Two-colour Pyrometry Research Articles

Characterization of the ignition and combustion processes of spray injected by a hole-type nozzle for a direct-injection spark ignition engine

The spray-guided direct-injection spark ignition engine needs a stable ignition and combustion system for favourable operation. In this study, the effects of the ignition position (e.g. upstream, middle or downstream of the spray) and the timing (e.g. before, at or after the end of injection) respectively on the flame development and combustion processes of gasoline spray injected by a hole-type nozzle were investigated in a quiescent constant-volume vessel. OH* chemiluminescence was used to characterize the temporal and spatial distributions of the combusting activity and flame evolution. The soot formation process was clarified by using the high-speed imaging of two-colour pyrometry. At all the ignition positions, a moderate jet-to-jet variation in the maximum integrated OH* intensity was present as the fuel was ignited in the middle region of the spray. The over-lean mixture at the spark gap led to early flame decay and enhanced the variation in the combustion intensity. When the flame started to propagate, the decreased equivalence ratio distribution downstream of the ignition position tended to result in incomplete combustion with a pronounced long narrow flame shape and lower OH* emissions. The flame was impeded owing to the lean unburned mixture and the high flow velocity greater than the flame speed above the ignition position, causing it to propagate towards upstream of the spray. An over-rich mixture produced more soot during combustion, in accordance with the KL factor distribution. A potentially favourable condition for development of the flame and the combustion process was found when the fuel was ignited in the middle region of the spray, and the time when the injection was ended.

Measurement of surface temperature and emissivity of different materials by two-colour pyrometry

An experimental investigation is performed to substantiate the capability of a charge coupled device camera to measure local temperature and emissivity of different materials heated to temperatures above 500 °C by two-colour pyrometric technique using colorimetric method. Materials investigated are Inconel 718 with pyromark (high temperature paint), Inconel 718, stainless steel SS 304 and SS 316. Centerline temperature and emissivity distribution is obtained for target plates maintained at constant temperature by AC heating while complete temperature and emissivity distribution is provided for plates heated by flame impingement. The obtained results are compared with a calibrated infrared camera and thermocouples and the temperature distribution is found to be in close agreement. These results pertain to partially oxidized metal alloys covered in this study. Deviation in the measurement of emissivity can be attributed to its dependence on wavelength range, oxidation, and sensitivity of the image detector.

Electrode temperature measurements of multi-phase AC arc by high-speed video camera

The multi-phase AC arc plasma has been applied in the glass melting technology as a promising heat source. The electrode erosion of the multi-phase arc is one of the most important issues to be solved. In the present work, the theory of the two-colour pyrometry by using the high-speed video camera with band-pass filters was applied to the electrode temperature measurements. First, the spectroscopic measurements of the electrode region in the multi-phase arc were conducted to select the appropriate wavelengths of band-pass filters. Then, the electrode temperatures of 2-phase, 6-phase, and 12-phase arcs were measured. The electrode tip temperature and the molten area were evaluated from the obtained 2-dimensional temperature distributions. Results indicated that the increase of the number of the phases leads to the lower tip temperature and the larger molten area. Observation of the multiple arcs further revealed the particular characteristics of the multi-phase arc, such as the periodical arc motion has important role on the electrode molten state.

In-flight particle measurement of glass raw materials in hybrid heating of twelve-phase AC arc with oxygen burner

The high temperature provided by a 12-phase AC arc plasma is beneficial to finish vitrification reaction in milliseconds. Another heating method called “hybrid plasma” combines multi-phase AC arc and oxygen burner are expected to improve glass quality and increase productivity with minimum energy consumption. In this study, recent works on the development of in-flight particle measurement in hybrid plasma system are presented. Two-colour pyrometry offers considerable advantages for measuring particle temperatures in flight. A high-speed camera equipped with a band-pass filter system was applied to measure the in-flight temperatures of glass particles. The intensity recorded by the camera was calibrated using a tungsten halogen lamp. This technique also allows evaluating the fluctuation of the average particle temperature within millisecond in plasma region.

Effects of engine operating parameters on diesel low-temperature combustion with split fuel injection

