Heavy-duty natural gas engines offer air pollution and energy diversity benefits. However, current homogeneous-charge lean-burn engines suffer from impaired efficiency and high unburned fuel emissions. Natural gas direct-injection engines offer the potential of diesel-like efficiencies, but require further research. To improve understanding of the autoignition and emission characteristics of natural gas direct-injection compression-ignition combustion, the effects of key operating parameters (including injection pressure, injection duration, and pre-combustion temperature) and gaseous fuel composition(including the effects of ethane, hydrogen and nitrogen addition) were studied. An experimental investigation was carried out on a shock tube facility. Ignition delay, ignition kernel location, and NOx emissions were measured. The results indicated that the addition of ethane to the fuel resulted in a decrease in ignition delay and a significant increase in NOx emissions. The addition of hydrogen to the fuel resulted in a decrease in ignition delay and a significant decrease in NOx emissions. Diluting the fuel with nitrogen resulted in an increase in ignition delay and a significant decrease in NOx emissions. Increasing pre-combustion temperature resulted in a significant reduction in ignition delay, and a significant increase in NOx emissions. Modest increase in injection pressure reduced the ignition delay; increasing injection pressure resulted in higher NOx emissions. The effects of ethane, hydrogen, and nitrogen addition on the ignition delay of methane were also successfully predicted by FlameMaster simulation. OH radical distribution in the flame was visualized utilizing Planar Laser Induced Fluorescence (PLIF). Single-shot OH-PLIF images revealed the stochastic nature of the autoignition process of non-premixed methane jets. Examination of the convergence of the ensemble-averaged OH-PLIF images showed that increasing the number of repeat experiments was the most effective way to achieve a more converged result. A combustion model, which incorporated the Conditional Source-term Estimation(CSE) method for the closure of the chemical source term and the Trajectory Generated Low-Dimensional Manifold (TGLDM) method for the reduction of detailed chemistry, was applied to predict the OH distribution in a combusting non-premixed methane jet. The model failed to predict the OH distribution as indicated by the ensemble-averaged OH-PLIF images, since it cannot account for fluctuations in either turbulence or chemistry.

Introduction Very light jet is a hot subject growing stronger and stronger. The new type of air craft is an air plane that weighs less than 10000 pounds and uses a jet engine. Problem The student was proposed to designing a conceptual very light jet that could be used for inspiration and accepted the challenge. Method In this thesis the reader can follow the project progress in detail, the proposed methods and the results. The student divided the project into four activities analysis, creation, development and documentation. Result The project ended with a concept very light jet with simple specifications. Illustrations for inspirational usage and a simulation testing for verification of the proposed concept specifications.

The paper extends the analytical results obtained by Hwung et al. (1981) and further considers the non-linearity of waves to investigate variation horizontal velocity, temperature distribution induced by interaction of 2-D plane jet and waves. On the steady state, the nonlinear wave is considered as external force in motion equations, the property of momentum conservation of jet flow, and radiation stress are applied to analyze the interaction of waves- jet flow in arbitrary profile. The scale function 1 £` £\1(x) , 2 2£` £\ (x) between the variation function f (x,y) and velocity distribution can also be obtained. The non-dimensional theoretical solution is also useful to estimate the relative characteristics in the physical field. The momentum equation and velocity distribution of interaction without property of temperature diffusion are employed to find the temperature distribution for arbitrary sections. Based on the experiments and theory solution obtained by Hwung et al. (1981) it is found that time-averaged horizontal velocity and temperature are Gaussian distribution, the coefficient of horizontal velocity 1 c , and temperature distribution 2 c are 0.105, 0.148, respectively. In the present, two coefficients considered as non-linearity of waves 1 c = 0.124 and 2 c = 0.152 are determined. In other words, it is shown that exact solution and boundary effect included non-linearity of waves is related to velocity of jet flow, wave periods, relative depth and steepness of waves respectively. Comparing with experiments indicated that the analytical solution of the present for MSE is well confirm the experimental results and better than linear results obtained by Hwung et al. (1981) The influence due to interaction of 2-D turbulent jet flow and Stokes waves can be obtained by using dimension analysis. Moreover, the related properties inside the flow also can be estimated.

