Influence of Cavitation in the Injection Nozzle on Combustion in Diesel Engines

Abstract

This paper is concerned with the influence of cavitation in the injection nozzle on combustion in diesel engines. After an overview of the fundamental definitions to characterize nozzles — where above all the injection pressure, the back pressure, the injection mass flow, and the spray momentum through the nozzle as well as the geometry play a role — the difference between a cavitating and a non-cavitating nozzle will be clarified both theoretically and based on engine measurements. To observe the influence of cavitation on combustion in isolation, a cavitating and a non-cavitating nozzle were designed in such a way that they possessed the same mass flow and the same nozzle discharge velocity. In addition to the manufacturer's measurement, the nozzles were measured using a combined flowrate—spray momentum device at levels of injection pressure and back pressure close to those in an engine. A single-cylinder research engine with a modern common rail injection system served as the test engine for the experiments. The experiments revealed striking differences in emission levels. Especially notable are the differences in the soot values. To explore in more detail these differences between the cavitating and non-cavitating nozzle, optical investigations were conducted in an injection chamber. CCD high-speed imaging was used to visualize mixture formation of the two different nozzles.

Heat and mass transfer effects in the nozzle of a fuel injector from the start of needle lift to after the end of injection in the presence of fuel dribble and air entrainment

“…The resulting flow rate predicted by the k-ω SST model was found to match well the flow rate of the experiment in the first half of the injection event. A similar type of behaviour has been noticed in [87,88]. The k-ε model that appeared to be in better agreement with the experimental results in the first part of the simulation when the nominal pressure of 400 bar was applied, produced much lower flow rate with 360 bar than that shown in Figure 2.…”

On the rate of injection modeling applied to direct injection compression ignition engines

“…Usually, the injection strategy determines the achievement of the emission targets or the engine efficiency. 1,2 Due to the flexibility of the common rail injection system, a huge variety of strategies can be employed, going from the traditional single-injection event to the most sophisticated pilot-main-post multi-injection cases, where the diversity of possibilities involves the injection duration and the separation between them, with further consequences on the combustion–emission performance.…”

Fuel concentration in isothermal Diesel sprays through structured planar laser imaging measurements

“…In direct injection Diesel engine, the injection law mainly drives the combustion process and therefore, the global mixing is directly related to the development of sprays [2,3,4]. At the same time, analyzing sprays out of a multi-hole nozzle in an engine is really challenging and for that reason, researchers often have recourse to specific installations.…”