This paper shows that a split-fuel-injection strategy can achieve robust, near-zero smoke and nitrogen oxide emissions at reduced exhaust gas recirculation levels under low-temperature combustion conditions. The overall objective of the work was to investigate the sensitivity (in terms of the engine emissions and the fuel economy) of a 50:50 (by mass) split-injection strategy to variations in the key engine operating parameters. Experiments were performed at operating conditions corresponding to a gross indicated mean effective pressure of 500 kPa at an engine speed of 1500 r/min in a 0.51 l single-cylinder high-speed direct-injection diesel engine. The paper presents the effects of different relative fuel injection timings at a variable intake oxygen mass fraction (10.5% and 12%) at a constant intake pressure (120 kPa, absolute) on the smoke, total hydrocarbon and carbon monoxide emissions with the split-main-injection strategy. The effects of a variable fuel injection pressure (90 MPa and 110 MPa) on diesel low-temperature combustion with split injection are also reported, as are the effect of an increased intake pressure (150 kPa, absolute). The combined effects of the operating parameters and the fuel injection timing on the smoke, nitrogen oxide, total hydrocarbon and carbon monoxide emissions and the gross indicated specific fuel consumption are described. For selected operating conditions, the cycle-resolved spray and combustion processes are visualized together with the flame temperature measurement using two-colour optical pyrometry to understand the combustion phenomena occurring in the split-injection strategy. The results of the optical studies show that different low-temperature combustion operating conditions producing similarly low levels of ‘engine-out’ smoke emissions have substantially different histories of soot formation and soot oxidation. An increase in the intake oxygen mass fraction reduced the total hydrocarbon emissions and the gross indicated specific fuel consumption at a given intake pressure, while a higher intake pressure reduced them further. Although significant soot formation took place from the second injection event, the majority of the soot was subsequently oxidized because of a slightly higher flame temperature and slightly higher oxygen concentration than in single-injection high-exhaust-gas-recirculation low-temperature combustion. A higher injection pressure did not have any significant effect on the emissions and the gross indicated specific fuel consumption.

Characteristics of the ignition and combustion of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine

The effect of injection pressures at 100 MPa and 200 MPa respectively on the ignition and combustion characteristics of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine was investigated. Two biodiesel fuels (namely biodiesel fuel from palm oil (BDFp) and biodiesel fuel from cooking oil (BDFc)) and JIS#2 diesel fuel were utilized in this research. The Mie scattering technique was used to characterize both the non-evaporating and the evaporating spray formation processes. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. Two-colour pyrometry was applied for the soot formation processes. At all injection pressures, the biodiesel fuels (especially BDFp) gave a longer spray tip penetration and a smaller spray angle under the non-evaporating conditions while the liquid-phase penetration length was longer for the biodiesel fuels than for diesel under the evaporating conditions. From estimation using a simplified model for air entrainment by the sprays, the BDFp and BDFc exhibited lower mass ratios of air to fuel than diesel did. The ignition delay was longest for the BDFc while it was shortest for the BDFp. Both the experimental and the predicted flame lift-off lengths for the BDFp were the shortest, indicating the least percentage of entrained stoichiometric air upstream. There was no significant difference between the integrated and averaged KL factors at 100 MPa injection pressure for the BDFc and diesel fuels. At 200 MPa, the BDFc presented much lower integrated and averaged KL factors than diesel did. The averaged flame temperatures of the BDFc were found to be lower than that of diesel. The oxygen content in the BDFc played a significant role in the soot formation in comparison with the oxygen from the percentage of stoichiometric air entrained upstream of the lift-off length.

The measurement of metal droplet temperature in GMA welding by infrared two-colour pyrometry

The temperature of metal droplets is essential for clarifying the phenomenon of metal droplet transfer and the melting behaviour of wire; also, it governs the emission of fumes. On the other hand, in situ measurement of the temperature of a metal droplet formed at the tip of a wire during welding was difficult. Hence, this temperature was obtained in many experiences of measurements by such a way that several numbers of metal droplets were collected in a calorimeter to measure the amount of heat content of metal droplet and the heat was converted to temperature. With this way, however, the reliability of the measurement is not necessarily high because the heat loss of the metal droplet during the time when detaching from the wire tip and entering into the calorimeter has to be estimated properly. In this research, two-colour pyrometry has been conducted to obtain the temperature of metal droplets, in which metal droplets have been photographed by a high-speed camera during arc welding, two wavelengths (950 and 980 nm) of light in the infrared range have been selected from the thermal radiation light emitted from the metal droplet at the instant of arc extinguishment by using an imaging spectroscope, and the temperature has been obtained from the intensity ratio of the two waves of light. Consequently, in CO2 arc welding, it has been revealed that the constricted arc causes high-heat input density locally at the arc root portion of a metal droplet and thereby the arc root portion exhibits a higher temperature. By contrast, in MAG (80% Ar–20% CO2) arc welding, it has been disclosed that because the arc covers metal droplets, the temperature distribution in a metal droplet is relatively uniform and the average temperature is lower than in CO2 arc welding.

Simultaneous measurement of the surface temperature and the release of atomic sodium from a burning black liquor droplet

Simultaneous measurement of the concentration of released atomic sodium, swelling, surface and internal temperature of a burning black liquor droplet under a fuel lean and rich condition has been demonstrated. Two-dimensional two-colour optical pyrometry was employed to determine the distribution of surface temperature and swelling of a burning black liquor droplet while planar laser-induced fluorescence (PLIF) was used to assess the temporal release of atomic sodium. The key findings of these studies are: (i) the concentration of atomic sodium released during the drying and devolatilisation stages was found to be correlated with the external surface area; and (ii) the insignificant presence of atomic sodium during the char consumption stage shows that sodium release is suppressed by the lower temperature and by the high CO 2 content in and around the particle.

