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Technical Paper

Investigation of the Fuel Distribution and the In-cylinder Flow Field in a Stratified Charge Engine Using Laser Techniques and Comparison with CFD-Modelling

1999-10-25
1999-01-3540
This paper presents an investigation of a Volvo Direct Injection Spark Ignition (DISI) engine, where the fuel distribution and the in-cylinder flow field have been mapped by the use of laser techniques in an engine with optical access. Along with the experimental work, CFD-modelling of flow and fuel distribution has been performed. Laser Induced Fluorescence (LIF) visualisation of the fuel distribution in a DI-engine has been performed using an endoscopic detection system. Due to the complex piston crown geometry it was not possible to monitor the critical area around the sparkplug with conventional, through the piston, detection. Therefore, an endoscope inserted in the spark plug hole was used. This approach gave an unrestricted view over the desired area. In addition, the in-cylinder flow fields have been monitored by Particle Image Velocimetry (PIV) through cylinder and piston. The results from both the LIF and the PIV measurements have been compared with CFD-modelling at Volvo.
Technical Paper

Experimental Investigations of Flow and Temperature Fields in an SI Engine and Comparison with Numerical Analysis

1999-10-25
1999-01-3541
Two-dimensional cycle-resolved burnt gas temperatures were measured using two line atomic fluorescence (TLAF) in a single cylinder spark ignition car engine. Mapping of the in-cylinder flow was done under the same operating conditions using Particle Imaging Velocimetry (PIV). Experimental data for temperature and flow was compared to results from numerical simulations.
Technical Paper

A Simple Approach to Studying the Relation between Fuel Rate Heat Release Rate and NO Formation in Diesel Engines

1999-10-25
1999-01-3548
Modern diesel engine injection systems are largely computer controlled. This opens the door for tailoring the fuel rate. Rate shaping in combination with increased injection pressure and nozzle design will play an important role in the efforts to maintain the superiority of the diesel engine in terms of fuel economy while meeting future demands on emissions. This approach to studying the potential of rate shaping in order to reduce NO formation is based on three sub-models. The first model calculates the fuel rate by using standard expressions for calculating the areas of the dimensioning flow paths in the nozzle and the corresponding discharge coefficients. In the second sub-model the heat release rate is described as a function of available fuel energy, i.e. fuel mass, in the cylinder. The third submodel is the multizone combustion model that calculates NO for a given heat release rate under assumed air /fuel ratios.
Technical Paper

A Skeletal Kinetic Mechanism for the Oxidation of Iso-Octane and N-Heptane Validated Under Engine Knock Conditions

1999-10-25
1999-01-3484
A method for automatic reduction of detailed kinetic to skeletal mechanisms for complex fuels is proposed. The method is based on the simultaneous use of sensitivity and reaction-flow analysis. The resulting skeletal mechanism is valid for the parameter range of initial and boundary values, the analysis have been performed for. The gas-phase chemistry is analyzed in the end gas of an SI-engine, using a two-zone model. Species, not relevant for the occurrence of autoignition in the end gas, are defined as redundant. They are identified and eliminated for different pre-set levels of minimum reaction flow and sensitivity. The error in the mechanism increases monotony with increasing pre-set level of minimum reaction flow.
Technical Paper

A Multi-Zone Model for Prediction of HCCI Combustion and Emissions

2000-03-06
2000-01-0327
Homogeneous Charge Compression Ignition (HCCI) combustion is a process dominated by chemical kinetics of the fuel-air mixture. The hottest part of the mixture ignites first, and compresses the rest of the charge, which then ignites after a short time lag. Crevices and boundary layers generally remain too cold to react, and result in substantial hydrocarbon and carbon monoxide emissions. Turbulence has little effect on HCCI combustion, and may be most important as a factor in determining temperature gradients and boundary layer thickness inside the cylinder. The importance of thermal gradients inside the cylinder makes it necessary to use an integrated fluid mechanics-chemical kinetics code for accurate predictions of HCCI combustion. However, the use of a fluid mechanics code with detailed chemical kinetics is too computationally intensive for today's computers.
Technical Paper

Simple Feedback Control and Mode Switching Strategies for GDI Engines

2000-03-06
2000-01-0263
A novel approach to the control of a GDI engine is presented. The controller consists of a combination of sub-controllers, where torque feedback is a central part. The sub-controllers are with a few exceptions designed using simple linear feedback and feedforward control design methods. Special mode switch strategies are used to minimize the torque bumps during combustion mode changes. The controller has been evaluated on the European driving cycle using a dynamic simulation model, including a powertrain model and a driver model, with good results.
Technical Paper

Demonstrating the Multi Fuel Capability of a Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio

1999-10-25
1999-01-3679
The potential of a Homogeneous Charge Compression Ignition (HCCI) engine with variable compression ratio has been experimentally investigated. The experiments were carried out in a single cylinder engine, equipped with a modified cylinder head. Altering the position of a secondary piston in the cylinder head enabled a change of the compression ratio. The secondary piston was controlled by a hydraulic system, which was operated from the control room. Dual port injection systems were used, which made it possible to change the ratio of two different fuels with the engine running. By mixing iso-octane with octane number 100 and normal heptane with octane number 0, it was possible to obtain any octane rating between 0 and 100. By using an electrical heater for the inlet air, it was possible to adjust the inlet air temperature to a selected value.
Technical Paper

