Experimental Study on Enhancing Dynamic Performance of NGV Engine by Using Oxygen-rich Air

NGV engine adopts the fuel supply method of premixing natural gas and air in the premixing chamber out of cylinder, which results in the engine dynamic performances decline. It is an obstacle to popularizing and applying NGV. Using air rich in oxygen to support combustion can decrease ignition point of the fuel, enhance combustion efficiency and make much more heat available. The dynamic perfonnances and fuel consumption rate of a NGV engine with different oxygen concentration are researched in detail. The results show that the increase of oxygen concentration has remarkable influence on the dynamic performances of NGV engine. Power and Torque performances increase and fuel consumption rate decreases when oxygen concentration of premixed gas increases. The results of theory analysis and experiment research indicate that combustion-supporting using oxygen-rich air can enhance the dynamic performances of NGV engine.     

Key Techniques for Design and Manufacture of Micro Gas Turbine Engine

The characteristics of flow and combustion in micro gas turbine engine with the low Reynolds number and the high Mach number, the high Couette number and the low Biot number, as well as the ultra high duty ratio of combustion in very small space are analyzed, which are remarkably distinguished from those on macro scale. At the meantime, the limitation of traditional dynamic lubrication theory at ultra high speed on micro scale is presented, and the possibility of making the gas bearing to be able to work at ultra high speed by utilizing boundary slip is investigated. Due to the applied prospect of silicon carbide in the field of MEMS especially under high temperature and high strength conditions, the technical process of combining silicon etching with reactive sintering and grinding machining of silicon carbide is put forward so that the miniature machining of silicon carbide for micro gas turbine engine becomes possible.     

Influence numerical analysis of combustion chamber thermal boundary conditions on unsteady combustion characteristics in micro ICE

To research the influence of combustion chamber thermal boundary conditions on micro combustion characteristics in micro ICE, the laminar flow finite rate model is adopted to simulate the micro combustion process. Firstly, the influence of grid scale, the time step length and the maximum iterations per time step on accuracy of simulation results are explored. The results show that simulation results agree well with experimental results. And then, the influences of heat transfer coefficient, wall thickness and material on combustion characteristics are discussed. The results indicate that heat transfer coefficient has obvious influence on combustion characteristics. The pressure rise rate decreases, the ignition delays and the highest pressure value drops 2 atmospheres as heat transfer coefficient increases from 0 to 55 W/(m 2·K). The wall thickness and material have a little effect on combustion characteristics. This is because that the main heat transfer resistance in the heat flow path from cylinder to external environment lies between the outer wall and environment.     

Simulation of methanol steam reforming in micro channel with lattice Boltzmann method

Lattice Boltzmann method is used to simulate the methanol steam reforming process in a micro channel. Lattice evolution model with dual rate kinetic parallel reaction mechanism is established. The impacts of boundary temperature, inlet velocity on reaction outlet parameters, such as methanol conversion rate, outlet concentrations of hydrogen and carbon monoxide and maximum temperature difference, are studied. It is found that under a certain boundary temperature and inlet velocity, when the methanol molar ratio, boundary temperature and inlet velocity are 1.3, 523 K and 0.1 m/s respectively, the methanol conversion ratio can reach the highest value of 94.36%, together with the concentrations of hydrogen and carbon monoxide of 0.098 9 and 0.009 5% respectively. With the increase of boundary temperature and decrease of inlet velocity, the concentration of CO will increase.     

