0


RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1988;110(3):313-320. doi:10.1115/1.3240123.

A nonlinear, “sliding mode” fuel-injection controller is designed based on a physically motivated, mathematical engine model. The designed controller can achieve a commanded air-to-fuel ratio with excellent transient properties, which offers the potential for improving fuel economy, torque transients, and emission levels. The controller is robust to model errors as well as to rapidly changing maneuvers of throttle and spark advance. The sliding mode control method offers a great potential for future engine control problems, since: it results in a relatively simple control structure that requires little on-line computing and no table lookups; it is robust to model errors and disturbances; and it can be easily adapted to a family of engines.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):321-324. doi:10.1115/1.3240124.
Abstract
Topics: Engines
Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):325-333. doi:10.1115/1.3240125.

This paper describes a combined analytical and experimental hardware-in-the-loop powertrain systems analysis methodology. Central to the implementation of this methodology is a real-time dynamic system simulation computer such as the high-speed Applied Dynamics Model AD10. For automotive engine control system studies, wide bandwidth in-cylinder combustion pressure sensor signals are input to the AD10 computer. Control commands are calculated and communicated at high data rates to throttle valve, spark ignition, and fuel injector actuators. Both simulation and experimental results are presented. Using this approach, the functional improvements associated with various control philosophies can be determined.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):334-342. doi:10.1115/1.3240126.

Engines today must satisfy stringent emission requirements but must at the same time have low fuel consumption. One method of approaching both of these goals in spark-ignited natural gas engines is with lean combustion. The use of as much as 80 percent excess air significantly reduces the peak combustion temperature and, as compared to a stoichiometric engine, reduces the NOx emissions by up to 90 percent and the fuel consumption by up to 15 percent. One limitation on lean combustion, however, is the high energy needed for ignition. In larger engines, a small prechamber containing an easily ignitable near-stoichiometric mixture has proved to be both successful and popular as one method of producing the necessary high ignition energy. Although this form of stratified charge combustion has been known for many years, its development has largely been the result of “cut and try” procedures. Lack of access for suitable instrumentation, combined with the difficulty of isolating the individual variables which affect performance, has limited the fundamental understanding of the mechanism of prechamber combustion. This paper summarizes results from a research program where a constant-volume combustion rig is used to simulate engine operation. Emphasis is placed on high-speed photography of the prechamber combustion. A second program on a single-cylinder prechamber spark-ignited gas engine and a third on a multiple-cylinder engine will be reported in subsequent papers.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):343-348. doi:10.1115/1.3240127.

It is important to reduce emissions from diesel engines, which are used in the cogeneration systems. The mass transfer to the fuel spray plays various roles in fuel consumption rate and in trace species emission. High injection pressure and a re-entrant combustion chamber were used to make the mass transfer larger. The need for high injection pressure and controlled injection timing for NOx led the authors to use the new Komatsu fuel injection pump. This pump, which has a re-entrant combustion chamber, resulted in clean engine emissions and confirmed the importance of air entrainment to the spray.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):349-355. doi:10.1115/1.3240128.

SEMT PIELSTICK has developed since 1971 a range of medium-speed dual-fuel engines with relatively high air-fuel ratios, which enable ratings similar to diesel engines. The PC 2.3 DF.C of 1971 was developed up to 535 hp/cyl. and was followed by the PC 2.5 DF.C of 600 hp/cyl. This later engine was applied in the West German cogeneration plan of a textile factory, giving more than 82 percent use of primary energy. This engine may also be used as a pollution-abating machine, because it traps toxic solvent vapors, which are burned in the engine, reducing furthermore the apparent (paid) energy consumption. Thanks to the lean air-gas mixture, the very severe West German limits on pollution could be fulfilled without any extra depolluting device. The newest development is the PA 5 DF engine of the same philosophy, which will cover the 1000 to 3600 kW range.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):356-360. doi:10.1115/1.3240129.

