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EDITORIAL

J. Eng. Gas Turbines Power. 1990;112(3):267. doi:10.1115/1.2906490.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1990;112(3):268-275. doi:10.1115/1.2906491.

The conflicting legislative and customer pressures on engine design, for example, combining low friction and a high level of refinement, require sophisticated tools if competitive designs are to be realized. This is particularly true of crankshafts, probably the most analyzed of all engine components. This paper describes the hierarchy of methods used for crankshaft stress analysis with case studies. A computer-based analysis system is described that combines FE and classical methods to allow optimized designs to be produced efficiently. At the lowest level simplified classical techniques are integrated into the CAD-based design process. These methods give the rapid feedback necessary to perform concept design iterations. Various levels of FE analysis are available to carry out more detailed analyses of the crankshaft. The FE studies may feed information to or take information from the classical methods. At the highest level a method for including the load sharing effects of the flexible crankshaft within a flexible block interconnected by nonlinear oil films is described. This method includes the FE modeling of the complete crankshaft and the consideration of its stress field throughout an engine cycle. Fatigue assessment is performed to calculate the distribution of fatigue safety factor on the surface of the crankshaft. This level of analysis can be used for failure investigation, or detailed design optimization and verification. The method is compatible with those used for vibration and oil film analysis.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):276-279. doi:10.1115/1.2906492.

The purpose of this paper is to describe the concept, design, and analysis of a two-piece articulated piston for the Caterpillar 3500 diesel engine. Utilization of computer design and analysis enabled the piston to be optimized for structural capability, weight, and performance. Extensive analysis was performed on the steel upper structure. Models generated in two and three dimensions evaluated mechanical, thermal, and combined load cases. The result of this design and analysis is a piston that meets the engine’s objectives and provides additional value to the engine product.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):280-286. doi:10.1115/1.2906493.

The general theme of the growing use of electronic systems for the control and monitoring of large diesel engines is discussed. Central to the theme is a new digital governing system for industrial, traction, and marine diesels. This new governing system is capable also of being a marine propulsion controller or engine management/protection system and thus can be a very cost-effective package. In wider use it can work under the overall control of a power management host computer and interface with engine health monitoring equipment. Experience to date with the new governor is reported and plans for its future use outlined.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):287-300. doi:10.1115/1.2906494.

The microgeometry of the piston, rings, and skirt relative to the liner strongly influences lubrication in a reciprocating engine. This study develops an approximation technique that decouples the thermomechanical piston-skirt distortions from the complex lubricant support in a large diesel engine. The model considers the limiting case of starved skirt lubrication with large clearance. It permits efficient design of machined three-dimensional piston-skirt contours for piston support. In the calculations, a three-dimensional finite-element model is coupled with a postprocessing algorithm to predict skirt distortions, piston tilt, operating clearance, and oil-film contact area as a function of machined profile, thermal expansion, cylinder pressure, piston inertia, and transient side loads. A piston dynamics model is developed that defines the transient piston side force based on engine geometry, cylinder pressure, inertial loads, and wrist-pin offset. The results of this study indicate that (1) the transient skirt distortions due to cylinder pressure on the compression and power strokes result in a significant increase in oil-film contact area; (2) the piston skirt operating shape depends on the location and area of oil-film contact; (3) the contact area and location during intake and exhaust strokes vary substantially from that during the compression and power strokes; (4) the wrist-pin offset reduces the maximum side load and piston slap intensity occurring in the region of maximum cylinder pressure; (5) effective three-dimensional skirt profile design may result in significant changes in oil-film contact area and location on the skirt throughout the cycle.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):301-307. doi:10.1115/1.2906495.

