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IN THIS ISSUE


RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1993;115(4):679-692. doi:10.1115/1.2906760.

In the United States, private personal transportation has become dominated by the automobile, a platform supported on four wheels and propelled by an internal combustion engine (ICE). Some of the reasons why this combination has emerged as the preferred choice are reviewed. Since urban air quality has become an issue, the ICE has kept pace with progressively more stringent exhaust-emissions regulations. Future emissions standards will encourage the use of alternative fuels and battery-electric propulsion. Looking far into the future, the depletion of fossil-fuel resources and/or definitive evidence that greenhouse gases are actually changing the global climate would foster a shift toward nuclear and solar energy. The automobile platform is compatible with such a shift. The ICE and the electric motor remain as potential motive sources, although they would face some difficult challenges.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):693-699. doi:10.1115/1.2906761.

Abrasive particles entering an engine because of inadequate air filtration can cause excessive wear, which may lead to premature engine failure. Despite the importance of filtration in engine systems, there is little understanding of the dynamics of the filtration process. Often, limited space is available for an engine air induction system. Therefore, filters are designed in smaller packages, resulting in higher aerosol velocities through the primary filter material. High aerosol velocities may cause dust re-entrainment and increase the amount of dust penetrating the filter. Our experiments with cellulose and synthetic-type filter media show examples of dust reentrainment for fine and coarse dust. Conditions for dust particle re-entrainment are discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):700-705. doi:10.1115/1.2906762.

Improving the efficiency of engine performance will require the design of systems with higher operating temperatures and pressures. These conditions will stress traditional lubricants beyond their current performance capabilities, and require the development of improved methods for friction and wear reduction. The most revolutionary approach to high-temperature lubrication is the concept of vapor phase delivery. An ashless organic compound can be vaporized by the heat of the operating engine or a carrier gas, and introduced into the ring zone of the cylinder. The vapor condenses or chemically binds with the piston ring or cylinder wall, and provides boundary lubrication. A minute amount of lubricant is constantly introduced in order to maintain a lubricating film. Each stroke of the piston shears off a portion of the lubricant layer, but condensing vapor continually replaces the surface film. Lubricant contributions to exhaust emissions are expected to be lower than those currently resulting from liquid lubricants. Vapor phase lubrication is an emerging concept that may be the key to the development of a commercial low heat rejection engine with improved energy efficiency and reduced emissions. The Department of Energy continues to fund research at a variety of industrial and academic institutions. Basic concepts and recent developments in the field of vapor phase lubrication will be reviewed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):706-710. doi:10.1115/1.2906763.

Overlays of either lead-indium or lead-tin-copper are electroplated onto both lead-bronze and aluminum alloy crankshaft bearings to improve seizure resistance and conformability during the initial running-in period. In addition, both the corrosion resistance, particularly of lead-bronze, and the effective fatigue strength of the composite bearing are improved by this layer. The life of the overlay is largely dependent upon the diffusion rate of the low melting point species to the substrate. Thus, migration of either the indium or the tin will determine both the corrosion and wear rates of the overlay. Owing to the processing requirements, aluminum bearings require a nickel or copper interlayer prior to final overlaying with either of the lead alloys. For diffusion control reasons, when depositing lead-tin-copper onto lead-bronze it is usual to have a thin nickel dam to retard the formation of copper-tin intermetallics, which under given conditions may reduce the overall strength and adhesion; lead-indium does not require such a dam on lead-bronze. The principal differences between the two overlays lie in their respective fatigue and wear properties. Thus, lead-indium has a higher fatigue strength but lower wear resistance than lead-tin-copper. This paper compares these two major overlays and considers the selection criteria for the overlay employed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):711-720. doi:10.1115/1.2906764.

Design analyses of crankshafts, including bearings, are necessary for both the layout of new engines and the modification of existing engines (increased power output, etc.). To improve the existing calculation systems for crankshafts and bearings, AVL has developed a new method. This method enables the coupled vibrations in the torsional, bending, and axial directions, including gyroscopic effects, to be analyzed. For simulation of multibearing effects, the bearing models consider both the hydrodynamic oil film and the stiffness of the bearing structure. The calculation of forced vibrations is carried out using the gas and mass forces acting upon the rotating crankshaft. Comparisons of calculated to measured results demonstrate the accuracy of this calculation technique. The method can be used for passenger car, truck, and medium speed engines. In this paper examples of truck and passenger car engine applications confirm the additional possibilities for the estimation of crankshaft dynamics. Also the improvement of the results obtained from the new technique compared with those from classical calculation methods is described.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):721-727. doi:10.1115/1.2906765.

