Showing papers on "Compression ratio published in 1994"

Compression ratio of an optimized air standard Otto-cycle model

Abstract: We propose an irreversible simplified model for the air standard Otto thermal cycle. This model takes into account the finite-time evolution of the cycle's compression and power strokes and it considers global losses lumped in a friction like term. The proposed model permits the maximization of quantities such as the power output and the efficiency in terms of the compression ratio r. The optimum r values obtained compare well with standard r values for real Otto engines. Our model leads to loop-shaped power-versus-efficiency curves as is common to almost all real heat engines.

Part load gas exchange strategy for an engine with variable lift camless valvetrain

Abstract: A variable engine valve control system and method of operation thereof wherein each of the reciprocating engine valves is hydraulically or electrically controlled and can vary its lift schedule for various engine operating conditions. During part load operation of the engine, the intake valve is opened and the exhaust valve is closed during the exhaust stroke, prior to a piston's top dead center position, so that the intake port receives exhaust gas, which is then returned to the cylinder during the intake stroke to eliminate the need for an external exhaust gas recirculation system and to improve fuel evaporation into the intake air. Further, during part load, the intake valve is closed before the end of the intake stroke and the intake air is heated by a heat exchanger prior to entry into the cylinder to eliminate the need for air throttling without compromising the compression ratio and ignition characteristics.

Joint Photographic Experts Group (JPEG) compatible data compression of mammograms

Abstract: We have developed a Joint Photographic Experts Group (JPEG) compatible image compression scheme tailored to the compression of digitized mammographic images. This includes a preprocessing step that segments the tissue area from the background, replaces the background pixels with a constant value, and applies a noise-removal filter to the tissue area. The process was tested by performing a just-noticeable difference (JND) study to determine the relationship between compression ratio and a reader's ability to discriminate between compressed and noncompressed versions of digitized mammograms. We found that at compression ratios of 15∶1 and below, image-processing experts are unable to detect a difference, whereas at ratios of 60∶1 and above they can identify the compressed image nearly 100% of the time. The performance of less specialized viewers was significantly lower because these viewers seemed to have difficulty in differentiating between artifact and real information at the lower and middle compression ratios. This preliminary study suggests that digitized mammograms are very amenable to compression by techniques compatible with the JPEG standard. However, this study was not designed to address the efficacy of image compression process for mammography, but is a necessary first step in optimizing the compression in anticipation of more elaborate reader performance (ROC) studies.

Methods and apparatus for vaporizing and utilizing fuels of various octane ratings

Abstract: Modifications to the cylinder head of internal combustion engines in which the efficiency of fuel combustion is raised by the use of a plurality of liquid, vaporized liquid, and gaseous fuels through the alteration of cylinder compression ratios and spark timing to burn those fuels. It has been demonstrated that certain fuels have salient advantages under specified engine speed and load conditions, and in selected enviroments and vehicle applications, but that no single fuel is capable of excelling in all potential application scenarios. Burning each of these fuels efficiently has required engine specifications optimized to a single fuel or fuel state, such as compression ratio, intake tract design, electronic fuel injector duration and timing, and spark timing curves, which have been severely compromised when they were required to cope with the demands of a second fuel. The solutions demonstrated seek to show how these past compromises may be eliminated or minimized to enable the singular and simultaneous use of selected fuels to increase performance, reduce combustion pollutants, and increase the engine life of internal combustion engines. In addition, many of the possible alternate fuels which may be adapted to this proposal are in abundant domestic supply, and would reduce the undesirable economic effects which accompany large-scale petroleum imports; the consequential balance of trade deficits, dependence on volatile foreign sources,and vunerable tanker fleets and refining facilities.

Camera capable of selecting compression ratio efficiency

Abstract: The still camera includes: an imaging section which forms an image of an object to be photographed and outputs analog image data; an A/D conversion section which performs A/D conversion upon this analog image data; an aperture device which controls the amount of light incident upon the imaging device; a compression processing section which compresses the digital image data from the A/D conversion section; a memory card upon which the digital image data thus compressed by the compression processing section is stored; a photometric section which measures the brightness of the object to be photographed; and a compression ratio setting section which derives and controls the compression ratio for the compression processing section, based at least upon the brightness measured by the photometric section.

