Rothamer D.A. Investigation of Flame-Front Equivalence Ratio during Stratified Engine Combustion

University of Wisconsin, Madison, 2002. 148 р. Master of Science (Mechanical Engineering)Abstract
Stratified engine combustion was investigated using simultaneous imaging of the fuel distribution and flame front in an optically accessible direct-injection spark-ignition engine. Planar laser-induced fluorescence of 3-pentanone doped into iso-octane and the OH radicals naturally occurring in the combustion products were imaged with two intensified CCD cameras. The 3-pentanone images provide a quantitative measure of fuel concentration and the OH images allowed for the position of the flame front to be accurately determined. These results represent the first data taken during stratified combustion using a two-camera technique. Using the image data a novel method was developed to determine the flame-front equivalence ratio during stratified combustion. The results of the method provide insights into the stratified combustion process. Additionally, engine-out NOx and CO measurements are presented and an effort to determine a correlation between the flame-front equivalence ratio and measured emissions is made where the flame-front equivalence ratio is thought to be a major factor in pollutant emission formation during stratified combustion. The effects of engine speed, engine load, spark timing, and ignition timing were investigated.
The data indicate that a wide range of equivalence ratios are present along the flame
front. The limited field of view was found to significantly influence the data. The flame-front equivalence ratio data taken for conditions with varying injection and varying spark
timing at equivalence ratios of Φ = 0.32 and Φ = 0.42 at 600 rpm showed little correlation
with the measured emissions. However, the NOx data did clearly reflect the trends of peak
pressure. The available field of view may have been one cause for the lack of correlation, but the pressure trends and emissions data also indicate that combustion phasing has a
strong influence on NOx emissions with changes in spark timing of 10 crank angle degrees
causing almost a factor of two change in measured engine-out NOx.Abstract
AcknowledgementsList of Figures
List of TablesMotivation
Objective
Approach
Outline
Literature Review
DISI Engines
A Brief History of DISI Engines
Advantages and Disadvantages of DISI Over PFI Operation
Homogeneous Operation
Stratified Operation
NOx Formation During Stratified Charge Operation
Planar Laser Induced Fluorescence (PLIF) Imaging
Description of PLIF Technique
Experimental Considerations
Laser Selection
Fluorescence Detection System
Selection of Dopant for Fuel Concentration Measurements
CCD Camera Noise
Image Intensifiers
Influence of PLIF System Noise on the Quantitative
Interpretation of Data
Application of PLIF in Engines
Experimental Setup
Optical Engine
Engine Dimensions
Combustion Chamber Design
Optical Access
Fuel Injectors, and Fuel System
Engine Timing
Pressure Measurement
Experimental Running Conditions
Emissions Measurement (NOx and CO)
PLIF Imaging
Lasers and Optics
Camera Setup
Camera Field of View, Spatial Resolution
Image Correction Procedure
Image Signal-to-Noise Ratio (SNR)
Experimental Method
Description of Method
Fuel Image Correction
Alignment of Images
Edge Detection of Flame Front
Sample Results for Homogeneous Operation
Equivalence Ratio Histograms Under
Homogeneous Operation
Equivalence Ratio PDFs Under Homogeneous Operation
Accuracy and Fidelity of the Method
Flame-Front Equivalence Ratio During Stratified CombustionFactors Affecting the Interpretation of the PDF and Image Data
Field of View
Dataset
Effect of Engine Speed
Effect of Engine Speed, Φ = 0.69
Effect of Engine Speed, Φ = 0.61
Effect of Engine Speed, Φ = 0.42
Effect of Engine Speed, Φ = 0.32
Effect of Engine Load (Overall Equivalence Ratio)
Effect of Engine Load, 600 rpm
Effect of Engine Load, 1200 rpm
Effect of Injection Timing
Effect of Injection Timing, Φ = 0.32, 600 rpm
Effect of Injection Timing, Φ = 0.42, 600 rpm
Effect of Injection Timing, Φ = 0.32, 1200 rpm
Effect of Injection Timing, Φ = 0.42, 1200 rpm
Effect of Ignition Timing
Effect of Ignition Timing, Φ= 0.32, 600 rpm
Effect of Ignition Timing, Φ = 0.42, 600 rpm
Effect of Ignition Timing, Φ = 0.32, 1200 rpm
Effect of Ignition Timing, Φ = 0.42, 1200 rpm
Emission Results
Injection Timing Effect, Φ = 0.32, 600 rpm
Ignition Timing Effect, Φ = 0.32, 600 rpm
Injection Timing Effect, Φ = 0.42, 600 rpm
Ignition Timing Effect, Φ = 0.42, 600 rpm
Discussion
Conclusions and RecommendationsAppendix A Average Pressure Traces for Emission Measurements