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Viewing 121 to 150 of 42300
1989-09-01
Technical Paper
892073
Ömer L. Gülder Boris Glavinčevski, Norman N. Kallio
Our previous methodology of predicting the cetane number of middle distillates and heavy marine diesel fuels from hydrogen type distribution determined by proton NMR has been extended to cover the olefinic hydrocarbon structures and pure hydrocarbon compounds. Although, an ability to predict cetane numbers of olefinic fuels and pure hydrocarbons is not of immediate practical importance, from a more fundamental point of view, such a capability may lead to a better understanding of the ignition/fuel structure relationship in diesel engine combustion. The proposed technique is capable of predicting the ignition quality of almost all types of petroleum liquids including pure hydrocarbons.
1989-09-01
Technical Paper
892080
Paul T. Williams, Yanjin Shen, Gordon E. Andrews, Keith D. Bartle
Lubricating oil taken from the sump of a direct injection diesel engine has been analysed for the concentration of hydrocarbon contamination over a period of time. The oil was filtered and the sediment SOF analysed together with the filtrate. The results showed that there was an increase in the contamination in the used oil for both the filtrate and sediment hydrocarbon contamination. The carbon number distribution of the filtrate and sediment SOF were different. The filtrate representing contamination of the oil by fuel dilution and the sediment SOF contamination by particulates adsorbed into the oil in the combustion chamber. The highest contribution to the hydrocarbon contamination of the oil was from the filtrate in the early ageing period with an increasing contribution from the SOF of the sediment.
1989-09-01
Technical Paper
892083
Yongseo Ko, Richard W. Anderson
Heat transfer from the flame kernel to the electrodes during the spark ignition process is of interest for predicting the minimum ignition energy at a given engine operating condition. Experiments conducted in a constant volume bomb at near ignition limit conditions with small and large electrode surface areas (comparable to J gap plug), coupled with a phenomenological model, show the lumped heat transfer coefficient to range from 150-200 W/m2 K during the first 3 milliseconds of the ignition period. An additional analytical approach that uses the measured time dependent kernel-electrode contact areas gives reasonable agreement with the experimentally determined heat transfer coefficient and demonstrates that the dominant mechanism is thermal conduction. Heat loss from the flame kernel is comparable to the net ignition energy for the small electrodes after 3 milliseconds while that for the large electrodes is shown to equal the net ignition energy within 800 microseconds.
1989-09-01
Technical Paper
892085
Rolf D. Reltz, Tang-wel Kuo
Multi-dimensional computations were made to assess the effect of crevice flows through piston-cylinder-ring crevices on combustion and engine-out hydrocarbon emissions. The computations were made using the KIVA code with a characteristic time combustion sub model that accounts for laminar kinetics and turbulent-mixing effects. The crevice-flow boundary conditions were specified using a phenomenological crevice-flow model. A central-ignition pancake-chamber engine was considered, and the effects of top-land crevice design and engine operating condition were examined. The computed peak cylinder pressure was found to be 6 to 8 percent lower in cases with crevice flow than without because the crevice flow reduced the effective in-cylinder charge mass by similar percentages during the main stages of combustion. However, the details of combustion were essentially unchanged by the crevice flow.
1989-09-01
Technical Paper
892084
Deana D. Brehob
In many operating regimes, exhaust gas recirculation (EGR) while maintaining MBT spark timing improves cycle efficiency in SI engines. As the level of exhaust dilution is increased, the flame speed is reduced and the combustion rate is impaired. This leads to a drop in fuel economy as EGR rates are increased beyond the optimal level. To take advantage of the efficiency benefit of EGR without incurring the penalties of late combustion, a sensor which detects late combustion is tested. The signal from an ionization sensor placed near the exhaust port has been found to correlate to combustion which continues late into the expansion stroke. It may be possible to use the output from the ion sensor to maintain the EGR at the the optimum for fuel economy.
