Investigations of the Influence of Mixture Preparation on Cyclic Variations in a SI-Engine, Using Laser Induced Fluorescence

Abstract

To study the effect of different injection timings on the charge inhomogeneity, planar laser-induced fluorescence (PLIF) was applied to an operating engine. Quantitative images of the fuel distribution within the engine were obtained. Since the fuel used, iso-octane, does not fluoresce, a dopant was required. Three-pentanone was found to have vapour pressure characteristics similar to those of iso-octane as well as low absorption and suitable spectral properties.A worst case estimation of the total accuracy from the PLIF images gives a maximum error of 0.03 in equivalence ratio. The results show that an early injection timing gives a higher degree of charge inhomogeneity close to the spark plug. It is also shown that charge inhomogeneity gives a more unstable engine operation. A correlation was noted between the combustion on a cycle to cycle basis and the average fuel concentration within a circular area close to the spark plug center. The correlation coefficient when a second order polynomial was fitted reached a value of -0.8 when the engine operated with a high degree of inhomogeneity. The highest correlation coefficient between the duration of 0-0.5% heat released and the average fuel concentration was obtained within a radius of approximately 5-10 mm from the spark plug. When the standard disc-shaped combustion chamber was replaced with a turbulence generating geometry, the inhomogeneity of the charge became very low, independent of injection timing. No cycle to cycle correlations between fuel/air equivalence ratio and combustion were then noted.

Supercharged Homogeneous Charge Compression Ignition

“…With a pressure transducer, indicated results can be used instead. The most important engine parameters are shown in table 1. Futher details on the engine can be found in [14].…”

“…In SI engines, large cycle-to-cycle variations occur since the early flame development varies considerably due to mixture inhomogeneities in the vicinity of the spark plug [1]. With HCCI, cycle-to-cycle variations of combustion are very small, since combustion initiation takes place at many points at the same time.…”

Planar Laser-Induced Fluorescence of H20 to Study the Influence of Residual Gases on Cycle-to-Cycle Variations in SI Engines

“…We have also performed a series of engine measurements with a variety of inlet pressures, air/fuel ratios and fuel flows. Because of the automotive engineering approach of these measurements, these results are presented in another paper (Johansson et al, 1995b).…”

“…The pressure traces were measured with a similar piezoelectric transducer, but equipped with a higher resolution A/D Downloaded by [Northeastern University] at 14:19 03 January 2015 converter (Data Translation, DT2823 100kHz, 16bit). For further experimental details, we refer to Johansson et al (1995b).…”

“…It is relatively straightforward to apply in engines and it allows for two-dimensional (or planar) imaging. Planar LIF (PLIF) has previously been applied to a running SI engine for imaging of a variety of species, e.g., OH-radicals (Felton et al, 1988;Becker et al, 1990) and fuel molecules (Andresen et al, 1990;Baritaud and Heinze, 1992;Wolff et al, 1994;Johansson et al, 1995b;Berckmiiller et al, 1997). An indirect method has been developed for measuring the residual gas distribution using PLIF, where the intake air is seeded with biacetyl and the residual gases can be identified as non-fluorescing portions in the images of the pre-ignition mixture (Deschamps and Baritaud, 1996).…”