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New Conceptual Insights into Diesel Engine Fuel-Injection Processes

By combining advanced theory and high-fidelity large eddy simulation, Combustion Research Facility (CRF) researchers Rainer Dahms and Joe Oefelein (both in 8351) have provided new conceptual insights that promise to improve the understanding and prediction of fuel-injection processes in high-pressure diesel engine conditions. Their results, which experiments performed by CRF researchers Lyle Pickett and Julien Manin (both in 8362) corroborated, have demonstrated that under certain high-pressure conditions the distinct interface between the injected liquid and ambient gas vanishes.

Regime diagram (left) for n-dodecane injected into nitrogen at various ambient pressure and temperature conditions. The diagram suggests dense-fluid jet presence (grey region) under diesel-engine conditions (highlighted area) without drop formation. Classical spray processes (white region) do not necessarily apply at such conditions. High-speed imaging (right) of both a dense-fluid jet (top) and a spray (bottom) corroborates the theory.

Regime diagram (left) for n-dodecane injected into nitrogen at various ambient pressure and temperature conditions. The diagram suggests dense-fluid jet presence (grey region) under diesel-engine conditions (highlighted area) without drop formation. Classical spray processes (white region) do not necessarily apply at such conditions. High-speed imaging (right) of both a dense-fluid jet (top) and a spray (bottom) corroborates the theory.

Their result suggests that, contrary to conventional wisdom, classical spray phenomena do not occur under typical diesel-engine injection conditions. Instead, fuel is injected as a dense-fluid jet with diminished surface-tension forces leading to diffusion-dominated mixing dynamics—the injected fuel evolves without droplet formation or evaporation, raising questions about the validity of widely applied spray atomization models for such high-pressure conditions. This new conceptual insight should prove important to refining predictive combustion and emissions models, which could ultimately be used to design cleaner, more efficient diesel engines.

Read the full article in CRF News.

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