1989-09-01
Technical Paper
892086
Stephen C. Bates
Sets of sequential-cycle instantaneous flame images are used to study cycle-by-cycle variation of lean combustion in a spark-ignition four-stroke optical engine. Stereo gated image-intensified NTSC video cameras record flame radiation to show three-dimensional structure, while flame development is measured in each cycle by super-imposing early and later flame images. A variety of physical causes for cyclic variation are identified from the images. Correlations of flame geometry with mass burned fraction show that a larger initial flame kernel size results in a faster early burn in the cycle, and that flames that are flatter on a large scale cause lower peak burn rates than round flames. The early flame kernel is shown to vary greatly in size, shape, and location. This kernel has a major effect on combustion by setting the basic flame shape in mid-cycle.
1989-09-01
Technical Paper
892096
J. C. Kent, A. Mikulec, L. Rimal, A.A. Adamczyk, S. R. Mueller, R.A Stein, C. C. Warren
Intake-generated flow fields and subsequent combustion characteristics were studied respectively in a reciprocating piston water analog flow apparatus and in firing engines. Three 1.6L, I4, 4-valve engine cylinder heads were tested with and without one intake port blocked to generate six distinctly different inducted flow fields. Fluid velocity distributions and flow field structure (“zero mean motion”, “swirl”, and “tumble”) were determined at BDC of the induction stroke using 2-D or 3-D particle tracking velocimetry. Swirl ratios based on steady-flow data were also obtained. The burn duration for each case was determined from cylinder pressure data. The results show that burn duration decreased with increases in tumble or swirl strength. Previously observed correlations between burn duration and swirl hold if swirl is the major component of the large-scale motion.
1989-09-01
Technical Paper
892213
Calvin L. Ball
A historical perspective of the impact of advanced technologies on compression system design and development for aircraft gas turbine applications is presented. A bright view of the future is projected in which further advancements in compression system technologies will be made. These advancements will have a significant impact on the ability to meet the ever-more-demanding requirements being imposed on the propulsion system for advanced aircraft. Examples are presented of advanced compression system concepts now being studied. The status and potential impact of transitioning from an empirically derived design system to a computationally oriented system are highlighted. A current NASA Lewis Research Center program to enhance this transitioning is described.
1989-09-01
Technical Paper
892226
Edward V. Scicchitano, Thomas D. Yanik
This paper presents a basic guide of considerations for successful application of the integrated drive generator (IDG) to aircraft. Intrinsic to this guide is open communication and a close working relationship between the IDG supplier, buyer, and end-user. “Successful application” is defined as the interfaces which are optimized for and perform satisfactorily on the aircraft. This usually requires more than designing, developing, and qualifying the IDG or other subsystem to the design/procurement specification. The specification is typically a before-the-fact design document; it does not necessarily ensure interface with or satisfactory performance on the aircraft. Although the specification is what the supplier is contractually obligated to meet, the supplier and buyer must be willing to work together to make the IDG or other subsystem work on the aircraft, resulting in positive end-user experiences.
1989-09-01
Technical Paper
892252
Eike Richter
The idea of an all electric aircraft (secondary power) has been around for many years. Its benefits in terms of weight and operational cost savings have been in-creasingly better defined over time. Little has hap-pened, however, toward realizing this system, pro-bably, because one of the key components of such a system, the electrical generator has not achieved the acceptance in the engine world to warrant any more definite steps toward the all electric system. Support and size considerations dictate that this generator be integrated into the gas turbine (Integral Starter/Generator - IS/G). The last IS/G studies in the middle and late 70's found that even the best technology of the day, the PMG technology, did not solve all the concerns about its application to the IS/G task. Developments in the power electronics area since then have made an old electrical machine concept, the switched reluctance machine, a viable alternative for the integral starter/generator function.
1989-09-01
Technical Paper
892237
Jacques Hege
CURRENT CONDITIONS ARE FAVORABLE FOR SUPERSONIC TRANSPORTS. STUDIES FOR A REPLACEMENT FOR THE CONCORD HAVE BEEN ON GOING FOR SOME TIME. THIS PAPER REVEALS THE PROS AND CONS OF DEVELOPING SUCH A REPLACMENT BASED ON PREVIOUS STUDIES.
