EXPERIMENTAL TECHNIQUES IN COMBUSTION USE OF IN-CYLINDER IONISATION FOR THE INVESTIGATION AND CONTROL OF SPARK IGNITION ENGINES.

Ions generated during combustion have been used in three ways to give qualitative combustion information. Langmuir type probes have been inserted into the combustion chamber opposite the spark plug location. The centre electrode of the sparking plug itself has been used to produce an ionisation signal from the slightly ionised gases remaining after the flame front has departed. The spark discharge at ignition time has been used as an anemometer.

Spark ignition of turbulent premixed and non-premixed opposed jet flames

The probabilistic nature of ignition of premixed and non-premixecl turbulent opposed-jet flames has been examined and the flame structures following ignition have been visualized directly and with OH-PLIF. It has been found that high bulk velocities decrease the ignition probability in all locations and for all flames. Ignition is sometimes possible even in locations where there is negligible probability of finding flammable mixture and is sometimes impossible in locations with high probability of flammable fluid. The edge flame propagation speed is also estimated.

Particulate matter emission during start-up and transient operation of a spark-ignition engine

In order to understand why emissions of Particulate Matter (PM) from Spark-Ignition (SI) automobiles peak during periods of transient operation such as rapid accelerations, a study of controlled, repeatable transients was performed. Time-resolved engine-out PM emissions from a modern four-cylinder engine during transient load and air/fuel ratio operation were examined, and the results could be fit in most cases to a first order time response. The time constants for the transient response are similar to those measured for changes in intake valve temperature, reflecting the strong dependence of PM emissions on the amount of liquid fuel in the combustion chamber. In only one unrepeatable case did the time response differ from a first order function: showing an overshoot in PM emissions during transition from the initial to the final steady state PM emission level. PM emissions during controlled, motored start-up experiments show a peak at start-up followed by a period during which emissions are either relatively constant or drift somewhat. When the fuel injection and ignition are shut off, PM emissions also peak briefly, but rapidly decay to low levels. Qualitative implications on the study and modeling of PM emissions during transient engine operation are discussed. Copyright © 1999 Society of Automotive Engineers, Inc.

Investigation of the dilution process for measurement of particulate matter from spark-ignition engines

Measurements of particulate matter (PM) from spark ignition (SI) engine exhaust using dilution tunnels will become more prevalent as emission standards are tightened. Hence, a study of the dilution process was undertaken in order to understand how various dilution related parameters affect the accuracy with which PM sizes and concentrations can be determined. A SI and a compression ignition (CI) engine were separately used to examine parameters of the dilution process; the present work discusses the results in the context of SI exhaust dilution. A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution, number density, and volume fraction of PM. Temperature measurements in the exhaust pipe and dilution tunnel reveal the degree of mixing between exhaust and dilution air, the effect of flowrate on heat transfer from undiluted and diluted exhaust to the environment, and the minimum permissible dilution ratio for a maximum sample temperature of 52°C. Measurements of PM concentrations as a function of dilution ratio show the competing effects of temperature and particle/vapor concentrations on particle growth dynamics, which result in a range of dilution ratios-from 13 to 18-where the effect of dilution ratio, independent of flowrate, is kept to a minimum. This range of dilution ratios is therefore optimal in order to achieve repeatable PM concentration measurements. Particle dynamics during transit through the tunnel operating at the optimal dilution ratio was found statistically insignificant compared to data scatter. Such small differences in number concentration may be qualitatively representative of particle losses for SI exhaust, but small increases in PM volume fraction during transit through the tunnel may significantly underestimate accretion of mass due to unburned hydrocarbons (HCs) emitted by SI engines. The fraction of SI-derived PM mass due to adsorbed/absorbed vapor, estimated from these data, is consistent with previous chemical analyses of PM. © 1998 Society of Automotive Engineers, Inc.

