Refine Your Search

Topic

Affiliation

Search Results

Technical Paper

Effect of Tumble Strength on Combustion and Exhaust Emissions in a Single-Cylinder, Four-Valve, Spark-Ignition Engine

1998-02-23
981044
Direct flame imaging and pressure analysis were applied to the combustion of gasoline and compressed natural gas (CNG) in a single-cylinder, four-valve spark-ignition engine equipped with optical access via quartz windows in the cylinder liner and piston crown. Tests were performed at three engine speed/load conditions and at equivalence ratios of 1.0, 0.9 and 0.8. The four-valve head incorporated two different port geometries, with and without metal sleeves to deflect the intake air flow, in order to investigate the effect of tumble strength on combustion and engine-out emissions of unburned hydrocarbons and NOx. The results showed that sleeving of the intake ports produced a significant increase in IMEP and a reduction in CoV IMEP for both CNG and gasoline, due to the greatly reduced bum duration.
Technical Paper

Measurements of the Lubricant Film Thickness in the Cylinder of a Firing Diesel Engine Using LIF

1998-10-19
982435
A laser-induced fluorescence (LIF) system has been developed to obtain measurements of the instantaneous lubricant film thickness in the piston-cylinder assembly of a firing single-cylinder, direct-injection diesel engine. Measurements were made at top-dead-centre (TDC), mid-stroke and bottom-dead-centre (BDC) position by means of three fibre optic probes inserted into the cylinder liner and mounted flush with its surface. Following extensive repeatability tests, the cycle-averaged lubricant film thickness was estimated for different multi-grade oils as a function of engine speed, load and temperature. The results quantified the dependence of the film thickness ahead, under and behind the piston rings on oil chemistry and viscometric properties, thus confirming the important role of the LIF technique in the development and formulation of new engine oils.
Technical Paper

Cold-start Measurements of the Lubricant Film Thickness in the Cylinder of a Firing Diesel Engine

1998-10-19
982436
Laser induced fluorescence (LIF) was used in the cylinder liner of a firing single-cylinder direct-injection diesel engine to characterise the development of the lubricant film during the first 200 engine cycles under cold-start conditions. The results have provided information on the rate of oil film development which has proved to be a highly unsteady process due to the complicated oil transport processes through the ring-pack.
Technical Paper

Droplet Velocity/Size and Mixture Distribution in a Single-Cylinder Four-Valve Spark-Ignition Engine

1998-02-01
981186
Laser Doppler velocimetry, phase Doppler anemometry and Mie scattering were applied to a single-cylinder, four-valve, spark-ignition gasoline research engine equipped with a fully transparent liner and piston, to obtain information about the tumble flow and the droplet size and velocity distributions during induction and compression, for lean air/fuel mixture ratios of 17.5 and 24 and with closed-valve and open-valve fuel injection. The mixture distribution obtained with the two injection strategies was correlated with flame images, pressure analysis and exhaust emissions which confirmed the advantages of combining open-valve injection with tumble to allow stable and efficient engine operation at an air/fuel ratio of 24 through charge stratification and faster flame growth.
Technical Paper

Effect of EGR on Spray Development, Combustion and Emissions in a 1.9L Direct-Injection Diesel Engine

1995-10-01
952356
The spray development, combustion and emissions in a 1.9L optical, four-cylinder, direct-injection diesel engine were investigated by means of pressure analysis, high-speed cinematography, the two-colour method and exhaust gas analysis for various levels of exhaust gas recirculation (EGR), three EGR temperatures (uncontrolled, hot and cold) and three fuels (diesel, n-heptane and a two-component fuel 7D3N). Engine operating conditions included 1000 rpm/idle and 2000 rpm/2bar with EGR-rates ranging from 0 to 70%. Independent of rate, EGR was found to have a very small effect on spray angle and spray tip penetration but the auto-ignition sites seemed to increase in size and number at higher EGR-rates with associated reduction in the flame luminosity and flame temperature, by, say, 100K at 50% EGR.
Technical Paper

