Sang-Hak Ghal

The Performance Evaluation With Diffuser Geometry Variations of the Centrifugal Compressor in a Marine Engine (70MW) Turbocharger

An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30-50% of the shaft work input to the compressor stage; for energy efficiency, it is important to recover as much of this as possible. This is the function of the diffuser, which follows the impeller. Effective pressure recovery downstream of an impeller is very important in order to realize a centrifugal compressor with a high efficiency and a high pressure ratio, and an appropriate selection of a diffuser for a specific impeller is a critical step in order to develop the compressor accordingly. The purpose of this study is to investigate the sensitivity of how compressor performances change as the vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and compared with its results. The first vaned diffuser type is based on a modified NACA airfoil, the second is a channel diffuser, and the third is a conformal transformation of NACA 65-(4A10)06 airfoil. A mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. Computational fluid dynamic (CFD) analyses and a detailed interior flow pattern study have been done. In this study, the off-design behavior of three different types of diffusers, given by the mean-line prediction, was investigated using CFD results and the NACA 65 diffuser geometry, which satisfies a wider operating range and has a higher pressure recovery than the others, was selected. The numerical results were compared with experimental data for validation and showed good agreement.

NOx Reduction of a Medium Speed Diesel Engine Using a Charge Air Moisturizer System

It is well known that water can be used to prevent NOx formation during a combustion process. It is based on the principle by decreasing flame temperature with increasing the specific heat capacity of combustion air by adding water to a combustion chamber. Introducing water into a charge air enables much more water addition into a combustion chamber than other methods, which can reduce NOx emission to lower level than the others. The method has also the advantage of low installation cost. In a general water injection system for a charge air only hot water is sprayed into the charge air and vaporized, but more effective means to introduce water into the charge air is needed because only small amount of water is evaporated in hot water injection system. In this study, steam and hot moisturizing water are injected simultaneously. The steam supplies steady additional energy for evaporation of the water and can be vapor by itself. The new method was evaluated for NOx reduction performance on a medium speed diesel engine. NOx emission was reduced to 10∼38% on the 27∼59gram water per kilogram dry air.Copyright

Centrifugal Compressor Aerodynamic Design of Marine Engine Turbocharger by Three Dimensional Numerical Simulation

For the centrifugal compressor aerodynamic design of a turbocharger, first of all, the works for system matching to the engine specification must be preceded. Then, mean line design together with performance prediction should be carried out for preliminary design. In the mean line prediction, a slip factor is adopted as a function of flow coefficient and geometry instead of Wiesner’s equation, and it is found that the predicted result of slip magnitude is more accurate than that of conventional slip factor. Also, three-dimensional blade profile shape is generated on the basis of the preliminary design. The Navier-Stokes Equation solver with a turbulent model is used to find whether three-dimensionally designed geometry is reasonable by analyzing loading distribution of the blade. By investigating diffuser flow field of the simulated result, the diffuser inlet and exit angles were modified for the flow to move smoothly along the diffuser geometry. Modified performance prediction results shows better than those of original specification. Consequently, off design performance prediction results and numerical simulation result show good agreement with the experimental data. The modified design results show more increased compression ratio and efficiency than those of previous design results. The increased choke margin has made a stable operating range larger.Copyright

A Study on Cavitation Damage Reduction in Fuel Injection Pumps

Cavitation phenomena during the spill process of the Bosch type fuel injection pump for medium-speed diesel engine were investigated by optical observations. Typically, these phenomena can cause a surface damage with material removal or round-off at the plunger and barrel port etc., and may shorten their expected life time. The images, which were recorded with high speed CCD camera and borescope, show that the plunger damage is mainly affected by fountain-like cavitation generated before the end of delivery. And the damages of barrel port and deflector are caused by jet-type cavitation generated after end of delivery. Based on the results of optical investigation, 12 different type pumps varied in the geometry of components were designed to alter the direction, distribution, and intensity of cavitations. Finally, the effects of each countermeasure were evaluated by the durability test on actual diesel engine (HiMSEN H21/32).Copyright

A Study on the Applicability of Straight Vegetable Oils to Medium Speed Diesel Engines

Straight vegetable oil (SVO) fuels such as palm oil, animal fat oil and waste vegetable oil were tested as fuels in a single-cylinder diesel engine to evaluate applicability to medium-speed diesel engines. Fuel-related properties of the SVO were assessed and compared with conventional marine diesel fuel oil (MDO). The total acid number (TAN) of the SVO fuels changed during a short interval in a drying oven which heated the SVO fuels to 170 degrees Celsius for several weeks. The SVO have not gone rancid any further after reaching limit. And the TAN of the SVO fuels was not related to corrosion of the parts. The SVO fuels needed to be heated to an appropriate temperature to use as fuel of the engine since the SVO fuels are more viscous than conventional diesel fuels. Both the injection period and the injection pressure increased due to low heating values of the SVO fuels. By the same token, fuel oil consumption increased over 10%. The overall exhaust emissions were lower with the SVO fuels, but NOx emission was as much as MDO at the higher loads.Copyright