A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging

1999-10-25
1999-01-3680
An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH. Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel. Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist.
Technical Paper

Optical Diagnostics Applied to a Naturally Aspirated Homogeneous Charge Compression Ignition Engine

1999-10-25
1999-01-3649
Basic optical properties have been investigated in order to characterize the HCCI-combustion process. Basic optical properties of a Homogeneous Charge Compression Ignition (HCCI) engine have been investigated in order to characterize the combustion process. The absorption of light propagating through the combustion chamber has been spectrally resolved for four different fuels. Significant differences between the fuels could be detected. Complementary information could be obtained by recording spontaneous emission of radiation during combustion. Raman point measurements were used to quantify cycle-to-cycle variations of the equivalence ratio. The homogeneity of the charge was monitored by the use of two-dimensional tracer LIF. That method was also utilized to investigate the flame development. The experiments were performed in a six-cylinder, truck-sized engine with one cylinder modified to allow for optical access.
Technical Paper

Interaction Between Turbulence and Flame in an S.I. Engine and in a Stationary Burner

1999-03-01
1999-01-0569
Turbulent flame speeds have been measured in a single cylinder S.I. engine and in a stationary atmospheric burner. One- and two-point LDA has been used to measure turbulence intensities and integral length scales. Stretching, in terms of Karlovitz numbers could be estimated from these measurements. The influence of moving average filtered turbulence on the flame speed in the S.I. engine is in agreement with the burner experiments. Previously reported signs of quenching of small flames in the S.I. engine, due to excessive turbulence could not be found for larger flames.
Technical Paper

Automatic Reduction of Detailed Chemical Reaction Mechanisms for Autoignition Under SI Engine Conditions

2000-06-19
2000-01-1895
A method for automatic reduction of detailed reaction mechanisms using simultaneous sensitivity, reaction flow and lifetime analysis has been developed and applied to a two-zone model of an SI engine fuelled with Primary Reference Fuel (PRF). Species which are less relevant for the occurrence of autoignition in the end gas are declared redundant. They are identified and eliminated for different pre-set minimum levels of reaction flow and sensitivity. The resulting skeletal mechanism is valid in the ranges of initial and boundary values for which the analyses have been performed. A measure of species lifetime is calculated from the chemical source terms, and the species with the lifetime shorter than and mass-fraction less than specified limits are selected for removal.
Technical Paper

Fuel Distribution in an Air Assist Direct Injected Spark Ignition Engine with Central Injection and Spark Plug Measured with Laser Induced Fluorescence

2000-06-19
2000-01-1898
The fuel distribution in an air assist direct injection engine was measured with Planar Laser Induced Fluorescence, PLIF. The engine was fueled with isooctane and 3-pentanon was used as the fuel tracer. The optical engine was of the prolonged piston type, with a quartz ring in the upper part of the cylinder. Both the fuel injector and the spark plug were centrally located in the cylinder head. Two different pistons were examined: flat piston and bowl in piston. Results show that the differences in fuel stratification are very large for the flat piston compared to the piston with a bowl.
Technical Paper

Hydrocarbon (HC) Reduction of Exhaust Gases from a Homogeneous Charge Compression Ignition (HCCI) Engine Using Different Catalytic Mesh-Coatings

2000-06-19
2000-01-1847
A FeCrAlloy mesh-type catalyst has been used to reduce hydrocarbons (HC) and carbon monoxide (CO) emissions from a 4-stroke HCCI engine. Significant for the HCCI engine is a high compression ratio and lean mixtures, which leads to a high efficiency, low combustion temperatures and thereby low NOx emissions, <5 pmm, but also low exhaust temperatures, around 300°C. It becomes critical to: 1. Ensure that the HCCI-combustion generates as low HC emissions as possible, this can be done by very precise control of engine inlet conditions and, if possible, compression ratio. 2. Ensure that the exhaust temperature is high enough, without loosing efficiency or producing NOx; in order to get an oxidizing catalyst to work. 3. Select proper catalyst material for the catalyst so that the exhaust temperature can be as low as possible.
Technical Paper

Prediction of Heat Transfer to the Walls for Autoignition Related Situations in SI Engines

2000-03-06
2000-01-1084
A theoretical investigation is presented concerning how the heat transfer process from the gas in the combustion chamber, burned as well as the unburned gas regions, to the walls is affected by the autoignition phenomenon in SI engines. The zonal model in ref. [1] is adapted for the calculations. The radiative heat flux during the heat release period and the heat transfer in the thermal boundary layer by convection are predicted for situations when autoignition has occurred. The cylinder wall temperature is also used as a parameter in this study. The effects of engine operating parameters such as engine speed, timing of ignition, duration time of flame propagation and the fuel parameter Research Octane Number, i.e., RON, on the heat flux to the walls have been studied. The heat release is calculated for a detailed chemical kinetic model, refs. [1, 2 and 3].
Technical Paper