1989-09-01
Technical Paper
892254
Tibor Bornemisza, Colin Rodgers
This paper discusses the results of analytical studies supported by current development efforts and research paths to implement fast start technology for small gas turbine APU's, using non-metallic rotor components. APU start system weights can be a significant fraction of the total installed APU weight, especially if fast starts are demanded under sub-Arctic environments. It is shown that both start system weight, and rotor containment armor weight are proportional to the product of rotational speed squared and rotating assembly inertia. Significant weight savings are therefore feasible with rotating assemblies using lower density materials such as ceramics and composites. Recent tests are described at the authors affiliation wherein a modified T20 small gas turbine was accelerated from zero to 100% speed in 2 1/2 seconds.
1989-09-01
Technical Paper
892255
Antonios I. Georgantas, Gino Carrese, Tadeusz Krepec
To overcome some problems encountered in the design of electronic fuel control units for small gas turbine engines, different digital controllers are analyzed and implemented. A tuning method involving multivariable optimization techniques is formulated. The controllers are realized on a microcomputer which also monitors the experiments and performs the tuning on a specially equipped test bench.
1989-09-01
Technical Paper
892251
J. R. Kidwell
The Multipurpose Small Power Unit (MPSPU) Advanced Development Program is structured to provide advanced technology for current and future United States Army or other Department of Defense auxiliary power unit/secondary power systems applications. The Garrett Auxiliary Power Division initiated development of the MPSPU in June 1986 under sponsorship by the Aviation Applied Technology Directorate, Ft. Eustis, Virginia. Development has proceeded through initial design, component development and initial power unit development. The current status of the program is discussed herein and is an update to reports presented previously (Reference 1 and 2).
1989-09-01
Technical Paper
892253
R.M. (Fred) Klaass
To increase crew and aircraft survivability for 21st century fighters, a power system is envisioned which can supply higher power at high altitudes at the touch of a button. In the event of an aircraft power outage, this emergency power would be used to get the aircraft back under control and to restart the propulsion engines. The heart of the power system is a gas turbine, an Integrated Power Unit (IPU), designed to meet these requirements by starting and supplying 200 horsepower in two seconds, using a stored oxidizer (from air storage tanks on board the aircraft). The compressor is “aerodynamically declutched” in this emergency power mode, minimizing the stored air needed by the IPU to supply the required power. In addition, the IPU can smoothly transition over to the normal air breathing mode, where the compressor supplies full flow and the stored air is not used at all.
1989-09-01
Technical Paper
892142
David B. Kittelson, Michael J. Pipho, Matthew L. Franklin
An adaptive control system which determines the optimum system parameters based on the engine response to changes in those parameters, has been tested as an ignition timing control system on several gaseous fueled engines. The changes in the MBT timing for speed, load, air-fuel ratio, and fuel type were explored. The ability of the control system to correct the timing for these parameters was demonstrated. An air-fuel ratio control based on the same technique is also discussed.
1989-09-01
Technical Paper
892149
Edward T. King, Granger K. Chul
A 22 hour engine test was developed to evaluate the effects of fuels, lubricants, and valvetrain dynamics on the wear of OHC 2.3L engine camshafts and finger followers. Procedures include a break-in to improve test repeatability and a test sequence to allow single-shift operation. A surface analyzer capable of measuring cam lobe wear profiles to micro-inch accuracy provided a quantitative wear comparison. A pure mineral oil, as expected, resulted in higher camshaft wear than using a fully formulated SF lubricant. Cam and follower wear increased significantly when ethanol replaced gasoline as fuel. The combination of ethanol, mineral oil and heavy duty valve springs was selected to increase test severity for hardware discrimination. The average wear of the intake lobes was greater than the exhausts. Kinematic analysis and visual inspection of the valve train mechanism revealed differences in the relative motion and contact stress pattern.
1989-09-01
Technical Paper
892137
W. Shiells, P. Garcia, S. Chanchaona, J. S. McFeaters, R. R. Raine
Two heavy duty turbocharged and aftercooled diesel engines have been converted to spark ignition (SI) for natural gas fuelling. One engine features two valves per cylinder, high primary swirl and a compact combustion chamber. The other engine has four valves per cylinder and a more open combustion chamber shape. Both engines were characterized on a dynamometer and subsequently put into service where one of the engines has been monitored extensively. When a diesel engine is converted to SI operation, there is an involved process which must be carried out to insure reliable and efficient operation. Many aspects of the conversion process are limited by the original configuration of the diesel engine. Some of these aspects, such as combustion chamber shape, are shown to be important to the optimization of an SI converted engine and are highlighted in the comparison of these two engines.