Effect of compression ratio in a slow-acting compression hearing aid: paired-comparison judgments of quality

Abstract: Paired-comparison judgments of quality were obtained from 20 hearing-impaired listeners (half with a small dynamic range and half with a large dynamic range) for speech-in-noise (vent, apartment, and cafeteria) processed through a slow-acting compression hearing aid. Compression ratio was varied (1, 1.5, 2, 3, 5, and 10:1). Compression threshold, attack time, and release time were fixed. Sound quality judgments were significantly affected by compression ratio, noise, and dynamic range. Preference decreased with increasing compression ratio. The selection of compression ratio. The selection of compression ratios 3:1. Less compression (no compression or 1.5:1) was preferred with the highest level noise (cafeteria noise) than with the lower level noises (vent or apartment). In particular, the small dynamic range group preferred compression with the vent and apartment noises (noise below the compression threshold), but preferred a linear hearing aid with the cafeteria noise (above the compression threshold). The large dynamic range group showed a slightly greater preference for the linear hearing aid for all three noises.

Compression timed pre-chamber flame distributing igniter for internal combustion engines

Abstract: A method and apparatus for compression timed ignition in internal combustion engines, the varying mass of the fuel-air mixture having controlling effect to retard timing by cooling a heater element to vary the current therethrough, and characterized by an igniter with a pre-chamber in communication with the engine combustion chamber via a restricted nozzle area for projecting burning plasma at high velocity into the engine combustion chamber.

Compression-ignition type engine and combustion method of same

Abstract: A compression-ignition type engine in which fuel is injected in a combustion chamber during the compression stroke or intake stroke before 60 degrees before top dead center of the compression stroke and in which the mean particle size of the fuel injected at that time is made a size in which the temperature of the fuel particles reaches the boiling point of the main fuel component, determined by the pressure in the combustion chamber, at substantially the top dead center of the compression stroke. After the injection and until about the top dead center of the compression stroke is reached, evaporation of the fuel by boiling from the fuel particles is prevented and the fuel of the fuel particles boils and evaporates and fuel is ignited and burnt after about the top dead center of the compression stroke.

Parallel and Sequential Approximations of Shortest Superstrings

Abstract: Superstrings have many applications in data compression and genetics. However the decision version of the shortest superstring problem is N P-complete. In this paper we examine the complexity of approximating a shortest superstring. There are two basic measures of the approximations: the compression ratio and the approximation ratio. The well known and practical approximation algorithm is the sequential algorithm GREEDY. It approximates the shortest superstring with the compression ratio of 1/2 and with the approximation ratio of 4. Our main results are: (1) An NC algorithm which achieves the compression ratio of 1/4+e. (2) The proof that the algorithm GREEDY is not parallelizable, the computation of its output is P-complete. (3) An improved sequential algorithm: the approximation ratio is reduced to 2.83. Previously it was reduced by Teng and Yao from 3 to 2.89. (4) The design of an RNC algorithm with constant approximation ratio and an NC algorithm with logarithmic approximation ratio.

Adiabatic, two-stroke cycle engine having piston-phasing and compression ratio control system

Abstract: An engine structure and mechanism that operates on various combustion processes in a two-stroke-cycle without supplemental cooling or lubrication comprises an axial assembly of cylindrical modules and twin, double-harmonic cams that operate with opposed pistons in each cylinder through fully captured rolling contact bearings. The opposed pistons are double-acting, performing a two-stroke engine power cycle on facing ends and induction and scavenge air compression on their outside ends, all within the same cylinder bore. The engine includes a control system which utilizes twin barrel cams with adjustable axial and angular positions enabling independent compression ratio and port phasing variation during operation. The engine control system comprises one or more electrohydraulic servos to set and maintain the axial and angular relationships of the cams either at extreme positions or controlled to particular positions and schedules thereof utilizing instantaneous piston position feedback information.