Two crankcase explosions occurred within one month in diesel engines that drive large emergency generator sets at a nuclear power plant in Eastern Pennsylvania. As a result, the electric utility conducted an extensive investigation to determine the root cause(s) of the problem. Initial inspections confirmed that the crankcase explosions were the result of pistons and liners becoming overheated. The technical challenge was to establish why the pistons and liners were overheating when other engines of the same type did not appear to have the problem in the same duty. Analytical models of piston motion, engine start, and run thermodynamics, and a finite element analysis of piston distortion during engine start and load transients were developed. Preliminary work with these models predicted a feature of the piston design that could adversely affect lubrication conditions during a rapid start and load transient. Final input data to refine the models were needed and these were obtained from tests carried out on a similar diesel generator operated by a municipality in Iowa. This paper describes the successful accomplishment of the field tests using state-of-the-art instrumentation and recording equipment. It also shows how the modeling and test work identified wear at certain locations on the piston skirt as the origin of distress leading to the crankcase explosions. Unfavorable engine starting and loading conditions as well as less than desirable piston skirt-to-liner lubrication conditions in the engines at the nuclear power plant have been identified as the root causes and corrective action has been initiated.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):728-733. doi:10.1115/1.2906766.

This paper presents the results of a new dual-fuel engine development program. The engine is the largest commercially available in terms of power output (650 hp/cyl) and features very low emissions (1 g/hp-hr NOx ) and excellent fuel consumption (43 percent thermal efficiency). A two-cylinder turbocharged prototype was designed and built for the initial development. Results from testing on 18-cylinder production versions are also reported.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):734-741. doi:10.1115/1.2906767.

Typical conventional diesel engine designs are based on arrangements of single piston and cylinder sets placed sequentially either in-line or offset (“V”) along the crankshaft. The development of other engines, such as the opposed piston type, has been motivated by potential advantages seen in such designs, which may not be viable in conventional in-line or V engine arrangements. Several alternatives to conventional engine design have been investigated in the past and some aspects of these designs have been utilized by engine manufacturers. The design and development of a proof-of-concept opposed piston diesel engine is summarized in this paper. An overview of opposed-piston engines is presented from early developments to current designs. The engine developed in this work is a two stroke and uses four pistons, which move in two parallel cylinders that straddle a single crankshaft. A prechamber equipped with a single fuel injector connects the two cylinders, forming a single combustion chamber. The methodology of the engine development process is discussed along with details of component design. Experimental evaluations of the assembled proof-of-concept engine were used for determining feasibility of the design concept. An electric dynamometer was used to motor the engine and for loading purposes. The dynamometer is instrumented for monitoring both speed and torque. Engine parameters measured include air flow rate, fuel consumption rate, inlet air and exhaust temperatures, and instantaneous cylinder gas pressure as a function of crank position. The results of several testing runs are presented and discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):742-746. doi:10.1115/1.2906768.

In order to reduce the maximum cylinder wall temperatures of an air-cooled TC&IC diesel engine with large longitudinal and circumferential temperature gradients, a curved, squared cross-sectional channel supplied with engine lubrication oil was introduced into the upper part of the cylinder wall. Numerical analyses of the heat transfer within the baseline air-cooled cylinder and intensive experimental work helped to understand the temperature situation in the cylinder at diverse engine running conditions. The results of the combined cooling were greatly affected by the design, dimensions, position of the channel, and the distribution of the cooling oil flow, and are presented in the paper.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):747-749. doi:10.1115/1.2906769.

