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Timothy A Shedd - One of the best experts on this subject based on the ideXlab platform.

  • towards working fluid properties and selection of rankine cycle based waste heat recovery whr systems for Internal Combustion Engines a fundamental analysis
    Applied Thermal Engineering, 2018
    Co-Authors: Xingyuan Su, Timothy A Shedd
    Abstract:

    Abstract Working fluid selection is one of the most important procedures in the design of Rankine cycle based waste heat recovery systems for Internal Combustion Engines. The system’s performance, cost, and environmental impacts can be greatly influenced by the properties of its working fluid. In this work, we present an original formulation of a theoretical thermal efficiency model to fundamentally understand how the working fluid properties affect the thermal performance of the Rankine cycle based waste heat recovery systems for Internal Combustion Engines. The derived theoretical thermal efficiency formula is validated under several different operating conditions. Overall very good agreements are achieved between the actual and theoretical approximated solutions. The results show that when the evaporation and condensation temperatures of the waste heat recovery system are fixed, the system’s thermal efficiency is simply governed by a non-dimensionalized parameter Jakob number. A working fluid with a smaller Jakob number is preferable in terms of system thermal efficiency. The observation is also further understood from a more fundamental physical perspective. Finally, a preliminary working fluid selection approach with a solid physics is proposed to screen the fluid candidates from the perspective of system performance.

T. Nejat Veziroglu - One of the best experts on this subject based on the ideXlab platform.

  • Internal Combustion Engines fueled by natural gas hydrogen mixtures
    International Journal of Hydrogen Energy, 2004
    Co-Authors: Selahaddin Orhan Akansu, Zafer Dulger, Nafiz Kahraman, T. Nejat Veziroglu
    Abstract:

    Abstract In this study, a survey of research papers on utilization of natural gas–hydrogen mixtures in Internal Combustion Engines is carried out. In general, HC, CO 2 , and CO emissions decrease with increasing H 2 , but NO x emissions generally increase. If a catalytic converter is used, NO x emission values can be decreased to extremely low levels. Consequently, equivalence zero emission vehicles (EZEV) standards may be reached. Efficiency values vary with H 2 amount, spark timing, compression ratio, equivalence ratio, etc. Under certain conditions, efficiency values can be increased. In terms of BSFC, emissions and BTE, a mixture of low hydrogen percentage is suitable for using.

Tatsumi Kitahara - One of the best experts on this subject based on the ideXlab platform.

  • piston ring friction in Internal Combustion Engines
    Tribology International, 1992
    Co-Authors: Yutaro Wakuri, Toshiro Hamatake, Mitsuhiro Soejima, Tatsumi Kitahara
    Abstract:

    Abstract The tribological phenomena of the sliding surfaces between piston rings and cylinder liners may be among the most complex in Internal Combustion Engines, and could become even more severe with an increase of the engine power. The friction between the piston rings and the cylinder liner significantly contributes to the mechanical power losses of the engine. The calculations of friction force for a piston ring pack are conducted based on hydrodynamic lubrication theory. The oil starvation within the piston ring pack is considered in the calculation of oil-film thickness. The friction characteristics of piston rings are evaluated with the frictional mean effective pressure. The instantaneous friction force of a piston assembly under firing engine conditions is measured by an improved floating liner method in which the cylinder liner is supported by means of hydrostatic bearings. The friction characteristics are made clear by analyses and experiments.

Hanserik Angstrom - One of the best experts on this subject based on the ideXlab platform.

Jerald A Cato - One of the best experts on this subject based on the ideXlab platform.

  • the thermodynamic characteristics of high efficiency Internal Combustion Engines
    Energy Conversion and Management, 2012
    Co-Authors: Jerald A Cato
    Abstract:

    Abstract Recent advancements have demonstrated new Combustion modes for Internal Combustion Engines that exhibit low nitric oxide emissions and high thermal efficiencies. These new Combustion modes involve various combinations of stratification, lean mixtures, high levels of EGR, multiple injections, variable valve timings, two fuels, and other such features. Although the exact combination of these features that provides the best design is not yet clear, the results (low emissions with high efficiencies) are of major interest. The current work is directed at determining some of the fundamental thermodynamic reasons for the relatively high efficiencies and to quantify these factors. Both the first and second laws are used in this assessment. An automotive engine (5.7 l) which included some of the features mentioned above (e.g., high compression ratios, lean mixtures, and high EGR) was evaluated using a thermodynamic cycle simulation. These features were examined for a moderate load (bmep = 900 kPa), moderate speed (2000 rpm) condition. By the use of lean operation, high EGR levels, high compression ratio and other features, the net indicated thermal efficiency increased from 37.0% to 53.9%. These increases are explained in a step-by-step fashion. The major reasons for these improvements include the higher compression ratio and the dilute charge (lean mixture, high EGR). The dilute charge resulted in lower temperatures which in turn resulted in lower heat loss. In addition, the lower temperatures resulted in higher ratios of the specific heats which account for a more effective conversion of thermal energy to work. Other thermodynamic features are described.