Performance studies with biomass-derived high-octane fuel additives in a two-stroke spark-ignition engine

Abstract: The intensive search for alternative fuels for spark-ignition engines has focused attention on fuels which can be derived from biomass. In this regard, orange oil and eucalyptus oil are found to be potential candidates for spark-ignition engines. Their properties are similar to gasoline in nature and they are miscible with gasoline without any phase separation. They can be used in spark-ignition engines with little engine modification as a blend with gasoline fuel. The high octane value of these fuels can enhance the octane value of the fuel when it is blended with low-octane gasoline. Hence, the knock-limited compression ratio (CR) can be further increased when these fuels are blended with gasoline. In the present work, 20% by volume of orange oil and eucalyptus oil were blended separately with gasoline and the performance, combustion and exhaust emission characteristics were evaluated at two different compression ratios. Test results indicate that the performance of fuel blends was much better than the gasoline fuel, in particular at the higher compression ratio. Hydrocarbons and carbon monoxide emission levels in the engine exhaust were considerably reduced with the fuel blends at both the compression ratios tested. Between the two fuel blends tested, eucalyptus oil blend provides better performance than the orange oil blend. The maximum percentage improvement in the brake thermal efficiency obtained with eucalyptus oil blend is about 20.5% at 2 kW, 3000 r.p.m. and CR 9 over the normal gasoline engine.

Effect of third-order dispersion on soliton-effect pulse compression.

Abstract: The effect of third-order dispersion on soliton-effect pulse compression is investigated. We show that third-order dispersion causes severe degradation in dispersion-shifted fibers in the compression of high-order soliton pulses. As much as an 80% reduction is found in the optimum compression ratio of 15th-order solitons of 1-ps width. We also show that fiber loss cannot be neglected in soliton-effect compression schemes, which gives rise to an initial pulse-width dependence in the compression ratio and to the existence of an optimum initial width.

Two-way rotary supercharged, variable compression engine

Abstract: A variable-compression internal-combustion engine has a two-stage cylinder with a relatively large diameter at a first-stage, supercharge end, which is also a power-takeoff end, than at a second-stage, combustion end of the cylinder. Intake air is drawn into the first-stage, supercharge end of the cylinder by a matching larger-diameter, first-stage, supercharge end of a two-stage piston during a compression stroke of a two-stroke cycle of the two-stage piston. During a power stroke, intake air is directed into and contained under pressure in an air-transfer passage that is positioned circumferentially and externally around an outside periphery of a bottom end of the first-stage cylinder. At a bottom end of the power stroke, intake air is directed from the air-transfer passage into a transfer conveyance extended from the supercharge end to tile second-stage head of the two-stage piston where the intake air is venturi-accelerated to the second-stage head of the two-stage cylinder while exhaust escapes through exhaust ports at a bottom of the second stage of the two-stage cylinder. Cylinder heads can be variable in distance from top dead center of piston travel to regulate compression ratio as desired for different operating conditions. Reciporcative travel of a plurality of the two-stage pistons is convened to rotary motion preferably by a pinch plate in working relationship to an angled cam plate. The pinch plate cam-drives the angled cam plate with a large contact surface for long wear life. Other rotational means can be employed.

Thermal management system for heat engine components

Abstract: Heat engine piston and combustion chamber construction enclosing a gas combustion zone, comprising: a piston body having a crown facing said gas combustion zone; combustion chamber surfaces cooperating with said piston to complete enclosure of said zone; and a thermal diffusivity coating on said crown and combustion chamber surfaces having an effective thickness to operate as a thermal diode to restrict heat transfer to said piston body and combustion chamber and to restrict heat transfer to said combustible charge prior to combustion. A method of thermally managing heat generated by an internal combustion engine, the engine having combustion chamber walls for combusting a gaseous mixture of air and fuel, a cooling jacket for cooling said walls, and a piston moveable along a portion of said walls, comprising: increasing the compression ratio of the engine to induce engine-knock for an uncoated chamber; coating at least the crown of the piston of said combustion chamber walls with a low thermal diffusivity layer that functions as a heat diode to restrict heat transfer in both directions normal to the coating; operating said engine with said coating chamber wall and increased compression ratio, whereby fresh intake of combustible mixture to said combustion chamber will be drawn thereinto at a lower temperature and volumetric efficiency with less heat from said combustion being wasted to said cooling jacket.