Previous works carried out in Istituto Motori laboratories have shown that natural gas is a suitable fuel for general means of transportation. This is because of its favorable effects on engine performance and pollutant emissions. The natural gas fueled engine provided the same performance as the diesel engine, met R49 emission standards, and showed very low smoke levels. On the other hand, it is well known that internal combustion engines emit some components that are harmful for human health, such as carbonyl compounds and polycyclic aromatic hydrocarbons (PAH). This paper shows the results of carbonyl compounds and PAH emissions analysis for a heavy-duty Otto cycle engine fueled with natural gas. The engine was tested using the R49 cycle that is used to measure the regulated emissions. The test analysis has been compared with an analysis of a diesel engine, tested under the same conditions. Total PAH emissions from the CNG engine were about three orders of magnitude lower than from the diesel engine. Formaldehyde emission from the CNG engine was about ten times as much as from the diesel engine, while emissions of other carbonyl compounds were comparable.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):750-755. doi:10.1115/1.2906770.

The effect of the electrical pulse width and the fuel temperature on dynamic flow and static flow rate of a gasoline fuel injector has been numerically and experimentally investigated. In numerical analysis, the physical domain covers the region from upstream of the valve seat to the injector exit. The three-dimensional unsteady Navier-Stokes equations in a curvilinear coordinate system are solved. Due to the needle movement in fuel injection, the physical domain is considered as a function of time. In the experimental study, the test stand consisting of a hydraulic system and an electrical system was designed to meet the requirements of Society of Automotive Engineers. The pulse width of 0.97–7.5 ms and the temperature of 20–100°C were used to study the pintle injector performance. Predicted dynamic flow and static flow rates show higher values at a temperature of 80°C, which are consistent with the test results.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):756-760. doi:10.1115/1.2906771.

The flow in a complex engine manifold is computed by generalizing the three-branch to the n -branch junction model. Energy-related pressure losses are implemented in the one-dimensional continuity equation and the effects of choked flow and changing flow patterns are considered. The computational results are compared with measurements on an engine with multi-entry pulse converter and compact single pipe exhaust systems. The influence of several parameters on the fuel consumption is determined.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):761-768. doi:10.1115/1.2906772.

A heat release correlation for oxygen-enriched diesel combustion is being developed through heat release analysis of cylinder pressure data from a single-cylinder diesel engine operating under various levels of oxygen enrichment. Results show that standard combustion correlations available in the literature do not accurately describe oxygen-enriched diesel combustion. A novel functional form is therefore proposed, which is shown to reproduce measured heat release profiles closely, under different operating conditions and levels of oxygen enrichment. The mathematical complexity of the associated curve-fitting problem is maintained at the same level of difficulty as for standard correlations. When the novel correlation is incorporated into a computer simulation of diesel engine operation with oxygen enrichment, the latter predicts pressure traces in excellent agreement with measured pressure data. This demonstrates the potential of the proposed combustion simulation to guide the application of oxygen-enriched technology successfully to a variety of multicylinder diesel systems.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):769-776. doi:10.1115/1.2906773.

A procedure has been developed and documented for determining the methane number of gaseous fuels. The methane number provides an indication of the knock tendency of the fuel. An experimental test matrix was designed for quantifying the effects of ethane, propane, butane, and CO2 . A unique gas mixing and control system was developed to supply test gases to the engine and to control the equivalence ratio and engine operation. The results of the experiments agreed well with the limited data published in the literature. Predictive equations were developed for the methane number (MN) of gaseous fuels using the gas composition. The forms of these equations are suitable for incorporation in a computer program or a spreadsheet.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):777-780. doi:10.1115/1.2906774.

An investigation of the effect of ambient gas temperature and density on diesel fuel spray penetration, spray angle, and wall impingement at an injection pressure of 75–134 MPa was conducted in a constant-volume bomb with a reconstructed Cummins PT fuel system by using a high-speed photographic technique. The results show that penetration does not increase monotonically with injection pressure, and ambient temperature has more effect on a high-pressure spray than on those with conventional pressures. With the high temperature, the penetration of a high injection pressure spray is reduced a bit, while the spray angle increases obviously. When the high-pressure spray impinges on a wall at ordinary temperature, the rebounding droplets can hardly be seen, but at higher wall temperature, a cloud of dense spray will be observed near the wall, and sometimes a vapor layer will be formed between the spray and the wall. Based on experimental results, an empirical formula considering the effects of both the ambient temperature and injection pressure is presented.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):781-789. doi:10.1115/1.2906775.