1989-09-01
Technical Paper
892138
Roy W. Duncan
The use of natural gas as a transit bus fuel is being demonstrated by The Hamilton Street Railway Company. The H.S.R. Is a public transit system operating two hundred diesel buses and fifty electric trolley buses. Six transit buses are operating in daily service using a spark ignited engine dedicated to natural gas fuel. The buses are used primarily for peak period extra service because of insufficient fuel tank capacity. The buses have performed well in service and have exhibited few serious fuel related problems. The fuel consumption however has been considerably higher than anticipated and a series of valve keeper failures occurred in the latter stages of the project.
1989-09-01
Technical Paper
892140
G. A. Karim, W. Jones, R. R. Raine
The ignition delay period occurring in dual fuel engines operating on a wide range of gaseous fuels and in diesel engines with various inert diluents added to the intake charge is examined. The observed differences in the delay period between dual fuel and diesel operations are then attributed mainly to changes in the oxygen concentration of the charge, the charge effective temperature and the chemical kinetic processes.
1989-09-01
Technical Paper
892145
Tracy Colgan, John C. Bell
Wear of valve train components is one of the most critical factors limiting the life of automotive engines and in the performance evaluation of lubricants. Finger and rocker follower systems, which are commonly used in modern OHC gasoline engines, are particularly wear-prone, the wear profiles of the cam and follower surfaces exhibiting features that have hitherto defied satisfactory explanation. A new mathematical model based on simple wear theory is presented which is shown to be capable of predicting the essential features of the wear profiles of engine cams and followers. The magnitude of the predicted wear is of the correct order and the influence of changing cam/follower clearance and of hydraulic adjustment are consistent with observations of wear in service. The effects of lubricant viscosity and operating speed on the distribution of wear are discussed. The model is also applied to a conventional cam/tappet OHC valve train system.
1989-09-01
Technical Paper
892150
B. P. Williamson, I. R. Galliard, S. Benwell
A motored cylinder head utilising a cam and inverted bucket follower configuration has been instrumented to measure the oil film thickness in the elastohydrodynamic (EHD) contact separating cam and follower. Measurements were carried out using a capacitive divider circuit originally designed for use with deep groove ball bearings. A method is presented to convert the electrical measurements of contact capacitance into actual oil film thickness. These oil film thickness measurements are compared with a theoretical EHD analysis for this cam and follower configuration at the test temperature of 100°C. Oil film thickness measurements are reported for seven single grade oils of viscosity range 5 to 23 mPa.s at 100°C. These oils are fully formulated with the same additive package but with base stocks varied to obtain the required viscosities. The tests were run at constant camshaft speed and temperature.
1989-09-01
Technical Paper
892161
J. W. Hodgson, R. N. McGIll
A study has been completed in which a single-cylinder engine was operated on iso-octane and iso-octane doped with a nitrogen compound (pyridine). Tests were conducted to investigate the effects of fuel-air mixing and spark advance on the conversion of the fuel-bound nitrogen to nitric oxide. The results of the present study are compared with those from previous studies and it is concluded that both fuel-air mixing and spark advance affect the amount of fuel-bound nitrogen that is converted to nitric oxide. The results of the present study also can be used to explain the discrepancies that had existed among three previous studies dealing with fuel nitrogen conversion in spark ignition engines.
1989-09-01
Technical Paper
892162
M. R. Swain, J. A. Blanco, M. N. Swain
Abnormal combustion in methanol fueled engines was investigated using a combination of ion gap detection and pressure versus crankangle measurements. The ability to differentiate between cool flames and surface ignition is shown. It is shown that cool flames do exist in methanol fueled engines. It is additionally shown that they can occur before the spark plug fires producing cycle to cycle variations in the chemistry of the gases present in the spark plug gap. An analysis of the effect of surface temperature, at the time of deposit formation, on deposit induced surface ignition tendency was made.