Effect of EGR on Combustion Development in a 1.9L DI Diesel Optical Engine

1995-02-01
950850
The effect of various levels of exhaust gas recirculation (EGR) on the combustion characteristics has been investigated in the four-cylinder 1.9L direct-injection optical VW diesel engine in terms of the cylinder pressure, flame development, temperature and KL-factor distributions. Images of the developing flame under twelve engine operating conditions including 1000rpm/idle, 2000rpm/2 bar bmep and 2000rpm/10 bar bmep at 0%, 30% and 50% EGR-rates were obtained by means of two CCD cameras, in the absence of external illumination, with and without interference filters in the optical path. Analysis of these images has revealed that increased EGR rates lead to increased cyclic pressure variations during the warm-up period of the engine, reduced and more fragmented high-temperature regions, reduced flame core temperatures, generally reduced soot oxidation rates but similar ignition delay times.
Technical Paper

Application of a FIE Computer Model to an In-Line Pump-Based Injection System for Diesel Engines

1997-02-24
970348
A computer model simulating the flow in fuel injection systems has been used in order to investigate the fuel injection processes in an in-line pump-based fuel injection system for direct-injection diesel engines. The model is one-dimensional and it is based on the mass and momentum conservation equations for the simulation of the fuel flow and on the equilibrium of forces for the simulation of the mechanical movements of the valves present in the system. The fuel injection system tested comprised an in-line pump whose characteristics were examined by using as input the measured line pressure signal and by modeling the pump operation itself as well as the fuel flow through single- and two-stage injectors. For the validation of the model, extensive comparison with experimental data has been performed for a wide range of pump operating conditions.
Technical Paper

Analysis of the Flow in the Nozzle of a Vertical Multi-Hole Diesel Engine Injector

1998-02-23
980811
An enlarged transparent model of a six-hole vertical diesel injector has been manufactured in order to allow flow measurements inside the sac volume and the injection holes to be obtained using a combination of laser Doppler velocimetry (LDV) and the refractive index matching technique under steady state conditions. The measurement points were concentrated in the sac volume close to the entrance of the injection holes as well as inside them on a vertical plane passing through the axis of two injection holes for two different needle lifts. The velocity flow field was characterized in terms of the mean velocity and the turbulent intensity. The results revealed that, under certain conditions, cavitation may occur in the recirculation zone formed at the entrance to the hole since the pressure in this region can reach the value of the vapor pressure of the flowing liquid; this was found to strongly depend on the needle lift and eccentricity.
Technical Paper

Flow and Combustion in a Four-Valve, Spark-Ignition Optical Engine

1994-03-01
940475
The in-cylinder flow during induction and compression in the pentroof chamber of a four-valve, single-cylinder, spark-ignition optical engine was quantified by LDV and correlated with combustion development especially under lean mixture conditions. The tumble-generating capacity of the cylinder head was first characterised by a tumble adaptor under steady flow conditions and, subsequently, enhanced by two sleeves introduced into the intake ports which generated a stronger tumbling motion.
Technical Paper

Flow and Heat Transfer Characteristics of Impinging Diesel Sprays Under Cross-Flow Conditions

1995-02-01
950448
The spray/wall interaction in small direct-injection diesel engines employing swirl was simulated in a bench-type experiment by a steady cross-flow of air acting on a transient diesel spray impinging normally onto a heated and unheated flat plate under atmospheric conditions. The droplet size and velocity characteristics in the radial wall-jet formed on the plate after spray impingement were investigated by phase-Doppler anemometry and the spray/wall heat transfer during impingement was measured using fast-response thermocouples. The results showed that the mechanism of secondary atomisation of the impinging droplets was altered as droplets from the approaching spray were entrained by the cross-flow, while the spray/wall heat transfer was reduced due to the lower droplet flux reaching the wall. Based on the approaching droplet velocity and size characteristics and wall temperature, an empirical correlation has been derived between the flow and heat transfer parameters.
Technical Paper