Numerical simulation of post-flame oxidation of hydrocarbons in spark ignition engines

About 50-90 percent of the hydrocarbons that escape combustion during flame passage in spark-ignition engine operation are oxidized in the cylinder before leaving the system. The process involves the transport of unreacted fuel from cold walls towards the hotter burned gas regions and subsequent reaction. In order to understand controlling factors in the process, a transient one-dimensional reactive-diffusive model has been formulated for simulating the oxidation processes taking place in the reactive layer between hot burned gases and cold unreacted air/fuel mixture, with initial and boundary conditions provided by the emergence of hydrocarbons from the piston top land crevice. Energy and species conservation equations are solved for the entire process, using a detailed chemical kinetic mechanism for propane. Simulation results show that the post-flame oxidation process takes place within a reactive layer where intermediate hydrocarbon products are formed at temperatures above 1100-1200 K, followed by a carbon monoxide conversion region closer to the hot burned gases. Model results show that most of hydrocarbons leaving the crevice are completely oxidized inside the cylinder. The largest contribution of remaining hydrocarbons are those leaving the crevice at temperatures below 1400 K. The largest fraction of non-fuel (intermediate) hydrocarbons results from hydrocarbons leaving the crevice when core temperatures are around 1400 K Copyright © 1997 Society of Automotive Engineers, Inc.

Extent of oxidation of hydrocarbons desorbing from the lubricant oil layer in spark-ignition engines

The extent of oxidation of hydrocarbons desorbing from the oil layer has been measured directly in a hydrogen-fueled, spark-ignited engine in which the lubricant oil was doped with a single component hydrocarbon. The amount of hydrocarbon desorbed and oxidized could be measured simultaneously as the dopant was only source of carbon-containing species. The fraction oxidized was strongly dependent on engine load, hydrogen fuel-air ratio and dopant chemical reactivity, but only modestly dependent on spark timing and nitrogen dilution levels below 20 percent. Fast FID measurements at the cylinder exit showed that the surviving hydrocarbons emerge late in the exhaust stroke. © Copyright 1996 Society of Automotive Engineers, Inc.

Reduce of threshold of laser inducing breakdown in atmosphere by introducing an electric spark

We report laser-generated plasmas in atmosphere with electrical spark generated by a synchronization circuit. The breakdown thresholds under the conditions that the electrical spark is used and not used are compared. The breakdown threshold has a distinct decrease after the electrical spark is used. Breakdown thresholds as a function of atmosphere pressure have also been measured at laser wavelengths 532 nm and 1064 rim for the laser pulse width of 15ns. We also discuss the principle and performances of the ionized atmosphere by Nd:YAG laser under the condition of electrical spark introduction. Multiphoton ionization and cascade ionization play important roles in the whole process of atmosphere ionization. The free electron induced by electrical spark can supply the initialization free electron number for multiphoton ionization and cascade ionization. A model for breakdown in atmosphere, which is in good agreement with the experimental results, is described.

Effects of spark discharge on the anodic coatings on magnesium alloy

Spark discharge was the representative phenomenon of Micro-arc oxidation (MAO) method distinguished from other electrochemical oxidation methods. Under the spark discharge treatment, characteristics of the anodic layer were significantly changed. To investigate the influences of the spark discharge, a piece of magnesium alloy AZ91D specimen was partly treated by MAO method in alkaline silicate solution. And the microstructure, element distributions as well as the surface potential distributions of the specimen were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and scanning Kelvin probe (SKP) technique. As a result of intensive spark discharge treatment, porous external layer with dense internal layer were formed on Mg alloy surface. At the same time, the depositions of OH- and SiO32- ions were accelerated, which resulted in the enrichment of element oxygen and silicon at the spark discharge region. Moreover, due to the compact internal layer, the intensive spark discharge region exhibited more positive potentials with respect to other regions, which meant this region could restrain the ejection of electron and provide effective protection to the substrate. In addition, it was found that oxygen played a vital role in determining the intensity and size of sparks, and abundant oxygen resulted in intensive and larger sparks. (c) 2005 Elsevier B.V. All rights reserved.