Numerical simulation of the influences of catalytic wall on methane combustion characteristics in micro combustor

In order to study the effects of different catalytic walls on combustion characteristics, the premixed catalytic combustion characteristics of methane/air in micro combustor are studied. It lays the foundation for the combustion technology of hydrocarbon fuel in micro engine. Numerical simulation of flow and catalytic combustion in micro combustor was done by using laminar finite rate and second order upwind discretization methods. The results show that when wall temperature,CH4/O2 mole ratio and methane mass flow rate change, the influence of lower catalytic wall on the methane catalytic combustion efficiency is biggest, followed by side catalytic wall, the smallest is upper catalytic wall. The methane catalytic combustion efficiency unit area of lower catalytic wall is about three times of that of upper catalytic wall. The utilization of catalyst on lower catalytic wall is maximal . Therefore, when coating catalyst, the quantity of katalyst on lower catalytic wall should be appropriate more, moderate on the side catalytic wall, as little as possible on the upper catalytic wall. The influence disciplinarian and contribution rate of different catalytic wall on methane combustion have been gained. The optimized strategy of catalyst coating was put forward and reduced the cost of catalytic combustion.     

Externally Pressurized Gas Journal Bearings in Power MEMS of Quasi Gas Power Cycle

An original thermodynamic idea for Power MEMS, which is called as quasi gas power cycle, is proposed to further intensify energy density and simplify structure of Power MEMS. Because gas supply with preset high pressure is set up in the Power MEMS engine of quasi gas power cycle, it is convenient for the Power MEMS engine to employ externally pressurized gas bearings to improve the performance of its bearings. Therefore mal design philosophy and structural type of the hyrostatic journal bearing as well as the hyrostatic thrust bearing in the Power MEMS engine are investigated, considering the limiting factor on meso scale. Then the structural and operational parameters are analyzed, and the optimal designs of typical externally pressurized gas bearings are put forward. Moreover the feasibility of the externally pressurized gas bearings applied to the Power MEMS engine is further verified by the calculation of load-carrying capacity of the hyrostatic gas bearings.     

Effect of space velocity on the performance of methane steam reforming in a plate micro channel reactor

A 2 D numerical simulation is conducted on the steam reforming reaction in a plate micro reactor by applying the general finite reaction rate model in the CFD software FLUENT and a detailed surface reaction kinetics mechanism. Catalyst space velocity(CSV) and gas space velocity(GSV) inlet mixture impact on the reaction is discussed. During the calculations, the space reaction effect is ignored and only the reaction of CH4 on catalytic surface is taken into account. Calculation results show that lower CSV or GSV can achieve high efficiency conversion of CH4 and H2 output; besides CSV and GSV, channel height is an important factor for the reforming performance of plate micro reactors.     

Numerical simulation of NO and N2O emission in fluidized bed reactor

Both NO and N2O emission in fluidized bed reactor are studied by numerical simulation. The effects of excess air ratio, coal composition and co combustion of coal and biomass are researched. The results show that NO and N2O are the main products of the NOx in the fluidized bed reactor combustion, and the emission of NO and N2O increases with the excess air ratio increasing. The NOx production has strong relationship with coal composition. The nitrogen content of the coal plays an important role in the production of NO and N2O, as well as oxygen to nitrogen mass ratio and hydrogen to nitrogen mass ratio. In the co combustion process of coal and biomass, carboxyl group have remarkable effect on HCN production, which reduces the content of NO and NO2. The co combustion of coal and biomass can reduce the emission of NO and N2O.     

A study on kinetic characteristics of auto Ignition process of natural gas hydrogen air mixture

Based on GRI Mech 3.0 mechanism, using kinetic model, the auto ignition characteristics of nature gas hydrogen air mixture are studied in different initial conditions under constant pressure. This study focuses on the changes of temperature and component concentrations,ignition delay time and flame propagation speed. The results show that under different initial conditions, with the increase of hydrogen fraction in the mixture, the ignition delay time decreases significantly and flame propagation speed increases significantly. On the other hand, Hydrogen fraction has been found of little influence on flame temperature.     

Cold Model Experimental Study Using Reburning Tecnology to Reduce the emissions of NOx

A cold model (its ratio is 1:12.5) of a 50 MW tangentially pulverized coal-fired boiler was built and the mixture characteristic between a simulating gas (hot air) and a main airflow (cold air) were gotten at different ejecting methods and quantities of the simulating gas through measuring the temperature pattern distributing in the furnace of the model. The simulating gas spouted from front and rear walls resulted a more even mixture characteristic, and the tangentially ejected simulating gas is more suitable for the tangentially pulverized coal-fired boiler, and the tangentially ejected OFA is also of advantage to it. The effect of quantities and locations of the simulating gas on the mixture characteristic was also discussed.     

