Showing papers in "SAE transactions in 1987"

Structure of High-Pressure Fuel Sprays

Abstract: A multi-dimensional model was used to calculate interactions between spray drops and gas motions close to the nozzle in dense high-pressure sprays. The model also accounts for the phenomena of drop breakup, drop collision and coalescence, and the effect of drops on the gas turbulence. The calculations used a new method to describe atomization (a boundary condition in current spray codes). The method assumes that atomization and drop breakup are indistinguishable processes within the dense spray near the nozzle exit. Accordingly, atomization is prescribed by injecting drops ('blobs') that have a size equal to the nozzle exit diameter.

Autoignition of adiabatically compressed combustible gas mixtures

Abstract: Measurements of explosion limits for fuel/air/diluent mixtures compressed by an expanding laminar flame have been made in a constant volume spherical bomb. The fuels studied to date range from butane to octane at fuel/air equivalence ratios from 0.8 to 1.3. The explosion pressures and temperatures range from 10 to 100 atm and 650 to 850 K. The pressure versus time curves show the behavior typical of the two-stage ignition process observed in rapid compression machines. A branched chain kinetic model has been developed to correlate the data. The model has been used to predict both the explosion limits measured in the current bomb experiments and ignition delays measured in prior rapid compression machine experiments. Good agreement between experiment and theory can be achieved with minor adjustment in published rate constants.

Heat insulation of combustion chamber walls ― a measure to decrease the fuel consumption of I.C. engines?

Abstract: Experimental investigations were made with a single-cylinder direct-injection Diesel engine with heat-insulated piston. The most important result is an inferior economy compared with the not insulated aluminum-piston engine. It was found that this phenomenon is not caused by neither a changed combustion process nor increased blowby nor different friction losses, but rather by a drastic increase of the heat transfer coefficient during the first part of combustion with increasing surface temperature. This is taken into account in a modified equation for the heat transfer coefficient. Cycle-simulations using this modified equation show that there is neither a gain in fuel economy of naturally aspirated nor of turbocharged nor of turbocompound Diesel engines with ''heat insulated'' combustion chamber walls.

Early flame development and burning rates in spark ignition engines and their cyclic variability

Abstract: Experiments by others have been analyzed to obtain both qualitative and quantitative information on early flame development and burning rates in a square piston premixed spark-ignition engine. Flame growth was observed using high speed Schlieren photography and simultaneous pressure records were obtained using piezo-electric transducers. To study the effects of in-cylinder gas motion several combinations of shrouded and unshrouded inlet valves, and flat and stepped pistons were used. Spark position was also varied. The analysis supports the wrinkled laminar flame model of turbulent flame structure in spark-ignition engines. It also suggests that cycle-by-cycle variations in the growth rate and location of the flame kernel at very early times are the major cause of cycle-by-cycle pressure variations in spark-ignition engines.

A study of velocities and turbulence intensities measured in firing and motored engines

Abstract: Laser Doppler velocimetry was used to make cycle-resolved velocity and turbulence measurements under motoring and firing conditions in a ported homogeneous charge S.I. engine. The engine had a flat pancake chamber with a compression ratio of 7.5. In one study, the effect of the intake velocity on TDC turbulence intensity was measured at 600, 1200, and 1800 rpm with three different intake flow rates at each speed. The TDC swirl ratio ranged from 2 to 6. The TDC turbulence intensities were found to be relatively insensitive to the intake velocity, and tended to scale more strongly with engine speed. For the combustion measurements, the engine was operated at 600, 1200, and 2400 rpm on stoichiometric and lean propane-air mixtures. Velocity measurements were made in swirling and non-swirling flows at several spatial locations on the midplane of the clearance height.

Effect of High Pressure Injection on Soot Formation Processes in a Rapid Compression Machine to Simulate Diesel Flames

Abstract: The characteristics of diesel spray and flame in a quiescent atmosphere were studied as a function of injection pressure ranging from 30 to 110 MPa. Measurements included the spray form and Sauter mean diameter of a non-evaporating spray, the liquid phase penetration of an evaporating spray and the visualization of sooting zone in a flame. Experimental results show that high pressure injection improves the atomization and air entrainment of non-evaporating spray and that the liquid phase penetration of evaporating spray is hardly affected by injection pressure, demonstrating a promotion of evaporation with injection pressure. Visualization of the sooting zone in a flame made it clear that high pressure injection is advantageous in reducing soot formation and shortening the combustion duration.

