P. G. Felton

Fractals and turbulent premixed engine flames

Abstract The fractal nature of premixed turbulent flames in an internal combustion engine is examined. A sheet of laser light, approximately 200 μm thick, is shone through the cylinder of a single-cylinder ported internal combustion engine. The homogeneous charge of propane and air is seeded with submicron TiO 2 particles and the scattered light is collected through a quartz window in the engine head and is imaged on a 100 × 100 diode array camera. The number density of the TiO 2 particles scales with the gas density so that a two-dimensional map of reactants and products is obtained. A field of view 2 × 2 cm in the center of the cylinder is examined and fractal analysis is performed on the front separating reactants from products. Results are presented for two equivalence ratios and three engine speeds, corresponding to different laminar flame speeds S 1 , laminar flame thicknesses δ 1 , turbulent intensities u ′, and Kolmogorov scales η. The examined flames were found to exhibit fractal character within a range of length scales as low as 200 μm and as high as 4.5 mm, which is twice the measured lateral integral length scale in this engine configuration. At stoichiometric conditions, the fractal dimension of the flame surface is found to be statistically different for engine speeds of 300, 1200, and 2400 rpm ( u′ S 1 = 0.5, 2, and 4 ). It increases with increasing u′ S 1 . At lean conditions (Φ = 0.59), when u′ S 1 ⪢ 1 , the fractal dimension does not change with engine speed. For 4 ≤ u′ S 1 and 0.1 η δ 1 ≤ 1 (estimated ranges), the fractal dimension is 2.36 ± 3%. A turbulent flame speed model based on fractal analysis is also briefly examined.

Preliminary turbulence length scale measurements in a motored IC engine

A recently developed laser Doppler velocimetry system for making two-point spatial correlation measurements of velocity fluctuations has been applied to the turbulent flow field of an IC engine. Fluctuation integral length scales have been measured within the clearance volume of a ported, single cylinder engine with a disc-shaped chamber and a compression ratio of 8.0. The engine was motored at 600 rpm and the engine flow field had a swirl ratio at top dead center of approximately 4. These measurements were made at the center of the clearance height at three-quarters of the cylinder radius. The integral length scale was found to reach a minimum of approximately one-fifth of the clearance height near TDC. Comparison of the results obtained using this technique with the integral length scales measured in engines by others authors using different methods gives agreement to within a factor of two.

Initial Two-Dimensional Laser Induced Fluorescence Measurements of OH Radicals in an Internal Combustion Engine

The imaging of two-dimensional laser-induced fluorescence is used for simultaneous, multiple point visualization of OH radical concentration in the combustion chamber of a single cylinder internal combustion engine. Sheet illumination from the frequency doubled output of a Nd:YAG pumped dye laser is used to excite the fluorescence which is detected using an image-intensified Reticon diode array camera. The camera is interfaced to an IBM-PC AT microcomputer for data acquisition and processing. The laser and camera are synchronized with the crankshaft of the engine so that 2-D images of the OH fluorescence can be obtained at different times through the engine cycle.

2-D Visualization of liquid and Vapor Fuel in an I.C. Engine

A sheet of laser light from a frequency tripled Nd-YAG laser approximately 200 μm thick is shone through the combustion chamber of a single cylinder, direct injection internal combustion engine. The injected decane contains exciplex-forming dopants which produce spectrally separated fluorescence from the liquid and vapor phases. The fluorescence signal is collected through a quartz window in the cylinder head and is imaged onto a diode array camera. The camera is interfaced to a microcomputer for data acquisition and processing. The laser and camera are synchronized with the crankshaft of the engine so that 2-D images of the liquid and vapor phase fuel distributions can be obtained at different times during the engine cycle

Two-color particle image velocimetry technique for an internal combustion engine

Abstract A two-color particle image velocimetry (PIV) technique has been applied to a single-cylinder motored research engine. Two-color PIV is a quantitative planar velocity measurement technique that can unambiguously determine the velocity magnitude and direction. The work includes the development of an interrogation system, a series of computer simulations to determine the performance of the technique under various conditions, the comparison of these results to similar ones obtained for an autocorrelation PIV system, and a test of the technique by reconstructing the velocity field of a uniform jet flow. The technique was then applied to the in-cylinder flow field of a motored single-cylinder, cup-in-head, research engine. A total of 27 instantaneous velocity fields were obtained at a single measurement plane for a single operating condition of the engine. The data were analyzed to yield ensemble-averaged velocity and velocity fluctuation.