Flow and Combustion in a Transparent 1.9 Litre Direct Injection Diesel Engine

Abstract: Two identical 1.9 litre direct injection (DI) diesel engines having optical access for application of laser diagnostics were operated at Volkswagen and Imperial College as part of the European programme (IDEA) on diesel engines. A variety of complementary laser-based techniques were used to characterize the flow-generating capacity of the intake system under steady flow conditions, the in-cylinder flow during induction and compression as well as the spray development, auto-ignition and combustion under three typical engine operating conditions. The most important results of this programme are presented and discussed here in view of their implications for improved combustion and reduction of exhaust emissions in small direct injection diesel engines, through better matching of the spray characteristics with the in-cylinder flow as a function of engine speed and load. The results were obtained in sufficient detail to allow validation of the multi-dimensional computer code developed within the IDEA programme.

Fuel tolerant combustion engine with reduced knock sensitivity

Abstract: A supplemental cylinder head assembly for operation of an engine in a homogeneous charge compression ignition combustion mode. The supplemental cylinder head assembly provides a movable accumulator piston position above the main combustion chamber. The accumulator piston is upwardly responsive to the combustion event in the main combustion chamber and downwardly to a preload force. An engine adapted to receive the supplemental cylinder head assembly is capable of efficiently operating on any fuel in the octane range of zero to 130.

Vapor force engine

Abstract: A vapor-driven piston-type engine having multiple stages that may be constructed as a single block or unit. Each stage has its own separate vapor power source and the fluids in each stage are different and have different heat/temperature characteristics such that the waste heat from one engine can be used to drive a succeeding engine.

Performance of Thin-Ceramic-Coated Combustion Chamber with Gasoline and Methanol as Fuels in a Two-Stroke SI Engine

Abstract: The performance of a conventional, carburated, two-stroke, spark-ignition (SI) engine can be improved by providing moderate thermal insulation in the combustion chamber. In the present investigation the combustion chamber surface was coated with a 0.5-mm thickness of partially stabilized zirconia, and experiments were carried out in a single cylinder, two-stroke SI engine with gasoline and methanol as fuels. The results indicate that with gasoline as fuel, the thin ceramic-coated combustion chamber improves the part load to medium load operation considerably, but it affects the performance at higher speeds and at higher loads to the extent of knock and loss of brake power by about 18%. However with methanol as a fuel the performance is better under most of the operating range and free from knock. Emissions are significantly reduced by about 3 to 4% volume, for both gasoline and methanol fuels due to relatively lean operation and more complete combustion. 35 refs., 13 figs., 3 tabs.

An LZ approach to ECG compression

Abstract: Two highly effective families of lossless compression methods were created by Ziv and Lempel (1977). However, these methods are normally ineffective when applied to digitized signals. We have successfully adapted the LZ77 method to take advantage of the repetitive nature of ECG waveforms. In our experiments, the resulting algorithm produces much better compression ratios than competing techniques while retaining the essential characteristics of the waveform. >

Image compression using quadtree partitioned iterated function systems

Abstract: Partitioned iterated function systems have been used to compress images, but in previous work, images have been partitioned into fixed size blocks. The authors present an image compression technique using variable block sizes based on quadtree partitioning. Experimental results show that it can achieve higher compression performance than the fixed-size partitioning technique. >

Control of fuelling rate of an engine

Abstract: Disclosed is a method of controlling the mass of fuel delivered to an engine subject to a change in engine load demand comprising determining a rate of change of fuel required per cycle with time in response to the change in engine load demand; and, applying a filter constant to the determined rate of change of fuel required per cycle with time to maintain a value of the rate of change of fuel required per cycle of the engine with time at no greater than a predetermined threshold level.

