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RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1994;116(4):727-732. doi:10.1115/1.2906879.

Development of vehicles to operate on nonpetroleum fuels began in earnest in response to the energy shocks of the 1970s. While petroleum will remain the predominant transportation fuel for a long time, petroleum supplies are finite, so it is not too soon to begin the difficult transition to new sources of energy. In the past decade, composition of the fuel utilized in the internal combustion engine has gained recognition as a major factor in the control of emissions from the tailpipe of the automobile and the rate of formation of ozone in the atmosphere. Improvements in air quality can be realized by using vechicles that operate on natural gas, propane, methanol, ethanol, or electricity, but introduction of these alternative fuel vehicles presents major technical and economic challenges to the auto industry, as well as the entire country, as long as gasoline remains plentiful and inexpensive.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):733-739. doi:10.1115/1.2906880.

In a joint project of FEV Motorentechnik and Ruhrgas AG, the design of stoichiometric and lean-burn Otto engines was optimized by selective modifications to the design and operating parameters to accommodate changing methane numbers (LPG addition to CNG). Of particular importance was knock-free engine operation at a low NOx output to meet the requirements of the German Clean Air Code while concurrently achieving both high efficiencies and mean effective pressures. Based upon the results obtained, concepts for the control of Otto-cycle gas engines to accept changing methane numbers were developed. The newly developed gas engine control device allows these concepts to meet the requirement of the German Clean Air Code with economically viable conditions while preventing engine knock. Furthermore, the test results show that dedicated Otto-cycle gas engines can meet the most stringent emission limits for commercial vehicles while maintaining high efficiencies.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):740-748. doi:10.1115/1.2906881.

The purpose of this paper is to describe and summarize the results of the Coal Fueled Diesel Engine Development Program, sponsored by the U.S. Department of Energy, Morgantown Energy Technology Center. The results of the program indicate that diesel engines can be designed to operate reliably on coal–water slurries. The engine must be modified to include hard-wear resistant rings and liners. The injection system design must be modified to accommodate the slurry and to incorporate hard materials for wear prevention.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):749-757. doi:10.1115/1.2906882.

In the early 1980s, General Electric—Transportation Systems (GE-TS), a manufacturer of locomotive diesel engines, announced plans to develop a coal-fueled locomotive due to the availability and low cost of coal. In 1985 and 1988, the General Electric Company (GE) was awarded major contracts from the Department of Energy, Morgantown Energy Technology Center, to continue the research and development of a coal-fueled diesel engine. This paper is a review of the technical accomplishments and discoveries of the GE coal-fueled diesel engine research and development program during the years 1982–1993. The results of an economic assessment completed by GE-TS indicated the merits for the development of a coal fueled diesel engine for locomotive applications and therefore, GE-TS embarked on an ambitious program to develop and commercialize a coal-fueled diesel engine. Among the major accomplishments of this program were the development of specialized fuel injection equipment for coal–water slurries, diamond compact inserts for the nozzle tips for wear resistance, and an integrated emissions control system. Over 500 hours of engine operation was accumulated using coal fuel during the duration of this program. A major milestone was attained when, during November and December 1991, a coal-fueled diesel engine powered a locomotive on the General Electric test track.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):758-764. doi:10.1115/1.2906883.

Improving the performance of the Chinese B135 six-cylinder direct injection turbocharged and turbocompounded Low Heat Rejection Engine (LHRE) was based on experimental and analytical studies. The studies were primarily applied on a B1135 single-cylinder LHR engine and a conventional water-cooled B1135 single cylinder engine. Performance of the B1135 LHRE was worse than that of the conventional B1135 due to a deterioration in the combustion process of the B1135 LHRE. The combustion process was improved and the fuel injection system was redesigned and applied to the B135 six-cylinder LHRE. The new design improved the performance of the LHRE and better fuel economy was realized by the thermal energy recovered from the exhaust gases by the turbocompounding system.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):765-773. doi:10.1115/1.2906884.