An Approach to Charge Stratification in Lean-Burn, Spark- Ignition Engines

1994-10-01
941878
A constant-volume combustion chamber was used to examine injection of a small quantity of slightly rich fuel/air mixture towards the spark plug around the time of ignition, in an overall very lean mixture rotating at velocities representative of modern spark-ignition engines. The results show that it is possible to achieve 100% ignitability with overall air-fuel ratios in excess of 50 and much faster burn rates than those with initially homogenous mixtures of the same equivalence ratio with high swirl and turbulence. The advantages of this method of local charge stratification have been demonstrated in terms of both pressure measurements and shadowgraphs of the early flame development while the transient characteristics of the injected rich mixture at the spark plug gap were monitored by a fast flame ionization detector.
Technical Paper

Evaluation of Pump Design Parameters in Diesel Fuel Injection Systems

1995-02-01
950078
A computer model solving the 1-D flow in a typical fuel injection system for direct-injection diesel engines is presented. A Bosch distributor - type VE pump connected to four Stanadyne pencil - type nozzles has been used to validate the computer model over a wide range of operating conditions. Validation of the developed computer code has been performed for eight representative test cases. The predicted values which were compared with the experimental ones include the pumping chamber pressure, the line pressure, the needle lift and the injection rate. Results using as input the measured pumping chamber pressure are also presented in order to identify the error in the injection rate signal attributed to the difference between the simulated and the experimental pumping chamber pressure. In addition, the total fuel injection quantity for pump speeds between 500 and 2000 rpm and lever positions between 20% to 100% was calculated and compared with measurements.
Technical Paper

Mixture Formation and Combustion in the Dl Diesel Engine

1997-08-06
972681
The diesel engine is the most efficient user of fossil fuels for vehicle propulsion and seems to best fulfill the requirements of the future. It is for this reason that Volkswagen has initiated a very broad research programme for diesels. The purpose of this paper is to build a bridge between fundamental research and technical developments which could allow evaluation of the prospects of direct- injection diesels as powerplants of choice for passenger cars in the turn of the century. The current knowledge on mixture formation, combustion and pollutant formation in diesel engines is presented and discussed with special emphasis given to the concept of the direct-injection diesel engine.
Technical Paper

Imaging of Lean Premixed Flames in Spark-Ignition Engines

1994-10-01
942052
Two optical single-cylinder spark-ignition engines equipped with two- and four-valve cylinder heads were used to examine the flow and flame interaction under lean mixture conditions. Images of the developing flame under quiescent, swirl, low tumble and high tumble flow conditions corresponding to a wide range of mean velocity and turbulence levels around the time of ignition were obtained with an image-intensified CCD camera using the light radiated by the flame and the flow in the vicinity of the spark plug was quantified by laser Doppler velocimetry. In the case of the tumbling flow, the flame images were software-processed to allow estimation of the total flame area, the displacement of its centre as a function of crank angle and their correlation with the cylinder pressure.
Technical Paper

Flow and Heat Transfer Characteristics of Impinging Transient Diesel Sprays

1994-03-01
940678
The spatial and temporal characteristics of transient diesel sprays impinging on unheated and heated walls were investigated by phase-Doppler anemometry (PDA) and the heat-transfer distribution in the vicinity of the impingement region was determined by fast response thermocouples. The results have provided quantitative evidence about the effect that the presence of the flat wall exerts on the spray characteristics. For example, independent of the thickness of the liquid film, the wall rearranges the droplet size distribution of the free spray with droplet collision and coalescence playing an important role in both the droplet redistribution and in the development of the wall-jet. Droplet sizes were reduced and mean tangential velocities increased with wall temperature at the upstream side and at the front of the wall-jet, respectively.
Technical Paper

Development of a Piston-Ring Lubrication Test-Rig and Investigation of Boundary Conditions for Modelling Lubricant Film Properties