The diagnostic technique described in this paper is based on measuring the instantaneous angular speed of both the front end and the flywheel on internal-combustion engines, recording more than 400 speed measurements per engine cycle. Two noncontacting transducers are added to an existing drive train without requiring drive train modifications. A digital circuit, which includes a microprocessor, samples and processes the raw speed data. The numerical analysis includes data noise filtering, and the numerical determination of front end and flywheel speed waveforms. When operating without external load, the engine accelerates only the inertial load. When neglecting friction and the small amount of torsional energy in the crankshaft, it is shown that the engine energy can be modeled as a lumped parameter system consisting of inertia on both engine front and flywheel ends, coupled by a torsional spring. The results from measurements on an eight-cylinder diesel engine with various cylinder faults show that reduced cylinder performance produces a drop of kinetic energy for the faulty cylinder. An engine performance criterion evaluates the performance of each cylinder, based on its contribution to total engine kinetic energy. The results demonstrate that fault conditions are detected with high reliability.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):308-316. doi:10.1115/1.2906496.

The physical properties of the fuel, such as density, viscosity, surface tension, and bulk modulus of elasticity, affect many aspects of the diesel injection process. The effects of these fuel properties on the fuel pressure in the high-pressure line, rate of injection, leakage, spray penetration, and droplet size distribution were determined experimentally. The mechanism of spray development was investigated by injecting the fuel into a high-pressure chamber. A pulsed Malvern drop-size analyzer, based on Fraunhofer diffraction, was utilized to determine droplet size ranges for various fuels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):317-323. doi:10.1115/1.2906497.

The behavior of an injection system with a rotative pump for reciprocating engines has been investigated. Experimental investigations were carried out using a specially designed apparatus to monitor several parameters, such as pressure inside the different chambers of the apparatus, moving part lift, and injected fuel quantity. In addition, a predictive mathematical model, based on mass momentum conservation laws, was developed to simulate such behavior and to predict all the most important parameters of the injection system. The comparison between numerical and experimental results has been satisfactory, allowing a generalization of the model and extensive theoretical predictions of the system behavior.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):324-330. doi:10.1115/1.2906498.

This paper reports on an experimental study of the autoignition behavior of several heavy fuel oils in a large constant-volume combustion chamber with single-shot injection. In the experiments the pressure and the temperature of the air in the combustion chamber before fuel injection varied between 30 and 70 bar and between 730 and 920 K. Illumination delay and pressure delay values have been correlated with these pressures and temperatures. It is shown that for all but one of the fuels examined, ignition delay ranking changes little with the choice of ignition delay definition, but more with the pressure and temperature conditions in the combustion chamber. The usefulness of the Calculated Carbon Aromaticity Index is discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):331-334. doi:10.1115/1.2906499.

Measurements of the radiant emission in the near infrared have been obtained in a spark-ignition engine over a wide range of operating conditions. The system includes an in-cylinder optical sensor and associated detector. Prior work has shown correlations between the measured radiance and pressure quantities such as maximum cylinder pressure, crank angle of maximum pressure, and Indicated Mean Effective Pressure. Here are presented comparisons between the radiant intensity and a simplified model of the radiation emission, which demonstrate that the measured intensity is a function of the mass-burn fraction, mean burned-gas temperature, and the exposed combustion-chamber surface area. Further simplification leads to the conclusion that the time of the maximum rate of change of radiant intensity is the same as for the maximum heat-release rate, leading to the possibility of feedback control of spark timing. In addition, the magnitudes of the maximum rate of change of radiant emission and maximum heat-release rate have a linear relationship over a range of different operating conditions.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):335-340. doi:10.1115/1.2906500.

A computational fluid dynamics code is used as a guide during the development stage of a passenger car spark ignition engine. The focus is on the flow properties of the inlet port as well as the heat transfer characteristics of the proposed cylinder head design. In the first part of this study, the aerodynamic characteristics of two slightly different inlet ports are considered and their effect on the development of in-cylinder flow is examined. The collected information is used to estimate geometric sensitivity and assess the effects of drifts between design and actual production specifications of inlet ports. In the second part, the same computational code is used to simulate in-cylinder combustion and determine the resulting temperature and heat flux distribution on the cylinder head walls. A comparison is then carried out between numerical results and experimental measurements and good agreement is obtained.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):341-347. doi:10.1115/1.2906501.

