Abstract
In a collaborative effort to identify key aspects of heavy-duty diesel injector behavior, the Engine Combustion Network (ECN) Spray C and Spray D injectors were characterized in three independent research laboratories using constant volume pre-burn vessels and a heated constant-pressure vessel. This work reports on experiments with nominally identical injectors used in different optically accessible combustion chambers, where one of the injectors was designed intentionally to promote cavitation. Optical diagnostic techniques specifically targeted liquid- and vapor-phase penetration, combustion indicators, and sooting behavior over a large range of ambient temperatures—from 850 K to 1100 K. Because the large-orifice injectors employed in this work result in flame lengths that extend well beyond the optical diagnostics’ field-of-view, a novel method using a characteristic volume is proposed for quantitative comparison of soot under such conditions. Further, the viability of extrapolating these measurements downstream is considered. The results reported in this publication explain trends and unique characteristics of the two different injectors over a range of conditions and serve as calibration targets for numerical efforts within the ECN consortium and beyond. Building on agreement for experimental results from different institutions under inert conditions, apparent differences found in combustion indicators and sooting behavior are addressed and explained. Ignition delay and soot onset are correlated and the results demonstrate the sensitivity of soot formation to the major species of the ambient gas (i.e., carbon dioxide, water, and nitrogen in the pre-burn ambient versus nitrogen only in the constant pressure vessel) when holding ambient oxygen volume percent constant.
Highlights
Emissions of particulate matter (PM) and nitric oxides (NOx) from compression-ignition engines have been curbed significantly over the past few decades
Using the procedure for projected liquid volume fraction described above, liquid length values were evaluated based on a time-averaged result between 1 and 3 ms after SOI for different ambient temperatures at IFP Energies Nouvelles (IFPEN) (Fig. 2)
The two different injectors considered in this work have minimal differences in mass flow and orifice diameter size; one of the injectors was manufactured with a straight hole and sharp orifice inlet to induce cavitation, while the other injector was subjected to hydro-erosive grinding and features a converging hole
Summary
Emissions of particulate matter (PM) and nitric oxides (NOx) from compression-ignition engines have been curbed significantly over the past few decades. Improved fuel/air mixing prior to the time of high-temperature ignition or upstream of the location where a mixing-controlled diesel jet flame stabilizes (i.e., the lift-off length) has been shown to be effective in reducing soot emissions [3,4]. Another injector with a conical (or converging tapered) hole that decreases the amount of cavitation, and the mass flow due to the reduced exit orifice diameter, produces more soot than the identical straight-hole version while injecting less fuel Their findings are based on a relatively reactive environment with a fixed ambient temperature of 1000 K and an ambient oxygen concentration of 21% O2, and it appears that there are confounding effects. The study provides new understanding as to how cavitation influences fuel-air mixing, ignition, high-temperature heat release, and soot formation for different gas temperature and pressures
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