Diesel engine particulate certification, heretofore limited to on-highway truck engines, will be expanded in scope beginning in 1996. “Mini-dilution” tunnels have been the European and Japanese systems of choice for dilute particulate emissions certification for non-U.S. truck diesel engines. However, repeatability, steady-state test correlation versus full dilution systems, portability, sampling time, size, and system cost have precluded universal industry and regulatory acceptance of existing “mini-system” designs. To address corporate particulate measurement needs, the author developed a device known internally as the “Micro-Dilution Particulate Measurement System,” which meets the following objectives: (1) correlation with full dilution systems within ISO 8178 equivalency standards, (2) short sampling time, (3) reduced setup effort, and (4) excellent portability. Since the system is a true fractional sampler, it is insensitive to engine size, requiring only a simple stack probe change to provide accurate, representative steady-state diesel stack sampling on any size diesel engine.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):774-783. doi:10.1115/1.2906885.

To enhance the effectiveness of intercity passenger rail service in mitigating exhaust emissions in California, the California Department to Transportation (Caltrans) included limits on exhaust emissions in its intercity locomotive procurement specifications. Because there were no available exhaust emission test data on which emission reduction goals could be based, Caltrans funded a test program to acquire gaseous and particulate exhaust emissions data, along with smoke opacity data, from two state-of-the-art intercity passenger locomotives. The two passenger locomotives (an EMD F59PH and a GE DASH8-32BWH) were tested at the Association of American Railroads Chicago Technical Center. The EMD locomotive was eqiupped with a separate Detroit Diesel, Corporation (DDC) 8V-149 diesel engine used to provide 480 V AC power for the trailing passenger cars. This DDC engine was also emission tested. These data were used to quantify baseline exhaust emission levels as a challenge to locomotive manufacturers to offer new locomotives with reduced emissions. Data from the two locomotive engines were recorded at standard fuel injection timing and with the fuel injection timing retarded 4 deg in an effort to reduce NOx emissions. Results of this emissions testing were incorporated into the Caltrans locomotive procurement process by including emission performance requirements in the Caltrans intercity passenger locomotive specification, and therefore in the procurement decision. This paper contains steady-state exhaust emission test results for hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx ), and particulate matter (PM) from the two locomotives. Computed sulfur dixoide (SO2 ) emissions are also given, and are based on diesel fuel consumption and sulfur content. Exhaust smoke opacity is also reported.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):784-792. doi:10.1115/1.2906886.

A significant source of unburned hydrocarbon emissions from internal combustion engines originates from the flow of unburned fuel/air mixture into and out of crevices in the piston-cylinder-ring assembly. During compression, fuel vapor flows into crevice regions. After top dead center, the trapped fuel vapor that returns into the cylinder escapes complete oxidation and contributes to unburned hydrocarbon emissions. In this work, the crevice flow model developed by Namazian and Heywood is implemented into KIVA-II, a multidimensional, reacting flow code. Two-dimensional, axisymmetric simulations are then performed for a 2.5 liter gasoline engine to investigate the effects of engine speed and selected piston-ring design parameters on crevice flows and on unburned hydrocarbon emissions. Results suggest that engine-out unburned hydrocarbon emissions can be reduced by optimizing the ring end gap area and the piston-cylinder side clearance.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):793-798. doi:10.1115/1.2906887.

Sluggish flame initiation and propagation, and even potential misfiring, become major problems with lean-fueled, premixed-charge, spark-ignited engines. This work studies torch ignition as a means for improving combustion, fuel economy, and emissions of a retrofitted, large combustion chamber with nonideal spark plug location. A number of alternative configurations, employing different torch chamber designs, spark-plug locations, and materials, were tested under full-load and part-load conditions. Results indicate a considerable extension of the lean operating limit of the engine, especially under part-load conditions. In addition, torch ignition can lead to substantial thermal efficiency gains for either leaner or richer air-fuel ratios than the optimum for the conventional ignition system. On the richer side, in particular, the torch-ignited engine is capable of operating at maximum brake torque spark timings, rather than compromised, knock-limited spark timings used with conventional ignition. This translates into thermal efficiency improvements as high as 8 percent at an air-fuel ratio of 20:1 and full load.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):799-805. doi:10.1115/1.2906888.

