Combustion Characteristics of a Single Cylinder Spark Ignition Engine Fueled with Coal Mine Methane

An experimental investigation was conducted on combustion characteristics of a single cylinder spark ignition engine fueled with coal-mine methane （CMM）.The CMM was simulated by the compressed nature gas （CNG）/nitrogen blend fuels.The cylinder pressure was measured.The maximum heat release ratio,the flame development duration and the main combustion duration were analyzed with the nitrogen volume fraction in the blends changing from 0% to 35%.The results indicate that the maximum cylinder pressure,the maximum rate of pressure,the flame development duration and the main combustion duration increase and the maximum rate of heat release decreases with increasing nitrogen fraction.When the level of nitrogen volume fraction in coalmine methane is lower than 20%,the combustion process of engine is stable.But with the level of nitrogen volume fraction over 30%,the cycle to cycle combustion variation is large,especially under low load condition.

Theoretical Study of Fatigue Limit for Crack

The material parameter ρ*=4c/σ-13 is put forward, which represents the crack tip radius independent of crack length under the action of the fatigue limit stress. According to the fatigue notch factor of the crack propagation, Kt=Kt1/（3+n）=（4d/ρ*）1/3, the fatigue limits of sharp notch, long crack and short crack are calculated, which are very close to the measurements. The calculated results make it clear that for surface crack the transition point from long crack to short crack is a*=(ΔKth3/12.8c)2, the range of physical short crack （as） is ρ*/4≤as≤a*, the threshold of the fatigue crack initiation is ΔKth（i）=0.66 Δσ-1 （πρ*/4）1/2, the material parameter that indicates the fatigue crack sensitivity is ρ*/a*, which represents the blunting condition of crack tip under the action of the fatigue limit stress.

Prediction of Fatigue Notch Factor for Metallic Materials

The fatigue notch factors （Kf） of metallic materials with high and low notch sensitivities, which have been derived in theory, are Kt1/（1+n） and Kt2/（3+n） respectively. The diagram of Kf vs. Kt is obtained by means of comprehensive analysis of alarge number of data, and the applicable range of the above two Kc relations is given. The calculation results for steel and aluminum alloy agree with the measured values very well.The fatigue limit of smooth specimens are also derived in this paper, i. e. σtheory=（K/En）1/（1+n）. The calculation results are σtheory=σcy （cyclic yield strength）.

Two Dimensional Numerical Simulation of Transient Natural Convection in Freezer

A two dimensional model of the transient natural convection in a freezer is studied numerically by finite volume approach.The temperatures of the freezer outside surfaces and the evaporator vary in specified manners,which were taken from an experimental work.The fluid in the freezer is of the Bousinnesq type and the flow is assumed laminar,The transient heat conduction in the insulating layers and the temperature and velocity fields of the fluid are solved conjugately.The radiation heat transfer between the freezer inner surfaces is taken into account by using the additional source term method.The distributions of the local Nusselt number along the upper and lower surfaces of the evaporator and their average values in the period of periodically unsteady operation are calculated.Comparisons are made between the results with and without consideration of inner surface radiative heat transfer.It is found that the radiative heat transfer between the inner surfaces has a profound effect on the evaporator heat transfer characteristics.

Analytical Solution of Coupled Laminar Heat-Mass Transfer in a Tube with Uniform Heat Flux

Analytical solution is obtained of coupled laminar heat-mass transfer in a tube with uniform heat flux.This corresponds to the case when a layer of sublimable material is coated on the inner surface of a tube with its outer surface heated by uniform heat flux and this coated material will sublime as gas flows throught the tube.

Effect of Initial Concentrations on Solidification of Ammonium Chloride Water Solution

The effect of initial concentrations on solidification of ammonium chloride water solution is numerically investigated in detail.The solidifying process.with the cold wall temperature lower than the eutectic temperature,is assumed to be one-dimensional,and controlled by heat conduction only.The simulation reveals that:(1) The solid-mush interface grows in a linear manner,while the growth rate of the mush-liquid interface decreases in a parabolic manner,with increasing initial concentrations.(2) The temperature field in the whole region has parabolic characteristics,but is shows a linear feature in the solid zone and mushy zone.(3) The concentration always has linear characteristics in the much.(4)The solid fraction distribution is strongly affected by the initial concertration.The solidification process shows quite different features,especially at small and high initial concentrations.

Numerical Simulation of Natural Convection in Circular Enclosures with Inner Polygonal Cylinders,with Confirmation by Experimental Results

Numerical computations are performed for the natural convection in circular enclosures with inner polygonal cylinders.The polygon surface and the outer envelope are at constant but different temperatures.A body-fltted coordinate system is used.The coordinate system is generated via simple algebraic equations.The transformed governing equations are discretized on a control volume basis with power-law filite difference scheme.The SIMPLE-like algorithm is used to deal with the linkage between pressure and velocities.The numerical results are compared with the experimental data available in the literature ,and the agreement between the numerical and experimental results are very good.

Flow Patterns and Thermal Drag in a One-Dimen-sional Inviscid Channel with Heating or Cooling

In this paper investigations on the flow patterns and the thermal drag phenomenon in one -dimensional inviscid channel flow with heating or cooling are described and discussed:expressions of flow rate ratio and thermal drag coefficient for different flow patterns and its physical mechanism are presented.