1995-10-01
952468
A test-rig has been developed to simulate under idealised conditions the lubricating action between the piston-ring and the cylinder-liner in reciprocating engines. Complications arising in production engine piston-assemblies such as lubricant starvation, ring and piston dynamics, thermal and elastic deformations and blowby can thus be avoided so that the lubricant film characteristics are examined in isolation. The lubricant film thickness and friction at the piston-ring/liner interface were simultaneously measured throughout the stroke as a function of speed and load and compared with the solution of the Reynolds equation for a range of boundary conditions. The examined conditions included the Swift-Stieber (Reynolds), the separation and limiting cases of the Floberg and the Coyne & Elrod boundary conditions using a numerically efficient general purpose program.
Technical Paper

Effect of Fuel Injection Processes on the Structure of Diesel Sprays

1997-02-24
970799
A diesel spray model has been developed and validated against experimental data obtained for different injection and surrounding gas conditions to allow investigation of the relative importance of the different physical processes occurring during the spray development. The model is based on the Eulerian-Lagrangian approximation and the Navier-Stokes equations, simulating the gas motion, are numerically solved on a collocated non-uniform curvilinear non-orthogonal grid, while the spray equation is solved numerically using a Lagrangian particle tracking method. The injection conditions are determined by another recently developed model calculating the flow in the fuel injection system, the sac volume and injection holes area which accounts for the details of the injection velocity, the fuel injection rate per injection hole and occurrence of hole cavitation. Thus, differences between the sprays from inclined multihole injectors can be simulated and analysed.
Technical Paper

Transient Characteristics of Multi-Hole Diesel Sprays

1990-02-01
900480
The spatial and temporal characteristics of a diesel spray injected into the atmosphere through a multi-hole nozzle used in small DI Diesel engines have been investigated by laser techniques as a function of pump speed and load. The results showed that spray tip penetration and velocity depend on injection frequency rather than injected volume and the spray is asymmetric during the early and main part of the injection period. In the time/space domain different structures have been identified within the injection period, with the early injection period characterized by a well atomized cloud of droplets, the main period by the spray head and a dense core and the late injection period by the disintegrating dense core and the spray tail. IN DIRECT-INJECTION DIESEL ENGINES for passenger cars, fuel is injected through multi-hole nozzles at high pressure to promote mixing with the rapidly swirling air inside the combustion chamber.
Technical Paper

Swirl Center Precession in Engine Flows

1987-02-01
870370
The origin and development of swirl center precession in engine flows has been investigated in a steady flow rig, with and without a porous plate simulating a stationary piston, and in a model engine motored at 200rpm; swirl, in all cases, was generated by means of 60° vanes located in the axisymmetric inlet port. The swirl center performs a helical motion that originates as an instability in the forced-vortex core from its interaction with the axial flow at a free stagnation point and develops in the engine from the piston towards the cylinder head; an opposite trend has been observed in the steady flow case with the open-ended cylinder. In the ensemble-averaged measurements, swirl center precession has been identified by the increased tangential velocity fluctuations around the off-centre zero swirl velocity.
Technical Paper

Transient Characteristics of Single-Hole Diesel Sprays

1989-02-01
890314
Diesel fuel was injected through a pintle nozzle into quiescent ambient air and the transient characteristics of the spray were examined as a function of injection pump speed. The laser-based techniques characterised the spray in terms of its transient structure, tip penetration, droplet axial mean and rms velocities and average droplet size. The results, when correlated with the fuel line pressure and nozzle exit conditions, revealed the presence of four regimes in the transient spray development: an early injection period representing the first stage of droplet formation, the main injection period associated with the formation and break up of a dense core and representing the second stage of droplet formation, a late injection period corresponding to the collapse of the dense core and a post injection period where, depending on the injection conditions, liquid ligaments and/or large droplets are present near the nozzle and may give rise to a third stage of droplet formation.
X