A computer simulation has been modified to study the effects of valve event parameters (lift, duration, and phasing) on spark-ignition engine performance. The zero-dimensional model employs polynomial and dynamic techniques to generate cam profiles for valve event optimization. The model was calibrated and validated against data from a General Motors 2.5-liter engine. The simulation was then used to determine optimum valve events under different engine conditions. This insight was used to improve the cam design. Subsequent engine testing confirmed that a 3 percent improvement in peak torque could be obtained with the optimized cam.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):348-356. doi:10.1115/1.2906502.

Previous engine data suggest that slower flame propagation in lean-burn engines could be due to slower flame expansion velocity at lean conditions than at stoichiometric combustion. Two classes of model, a quasi-dimensional engine-simulation program and a multidimensional engine-flow and combustion code, were used to study this effect in detail and to assess the capabilities of the models to resolve combustion details. The computed flame-speed data from each program differed somewhat in magnitude, but the predicted trends at various equivalence ratios were quite similar. The trends include: (1) The peak in-cylinder burned-gas temperature decreases by about 300 K as the equivalence ratio is decreased from 0.98 to 0.70. (2) Both the laminar flame speed and the flame-propagation speed, the latter computed from the time derivative of flame radius, decrease with decreasing equivalence ratio. (3) The turbulent burning speed, defined as the ratio of specific fuel-burning rate to the product of the flame frontal area and unburned-mixture density, is relatively insensitive to equivalence-ratio variations at the same flame-radius position. The previous experimental finding that the reduction in flame-propagation speed with decreasing equivalence ratio is caused mainly by the lower thermal-expansion speed, calculated by subtracting the turbulent burning speed from the flame-propagation speed, was confirmed. This is a consequence of lower burned-gas temperature for the lean case. Regarding the reliability of the models to resolve the combustion details, limitations of the models are identified and discussed in detail.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):357-368. doi:10.1115/1.2906503.

A general method for analyzing the time-correlation and frequency-spectral structure of turbulence in IC reciprocating engines was developed and applied to the cycle-resolved turbulent velocity fluctuation and to the fluctuating motion in its more conventional sense. It is based on an alternative definition of the Eulerian temporal autocorrelation coefficient so as to reduce this to an even function solely of the separation time within specific correlation periods into which the engine cycle is divided. This procedure was shown to be a refined version of a previous approach to spectral analysis of engine turbulence used by the authors, and was compared to the one based on the rough application of two definitions of nonstationary autocorrelation coefficients in the standard approach for stationary flows. It was proved to be suitable for studying the average statistical properties of segmented nonstationary turbulence sample records, being easily extensible from temporal to spatial records. The method was applied to the analysis of the effects of different swirl flow conditions on correlation and spectral turbulence quantities in an automotive engine. The spatial distribution of the in-cylinder dissipation time scale of turbulence and, in particular, the influence of the wall on this parameter were also investigated.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):369-375. doi:10.1115/1.2906504.

A coal-fueled diesel engine holds the promise of a rugged, modular heat engine that uses cheap, abundant fuel. Economic studies have indicated attractive returns at moderate diesel fuel prices. The compositions of coal-water fuels are being expanded to cover the major coal sources. Combustion has been developed at 1000 rpm with mechanical and electronic fuel injection. Dual fuel operation can run the engine over the load range. Erosion of fuel nozzles has been controlled with diamond compacts. Wear of piston rings and cylinder liners can be controlled with tungsten carbide coatings. Emission measurements show higher particulates and SO2 and lower NOx , CO, and HC. Particulate and SO2 control measures are being investigated.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):376-383. doi:10.1115/1.2906505.

