical analysis. The potentialities of the simulation program as a powerful research and design tool complementary to experimentation were shown by the reliable prediction of the cause and effect relationship in some anomalies of the injection system behavior.