A lab session is an important component of a successful and effective cybersecurity curriculum in computer science. It gives students the opportunity to apply the cyber defense knowledge they have learned in the classroom into practice. Moreover, students in a lab session tend to be more interactive and engaging and often have a successful and effective learning experience. Course instructors who teach cybersecurity courses usually rely on textbook authors or publishers to provide some type of virtual lab. While this approach is convenient and time-efficient, as instructors can focus more on preparing the course, it has some challenges when adopting this approach.

Natural gas is thought to be one of the most promising alternatives to traditional vehicle fuels. Nowadays, the natural-gas-fueled engine has been realized in both the spark-ignition engine and the compression-ignition engine. Due to the complicated fueling systems in dual fuel mode and the loss in volumetric efficiency in port injection mode, direct injection spark-ignition natural gas engine can be utilized to avoid these defects and its mixture preparation flexibility will improve the fuel economy. The ability to increase the compression ratio can improve the engine performance. In addition, natural gas direct injection combustion can avoid smoke emission from gasoline direct injection combustion. Due to the high injection pressure requirement, special gas injector should be developed to match the injection and flow characteristics. Meanwhile, the arrangement of spark plug and fuel injector is very sensitive to the engine performance and emissions. The injection timings and ignition timings are very important operating parameters and the control of these parameters will determine the mixture concentration distribution in the cylinder and thus the combustion characteristics. Natural gas direct injection combustion can realize high combustion stability with less cycle-by-cycle variation and the lean burn limit can be extended compared with that of the port injection mode, and also the HC emission can be reduced based on appropriate charge stratification and gas flow condition. However, the particle number concentration and NOx emission will increase with the improvement of combustion status. Adding hydrogen into direct injection natural gas engine is expected to improve the engine performance and decrease engine emissions. By using the swirl injection system, this engine can realize the increase of brake thermal efficiency and the reduction of the brake NOx, HC, CO and CO2 emission simultaneously, when the hydrogen fraction exceeds 10 %. Nevertheless, further research in spark-ignition system and fuel injection system should be conducted before the product stage of this kind of engine.

An extended ethanol oxidation mechanism is presented and validated in this paper.The distribution law of the reactants,free radicals,carbon-based intermediate products and combustion in the 1D laminar flame structure of ethanol-air mixtures under different initial conditions is calculated by using the extended mechanism and molar concentration distribution curve of NOx is predicted.For the ethanol-air flame,the main conclusions are as follows: the concentration of the free radical OH,H and O increases with the increase of the initial temperature and decreases with the increase of initial pressure and dilution ratio.The changing principle of the free radicals under initial conditions can partially explains the changing law of laminar burning velocity obtained through experiments and calculation.

Combustion and emission characteristics of a spray guided direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were investigated. Results show that the brake thermal efficiency increases with the increase of hydrogen fraction and it shows an increasing and then decreasing trend with advancing fuel-injection timing. For later injection timings, the beginning of heat release is advanced with increasing hydrogen fraction, while the beginning of heat release is advanced and then retarded with the increase of hydrogen fraction at earlier injection timings. The flame development duration, rapid combustion duration and total combustion duration decrease with increasing hydrogen fraction. Maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate show an increasing and then decreasing trend with the increase of hydrogen fraction. Brake NOx emission is increased and then decreased, while brake HC, CO and CO2 emissions decrease with the increase of hydrogen fraction.

The dynamics of cycle-to-cycle variations (CCV) was investigated in a natural gas direct-injection spark-ignition engine. The method of continuous wavelet transform was used to analyze the time series of the indicated mean effective pressure (IMEP) and other combustion variables. The dominant oscillatory modes in the CCV were identified, and the engine cycles over which these modes may persist were delineated. Results were obtained for four compression ratios: CR = 8, 10, 12 and 14, at two engine speeds of 1200 and 1800 rpm. The results reveal that the CCV exhibit multiscale dynamics with fluctuations occurring at different timescales. At the engine speed of 1200 rpm, the spectral power of CCV for CR 12 was found to be significantly reduced at the different timescales compared to the CCV at other values of CR. At the higher engine speed of 1800 rpm, this reduction was less pronounced. In addition, cross wavelet transform was used to explore the relationships between the CCV of IMEP and those of flame development duration, main combustion duration and total combustion duration. Strong interdependence was found to exist between the IMEP and main combustion duration as well as total combustion duration, over a wide range of frequencies and engine cycles. (C) 2011 Elsevier Ltd. All rights reserved.