1989-09-01
Technical Paper
892156
W. H. Buck, J. R. Lohuls, J. A. Murphy
Methanol continues to be an important alternative fuel candidate for use in spark ignition engines. In addition to its potential as an alternative energy source, methanol has been claimed to provide benefits in possibly reducing reactive hydrocarbon emissions which contribute to ozone formation. This has resulted in considerable interest in using methanol fuels in several U.S. urban areas to assist in air pollution reduction. As a result of government incentives on these issues, engine builders are now developing new generations of vehicles capable of operating on methanol. Lubrication of these engines will require methanol-compatible oil formulations. Test work has shown that some current quality engine oils, designed for use with gasoline fuel, severely limit engine durability due to excessive wear of the valve train, cylinder bore, and bearings. A laboratory engine test program using a 2.3-liter engine has been conducted to evaluate methanol-fueled engine lubrication.
1989-09-01
Technical Paper
892163
W. K. Kahl
Direct injection stratified charge (DISC) engines have much potential for tolerating the broad range of properties encountered in modern alternative fuels, while maintaining acceptable efficiency and performance levels. In practice these engines experience low combustion efficiency at light loads, leading to degraded performance and excessive unburned fuel emissions. A comparative test program was carried out to investigate the potential for improving upon these limitations in a methanol fueled DISC engine by employing a thermal barrier coating in the primary combustion chamber. The results indicate that the potential for improvement was likely small or difficult to perceive due to heavy friction losses in the engine/dyno tandem. Emissions were generally in accord with previously published data and unburned fuel continued to be prevalent at low loads. Additional work should focus on more aggressive insulation techniques and optimization of injection/ignition parameters.
1989-09-01
Technical Paper
892214
Thomas A. Dickey
To protect the air conditioning system of a turbine powered aircraft from contamination by traces of oil in the air bled from main engines and APU, a catalyc converter was developed for each, and put in service in the British Aerospace 146. The development procedures and flight hardware are described, data for sizing and pressure drop are presented, and limited service experience outlined.
1989-09-01
Technical Paper
892205
Dana Morris Dunham, Garl L. Gentry
Abstract Propeller normal force is a major contributor to pitch and yaw stability on propeller driven aircraft. While it is well-known that propeller normal force is a function of the number of blades, there are no published data for the high numbers of blades that are used in the new designs such as the GE UDF and Pratt-Whitney-Allison 578-DX. This paper presents the results of a test conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel using a sting-mounted counterrotation propeller and nacelle. The configurations tested were combinations of 0, 4, and 8 blades per hub. Tests were conducted for blade angle settings of 31.34°, 36.34°, and 41.34° over an angle-of-attack range from −10° to 90° and over a range of advance ratios from .8 to 1.4. The results show that propeller normal force varies with both solidity and angle of attack.
1989-09-01
Technical Paper
892007
Wolfgang Strauss, Horst Behnke
The electronic fuel injection and ignition control units on the engines of the new Mercedes-Benz SL roadsters were further developed on the basis of the tried and tested control units. Introducing a communication interface between both ECU's has permitted coordinated functions such as maximum speed limitation. The ignition control unit contains an adaptive closed-loop anti-knock control algorithm for each individual cylinder.
1989-09-01
Technical Paper
892005
Hans Brüggemann, Ernst Goblen, Manfred schäfer
The well-known 3-liter injection engine with 2 valves per cylinder which for example is installed into model 300 SE has been further developed into the new 3.0-liter six-cylinder engine for the 300 SL. The 4-valve technology has been employed to increase the power rating. Mercedes-Benz has been using this kind of technology for a long time now. Models 190 E 2.3-16 and 190 E 2.5-16 have for example been equipped with it since 1984 and 1988 respectively. This experience constributed to the design of the new 6-cylinder engine. Great store has been set not only on a high power rating but naturally also on criteria like emission minimization, low noise level, long service life, good idle stability and - above all - high torque in the low engine speed range.
Viewing 121 to 150 of 42300

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