Fuel costs represent a major portion of the total operating expense of a heavy-duty engine in continuous service. Many new technologies are being developed to lower engine fuel consumption, but a 10–15 percent reduction in fuel costs is now achievable using Rankine Bottoming Cycle (RBC) technology. System economics require integration of state-of-the-art technology in the turbine, heat exchangers, and automatic controls. This paper describes the design and initial test results of a project to demonstrate a diesel engine-RBC power plant. The system was constructed for a Caterpillar 3500 series 16-cylinder (3516) engine with a combined output of 1415 kW. Initial test results have demonstrated a 10.4 percent fuel savings at a thermal efficiency of 44.5 percent. The RBC module is a steam-based, stand-alone unit featuring unattended operation through the use of on-board water treatment, a once-through boiler, automatic control system, and a unique design three-stage-dual pressure steam turbine. The modular concept allows the system to be adapted to other engines and alternative heat sources.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):361-368. doi:10.1115/1.3240130.

An experimental study of electrostatically atomized and dispersed diesel fuel jets has been conducted. A new electrostatic injection technique has been utilized to generate continuous, stable fuel sprays at charge densities of 1.5–2.0 C/m3 of fluid. Model calculations show that such charge densities may enhance spray dispersion under diesel engine conditions. Fuel jets were injected into room temperature air at one atmosphere at flow rates of 0.25–1.0 cm3 /s and delivery pressures of 100–400 kPa. Measured mean drop diameters were near 150 μm with 30 percent of the droplets being less than 100 μm in diameter at typical operating conditions. The electrical power required to generate these sprays was less than 10−6 times the chemical energy available from the fuel. The spray characteristics of an actual diesel engine injector were also studied. The results show considerable differences in spray characteristics between the diesel injector and electrostatic injection. Finally, ignition and stable combustion of electrostatically dispersed diesel fuel jets was achieved. The results show that electrostatic fuel injection can be achieved at practical flow rates, and that the characteristics of the jet breakup and dispersion have potential application to combustion systems.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):369-376. doi:10.1115/1.3240131.

This report deals with a study concerning the scavenging performance of a two-stroke cycle gasoline engine under the following conditions: the throttle of the carburetor is set at variable levels, the delivery ratio is set at a predetermined level, the engine speed is varied, and the scavenging and exhaust ports are set at different heights. If the properly selected factors stipulated for a scavenging model are used, the calculated results can be made as consistent as the measured results of the carburetor set at full throttle, as discussed in the previous reports [1, 2]. The mass diffusion, mixing, and short-circuit factors make up the essential coefficients. The factors represent major characteristics: blow-back, return-blow, and the loss of fresh gases. These phenomena are more clearly illustrated by three-dimensional representations of the gas components in the scavenging passage and exhaust pipe. The analyses of these functions may provide an effective means of improving the scavenging performance, i.e., the delivery ratio, trapping efficiency, and charging efficiency.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):377-384. doi:10.1115/1.3240132.

The authors have been conducting studies on the reduction of exhaust emissions using a high-speed diesel engine. By applying composite countermeasures consisting of five items: (1) timing retard, (2) optimization of fuel injection system, (3) water-in-oil type emulsified fuel, (4) application of ignition improver, and (5) an increase in airflow quantity, an exhaust NOx level less than half of the original was attained while retaining the original low levels of fuel consumption, smoke density, and engine noise. The authors developed new measuring instruments in order to grasp the true nature of combustion, especially to clarify the delicate change in combustion. By using these instruments, the combustion phenomena were analyzed accurately, speedily, and synthetically on various aspects such as combustion mode, vibration, noise, thermal loading, heat balance, etc. The complicated combustion behavior in the cylinder has been clarified in part by simultaneous measurement of cylinder pressure at several points.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):385-392. doi:10.1115/1.3240133.

In low-speed large diesel engines, low-grade or heavy petroleum fuels have long been used as an economy measure. Efficient use of various low-grade fuels has recently become a topic of great concern also for high-speed small diesel engines. This paper describes and analyzes improvements of the thermal efficiency and smoke emissions by fuel heating and blending with low-viscosity fuels in high-speed diesel engines with a range of low-grade or high-viscosity fuels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):393-398. doi:10.1115/1.3240134.

When a precombustion chamber type Diesel engine is operated under light loads and at low speeds, it is observed that the ignition flames in its main combustion chamber are generated in several stages under specific conditions of fuel injection. The authors, by observing the multistage ignition flames through an optical fiber probe inserted into the chamber, confirmed a number of band spectra emitted from some substances and CH radicals, existing in the flames, and have made clear some aspects of the chemical reactions taking place in Diesel combustion.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):399-404. doi:10.1115/1.3240135.

