In this experimental work, an optically accessible rapid compression machine is used to study the ignition and combustion process under engine relevant operation conditions for five different air-natural gas equivalence ratios (λ) ignited with either 12.2 mg or 6.7 mg of pilot diesel injected at 1,600 bar.Initial temperature of the ambient mixture, walls and injector was 333 K. Additionally, for the short (6.7 mg) diesel injection, the variation in the ID (ignition delay) for two higher ambient temperatures (343 K and 353 K) was measured.Pressure and piston displacement are recorded while two high-speed cameras simultaneously capture signals in the visible range spectrum and at 305 nm wavelength for OH* chemiluminescence respectively.ID is measured both from OH* and pressure rise.From the recorded data, the heat release ratio is estimated and compared with the visual signals.This gives an insight of the temporal and spatial evolution of the flame, as well as a qualitative perception of the transition from spray ignition into a premixed flame in the ambient fuel-air mixture.It was found that increasing the methane concertation delays the ignition, reduces the natural flame luminosity and enhances the OH* chemiluminescence signal.
: Controlling of the solution and precipitation for microalloying additions of Nb, V, Ti and their combination is the basic building block of microalloyed steels. Among three microalloying elements, Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing (TMP). However, Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process. What is more, hot working is usually carried out at high temperatures in the recrystallization regime, so it is difficult to exert conventional controlled rolling to obtain pancaked austenite, which has further affected the research and application of Nb in medium carbon long products. Because of these factors, studies of Nb in medium carbon long products were incomplete, and even some recognitions and conclusions are subjected to debate. In order to clarify the strengthening effects of Nb in medium carbon long products, the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working, cooling processes. In addition, qualitative and quantitative analyses of Nb’s state and distribution in reheating, rolling and cooling had been carried out to illustrate some singularities.
: Indium tin oxide (ITO) heating film is primarily used as the defogging component of an instrument observation window. Conventionally, a constant current is used to heat the film. Through the feedback of the temperature sensing component, the output current is adjusted to achieve a set temperature. However, the temperature of the heating film is nonuniformly distributed, and determining the correct output current is time-consuming. This study adopted finite element heat transfer analysis to determine a heating method (such as heat power and heat flux) for an ITO conductive heating film system. The results of the analysis may serve as a reference for temperature compensation in ITO conductive heating films.
: This paper provides a power series solution to the Duffing-harmonic oscillator and compares the frequencies with those obtained by the harmonic balance method. To capture the periodic motion of the oscillator, the power series expansion is used upon transforming the time variable into an “oscillating time” which reduces the governing equation to a form well-conditioned for a power series solution. A recurrence equation for the series coefficients is established in terms of the “oscillating time” frequency which is then determined by employing Rayleigh’s energy principle. The response of the oscillator is compared with a numerical solution and good agreement is demonstrated.
: An analytical approach based on the power series method is used to analyze the free vibration of a cantilever beam with geometric and inertia nonlinearities. The time variable is transformed into a “harmonically oscillating time” variable which transforms the governing equation into a form well-conditioned for a power series analysis. Rayleigh’s energy principle is also used to determine the vibration frequency. Convergence of the power series solution is demonstrated and excellent agreement is seen for the vibration response with a numerical solution.