The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechanism. The laminar burning velocities, the mass burning fluxes, the adiabatic flame temperature, the global activation temperature, the Zeldovich number, the effective Lewis number and the laminar flame structure of the methanol-air-nitrogen mixtures are obtained under different nitrogen dilution ratios. Comparison between experiments and numerical simulations show that the extended methanol oxidation mechanism can well reproduce the laminar burning velocities for lean and near stoichiometric methanol-air-nitrogen mixtures. The laminar burning velocities and the mass burning fluxes decrease with the increase of nitrogen dilution ratio and the effect is more obvious for the lean mixture. The effective Lewis number of the mixture increases with the increase of nitrogen dilution ratio, and the diffusive-thermal instability of the flame front is decreased by the nitrogen addition. Nitrogen addition can suppress the hydrodynamic instability of methanol-air-nitrogen flames. The decrease of the mole fraction of OH and H is mainly responsible for the suppressed effect of nitrogen diluent on the chemical reaction in the methanol-air-nitrogen laminar premixed flames, and the NO x and formaldehyde emissions are decreased by the nitrogen addition.

Laminar burning velocities and Markstein lengths of dissociated methanol-air-diluent mixtures were measured at different equivalence ratios,initial temperatures and pressures,diluents(N2 /CO2) and dilution ratios by using the spherically expanding flame.The influences of these parameters on laminar burning velocity and Markstein length were analyzed.The results show that laminar burning velocities of the dissociated methanol-air mixture are increased with the increase of initial temperature and are decreased with the increase of initial pressure.Peak laminar burning velocity occurs at equivalence ratio of 1.8.Markstein lengths are decreased with the increase of initial temperature and initial pressure.Mixture diluents(N2 and CO2) will decrease laminar burning velocities of mixtures.Markstein length increases with the increase of dilution ratio except for very lean mixture(фless than 0.8).CO2 dilution has a larger impact on laminar flame speed compared to N2.

Several fundamental parameters characterizing the ethanol-air premixed mixtures at different equivalence ratios, initial pressures and temperatures, and dilution ratios, like the adiabatic flame temperature, the laminar burning velocity, the laminar burning flux, the laminar flame thickness and the burntgas Markstein length, were studied by using a constant volume combustion bomb and high-speed schlieren photography system. The results show that, for ethanol-air premixed mixture at given initial condition, adiabatic flame temperature, laminar burning velocity and laminar burning flux get their maximum values at the equivalence ratios between 1.0 and 1.1, while laminar flame thickness gets its minimum value at the equivalence ratio of 1.1. Markstein length decreases with the increase of equivalence ratio. For ethanol-air premixed mixture at given equivalence ratio, adiabatic flame temperature increases with the increase in initial pressure and temperature, and it decreases with the increase in dilution ratio. Laminar burning velocity decreases with the increase in initial pressure and dilution ratio, and it increases with the increase in initial temperature. Laminar burning flux increases with the increase in initial pressure and temperature, and it decreases with the increase in dilution ratio. Laminar flame thickness and Markstein length decrease with the increase in initial pressure and temperature, and they increase with an increase in dilution ratio.

Taking lexical hypothesis of personality trait theory as methodology, this paper attempts to give a quantitative analysis on the personality structure of Shanxi business-tycoons in the Chinese Ming and Qing dynasties (PSSM) from psychology views.Exploratory factor analysis (EFA) of data from a sample of 152 effective questionnaires shows that their personalities consisted of four factors, including "honest and righteous", "wise and confident", "calm and persevering" and "determined and promising".Confirmatory Factor Analysis (CFA) of data from another sample of 305 effective questionnaires further confirmed PSSM factorial validity, and fitting indexes were all reasonable.The above results have indicated the cultural inheritance of personality trait as well as the uniqueness and continuity of regional personality trait.

Effect of hydrogen addition on early flame growth of lean burn natural gas–air mixtures was investigated experimentally and numerically. The flame propagating photos of premixed combustion and direct-injection combustion was obtained by using a constant volume vessel and schlieren photographic technique. The pressure derived initial combustion durations were also obtained at different hydrogen fractions (from 0% to 40% in volumetric fraction) at overall equivalence ratio of 0.6 and 0.8, respectively. The laminar premixed methane–hydrogen–air flames were calculated with PREMIX code of CHEMKIN II program with GRI 3.0 mechanism. The results showed that the initial combustion process of lean burn natural gas–air mixtures was enhanced as hydrogen is added to natural gas in the case of both premixed combustion and direct-injection combustion. This phenomenon is more obvious at leaner mixture condition near the lean limit of natural gas. The mole fractions of OH and O are increased with the increase of hydrogen fraction and the position of maximum OH and O mole fractions move closing to the unburned mixture side. A monotonic correlation between initial combustion duration with the reciprocal maximum OH mole fraction in the flames is observed. The enhancement of the spark ignition of natural gas with hydrogen addition can be ascribed to the increase of OH and O mole fractions in the flames.

