A Specifically Designed Injector for Controlled Lube Oil Addition in View of Investigation of Pre-Ignition Phenomena in Dual–Fuel/Gas Engines

Abstract

Internal combustion engines will continue to play a role during a transitional phase, especially in heavy-duty or marine applications. In this context, lean-burn gas/dual-fuel combustion is an attractive concept to reduce CO2, combined with considerably lower particulate and NOX pollution, and with efficiencies comparable to diesel combustion. However, ignition processes still pose considerable challenges, with pre-ignition in particular being a major issue. The underlying mechanisms are probably based on self-ignition of lube oil in hot zones. In order to investigate fundamentals of such phenomena in optically accessible test rigs, a novel injector was specifically developed to induce pre-ignitions artificially. The so-called “PieZo-Droplet-Injector” (PZDI) enables dosing of minor amounts of lubricating oil or even the injection of single droplets with diameters in the range of 100–200 µm. The working principle relies on a needle actuated with a piezo stack, which pushes a certain amount of lube oil in a bore so that (even single) droplets can be ejected through an adjustable nozzle. To confirm the PZDI functionality and to investigate droplet characteristics based on adjustable operating parameters, tests were performed under ambient conditions as well as in a constant volume combustion chamber under reasonable pressure and temperature conditions. Overall, the PZDI showed an excellent behavior in terms of capabilities to inject small amounts or even single droplets of lube oil. At last, this specially developed injector allows selective lube oil addition in an optically accessible engine test facility for upcoming examination of pre-ignition phenomena under real operating conditions.

Experimental study of lube oil pre-ignition in an optical gas engine test rig

“…First investigations were carried out on an optically accessible constant volume combustion chamber (CVCC) 21 to examine the injection performance of the injectors under reasonable pressure and temperature conditions. 15 Possibilities of lube oil injection and the subsequent droplet formation, characteristics and penetration was investigated for distinct injector operating parameters under different ambient conditions as well as to generate validation data on the temporal course of droplet evaporation for a corresponding simulation model. The specifically designed piezo droplet injector (PZDI) showed an excellent behavior in terms of capabilities to inject small amounts or even single droplets of lube oil even under engine-like conditions at the CVCC.…”

“…A previous investigation studies the fundamentals of the underlying mechanisms of pre-ignition of lube oil in hot zones in an optically accessible test rig with a novel injector that was specifically developed to induce preignitions artificially. 15 To investigate droplet characteristics based on adjustable operating parameters, tests were performed under ambient conditions as well as in a constant volume combustion chamber under engine relevant pressure and temperature conditions. As a first step, the injector able to produce small lube oil droplets under both ambient conditions and at elevated pressure levels.…”