Research was performed to optimize the high-efficiency jet ejector geometry by varying motive velocities from Mach 0.50 to 3.25, and mass flow ratio from 0.02 to 100.0. The high-efficiency jet ejector was simulated by Fluent Computational Fluid Dynamics (CFD) software. A conventional finite-volume scheme was utilized to solve two-dimensional transport equations with the standard k-ε turbulence model. In the optimization study of the constant-area jet ejectors, all parameters were expressed in dimensionless terms. The objective of the study was to investigate the optimal length, throat diameter, and optimal nozzle diameter at any operating conditions. Also, the optimum compression ratio and efficiency were calculated. By comparing simulation results to an experiment, CFD modeling has shown high-quality results. The overall deviation was 8.19%, thus confirming the reliability of the modeling results. The results from the optimization study indicate that the jet ejector efficiency improves significantly compared to a conventional jet-ejector design. In cases with a subsonic motive velocity, the efficiency of the jet ejector is greater than 90%. A high compression ratio can be achieved with greater motive velocity and mass flow ratio. The ejector performance between the optimal jet ejectors and conventional jet ejectors provided by Graham Corporation was compared. The results show that substituting a single optimal jet ejector for a single conventional ejector reduces the motive stream consumption by about 10% to 30%, which could decrease operating costs tremendously. Dimensionless group analysis reveals that the research results are valid for any fluid, operating pressure and geometric scale for a given motive-stream Mach number and momentum ratio. The explanation of how to implement the optimization results and selecting the best operating conditions to minimize the motive stream consumption was included at the end of the dissertation.

Research was performed to optimize high-efficiency jet ejector geometry (Holtzapple, 2001) by varying nozzle diameter ratios from 0.03 to 0.21, and motive velocities from Mach 0.39 to 1.97. The high-efficiency jet ejector was simulated by Fluent Computational Fluid Dynamics (CFD) software. A conventional finite-volume scheme was utilized to solve two-dimensional transport equations with the standard k-?? turbulence model (Kim et. al., 1999). In this study of a constant-area jet ejector, all parameters were expressed in dimensionless terms. The objective of this study was to investigate the optimum length, throat diameter, nozzle position, and inlet curvature of the convergence section. Also, the optimum compression ratio and efficiency were determined. By comparing simulation results to an experiment, CFD modeling has shown high-quality results. The overall deviation was 8.19%, thus confirming the model accuracy. Dimensionless analysis was performed to make the research results applicable to any fluid, operating pressure, and geometric scale. A multi-stage jet ejector system with a total 1.2 compression ratio was analyzed to present how the research results may be used to solve an actual design problem. The results from the optimization study indicate that the jet ejector efficiency improves significantly compared to a conventional jet-ejector design. In cases with a subsonic motive velocity, the efficiency of the jet ejector is greater than 90%. A high compression ratio can be achieved with a large nozzle diameter ratio. Dimensionless group analysis reveals that the research results are valid for any fluid, operating pressure, and geometric scale for a given motive-stream Mach number and Reynolds ratio between the motive and propelled streams. For a given Reynolds ratio and motivestream Mach number, the dimensionless outlet pressure and throat pressure are expressed as Cp and Cpm, respectively. A multi-stage jet ejector system with a total 1.2 compression ratio was analyzed based on the optimization results. The result indicates that the system requires a lot of high-pressure motive steam, which is uneconomic. A high-efficiency jet ejector with mixing vanes is proposed to reduce the motive-steam consumption and is recommended for further study.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains x, 140 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 120-131).

Thesis--M. Phil., University of Hong Kong, 1978.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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