It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current wave forms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. While earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high-speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the freestream gas velocity. A lower velocity threshold exists below, which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the freestream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.
It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current waveforms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. Whereas earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the free stream gas velocity. A lower velocity threshold exists below which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the free stream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.
Correct functioning of fuel nozzles is paramount to the efficient operation of gas turbine engines. Nozzles exhibiting poor distribution of droplets can be detrimental to combustion and overall engine life due to the creation of hot spots and potential for torching. The traditional technique of assessing nozzle performance involves operation in stagnant air conditions. Fuel spray is collected in the subdivided bins of a mechanical patternation system to determine spray symmetry. Recent improvements in spray analysis involve the use of laser light sheets to illuminate specific ‘slices’ of sprays in either cross sectional or axial planes. Typically, scattered light from the intersection of a laser sheet and a spray is recorded by a digital video camera, and images are averaged and corrected to determine the quality of the spray pattern. Such optical means of assessing spray quality provide great improvement over conventional means in terms of speed, convenience, and information retrieved. Nonetheless, data obtained in stagnant air conditions do not give an indication of spray geometry within combustion chambers under realistic operating conditions of airflow and combustion. This paper describes a project which applied laser-based optical patternation in a T-56 gas turbine combustion chamber rig with optical access under realistic flow conditions. As such, nozzle spray pattern was observed for various air and fuel flows in both cross sectional and plume (chamber axial) orientations. A deliberately damaged nozzle was also assessed for comparison with a good nozzle. Using optical filtration, spray patterns were observed under operationally representative combustion conditions.
This paper describes experimental research aimed at developing techniques for monitoring the growth of combustion chamber deposits in diesel engines using data obtained from cylinder pressure and exhaust temperature measurements. A naturally aspirated single cylinder research engine was operated alternately between low load “coking” conditions (2.5 bar BMEP) and higher load “decoking” conditions (5.5 bar BMEP) intended to promote the formation and removal, respectively of combustion chamber deposits. The polytropic exponent of compression was observed to increase during coking runs and decrease during decoking runs. The peak heat release rate was observed to decrease during coking runs and increase during decoking runs. The peak cycle value of the first derivative of the exhaust thermocouple signal decreased during coking runs but exhibited no clear trend during decoking runs. Conventional exhaust temperature measurements showed no consistent trend during coking runs but the exhaust temperature decreased during decoking runs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.