The effects of wall parameters on CH4 catalytic combustion in micro-channels

The paper uses CFD simulation to investigate the catalytic surface reaction and heat loss characteristics of premixed CH4/air in micro-channels with Platinum catalyst. A 3D model is used with the detailed surface elementary reaction mechanism, which includes the coupled heat transfer of wall and flow domain, solid wall thermal conductivity and the convection and surface radiation between wall and the environment. The results show that the thermal conductivity has a big impact on the uniformity of wall temperature. The convective heat transfer coefficients and the surface emissivity are the key factors to determine the external heat loss of micro-combustor. An increase of wall depth can reduce the external heat loss per unit area, but it increases the total heat loss. The change of the amount of heat loss changes the reaction rate and residence time of mixed gas in the channel, which affect the methane conversion. The research indicates that the material with bigger thermal conductivity is better to fabricate micro-combustors, and the multi-methods are needed to reduce the wall heat loss.     

Emission characteristics on nature gas engine by additional injection of hydrogen peroxide into the premix chamber

In order to improve combustion efficiency of natural gas(NG) and reduce pollution emission in nature gas engine, additional injection of hydrogen peroxide (H2O2) into the premix chamber is proposed. With the test of CO, HC and NOx concentration, exhaust temperature, NG consumption etc., it is found that the emission of HC、CO and NOx decreased and the dynamic and economic performance of CNG engine is improved. H2O2 can make reduction of the combustion temperature while increase of the oxygen concentration. The pivot factors affecting NOx emission are temperature and oxygen concentration. The optimum mass proportion of nature gas and H2O2 is between 4.5 and 5.8 for NG consumption and pollution emission.     

Numerical simulation on multi jet diffusion combustion of low concentration coal bed methane

It is important to utilize coal bed methane to achieve the safe, environmental and economic benefits. The authors simulate the processes of multi jet diffusion combustion of low concentration coal bed methane using k ε turbulence model,non premixed combustion model and P1 radiation model. The influences of different geometrical structures and operating parameters on the combustion process are compared with each other. The results show that the distance between the gas nozzles and central axis,the angle of gas deflected from air ,the velocity ratio of air to gas have important impacts on the combustion. When the distance, the deflection angle and the velocity ratio are 30 mm,45 °and 2, respectively. The best combustion result can be achieved.     

Simulation analysis of piston slap of internal combustion engine

A finite element model of a piston and a block surface was established. After boundary and work conditions were applied, an initial transient analysis of the model was carried out. The simulation result of vibration acceleration on the block surface conformed well with the experiment, thus validating the model. Based on the model, the motion law of pistons in blocks was studied. The variation trend of the piston slap force, piston clearance on the piston slap force, and the effect of piston pin offset on the piston slap force at different crankshaft speeds were analyzed. Results show that suitable piston pin offset and smaller piston clearance reduce the piston slap force quite well; and the contribution of the piston force at the point when gas breaks out is dominant at low speed, which is not obvious at high speed. The findings provide evidence for the performance improvement of internal combustion engine development.      

3-D Simulation of Methanol-steam Reforming for Hydrogen Production in Microreactor

In order to investigate the effects of inlet temperature,velocity and water methanol molar ratio on methanol- steam reforming for hydrogen production in microreactor, we carry out 3-D simulation of methanol-steam reforming for hydrogen production in self-designed plate microreactor with the application of general finite reaction rate model in CFD software of FLUENT, The kinetics used are DE and SR model, The results show that, At the conditions of inlet velocity, temperature and water methanol molar ratio are 2.88 m/s, 493 K and 1.3 respectively, methanol conversion at the reactor outlet reaches 79.8%. Through the simulation, we can see that in microreactor it can be maintain higher hydrogen molar fraction and methanol conversion at high reactant flow rate.     