Three-dimensional computations of flows in a stratified-charge rotary engine

Abstract: The first three-dimensional rotary-engine computations are reported of exhaust, intake (with side and peripheral ports, and with different intake turbulence intensities and length scales), compression, homogeneous-charge combustion, dual liquid fuel injection, and dual liquid fuel injection and combustion The model includes a k-epsilon submodel for turbulence, a stochastic treatment of the fuel drops and a hybrid laminar and mixing-controlled submodel for the conversion of reactant to products The code is an extensively modified version of KIVA The latter was developed at the Los Alamos National Laboratory for reciprocating engines The modifications include: dynamic rezoning of the grid in both the x-y and the x-z planes; adoption of a cartesian coordinate system fixed to the housing with analytical grid generation and grid velocities related to the rotor velocity; inclusion of radial and tangential ports for both intake and exhaust

Fuel injection and combustion phenomena in a high speed DI diesel engine observed by means of endoscopic high speed photography

Abstract: After a short description of the Endoscopic High Speed Combustion Photography Technique used, the results obtained through observation of the following phenomena in a 0.5 litre HSDI Diesel engine are presented: the wall jet development and the role of swirl, the effect of wall temperature (cold and warm engine) on combustion development, and the effect of pilot injection on mixture formation and combustion. To document these phenomena, typical high speed films are presented supplemented by cylinder pressure, injector needle lift, rate of heat release, and light radiation (flame luminosity) intensity data recorded simultaneously by means of a digital acquisition system.

Spark Ignition, Early Flame Development and Cyclic Variation in I.C. Engines

Abstract: Allumage, debut de propagation de la flamme et variations cycliques dans les moteurs a combustion interne a allumage par etincelle

Development of an Automatic Engine Oil-Change Indicator System

Abstract: To insure maximum engine life, it is essential that engine oil be changed as required. Some drivers are not aware that the oil should be changed, and others do not know how often to change it. To assist the driver in this regard, an automatic oil-change indicator was developed. In developing the oil-change indicator, it was found that oil temperature, vehicle mileage, engine resolutions, and changes in the physical and chemical properties of the oil during use all provided and indication of oil degradation. Based on these measurements, a mathematical model was developed which relates oil life to oil temperature and either vehicle mileage or engine revolutions. Computer hardware and software suitable for use in a vehicle were developed based on the mathematical model.

Fuel sulfur reduction for control of diesel particulate emissions

Abstract: The impact of diesel fuel sulfur reduction on directly-emitted and secondary atmospheric particulate is evaluated by experiment and analysis. Experimental evidence shows that fuel sulfur conversion rate to particulate sulfate is linear down to zero sulfur level. Analysis shows that sulfur-derived particulate accounts for the vast majority of atmospheric particulate from diesel engines. Consequently, fuel sulfur reduction would have a far greater impact in reducing atmospheric particulate burden than any other diesel engine particulate control strategy.

Individual cylinder knock control by detecting cylinder pressure

Abstract: To improve available power, tolerance to variation in fuel octane number and high engine speed knock control, an individual cylinder knock control has been developed. Knock are detected by spark plug washer transducers, which indicate individual cylinder pressures.) Last year the authors read a paper entitled ''Cylinder Pressure Vibration Analysis Indicates Accurate Knock Detection''. They read continuously on the following items. Spark plug washer transducers - These are piezoelectric ceramic rings which fit beneath individual spark plugs. These can detect knock at high engine speed, and are very durable. Knock detection and control algorithm - Knock is indicated by the transducer's cylinder pressure vibration signal. When knock occurs in the cylinder, the ignition timing of the cylinder is controlled. During the transient condition, control response is fast by learning control. Fail safe - At transducer trouble, the ignition timing of the cylinder is controlled by other transducer signals. Electric control unit - It is included in NISSANs Electronic Concentrated Engine Control System (ECCS). Effects of this control - It improved WOT torque by 7-15%, torelance to variation in fuel octane number, and high engine speed control performance.