Effect of Inhomogeneities in the End Gas Temperature Field on the Autoignition in SI Engines

2000-03-06
2000-01-0954
This paper reports an one–dimensional modeling procedure of the hot spot autoignition with a detailed chemistry and multi–species transport in the end gas in an SI engine. The governing equations for continuity of mass, momentum, energy and species for an one–dimensional, unsteady, compressible, laminar, reacting flow and thermal fields are discretized and solved by a fully implicit method. A chemical kinetic mechanism is used for the primary reference fuels n–heptane and iso–octane. This mechanism contains 510 chemical reactions and 75 species. The change of the cylinder pressure is calculated from both flame propagation and piston movement. The turbulent velocity of the propagating flame is modeled by the Wiebe function. Adiabatic conditions, calculated by minimizing Gibb's free energy at each time step, are assumed behind the flame front in the burned gas.
Technical Paper

Reacting Boundary Layers in a Homogeneous Charge Compression Ignition (HCCI) Engine

2001-03-05
2001-01-1032
An experimental and computational study of the near-wall combustion in a Homogeneous Charge Compression Ignition (HCCI) engine has been conducted by applying laser based diagnostic techniques in combination with numerical modeling. Our major intent was to characterize the combustion in the velocity- and thermal boundary layers. The progress of the combustion was studied by using fuel tracer LIF, the result of which was compared with LDA measurements of the velocity boundary layer along with numerical simulations of the reacting boundary layer. Time resolved images of the PLIF signal were taken and ensemble averaged images were calculated. In the fuel tracer LIF experiments, acetone was seeded into the fuel as a tracer. It is clear from the experiments that a proper set of backgrounds and laser profiles are necessary to resolve the near-wall concentration profiles, even at a qualitative level.
Technical Paper

Employing an Ionization Sensor for Combustion Diagnostics in a Lean Burn Natural Gas Engine

2001-03-05
2001-01-0992
An ionization sensor has been used to study the combustion process in a six-cylinder lean burn, truck-sized engine fueled with natural gas and optimized for low emissions of nitric oxides. The final goal of the investigations is to study the prospects of using the ionization sensor for finding the optimal operating position with respect to low NOx emission and stable engine operation. The results indicate that unstable combustion can be detected by analyzing the coefficient of variation (CoV) of the detector current amplitude. Close relationships between this measure and the CoV of the indicated mean effective pressure have been found during an air-fuel ratio scan with fixed ignition advance.
Technical Paper

Laser-Rayleigh Imaging of DME Sprays in an Optically Accessible DI Diesel Truck Engine

2001-03-05
2001-01-0915
Laser-Rayleigh imaging has been employed to measure the relative fuel concentration in the gaseous jet region of DME sprays. The measurements were performed in an optically accessible diesel truck engine equipped with a common rail injection system. A one-hole nozzle was used to guarantee that the recorded pressure history was associated with the heat release in the imaged spray. To compensate for the low compression ratio in the modified engine the inlet air was preheated. Spray development was studied for two levels of preheating, from the start of injection to the point where all fuel was consumed. The results indicate that there is a strong correlation between the amount of unburned fuel present in the cylinder and the rate of heat release at a given time. The combustion can not be described as purely premixed or purely mixing-controlled at any time, but always has an element of both. After all fuel appears to have vanished there is still an extended period of heat release.
Technical Paper

Comparison of Heat Release and NOx Formation in a DI Diesel Engine Running on DME and Diesel Fuel

2001-03-05
2001-01-0651
Although there seems to be a consensus regarding the low emission potential of DME, there are still different opinions about why the low NOx emissions can be obtained without negative effects on thermal efficiency. Possible explanations are: The physical properties of DME affecting the spray and the mixture formation Different shape and duration of the heat release in combination with reduced heat losses In this paper an attempt is made to increase the knowledge of DME in relation to diesel fuel with respect to heat release and NOx formation. The emphasis has been to create injection conditions as similar as possible for both fuels. For that purpose the same injection system (CR), injection pressure (270 bar), injection timing and duration have been used for the two fuels. The only differences were the diameters of the nozzle holes, which were chosen to give the same fuel energy supply, and the physical properties of the fuels.
Technical Paper

The Effect of Knock on the Heat Transfer in an SI Engine: Thermal Boundary Layer Investigation using CARS Temperature Measurements and Heat Flux Measurements

2000-10-16
2000-01-2831
It is generally accepted that knocking combustion influences the heat transfer in SI engines. However, the effects of heat transfer on the onset of knock is still not clear due to lack of experimental data of the thermal boundary layer close to the combustion chamber wall. This paper presents measurements of the temperature in the thermal boundary layer under knocking and non-knocking conditions. The temperature was measured using dual-broadband rotational Coherent anti-Stokes Raman Spectroscopy (CARS). Simultaneous time-resolved measurements of the cylinder pressure, at three different locations, and the heat flux to the wall were carried out. Optical access to the region near the combustion chamber wall was achieved by using a horseshoe-shaped combustion chamber with windows installed in the rectangular part of the chamber. This arrangement made CARS temperature measurements close to the wall possible and results are presented in the range 0.1-5 mm from the wall.
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