The self-ignition process in diesel engines is influenced by many parameters, which are partially interrelated. In order to separate the influence of basic parameters, a special high-pressure, high-temperature vessel has been designed that allows injection in short intervals under defined and repeatable conditions. The evaluated parameters include: cetane number, viscosity and volatility, vaporization behavior, and ignition improving additives. In addition to other factors, the investigations showed that the cetane number itself is not sufficient to characterize the self-ignition properties especially of heavy fuels and fuels containing ignition improvers. Additionally, the influence of injection parameters was evaluated, including injection quantity, pressure level, and nozzle design.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):405-414. doi:10.1115/1.3240136.

As part of a comprehensive simulation of a prototype locomotive propulsion system, a detailed model has been developed that predicts the dynamic response of an experimental two-stroke, turbocharged and intercooled diesel engine. Engine fueling and brake torque are computed from regression equations derived from an extensive data base. Corrections are applied to the calculated steady-state torque to account for dynamic deviations of in-cylinder trapped air-fuel ratio from the steady-state value. The engine simulation accurately represents the operation of the turbocharger, which is gear-driven at low turbocharger speeds, and freewheels through an overrunning clutch when exhaust energy accelerates the turbocharger beyond its geared speed. Engine fueling level, i.e., rack, is determined from a dynamic simulation of an electrohydraulic governor, which responds to the difference between the desired and the actual engine speeds. The governor representation includes: (1) finite rate of change of engine set speed; (2) load regulator feedback for control of applied engine loads; and (3) fuel limiting under conditions of excessively high load demand. The fundamentals of the engine/governor model are given in the paper along with examples that emphasize the dynamic operation of these particular components.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):415-422. doi:10.1115/1.3240137.

A micronized de-ashed coal-water slurry (CWS) fuel of approximately 50 percent coal loading has been successfully ignited and burned in one GE 7FDL engine cylinder at 1050 rpm. For this study, only about 1/3 of the full load fuel engery was supplied due to limitations of the fuel injection equipment used. Three types of ignition methods have been investigated: compression ignition with no ignition aid; separate diesel pilot fuel injection to ignite the CWS fuel; combined CWS and pilot diesel fuel injection (stratified pilot ignition). Conditions of ignition and the burning characteristics that immediately followed using the above three ignition methods are described.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):423-430. doi:10.1115/1.3240138.

Full load (186 kW/cyl) operation using CWS fuel at 1050 rpm has been achieved on a single-cylinder GE-7FDL test engine. No major changes in engine parameters were made. With normal inlet air conditions, 3–5 percent pilot diesel fuel, separately injected or stratified into the main coal charge, was used. Inlet air temperature had to be raised about 40°C if no pilot diesel fuel was used. The coal burnout was about 95 percent and the cycle efficiency was comparable to using diesel fuel. The NOx and CO emissions were about 1/2 of those obtained normally with diesel fuel. The maximum heat release rate was higher than diesel fuel operation which resulted in higher maximum cylinder firing pressure. The combustion characteristic and its dependence on some fuel characteristics and inlet air parameters are discussed. Increasing coal burnout while limiting maximum cylinder firing pressure is the main objective of near future studies.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):431-436. doi:10.1115/1.3240139.

Successful operation of the Cooper-Bessemer JS-1 engine on coal–water slurry (CWS) fuel has been achieved at full power output, part load, and part speed conditions with varying degrees of diesel pilot fuel including zero pilot (auto-ignition of CWS). Selected results of the effect of pilot fuel quantity, pilot fuel timing, and manifold air temperature on engine performance are presented. Also, the influence of injector nozzle hole size and CWS mean particle size on engine performance is studied. High injection pressures resulted in good atomization of CWS and in combination with heated combustion air resulted in short ignition delays and very acceptable fuel consumption. Low CO/CO2 ratios in exhaust gas analysis confirmed good combustion efficiency. NOx emissions are compared for CWS and diesel fuel operation of the engine. Effect of injector nozzle hole size and manifold air temperature on NOx emissions is studied.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):437-443. doi:10.1115/1.3240140.