Diesel Fuel Ignition Quality as Determined in a Constant Volume Combustion Bomb

Abstract: The ignition delay times of forty-two different fuels were measured in a constant volume combustion bomb. The measurements were performed at three different initial air temperatures using fuels ranging from the primary reference fuels for cetane rating to complex mixtures of coal-derived liquids. The ignition delay times were examined in terms of the classical definitions of the physical and chemical delay times. The previously used definitions were found to be inadequate, and new definitions have been proposed. The total ignition delay times were studied in the context of providing a means for rating the ignition quality of the fuels. Fuel ignition quality rating schemes are discussed, including one based on the current cetane number scale as well as one based on a new scale which includes a measure of the sensitivity of the various fuels to the air temperature.

Turbulence intensity and spatial integral scale during compression and expansion strokes in a four-cycle reciprocating engine

Abstract: A laser homodyne technique is applied to measure turbulence intensities and spatial scales during compression and expansion strokes in a non-fired engine. By using this technique, relative fluid motion in a turbulent flow is detected directly without cyclic variation biases caused by fluctuation in the main flow. Experiments are performed at different engine speeds, compression ratios, and induction swirl ratios. In no-swirl cases the turbulence field near the compression end is almost uniform, whereas in swirled cases both the turbulence intensity and the scale near the cylinder axis are higher than those in the periphery. In addition, based on the measured results, the k-epsilon two-equation turbulence model under the influence of compression is discussed.

Autoignition of Methanol and Ethanol Sprays under Diesel Engine Conditions

Abstract: Methanol and ethanol are being considered as alternative fuels for diesel engines. One of the key concerns with using alcohol fuels in diesel engines is their poor ignition quality. This work presents the ignition characteristics of methanol and ethanol examined under simulated diesel engine conditions in a constant-volume combustion vessel. The ignition characteristics of isooctane and normal hexadecane (cetane) measured under the same conditions are also included for reference. Results show that to obtain ignition delays and rates-of-pressure-rise suitable for current diesel engine designs, methanol and ethanol require in-cylinder temperatures of about 1100 K at the time of injection. The results also show that the ignition delays of the alcohol fuels are independent of the chamber-pressure and are unaffected by the presence of 10% by volume of water in the fuel.

Intake Valve Deposits — Fuel Detergency Requirements Revisited

Abstract: Influence des proprietes detergentes du carburant sur la formation de depot sur les soupapes d'admission de moteurs

The Role of Low Temperature Chemistry in the Autoignition of N-Butane

Abstract: The authors studied the chemical aspects of the compression ignition of n-butane experimentally in a spark ignition engine and theoretically using computer simulations with a detailed chemical kinetic mechanism. The results of these studies demonstrate the effect of initial charge composition on autoignition. Experimentally, when the initial charge consisted of 80% fresh charge and 20% recycled products of combustion, the authors observed that autoignition was inhibited. On the other hand, charging with 80% fresh charge and 20% partial oxidation products from the previous motored cycle resulted in enhanced low-temperature chemistry (with the associated heat release and temperature increase) and autoignition. They assessed how well the detailed kinetic model could predict the autoignition and modified the model to better simulate the experimental observations. They also assessed how chemical preconditioning of the fuel-air charge affected the autoignition process.

The development of an air gap insulated piston

Abstract: The concept of an air gap insulated piston has been explored using bolted and welded/roll bonded designs. Pistons with bolted on crowns demonstrated the effectiveness of air gap insulation, but roll bonded and welded designs were found to be more robust and to provide the complete sealing of the air gap necessary for continued insulation. Evolution of the design to combine high insulation with adequate durability is discussed. Engine running times of up to 200 hours at full load have been achieved for an air gap piston which reduces heat flow to the crown by 33%. An improved design giving 41% reduction of heat flow has been tested for 78 hours at full engine load with no evident deterioration. Development is continuing to provide a fully durable piston achieving up to 50% reduction in heat flow.