Coal-water slurry having micronized coal particles with approximately 50 percent coal loading is successfully ignited and combusted in one cylinder of a two-cylinder 645 EMD engine by using diesel fuel pilot ignition aid. The effects of three different parameters, namely, (a) pilot timing, (b) pilot amount, and (c) CWS fuel amount, are investigated in detail. The physical trends of combustion under single parametric variations are presented in terms of the cylinder pressure, temperature, heat release rates, and cumulative heat release curves. CWS combustion with less than 5 percent of the energy of combustion coming from pilot fuel is achieved.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):384-390. doi:10.1115/1.2906506.

A combustion model has been developed for a direct-injected diesel engine fueled with coal-water slurry mixture (CWM) and assisted by diesel pilot injection. The model combines the unique heat and mass transport and chemical kinetic processes of CWM combustion with the normal in-cylinder processes of a diesel engine. It includes a two-stage evaporation submodel for the drying of the CWM droplet, a global kinetic submodel for devolatilization, and a char combustion submodel describing surface gasification by oxygen, carbon dioxide, and water vapor. The combustion volume is discretized into multiple zones, each of whose individual thermochemistry is determined by in-situ equilibrium calculations. This provides an accurate determination of the boundary conditions for the CWM droplet combustion submodels and the gas phase heat release. A CWM fuel jet development, entrainment, and mixing submodel is used to calculate the mass of unburned air in each of the burned zones. A separate submodel of diesel pilot fuel combustion is incorporated into the overall model, as it has been found that pilot fuel is required to achieve satisfactory combustion under many operating conditions. The combustion model is integrated with an advanced engine design analysis code. The integrated model can be used as a tool for exploration of the effects of fuel characteristics, fuel injection parameters, and engine design variables on engine performance, and in the assessment of the effects of component design modifications on the overall efficiency of the engine and the degree of coal burnout achieved.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):391-397. doi:10.1115/1.2906507.

An existing coal-water slurry fueled diesel engine cycle simulation was modified to include particle-to-particle and droplet-to-droplet interactions during the combustion and vaporization processes. Two aspects of these interactions, known as group effects, were considered. Group Effect Number 1 (GE1) relates to the species concentrations and temperature profiles between particles during combustion and between droplets during vaporization. Group Effect Number 2 (GE2) relates to the blockage of air entrainment to the fuel region due to the large momentum flux of volatiles and CO during combustion or water vapor during vaporization. The major conclusions were that GE1 affected the detailed process characteristics and in-cylinder conditions, and moderately affected the overall engine performance for the cases studied. These results were largely due to suppression of the water vaporization process relative to the case with no group effects. GE2 did not significantly affect the in-cylinder processes or the overall performance of the engine for the cases studied.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):398-406. doi:10.1115/1.2906508.

Periodically, there is discussion between engine and vehicle manufacturers and petroleum companies regarding fuels with new and different characteristics to match the needs of spark and compression-ignited engines. The most recent discussions are related to legislation and regulations that will possibly require fuels to be reformulated in the future. The objective will be to make fuels that, when burned in IC engines, emit pollution no greater than alternatives such as methanol or natural gas. The thesis of this paper is that a national fuel qualification could result in motor fuels that, when used in cars and trucks, would be environmentally acceptable. A speculated series of tests to qualify the fuel, one unleaded grade of gasoline, one type 2-D fuel for on-highway diesel trucks and buses, and one type 1-D fuel for city bases, is described. Once qualified, the refiner would certify that the fuel dispensed is in all material respects identical to the prototype fuel qualified. The industry qualification would be good for, say, five years or until the fuel was reformulated. Such a procedure would be industry regulated through periodic audit as well as self-audit provisions to assure fuel quality is maintained at the dispensing pump. Most of the needed procedures are available for such qualification. It remains for the manufacturers and refiners to agree on the need to reformulate gasoline and diesel fuel, develop pass/fail limits for acceptance, and establish a qualification approval protocol. An approach to demonstrate improved performance and emissions is suggested.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):408-412. doi:10.1115/1.2906511.