Cycle-by-cycle variations of it natural gas direct-injection spark ignition engine at different compression ratios were investigated. The results show that the lean burn limit of the natural-gas direct injection engine call be extended to a larger overall excess air ratio compared with that of the homogeneous charge natural gas engine, The coefficient of variations (CoV) of indicated mean effective pressure decreases with the increase of compression ratio. However, CoV of indicated mean effective pressure is increased at high engine load when compression ratio is larger than 12. The cycle-by-cycle variations are more clearly demonstrated in CoV of indicated mean effective pressure rather than in CoV of cylinder peak pressure. Average values of flame development duration, main combustion duration, and total combustion duration are decreased and combustion is improved with increasing compression ratio. This is the reason for decreasing cycle-by-cycle variations in the natural gas direct-injection engine. Better interdependence exists between the indicated mean effective pressure and the flame development duration, as well as between the indicated mean effective pressure and late combustion duration. Cycle-by-cycle variations of the natural gas direct-injection engine are resulted from cycle-by-cycle variations in flame development duration and late combustion duration. This shows some difference to that of homogeneous charge natural gas engine, where cycle-by-cycle variations are mainly influenced by the variations in early flame development stage.

An experimental study on the effects of hydrogen addition on the instabilities of spherically expanding propane–air flames was conducted in a constant volume combustion vessel over a wide range of mixture compositions and initial temperatures and pressures. The measured laminar burning velocities were compared with those calculated values by using one dimensional freely propagating flames and a recently developed detailed kinetic mechanism. Good agreement was obtained between the experiment and calculation. The schlieren images show that for lean mixture combustion, hydrogen addition will increase the hydrodynamic instability due to the decreased flame thickness and increase the diffusional-thermal instability due to the decreased Lewis number. While for rich mixture combustion, the flame front is initially destabilized and later tends to the stabilized with the increase of hydrogen fraction. This is due to the competing effects of the hydrodynamic instability and the diffusional-thermal instability.

Effect of partially premixed mixture and hydrogen addition on natural gas direct-injection lean combustion was studied experimentally using a constant volume vessel. Flame propagating photos and pressure derived combustion parameters were analysed at different premixed ratios (from 0% to 80%) and hydrogen fractions (from 0% to 40%) at overall equivalence ratio of 0.6, 0.8 and 1.0, respectively. The results show that the flame kernel is concentrated to the spark position with the increase of premixed ratio and/or hydrogen fraction. Flame propagating speed is decreased with the increase of premixed ratio while it increases as hydrogen is added to natural gas. Hydrogen addition has little effect on the partially direct-injection natural gas combustion at the stoichiometric fuel-air mixture condition and all premixed ratios. However, hydrogen addition significantly enhances the combustion rate of natural gas direct-injection combustion at lean mixture condition. Both the initial and main combustion durations are increased with the increase of premixed ratio, while they show the decreasing trend as hydrogen is added to natural gas at the lean mixture condition. Partially premixed direct-injection combustion combining with hydrogen addition can achieve the stable spark ignition and fast combustion at the lean mixture condition.

An experimental study on laminar burning velocities and onset of cellular instabilities of the premixed methane–hydrogen–air flames was conducted in a constant volume combustion vessel at elevated pressures and temperatures. The unstretched laminar burning velocity and Markstein length were obtained over a wide range of hydrogen fractions. Besides, the effects of hydrogen addition, initial pressure and initial temperature on flame instabilities were analyzed. The results show that the unstretched flame propagation speed and the unstretched laminar burning velocity are increased with the increase of initial temperature and hydrogen fraction, and they are decreased with the increase of initial pressure. Early onset of cellular instability is presented and the critical radius and Markstein length are decreased with the increase of initial pressure, indicating the increase of hydrodynamic instability with the increase of initial pressure. Flame instability is insensitive to initial temperature compared to initial pressure. With the increase of hydrogen fraction, significant decrease in critical radius and Markstein length is presented, indicating the increase in both diffusional-thermal and hydrodynamic instabilities as hydrogen fraction is increased.