The U.S. Department of Energy, Morgantown Energy Technology Center has assumed a leadership role in the development of coal-burning diesel engines. The motivation for this work is obvious when one considers the magnitude of the domestic reserves of coal and the widespread use of diesel engines. The work reported in this paper represents the preliminary engine experiments leading to the development of a coal-burning, medium-speed diesel engine. The basis of this development effort is a two-stroke, 900 rpm, 216-mm (8.5-in.) bore engine manufactured by Electro-Motive Division of General Motors Corporation. The engine, in a minimally modified form, has been operated for several hours on a slurry of 50 percent (by mass) coal in water. Engine operation was achieved in this configuration using a pilot injection of diesel fuel to ignite the main charge of slurry. A standard unit injector, slightly modified by increasing diametric clearances in the injector pump and nozzle tip, was used to inject the slurry. Under the engine operating conditions evaluated, the combustion efficiency of the coal and the NOx emissions were lower than, and the particulate emissions were higher than, corresponding diesel fuel results. These initial results, achieved without optimizing the system on the coal slurry, demonstrate the potential for utilizing coal slurry fuels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):444-452. doi:10.1115/1.3240141.

The combustion of 50 wt percent coal slurries, using water, diesel fuel, and methanol as carrier liquids, was investigated in a single-cylinder research engine. High temperatures were achieved in the engine cylinder using low-heat-rejection engine technology, electrically heated glow plugs, and heated inlet air. Comparisons of the fuels and different methods of providing high cylinder temperature were made using cylinder pressure data and heat release calculations. Autoignition of the coal/water slurries was attained using auxiliary heat input. The burning rates of all the autoignited slurries were significantly enhanced by using a pilot injection of diesel fuel. Under some operating conditions the engine thermal efficiency was equal to diesel fuel performance. It was apparent that engines designed for coal slurry should maximize the prechamber volume.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):453-461. doi:10.1115/1.3240142.

A quasi-steady gas-jet model was applied to examine the spray trajectory in swirling flow during the ignition-delay period in an open-chamber diesel engine timed to start combustion at top dead center. Spray penetration, deflection, and the fractions of too-lean-mixed, burnable, and overpenetrated fuel at the start of combustion were calculated by employing the measured ignition delay and mean fuel-injection velocity. The calculated parameters were applied to correlate the measured exhaust hydrocarbon (HC) emissions. The engine parameters examined were bowl geometry, compression ratio, overall air-fuel ratio, and speed. Both the ignition delay and the relative spray-penetration parameter, defined as the ratio of the spray-penetration distances at the moments of start of combustion and wall impingement, gave good correlations for some of the engine parameters examined but could not explain all the measured trends. However, good correlation of the measured exhaust HC emissions was obtained by using the calculated too-lean-mixed and overpenetrated fuel fractions at the start of combustion. Correlation of the overpenetrated fuel with the measured HC indicated that approximately 2 percent of the fuel mass that overpenetrated before start of combustion emitted from the engine as unburned HC. This could account for 0 to 65 percent of the total HC emission from this engine. Additionally, it was found that the too-lean-mixed fuel could contribute 10 to 30 percent of the total HC emission, as found in a previous study on a somewhat similar engine. The remaining HC emission is caused by other sources such as bulk quenching.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):462-469. doi:10.1115/1.3240143.

The maximum power that can be extracted from an engine operating at a given condition was determined by means of analyses based on the first and second laws of thermodynamics. These analyses were applied to a heavy-duty single-cylinder open-chamber diesel engine operated at constant speed. Over the range of operating conditions investigated, the second-law efficiency (ratio of brake power to maximum extractable power) of the engine, which increased with engine load, was found to vary from 22 to 50 percent. It was concluded that besides heat transfer, the combustion process was the most important source of irreversibility and accounted for 25 to 43 percent of the lost power.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):470-474. doi:10.1115/1.3240144.

An experimental and theoretical study of inlet flow was carried out on a Ford V6 Zephyr four-stroke cycle spark ignition engine. Details of measurements of individual cylinder flows were made on one bank of three cylinders (Nos. 4, 5, and 6) over a range of engine speeds from 1500 to 3500 rpm and throttle positions, full (WOT) down to 1/4 position. The object of the investigation was, first, to determine experimentally the extent of the variation of flow rate from cylinder to cylinder with changes in throttle position and engine speed and, secondly, to determine whether the computer simulation could confirm the trend. The main results of the tests showed that the outer two cylinders, No. 4 and No. 6, had the same flow rate within a variation of about 1/2 percent and that the middle cylinder, No. 5, had about 3 percent more flow at low speeds and 1 percent more at high speeds. In the main these were confirmed by the computer calculations. The volumetric efficiencies were also determined; these produced fairly smooth curves decreasing about 4 to 6 percentage points over the speed range and decreasing progressively as the throttle was reduced. There was evidence of recovery in the magnitude of volumetric efficiency at higher speeds and smaller throttle openings. The computer results also produced these trends.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):475-481. doi:10.1115/1.3240145.