The measurement of exhaust components from large natural gas transmission engines involves collection of the exhaust sample, transfer of the sample to the analytical instrumentation, measurement of individual component concentrations, and calculations of emission results in terms of mass, fuel specific, and brake specific rates. The major exhaust components measured include nitrogen oxides (NOx ), total hydrocarbons (THC), carbon dioxide (CO2 ), carbon monoxide (CO), and oxygen (O2 ). Collection of the exhaust sample requires proper probe design and placement in the exhaust system. Transfer of the sample to the analytical instruments must maintain sample integrity from the point where the sample is removed from the exhaust stream to the point at which the sample enters the instrument for analysis. Various analytical techniques are used to measure the exhaust emission concentrations. These techniques include chemiluminescence for NOx , flame ionization for THC, nondispersive infrared (NDIR) for CO2 and CO, and polarography for O2 . Calculation of the emission results in terms of mass fuel specific, and brake specific rates utilizes the measured emission concentrations, the engine operating parameters, and the “total carbon” method for data reduction and presentation.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):413-421. doi:10.1115/1.2906512.

Current dual fuel engines utilizing standard mechanical (Bosch type) fuel injection systems set to 5–6 percent pilot delivery do not appear capable of reducing NOx emissions much below the current minimum of 4 g/bhp-h without incurring substantial penalties in efficiency and operability. A prototype Electronic Pilot Fuel Injector (EPFI) was designed that overcomes the shortcomings of the mechanical injection system, consistently delivering 3 percent or less pilot at pressures as high as 20,000 psi. The EPFI was installed and tested in one cylinder of a standard production dual fuel engine operating at a waste water treatment facility. A feasibility test confirmed that the engine would indeed operate satisfactorily at 2.9 percent pilot. Comparisons with baseline data revealed the EPFI yielded a 45 percent reduction in NOx emissions with a 3 percent or greater improvement in efficiency. Further optimization of the system, discussed in Part II, indicates that even greater reductions in NOx emissions can be obtained without incurring a penalty in fuel consumption.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):422-430. doi:10.1115/1.2906513.

Single-cylinder testing of an Electronic Pilot Fuel Injection (EPFI) system (reported in Part I) indicated that a 45 percent reduction in NOx emissions could be obtained with a 3 percent improvement in fuel consumption by replacing the mechanical system, delivering 6 percent pilot, with the EPFI at 2.9 percent delivery. Further optimization testing of this system at pilot levels down to 0.7 percent over a wide range of timings and air/fuel ratios resulted in even further reductions in NOx emissions without fuel penalty. The EPFI system can yield NOx emissions levels significantly below 2 g/BHP-h with an improvment in fuel consumption of at least 3–4 percent, and probably yield emissions level as low as 0.5 g/BHP-h without substantial penalties in efficiency or operability.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1990;112(3):431-437. doi:10.1115/1.2906514.

A refinement of the honeycomb trap model developed by the authors for analyzing the temperature history of the trap channels during the regeneration period is presented. The first results obtained, shown in previous papers [1, 2], encouraged the authors to improve the model in order to account for the heat transfer not only along the channel length, but also in the radial direction. In order to achieve this objective, a control volume approach was used to simulate the soot regeneration in all contiguous channels along the axial and radial directions of the monolith, and to determine the wall temperature and soot oxidation as a function of time. Different thermodynamic conditions of the exhaust gas at the trap inlet were considered in order to examine the effects of cold regeneration. For the same soot amount accumulated in the trap, the soot burnup time and temperature history depend on the inlet temperature. In addition to varying the gas initial conditions, the effects of the amount of soot collected and its radial distribution in the channels, before the regeneration process takes place, were also considered in order to predict the wall temperature rise and the soot oxidation rate. The results show the temperature peak values and their location inside the trap, and permit estimation of the conditions under which the trap temperature can reach unbearable values.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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