High-speed Color Camera Research Articles

Visualization of auto-ignition and pressure wave during knocking in a hydrogen spark-ignition engine

Visualizations of auto-ignition inside the end-gas region due to flame propagation and pressure waves that occur during knocking were carried out in a hydrogen spark-ignition engine using a high-speed camera. Our results demonstrated that auto-ignition in an end-gas region that was compressed by the propagating flame front could be visualized using the high-speed color camera. A large amount of unburned mixture caused by the auto-ignited kernel explosion generated the strong pressure waves. Strong pressure wave oscillations induced by the initial auto-ignition could be visualized using a video camera with a speed of 250 kframes/s. The auto-ignition and pressure waves caused the thermal boundary layer to breakdown near the cylinder wall and piston head, therefore combustion of the lubricant oil grease was visible inside burned gas region. This auto-ignition and pressure waves may result in damage to the cylinder wall and piston head during engine knocking.

Frequency response of a surface thermometer based on unencapsulated thermochromic liquid crystals

Thermochromic liquid crystals (TLCs) are used by many researchers for temperature field analysis in fluid dynamic experiments. This study is targed on the transient behaviour of a TLC system. Therefore, unencapsulated TLCs are filled into flat microchannels by capillary forces, whereby different thicknesses of the TLC layer could be realised. On the back side of the TLC channel a thin metallic foil is used as a plane electric heater, which allows harmonic stimulation at variable frequencies. Evaluation of the TLC temperature response was realised by analysing the fluctuation of the TLC colour play using a high speed colour camera with a frame rate of 1000 Hz. In a test series different TLC layers (10, 20 and 30 μm thick) were investigated with harmonic stimulations at frequencies between 3 and 70 Hz. Additionally, the specific heat of the pure TLC substance was measured accurately with a differential scanning calorimeter (DSC). The system was described with an analytical approach and modelled with a MATLAB partial differential equation (PDE) tool. It was figured out that inside the analysed frequency band the amplitude of the TLC temperature response is attenuated and the phase is shifted in contrast to the temperature of the plain heating foil. The ratio of the amplitudes is about 20% with a 30 μm thick TLC layer and about 35% with a 10 μm TLC layer. The maximum frequency where a detectable sine curve could be displayed was around 70 Hz. Validation with numerical results shows that most of the amplitude attenuation and phase shift is caused by heat conduction. A residual permanent phase shift of about 1 ms might be caused by an averaging process over the thickness of the TLC layer, or it is an intrinsic physical lag of the TLC molecules. However, for transient processes inside the analysed frequency range numeric calculations or solutions of the inverse heat conduction problem are required to obtain the actual temperature of the heater surface.

Experimental study of nucleate boiling heat transfer under low gravity conditions using TLCs for high resolution temperature measurements

Heat transfer in nucleate boiling is strongly influenced by a very small circular area in the vicinity of the three phase contact line where a thin liquid film approaches the heated wall. This area is characterised by high evaporation rates which trigger a local temperature drop in the wall. The wall temperature drop can be computed using an existing nucleate boiling model. To verify the complex model and the underlying assumptions, an experiment was designed with an artificial nucleation site in a thin electrically heated wall featuring a two-dimensional, high resolution temperature measurement technique using unencapsulated thermochromic liquid crystals and a high speed colour camera. The shape of the bubble is observed simultaneously with a second high speed camera. Experiments were conducted in a low gravity environment of a parabolic flight, causing larger bubble departure diameters than in normal gravity environments. Thus, it was possible to measure the evolution of the predicted temperature drop in a transient boiling process.

Effect of second handle positions on EMG activities during snow shoveling

When a flame passes along a tube that is open at both ends a self induced fluctuating pressure/flow field is created which the flame has to traverse. Here fuel rich (1.1 < ϕ < 1.4) propane-air flames have been filmed travelling along a 20 mm internal diameter quartz tube. Fluctuations in the flame’s progression were observed to increase as the flame propagated, achieving a maximum oscillation amplitude of ±10 mm at 220 Hz that decayed as the flame progressed further towards the end of the tube. The impact of the periodic pressure gradients on the flame shape could be discerned with tongues of unburned reactants pushed into the products as well as the corresponding rapid acceleration of the flame into the unburned mixture. The impact of the fluctuations on flame chemistry was monitored by capturing the CH∗ and C2 chemiluminescence using a high speed colour camera. The CH∗/C2∗ ratio was observed to decrease as the flame was pulled back towards the burned mixture; and increased when the flame was pushed forwards. This was consistent throughout the flame progress even when small oscillations in the flame position were measured. This could be a significant feature of flames in this environment.

Pure rolling elastohydrodynamic lubrication of short stroke reciprocating motion

The behavior of point contact elastohydrodynamic lubrication (EHL) films under pure rolling short stroke reciprocating motion is investigated using both optical interferometry technique and theoretical analysis. The EHL films are recorded with a high-speed color camera and simulated with multigrid techniques. General variation of oil film under point contact reciprocating motion is explained by a comparison between a fully flooded simulation and an experiment with a frequency of 7.78 Hz. Influence of starvation is considered by another simulation under a higher working frequency of 14.4 Hz and the simulated results are compared with experimental results. Both simulations show good agreements quantitatively with experiments. In addition, general tribo-characteristics of EHL under fully flooded and starved conditions are discussed.