The low-heat-rejection (LHR) diesel promises decreased engine fuel consumption by eliminating the traditional liquid cooling system and converting energy normally lost to the coolant into useful shaft work instead. However, most of the cooling energy thus conserved is transferred into the exhaust stream rather than augmenting crankshaft output directly, so exhaust-energy recovery is necessary to realize the full potential of the LHR engine. The higher combustion temperature of the LHR diesel favors increased emission of NOx , with published results on hydrocarbon and particulate emissions showing mixed results. The cylinder insulation used to effect low heat rejection influences convective heat loss only, and in a manner still somewhat controversial. The cyclic aspect of convective heat loss, and radiation from incandescent soot particles, also deserve attention. The temperatures resulting from insulating the cylinder of the LHR diesel require advancements in lubrication. The engine designer must learn to deal with the probabilistic nature of failure in brittle ceramics needed for engine construction. Whether ceramic monoliths or coatings are more appropriate for cylinder insulation remains unsettled. These challenges confronting the LHR diesel are reviewed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):482-488. doi:10.1115/1.3240146.

Recently great expectations were put into the insulation of combustion chamber walls. A considerable reduction in fuel consumption, a marked reduction of the heat flow to the cooling water, and a significant increase of exhaust gas energy were predicted. In the meantime there exists an increasing number of publications reporting on significant increase of fuel consumption with total or partial insulation of the combustion chamber walls. In [1] a physical explanation of this effect is given: Simultaneously with the decrease of the temperature difference between gas and wall as a result of insulation, the heat transfer coefficient between gas and wall increases rapidly due to increasing wall temperature, thus overcompensating for the decrease in temperature difference between gas and wall. Hence a modified equation for calculation of the heat transfer coefficient was presented [1]. In the paper to be presented here, recent experimental results are reported that confirm the effects demonstrated in [1], including the influence of the heat transfer coefficient, which depends on the wall temperature, on the performance of naturally aspirated and turbocharged engines.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):503-508. doi:10.1115/1.3240163.

This paper presents new insight into the causes of cylinder-to-cylinder variation in swirl torque and airflow in uniflow scavenged, two-stroke diesel engines. A V-6 model of such an engine was investigated as a flow rig under steady-state conditions. These variations were found to be primarily caused by the effect of the airbox walls on the air motion. The maximum difference in the baseline cylinder-to-cylinder swirl torque and airflow rate was 11 and 3.5 percent, respectively. Two airbox design modifications, resulting from the study, in turn demonstrated increased cylinder airflow rate and reduced cylinder-to-cylinder swirl torque variation on the flow rig.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):509-514. doi:10.1115/1.3240164.

Steady flow measurements of velocity and mass flux distributions around the intake valve were used as input to a General Engine Simulation Model (GESIM) to assess the assumptions of uniform velocity and mass flux distributions and their effects on in-cylinder turbulence intensity and burn rate. In addition, an improved submodel for calculating the instantaneous velocity past the intake valve was developed and its effects on intake generated turbulence and burn rate assessed. Using the improved, inlet velocity submodel, a study was carried out for three different intake port configurations. Burn rate measurements were compared with model results for these configurations, which utilized the same engine head and block assembly. Model predictions, based on the standard port/valve discharge coefficient, indicated that velocity and mass distributions alone had a small effect on the in-cylinder turbulence intensity and burn rate. Significant differences in burn rate and turbulence intensity were predicted when the improved submodel for valve discharge coefficient was used. The new predictions agreed well with experimental measurements of burn rate. This implies that the increased mean velocities (which occur due to the restriction that creates the velocity and mass flow distributions) are the major cause for increased turbulence levels.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):515-522. doi:10.1115/1.3240165.

This paper describes pressure and velocity measurements on a multipulse converter under steady-state conditions. Pressure loss coefficients were measured on this four-entry pulse converter system for a large number of flow configurations. Three-dimensional velocity measurements were done (with Laser-Doppler anemometry) for several flow configurations and at different cross sections in the converter. The normal flow situation (incoming flow at the four entries) and back flow situations were examined. For each cross section the axial velocity profiles, the secondary flow patterns, and the turbulent velocities are presented. From the pressure measurements mixing losses are derived. These are compared with the results of a one-dimensional calculation, which is based on the impulse law for incompressible flow. Taking into account the velocity measurements, this simplified model gives a remarkable agreement with the measured mixing losses.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):523-530. doi:10.1115/1.3240166.