The Performance Evaluation of Variations of Diffuser Geometry of the Centrifugal Compressor in a Marine Engine (70MW) Turbocharger

An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30–50% of the shaft work input to the compressor stage, and for energy efficiency it is important to recover as much of this as possible. This is the function of the diffuser which follows the impeller. Effective pressure recovery downstream of an impeller is very important to realize a centrifugal compressor with high efficiency and high pressure ratio, and an appropriate selection of a diffuser for a specific impeller is a critical step to develop the compressor accordingly. The purpose of this study is to investigate the sensitivity of how compressor performances changes as vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and its results were compared. First vaned diffuser type is based on modified NACA airfoil and second is channel diffuser and third is conformal transformation of NACA 65 airfoil. A mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. And CFD analyses have been done for comparison and detailed interior flow pattern study. In this study, the off-design behavior of three different types of diffusers, given by mean-line prediction, was investigated using CFD results and selected the NACA 65 diffuser geometry which satisfy wider operating range and higher pressure recovery than the others. The numerical results were compared with experimental data for validation.Copyright

Aerodynamic Three Dimensional Geometry and Combustor Design for the Compressor of the Medium Speed Diesel Engine Turbocharger

An aerodynamic design for centrifugal compressor which was applied to medium speed diesel engine has been done. First of all, exact compressor specifications must be defined by accurate engine system matching. This matching program has been developed. Using the meanline prediction method, geometric design and performance curves for compressor were established and verified by comparing three dimensional viscous CFD results. The deviation at the design point was about 2.3%. Combustor has been designed and manufactured for the performance test of medium speed diesel engine turbocharger. Fuel nozzle of combustor was designed and its characteristics was analyzed by PIV and PDPA test equipment. Through these results, spray characteristics were studied and flow coefficient equation was deduced.

The Numerical Study on the Performance Evaluations and Flow Structures for the Diffuser of Centrifugal Compressor in a Marine Engine Turbocharger

The centrifugal compressor of marine engine turbocharger is composed of impeller, 1st vaneless diffuser, vaned diffuser, 2nd vaneless diffuser and volute casing. An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30–50% of the shaft work input to the compressor stage, and for energy efficiency it is important to recover as much of this as possible. This is the function of the diffuser which follows the impeller. Effective pressure recovery downstream of an impeller is very important to realize a centrifugal compressor with high efficiency and high pressure ratio, and an appropriate selection of a diffuser for a specific impeller is a critical step to develop the compressor accordingly. The purpose of this study is to investigate the sensitivity of how compressor performances changes as vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and its results were compared. First vaned diffuser type is based on NACA airfoil and second is channel diffuser and third is conformal transformation of NACA 65 airfoil. Mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. And CFD analyses have been done for comparison and detailed interior flow pattern study. In this study, the off design behavior of three different type of diffuser, given by mean-line prediction, was investigated using CFD results and selected best diffuser geometry which satisfy wider operating range and higher pressure recovery than the others. The numerical results were compared with experimental data for validation.Copyright

A Numerical Approach for the Design of the Compressor Impeller Exit Diameter Variations in a Marine Engine Turbocharger

A turbocharger has been designed to fulfill the requirements of medium speed marine engines, 900 kW output power at nominal operation point. The main objective of the design was to meet the requirements of engine power and increased engine operating range. This must be achieved by improving the degree of aerodynamic efficiency and the pressure ratio. The design was performed by the two stages. First, quasi-two dimensional program code was used to determine the main geometry of the compressor. Second, the detailed geometries of compressor blade were completed by using a three dimensional fluid flow analysis. The analyzed performance results were compared with the experimental data for the verification of their validity. Also, the designed three different impeller exits allow for a substantial performance variation. Increased compression ratio and mass flow rate of new optimized impeller were 10.08 and 27.3 percent higher than those of origin impeller, respectively. This simple change of design parameter offers considerable advantages to customers when upgrading their engines.Copyright

A Study on NOx Reduction in a Medium Speed Diesel Engine Using a Charge Air Moisturizing Method

NOx forms during a combustion process and contributes to ozone, smog, acid rain, eutrophic soil, etc. The use of water to prevent NOx formation during the combustion process is well known. Adding water to the combustion process reduces the flame temperature by increasing the specific heat capacity of charge air. Moisturizing a charge air is one of the most effective methods to add water to the combustion process. In this study, the characteristics of charge air moisturizing method were evaluated on cylinder pressure, heat release rate, exhaust gas temperature, specific fuel oil consumption, NOx reduction rate, etc., using the medium speed diesel engine with a single cylinder.Copyright