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The Influence of Fuel Properties on Transient Liquid-Phase Spray Geometry and on Cl-Combustion Characteristics
Abstract:
A transparent HSDI CI engine was used together with a high speed camera to analyze the liquid phase spray geometry of the fuel types: Swedish environmental class 1 Diesel fuel (MK1), Soy Methyl Ester (B100), n-Heptane (PRF0) and a gas-to-liquid derivate (GTL) with a distillation range similar to B100.
The study of the transient liquid-phase spray propagation was performed at gas temperatures and pressures typical for start of injection conditions of a conventional HSDI CI engine. Inert gas was supplied to the transparent engine in order to avoid self-ignition at these cylinder gas conditions.
Observed differences in liquid phase spray geometry were correlated to relevant fuel properties. An empirical relation was derived for predicting liquid spray cone angle and length prior to ignition. Fuel dependent differences in heat-release and emission characteristics from an all-metal engine at similar test conditions were explained by the former correlation and observations from the transparent engine.
It turned out that the cylinder gas density had the strongest effect on both the measured liquid spray angle and the liquid length for fuel with high volatility. Moreover it was observed that the inverse correlation between liquid spray length and cylinder gas density decreased with fuel volatility which had a strong effect on combustion and emission characteristics under highly premixed combustion at low load conditions.
The injection pressure was found to be a major combustion controlling parameter in order to compensate for deteriorated combustion properties of low volatile fuels at highly premixed combustion.
Even though B100 and GTL have similar volatility and liquid spray properties, the combustion behaviour differed considerably which was explained by the difference of oxidizer-fuel ratio at locally fuel-rich conditions.