Ignition and combustion mechanisms in diesel engines were studied using the KIVA code, with modifications to the combustion, heat transfer, crevice flow, and spray models. A laminar-and-turbulent characteristic-time combustion model that has been used successfully for spark-ignited engine studies was extended to allow predictions of ignition and combustion in diesel engines. A more accurate prediction of ignition delay was achieved by using a multistep chemical kinetics model. The Shell knock model was implemented for this purpose and was found to be capable of predicting successfully the autoignition of homogeneous mixtures in a rapid compression machine and diesel spray ignition under engine conditions. The physical significance of the model parameters is discussed and the sensitivity of results to the model constants is assessed. The ignition kinetics model was also applied to simulate the ignition process in a Cummins diesel engine. The post-ignition combustion was simulated using both a single-step Arrhenius kinetics model and also the characteristic-time model to account for the energy release during the mixing-controlled combustion phase. The present model differs from that used in earlier multidimensional computations of diesel ignition in that it also includes state-of-the-art turbulence and spray atomization models. In addition, in this study the model predictions are compared to engine data. It is found that good levels of agreement with the experimental data are obtained using the multistep chemical kinetics model for diesel ignition modeling. However, further study is needed of the effects of turbulent mixing on post-ignition combustion.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):790-797. doi:10.1115/1.2906776.

In the GE 7FDL single cylinder research diesel engine, in-cylinder high-speed photographic studies were conducted on coal-water slurry (CWS) fuel combustion. Distinct flames of pilot and CWS combustion were noticed. It was proven that the coal fuel burns after piston impingement and secondary atomization. Agglomerated particles will develop when combustion conditions are not favorable. Cylinder pressure data were simultaneously recorded for each film frame. Heat release data can thus be produced for each photo study. Most of the findings of earlier combustion studies on engine performances were confirmed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):798-800. doi:10.1115/1.2906777.

Many companies worldwide are implementing and applying for registration for the ISO 9000 series of quality standards. This implementation has the same effect on an organization as any other process that is changing the methods, procedures, or the basic culture of the company. The management style necessary to make these changes successful is the same as that which is necessary for any other transformational process. If the correct management style is present, ISO 9000 implementation, and any other change being attempted, will be successful. Change can be accomplished without transformational management but the overall effect and the cost benefit will not be maximized. This transformational management is the most important element. The technical aspects (the ISO 9000 hows and whys) are just a matter of someone within the organization learning them and developing a plan and system for management. The correct management style to achieve change is the most difficult. Strategies need to be clearly defined and methods developed in order to control the projects. Roadblocks need to be clearly identified and action planned to compensate for any shortcomings.

Topics: Matter
Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1993;115(4):801-809. doi:10.1115/1.2906778.

In Connolly and Yagle (1992, 1993) we presented a new model relating cylinder combustion pressure to crankshaft angular velocity in an internal combustion engine, primarily the fluctuations in velocity near the cylinder firing frequency. There are three aspects to this model. First, by changing the independent variable from time to crankshaft angle, a nonlinear differential equation becomes a linear first-order differential equation. Second, a new stochastic model for combustion pressure uses the sum of a deterministic waveform and a raised-cosine window amplitude-modulated by a Bernoulli-Gaussian random sequence, parametrizing the pressure by the sample modulating sequence. This results in a state equation for the square of angular velocity sampled every combustion, with the modulating sequence as input. Third, the inverse problem of reconstructing pressure from noisy angular velocity measurements was formulated as a state-space deconvolution problem, and solved using a Kalman-filter-based deconvolution algorithm. Simulation results in Connolly and Yagle (1992, 1993) show that the parametrized pressure can be deconvolved at low to moderate noise levels, and combustion misfires detected, all in real time. This paper presents and discusses experimental results that confirm this model, at least at the relatively low-speed, low-to-moderate load operating conditions analyzed. They show that cyclic combustion pressure variation is fairly well modeled and may be directly estimated from angular velocity measurements. They also show that the deconvolution algorithm is able to detect misfires and possibly classify their severity. Since the experimental data are taken from an actual V-6 automobile engine, and the algorithms are simple enough to be implemented in real time, these results are directly applicable to real-world combustion pressure identification.

Commentary by Dr. Valentin Fuster

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