Combustion characteristics of the methanol-air premixed mixtures were studied in a constant volume bomb at different equivalence ratios,initial pressures and temperatures,and dilution ratios.The results show that the combustion pressure,the mass burning rate and the burned gas temperature get the maximum value at the equivalence ratio of 1.1 while the flame development duration and the combustion duration get the minimum value at the equivalence ratio of 1.1.The flame development duration,the combustion duration and the peak combustion pressure decrease with the increase of the initial temperature,while the maximum burned gas temperature increases with the increase of the initial temperature.The peak combustion pressure and temperature increase with the increase of the initial pressure.The flame development duration and combustion duration increase with the increase of the dilution ratio,while the peak combustion pressure and temperature decrease with the increase of the dilution ratio.

Study of cycle-by-cycle variations in a spark ignition engine fueled with natural gas–hydrogen blends combined with exhaust gas recirculation (EGR) was conducted. The effects of EGR ratio and hydrogen fraction on engine cycle-by-cycle variations are analyzed. The results show that the cylinder peak pressure, the maximum rate of pressure rise and the indicated mean effective pressure decrease and cycle-by-cycle variations increase with the increase of EGR ratio. Interdependency between the above parameters and their corresponding crank angles of cylinder peak pressure is decreased with the increase of EGR ratio. For a given EGR ratio, combustion stability is promoted and cycle-by-cycle variations are decreased with the increase of hydrogen fraction in the fuel blends. Non-linear relationship is presented between the indicated mean effective pressure and EGR ratio. Slight influence of EGR ratio on indicated mean effective pressure is observed at low EGR ratios while large influence of EGR ratio on indicated mean effective pressure is demonstrated at high EGR ratios. The high test engine speed has lower cycle-by-cycle variations due to the enhancement of air flow turbulence and swirls in the cylinder. Increasing hydrogen fraction can maintain low cycle-by-cycle variations at high EGR ratios.

Using a high pressure constant volume combustion vessel, the propagation and morphology of spark-ignited outwardly expanding nitrogen diluted propane–air flames were imaged and recorded by schlieren photography and high-speed digital camera. The unstretched laminar burning velocities and Markstein lengths were subsequently determined over wide range of initial temperatures, initial pressures and nitrogen dilution ratios. Two recently developed mechanisms were used to predict the reference laminar burning velocity. The results show that the measured unstretched laminar burning velocities agree well with those in the literature and the computationally predicted results. The flame images show that the diffusional–thermal instability is promoted as the mixture becomes richer, and the hydrodynamic instability is increased with the increase of the initial pressure and it is decreased with the increase of dilution ratio. The normalized laminar burning velocities show a linear correlation with respect to the dilution ratio, indicating that the effect of nitrogen dilution is more obvious at higher pressures.

Combustion characteristics of the methanol–air premixed mixtures were studied in a constant volume bomb at different equivalence ratios, initial pressures and temperatures, and dilution ratios. The results show that the combustion pressure, the mass burning rate and the burned gas temperature get the maximum value at the equivalence ratio of 1.1 while the flame development duration and the combustion duration get the minimum value at the equivalence ratio of 1.1. The flame development duration, the combustion duration and the peak combustion pressure decrease with the increase of the initial temperature, while the maximum burned gas temperature increases with the increase of the initial temperature. The peak combustion pressure and temperature increase with the increase of the initial pressure. The flame development duration and combustion duration increase with the increase of the dilution ratio, while the peak combustion pressure and temperature decrease with the increase of the dilution ratio.

The laminar burning velocities and Markstein lengths for the dissociated methanol–air–diluent mixtures were measured at different equivalence ratios, initial temperatures and pressures, diluents (N2 and CO2) and dilution ratios by using the spherically outward expanding flame. The influences of these parameters on the laminar burning velocity and Markstein length were analyzed. The results show that the laminar burning velocity of dissociated methanol–air mixture increases with an increase in initial temperature and decreases with an increase in initial pressure. The peak laminar burning velocity occurs at equivalence ratio of 1.8. The Markstein length decreases with an increase in initial temperature and initial pressure. Cellular flame structures are presented at early flame propagation stage with the decrease of equivalence ratio or dilution ratio. The transition positions can be observed in the curve of flame propagation speed to stretch rate, indicating the occurrence of cellular structure at flame fronts. Mixture diluents (N2 and CO2) will decrease the laminar burning velocities of mixtures and increase the sensitivity of flame front to flame stretch rate. Markstein length increases with an increase in dilution ratio except for very lean mixture (equivalence ratio less than 0.8). CO2 dilution has a greater impact on laminar flame speed and flame front stability compared to N2. It is also demonstrated that the normalized unstretched laminar burning velocity is only related to dilution ratio and is not influenced by equivalence ratio.