Factors limiting the improvement in thermal efficiency of S. I. engine at higher compression ratio

Abstract: An analysis of the factors that limit the improvement in thermal efficiency at higher compression ratios was performed with both thermodynamic calculation and experiment. The results showed that the major factors were cooling loss and unburned fuel. Both of these factors increase with smaller swept volume, larger S/V ratio combustion chamber, and lower engine speed and load. These effects explain the observation that thermal efficiency peaks at relatively low compression ratio.

The Role of Lubricating Oil in Diesel Particulate and Particulate PAH Emissions

Abstract: The role of lubricating oil in total particulate emissions and in terms of polycyclic aromatic compounds (PAC) associated with the solvent organic fraction (SOF) of the particulate are investigated. Analysis of unused lubricating oil shows negligible concentrations of PAC. Used lubricating oil from a modified Perkins 4.236 Diesel engine, showed significant concentrations of PAC had accumulated in the oil in the form of PAC from unburnt fuel. Analysis of the oil was by gas chromatography using simultaneous parallel triple detection, allowing analysis of polycyclic aromatic hydrocarbons (PAH), nitrogen containing PAH (PANH) and sulphur containing PAH (PASH). Motoring the engine in the absence of fuel enable the contribution of lubricating oil to the exhaust particulate and particulate PAC emission to be determined. At high load and high speed the results indicated that the contribution of lubricating oil to the total exhaust particulate is over 40% and at low load and high speed reaches 70%. Analysis of the solvent organic fraction from the particulates using simultaneous parallel triple detection gas chromatography, revealed the presence of certain PAH which are also present in the lubricating oil. Thus the PAC content of the used oil acts as a source of PAC in particulate PACmore » emissions.« less

Transient Heat Conduction in Low-Heat-Rejection Engine Combustion Chambers

Abstract: Conduction de chaleur transitoire dans la chambre de combustion d'un moteur a faibles pertes de chaleur

Status Report on a Preliminary Survey of Strategies to Meet US-1991 HD Diesel Emission Standards Without Exhaust Gas Aftertreatment

Abstract: This paper presents a status report on a preliminary survey of strategies that might be employed to meet US-EPA 1991 heavy duty diesel emission standards without the use of a particulate trap. Although the survey of strategies is not yet complete, that portion dealing with the swirl supported diesel combustion process is sufficiently advanced to allow this status report to be published. It is anticipated that future related reports will provide a view of the complete survey, including quiescent combustion process. This report describes the techniques employed for the steady state approximation of the heavy duty transient test cycle and the analytical procedures used to characterize the particulate composition in terms of insolubles, and the fuel and lube oil related components.

Measurement and Multidimensional Prediction of Flow in a Axisymmetric Port/Valve Assembly

Abstract: Etude experimentale et calcul multidimensionnel de l'ecoulement dans un systeme d'admission (soupape et lumiere d'admission) axisymetrique

Piston slap induced noise and vibration of internal combustion engines (1st Report, Theoretical Analysis and Simulation)

Abstract: Bruit du au cognement du piston et vibrations des moteurs a combustion interne. Etude theorique et simulation

Velocity Measurements in the Wall Boundary Layer of a Spark-Ignited Research Engine

Abstract: Laser Doppler velocimetry has been used to measure velocity and turbulence intensity profiles in the wall boundary layer of a spark-ignited homogeneous-charge research engine. By using a toroidal contoured engine head it was possible to bring the laser probe volume to within 60 ..mu..m of the wall. Two different levels of engine swirl were used to vary the flow Reynolds number. For the high swirl case under motored operation the boundary layer thickness was less than 200 ..mu..m, and the turbulence intensity increased as the wall was approached. With low swirl the 700-1000 ..mu..m thick boundary layer had a velocity profile that was nearly laminar in shape, and there was no increase in turbulence intensity near the wall. When the engine was fired the boundary layer thickness increased for both levels of swirl.

The Effect of Ignition System Power on Fast Burn Engine Combustion

Abstract: Influence de la puissance du systeme d'allumage sur la combustion dans un moteur a combustion rapide

Measurements of Instantaneous Heat Flux to Metal and Ceramic Surfaces in a Diesel Engine

Abstract: Mesure des flux thermiques instantanes a travers des parois en metal et en ceramique dans un moteur diesel