The Influence of the Arrangements of Pipes on Gas solid Flow Characteristics in the Dense Section of the Stand Pipe

The influence of the arrangements of pipes on gas solid flow characteristics in the dense section of standpipe in the circulating fluidized bed is studied on a cold state experiment platform.The influence relationships of the percentage of area of pipes in the standpipe cross section and section shape of pipes and the circulation rate,adjusting range and distribution percentage of loose air are studied emphasizedly.     

Research of the Ignition Timing System for Compressed Natural Gas Vehicle

Compared to bi-fuel engine,it uses completely CNG(Compressed nature gas) to replace diesel which can save more oil fuel than bi-fuel engine that reffited diesel engine into CNG engine. A 4102 diesel engine is refitted into CNG engine and a mechanical ignition timing system is designed by the method of gear and belt. The principles and the construction of the system is introduced and the characteristics of the design is analyzed. The system performed well and had good liability when run in a platform. Compared with the previous one, it kept higher dynamic character and emitted lower. It is a cheap one and can be use to reform the diesel engines.     

Numerical simulation on phasing strategy for a gasoline engine with continuously variable intake camshaft

Intake camshaft equipped with continuously adjustable cam phasing units is applied to a 486Q gasoline engine. Phasing strategies are researched through engine cycle simulation to achieve superior engine performance. The simulation results show that at high load and low and moderate speed of the engine,phasing adjustment can lead to 6% to 8% increase in power performance because phasing advance contributes to suppressing intake backflow at IVC(intake valve closed). Cam phases obtained from numerical optimization have good agreement with engine test. At moderate load,cycle simulations show that phasing advance can increase residual gas coefficient from 9% to 20%,and reduce NO emission by 80%,BSFC(brake specific fuel consumption) by 2% at a demonstration operation. With regard to fuel economy and emissions,adjustment and optimization of intake phasing at moderate load are further verified by engine test. At low load,technical approaches to enhance combustion stability,reduce HC emission and improve cold start are investigated. The effectiveness of suppressing exhaust backflow into intake duct by phasing retard is testified by simulation. Phasing changes at the operating condition are optimally obtained by engine test for improvement of combustion stability.     

Migration and Distribution Rules of Tubifex in Filtration

The rules of migration and distribution regulation of tubifex in filtration were studied in the pilot system. Meanwhile, the influences of filtration rate, filtration cycle and backwashing on the worm’s migration and distribution in filtraion were discussed. The results showed that both the worm’s length and the particle size of filter media had obvious effects on migration and distribution: the smaller the worm’s length and the larger the particle size of filter media were, the stronger the worm’s migration capacity was. The filtration rate was the main migration power of tubifex in filtration, which meant high filtration rate could result in the worm’s leakage risk. Prolonging filtration cycle promoted migration, thus it is beneficial to control tubifex leakage risk that shortening filtration cycle. The remove of tubifex in a real sense can be realized by backwashing. And the stronger the backwashing intensity is, the better the removal efficiency is. Based on the experimental results, to control the worm’s leakage risk effectively, filtration rate and cycle would be lower than 9.4 m/h and 12 h, respectively. Backwashing intensity would be controlled about 25 L/s·m2, at which the obtained tubifex removal efficiency was 97.7%.     

Influence of oygen-enriched combustion technology on overall performance of 220 t/h gas boiler

A 220 t/h gas boiler of some steel group is taken as the study objectand the idea of oxygen-enriched stable combustion is proposed and proved to be feasible with the furnace heat transfer model in order to make reasonable use of existing resources and improve the combustion stability of gas boiler in low load operation.Detailed analysis has been made about the effects of oxygen-enriched combustion on the flu gas temperaturecombustion stability boiler thermal efficiency and so on.The results show that the oxygen-enriched combustion technology can greatly improve the overall performance of the boiler.