The effects of engine speed on the fresh air breathing characteristics of a uniflow, two-cycle engine were studied by using a multidimensional computational code for in-cylinder flows. Computed results are presented describing both global and detailed features of the flow field during the air breathing and compression stroke, at four different engine speeds, namely, 400, 700, 900, and 1000 rpm. Global features are presented including the variations of cylinder pressure, mass, angular momentum, turbulence kinetic energy, and the exhaust mass as a function of crank angle. Detailed features of the flow field are presented in terms of the velocity vector plots, fresh air concentration contour plots, and swirl velocity contour plots at certain crank angles. The volumetric scavenging, and charging efficiency decreases, but the trapping efficiency increases with increasing engine speed. A simple scavenging model (correlating the fraction of fresh air in exhaust to the fraction of fresh air in cylinder) suitable for use in engine performance algorithms is presented. Predictions indicate that the effect of engine speed on such a model is not negligible. The use of similar models would be questionable and limited in range, if they are insensitive to engine speed. The residual gas concentration at TDC is shown to be relatively uniform at low engine speeds, but at high speeds, the residual gases are more concentrated at the squish region and the fresh air is more concentrated near the bowl center.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):531-537. doi:10.1115/1.3240167.

A three-zone scavenging model for two-stroke uniflow engines was developed and used in conjunction with a control-volume-type engine simulation code for performance prediction of long stroke uniflow-type marine engines. In this model it is attempted to simulate the three different regions perceived to exist inside the cylinder during scavenging, namely the air, mixing, and combustion products regions, by modeling each region as a separate control volume. Two time-varying coefficients are used to specify the rates of entrainment of the air and the burned gases into the mixing region. Results of the use of the model for predicting the performance of a large marine two-stroke engine are presented.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):538-546. doi:10.1115/1.3240168.

A multidimensional investigation of the scavenging process in the GM6V53T General Motors diesel engine has been carried out. This six-cylinder two-stroke engine features uniflow scavenging with four exhaust valves per cylinder, direct fuel injection, and turbocharging. The conservative equations of mass, energy, concentration, turbulence kinetic energy, and energy dissipation rate have been written in finite difference form and solved explicitly in time. The scavenging process has been studied by using a configuration of two exhaust valves as compared with the actual configuration, which has four exhaust valves. The computed flow characteristics and scavenging efficiency are very similar if the exhaust areas of the two different configurations are equivalent.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):547-551. doi:10.1115/1.3240169.

The suitability of the analysis of the unsteady flow through the exhaust junction plays an important role in developing a computer program for matching a diesel engine to an exhaust turbocharger. This paper describes an improvement of the calculation procedure for computing the behavior of the unsteady gas flow at the exhaust junction. Measured values of pressure, temperature, and mass flow rate are compared with computer predictions using four different pipe junction computations: constant pressure model, momentum model, simplified model, and the improved exact model developed in this study. This comparison shows that the new technique gives the best agreement with the measured values, while the computer time required is twice as long. Under unsteady flow conditions the exhaust junction gives six types of flow configuration, and calculations indicate that only some of these types of flow dominate; the rest occur for only short intervals.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1988;110(3):552-561. doi:10.1115/1.3240170.

Experiments were performed using a five-port cobra probe to survey the flow field at the rotor inlet of a 110-mm-dia turbocharger radial inflow turbine wheel. The turbine housing was modified to accommodate a probe insert to position the probe tip 4.1 mm above the rotor tip while preserving the internal contour of the production turbine housing. The cobra probe was traversed axially and circumferentially to determine the rotor inlet flow properties while the turbine was operated at design flow conditions with a reduced turbine inlet temperature. Measurements were made with the probe tip in the near-nulled position to determine the local values of total pressure, static pressure, velocity, and flow angle as functions of Z and θ. Results are presented showing the distribution of the housing total pressure loss coefficient, the rotor inlet mass flux, and the rotor inlet tangential velocity. In addition, values for rotor inlet mass average properties are given.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

ERRATA

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In