System and method of detecting partial flame out in a gas turbine engine combustor

Abstract: A method of detecting partial flame out in a gas turbine engine combustor is provided which involves the steps of establishing a model for performance of the engine during a particular operating mode of the combustor, wherein the model assumes that all fuel supplied during the combustor operating mode is burned, calculating a value for an engine parameter in the model representative of engine performance, obtaining a sensed value for the engine parameter during operation of the engine at the combustor operating mode, and comparing the calculated value of the engine parameter and the sensed value of the engine parameter, wherein partial flame out of the combustor is detected when the sensed value of the engine parameter differs from the calculated value of the engine parameter by a predetermined amount. This method may be modified in order to take into account performance of the specific engine by establishing a reference value for the engine parameter based on the performance of the engine during the combustor operating mode at total fuel burn and comparing the difference of the sensed and calculated value of the engine parameter to the reference value of the engine parameter before determining whether the difference of the sensed and calculated values of the engine parameter differ by the predetermined amount. Alternatively, the predetermined amount may be modified according to any distinction between performance of the engine and the average performance of a gas turbine engine within the same engine line.

Compression ratio control for internal combustion engine

Abstract: An internal combustion engine has an intake valve and an exhaust valve. When the engine operates at low speed with low and medium load, the intake valve is operated to close at a relatively advanced timing for increased volumetric effeciency and increased real compression ratio. When the engine operates at low speeds with high load, the exhaust valve is operated to close at a relatively retarded timing with the intake valve being operated to close at the relatively advanced timing, whereby the volumetric efficiency is subject to a drop to prevent occurrence of knocking.

Lubricating system for engine

Abstract: An improved lubrication system for a two-stroke engine having a lubrication path from an oil sump directly to an induction valve assembly for noise reduction. The oil sump is divided into two chambers with a restricted passage therebetween to ensure lubrication of transmission gears upon startup while reducing drag during operation. A cross-drilled lubrication passage through each crankshaft throw terminates in a second passage proximate a dead-end plug, the second passage being in communication with the piston rod bearing. Each piston skirt includes at least one axial groove in registration with an oil supply passage. Circumferential grooves distribute the oil around the piston skirt from the axial grooves. The pistons may include ceramic top layers for heat insulation to increase the compression ratio possible by raising the ring positions. The engine incorporates an air/oil mixture separator within a balancer shaft chamber and air from the chamber is directed to the intake system.

Operational control device for two-cycle engines

Abstract: A two-cycle crankcase compression diesel engine having a scavenge control system for controlling the amount of scavenging flow and an exhaust control system for controlling the effective compression ratio and the effective flow area of the exhaust system. These controls are operated during normal engine running conditions at most speed ranges from a three dimensional map. However, special control routines and valve operating arrangements are provided for pre-starting, starting, idle, engine braking or deceleration and rapid acceleration so as to improve the running under these transient or non-normal conditions.

Compression method for a standardized image library

Abstract: A technique involving the standardization of the subject matter of an image and the compression of the image using features of the standardization can provide for a high compression ratio. This technique can be used to improve the quality of a restored image for a predetermined amount of storage space.

Camera system capable of storing compressed data

Abstract: A camera includes an image sensor for sensing an image of an object to be photographed and producing an image data, a first memory for storing information concerning compression, a setting device for setting a compression ratio based on the information stored in the first memory, a compression device for compressing the image data at the set compression ratio, and a second memory for storing the compressed image data. Also, This camera includes a displaying device for displaying an image corresponding to the compressed image data in the viewfinder system so that the photographer can observe the image quality deterioration caused by the compression.

Improvements to compression or spark ignition four-stroke internal combustion engines having a variable compression ratio enabling high supercharging pressure levels

Abstract: An engine including an assembly of at least two cylinders (2 and 3) with different displacements, and two crankshafts (4 and 5) coupled at the same rotational speed via a gear train (19, 20, 21) and a variably timed transmission having three concentric shafts (17, 28, 32) separable from the drive assembly (18) and designed to reduce the compression ratio as the intake pressure increases. The highest and lowest compression ratios are set within the angular displacement limits between the two crankshafts (4 and 5) by means of the compression ratios between the two cylinders (2 and 3), and between said two cylinders (2 and 3) and the clearance space, so that (a) the start of the variably timed transmission stroke increases the translation of the piston (8) by units of angular displacement between the two crankshafts (4 and 5) at the end of compression phase, and (b) the end of the variably timed transmission stroke combines combustion gas expansion on the piston (8) at least from the maximum torque on the crank of the short-stroke crankshaft (5).