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The present study investigated the effects of biodiesel blending under a wide range of intake oxygen concentration levels in a diesel engine. This study attempted to identify the lowest biodiesel blending rate that achieves acceptable levels of nitric oxides (NOx), soot, and coefficient of variation in the indicated mean effective pressure (COVIMEP). Biodiesel blending was to be minimized in order to reduce the fuel penalty associated with the biodiesels lower caloric value. Engine experiments were performed in a 1-liter single-cylinder diesel engine at an engine speed of 1400 rev/min under a medium load condition. The blend rate and intake oxygen concentration were varied independently of each other at a constant intake pressure of 200 kPa. The biodiesel blend rate varied from 0% (B000) to 100% biodiesel (B100) at a 20% increment. The intake oxygen level was adjusted from 8 to 19% by volume (vol %) in order to embrace both conventional and low-temperature combustion (LTC) operations. A fixed injection duration of 788 μs at a fuel rail pressure of 160 MPa exhibited a gross indicated mean effective pressure (IMEP) between 750 kPa and 910 kPa, depending on the intake oxygen concentration. The experimental results indicated that the intake oxygen level had to be below 10 vol% to achieve the indicated specific NOx (ISNOx) below 0.2g/kWhr with the B000 fuel. However, a substantial soot increase was exhibited at such a low intake oxygen level. Biodiesel blending reduced NOx until the blending rate reached 60% with reduced in-cylinder temperature due to lower total energy release. As a result, 60%-biodiesel blended diesel (B060) achieved NOx, soot, and COVIMEP of 0.2 g/kWhr, 0.37 filter smoke number (FSN), and 0.5, respectively, at an intake oxygen concentration of 14 vol%. The corresponding indicated thermal efficiency was 43.2%.

In-cylinder imaging of unburned hydrocarbon (UHC) distributions was performed via planar laser-induced fluorescence (PLIF) in a light-duty diesel engine employing a partially-premixed compression ignition (PPCI) combustion scheme.Measurernents were acquired in the bowl and clearance volume at a light load baseline condition with optimized iniectiontiming. With the fueling rate held constant, the iniection timing was both advanced and retarded to help clarify the source of high level UHC emissions. The UHC composition was fhrther investigated by spectral analysis of the fluorescence signal, Three major UHC sources were identified: nozzle dribble from the iniector tip, low-temperature mixture ofincomplete reactants within the cylinder core surrounding the iajectoT and crevice region fuel accumulation along the cylinder sidewalls. Iajection timing was fbund to infiuence UHC composition and concentration in each ofthe identified regions, amounts of CH20 are present only in low-temperature regions (T< 1200 K), associated with overly-lean (ip < O.5) or excessively-rich (ta > 3.S) mixtures. Since PAHs are forrned in hot, panially-reacted rich regions (T> 1500 K, ip>2) [15], they are expected to co-exist with fbrmaldehyde only