A study of natural gas (NG) direct injection (DI) processes has been performed using multidimensional computational fluid dynamics analysis. The purpose was to improve the understanding of mixing in DI NG engines. Calculations of injection into a constant-volume chamber were performed to document unconfined plume behavior. A full three-dimensional calculation of injection into a medium heavy-duty diesel engine cylinder was also performed to study plume behavior in engine geometries. The structure of the NG plume is characterized by a core of unmixed fuel confined to the near-field of the jet. This core contains the bulk of the unmixed fuel and is mixed by the turbulence generated by the jet shear layer. The NG plume development in the engine is dominated by combustion chamber surface interactions. A Coanda effect causes plume attachment to the cylinder head, which has a detrimental impact on mixing. Unconfined plume calculations with different nozzle hole sizes demonstrate that smaller nozzle holes are more effective at mixing the fuel and air.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):806-813. doi:10.1115/1.2906889.

A study of natural gas (NG) direct injection (DI) processes in engines has been performed using multidimensional computational fluid dynamics analysis. The purpose was to investigate the effects of key engine design parameters on the mixing in DI NG engines. Full three-dimensional calculations of injection into a medium heavy-duty diesel engine cylinder were performed. Perturbations on a baseline engine configuration were considered. In spite of single plume axisymmetric injection calculations that show mixing improves as nozzle hole size is reduced: plume merging caused by having too many nozzle holes has a severe negative impact on mixing; and increasing the number of injector holes strengthens plume deflection toward the cylinder head, which also adversely affects mixing. The optimal number of holes for a quiescent engine was found to be that which produces the largest number of separate NG plumes. Increasing the nozzle angle to reduce plume deflection can adversely affect mixing due to reduced jet radial penetration. Increasing the injector tip height is an effective approach to eliminating plume deflection and improving mixing. Extremely high-velocity squish flows, with penetration to the center of the piston bowl, are necessary to have a significant impact on mixing. Possible improvements in mixing can be realized by relieving the center of the piston bowl in typical “Mexican hat” bowl designs. CFD analysis can effectively be used to optimize combustion chamber geometry by fitting the geometry to computed plume shapes.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):814-830. doi:10.1115/1.2906890.

A production distributor-type fuel-injection system for diesel engines has been extensively investigated via computer-assisted simulation and experimentation. The investigation was mainly aimed at assessing and validating a sophisticated computational model of the system, developed with specific attention given to the pump and to some important aspects concerning the injection pressure simulation, such as the dynamic effects of the injector needle lift, the flow unsteadiness, and compressibility effects on the nozzle-hole discharge coefficient. The pump delivery assembly was provided with a valve of the reflux type. This presented a flat in the collar, forming a return-flow restriction with the seat, and had no retraction piston. A single-spring injector, with a reduced sac volume, was fitted to the system. The numerical analysis of transient flow phenomena linked to the mechanical unit dynamics, including possible cavitation occurrence in the system, was performed using an implicit finite-difference algorithm, previously set up for in-line injection equipment. Particular care was exercised in modeling the distributor pump so as to match the dynamics of the delivery-valve assembly to the pressure wave propagation in the distributor and its outlets. The so-called minor losses were also taken into account and it was ascertained that sudden expansion and contraction losses were significant for the type of pump examined. The experimental investigation was performed on a test bench at practical pump speeds. Pressures were measured in the pumping chamber, at two different pipe locations, and upstream to the needle seat opening passage. This last measurement was taken in order to evaluate the nozzle-hole flow coefficient with the support of the simulation, using experimental values of the needle lift, injection rate, and injected fuel quantity as known variables. The numerical and experimental results were compared and discussed, showing the validity of the model. The injection pressure time history and the influence of the delivery return-flow restriction on the system performance were numerically examined.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1994;116(4):831-837. doi:10.1115/1.2906891.

This paper considers the problem of properly accounting for the shafting inertia in torsional vibration analysis. It begins with a brief review of the two well-established methods: (1) arbitrarily lumping the shaft inertia with that of the disks, and (2) the continuum model, which considers both the flexibility and the inertia as distributed properties. Comments regarding the advantages and disadvantages of each are offered as motivation for the new method to be presented here. The new approach is then developed, using a Rayleigh-type approximation for the displacement between stations, with the full theory underlying it. The results of all three methods are then compared by application to several test cases.

Commentary by Dr. Valentin Fuster

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