Effect of the fuel injection strategy on the combustion process in a PFI boosted spark-ignition engine

In this paper, the effect of different fuel injection strategies on the combustion process was investigated in a boosted port fuel injection spark-ignition engine. The experiments were performed on a partially transparent single-cylinder engine, equipped with a four-valve head and boost device. Single and double fuel injection strategies were tested in the open-valve condition. Moreover, two fuel injection pressures were considered. Optical techniques based on 2D-digital imaging were used to follow the flame propagation in the combustion chamber. In particular, the diffusion-controlled flames near valves and on cylinder walls due to the fuel film burning were studied. Two-colour pyrometry was employed to measure soot concentration. In-cylinder optical investigations were correlated to the engine parameters and to the exhaust emissions.

Study of the multi-injection combustion process in a transparent direct injection common rail diesel engine by means of optical techniques

A combination of ultraviolet—visible optical diagnostics has been applied in the combustion chamber of a diesel engine in order to study the fuel injection, autoignition, and soot formation processes. Measurements were made in an optically accessible diesel engine equipped with a multivalve cylinder head and a common rail (CR) high-pressure injection system. Several multi-injection strategies, characteristic of new generation CR diesel engines, were tested. They consisted of two (pre + main) and three (pre + main + post) injections per cycle. Fuel injection and visible combustion were studied by imaging the natural flame luminosity, and soot formation and evolution were evaluated by means of the two-colour pyrometry method. The reactions that occur during autoignition and soot formation were investigated by chemiluminescence imaging, while the broadband ultraviolet—visible extinction and scattering spectroscopy (BUVESS) technique was used in order to measure the soot particle size and number concentration. For all the injection strategies investigated, pre injection has contributed to the reduction of the ignition delay of the main injection. Moreover, the present study showed that autoignition can be characterized to some degree by the presence of the OH radical. The effect of post injection on combustion development and soot particle diameter has also been observed and discussed.

Optical investigations of fuel deposition burning in ported fuel injection (PFI) spark-ignition (SI) engine

Abstract The present paper discusses the results obtained by experimental investigations of the diffusion-controlled flame near the valves due to fuel film deposition in a single cylinder, ported fuel injection (PFI), four-stroke spark-ignition (SI) engine with a four-valve production head. The engine was equipped with a transparent combustion chamber with a wide quartz window in the bottom. Optical techniques, based on 2D-digital imaging and natural emission spectroscopy, were used to follow the flame propagation and the chemical species involved in the fuel deposition burning near the valves. Two-colour pyrometry was applied to evaluate the flame temperature and soot concentration. Finally, exhaust particle size distributions were measured and correlated with the fuel deposition burning. The effects of different operating conditions in terms of speed, spark timings, and injection phasing were tested. Moreover, the effect of multi-component fuel was investigated by the comparison between commercial gasoline and pure iso-octane.

Combustion of bio-oil ethanol blends at elevated pressure

This paper reports an investigation on the combustion performance of bio-oil/ethanol blends. Experiments were conducted in a constant volume vessel operating at a pressure of 25 bar and temperature 1100 K. Bio-oil produced via the fast pyrolysis of a spruce feedstock was blended to ethanol to form three stable blends containing 10%, 20% and 40% bio-oil by weight. In addition, ethanol and standard automotive grade diesel were tested as reference fuels. Measured vessel pressure was used in a single-zone heat release analysis, while two-colour optical pyrometry was used to investigate particle loading and temperature. Results show that for similar injections of fuel energy, use of up to 20% bio-oil in ethanol has limited impact on the performance of ethanol while 40% bio-oil in ethanol produced instability in the pressure trace near the end of the combustion process. Burning rates are similar for blends and ethanol. Addition of bio-oil to ethanol was found to increase combustion generated particle load, and this increased with bio-oil concentration, but remained much lower than particle concentration in diesel. Addition of bio-oil also resulted in formation of char particles that appear as luminous clusters outside the boundary of the spray. This suggests these particles will cool rather than oxidize. The presence of unburnt char particles in large numbers may have consequences for bio-oil as an alternative diesel fuel.

Soot generation of diesel fuels with substantial amounts of oxygen-bearing compounds added

Two-colour pyrometry, thermodynamic analysis, and exhaust emissions analysis have been used to improve understanding of the formation of soot during combustion in a high speed direct-injection automotive diesel engine. Three fuel blends were used: a Base Fuel commercially available in Northern Europe; a blend of the Base Fuel (70%) and esterified rape-seed oil (RME) (30%) and a blend of the Base Fuel (90%) and an ether compound (diglyme) (10%). While the Base Fuel contained no oxygen, both the other two fuels contained equal amounts of oxygen of 3% by mass. The principal results show significant differences in soot generation during combustion between the two oxygenated fuel blends, despite both having the same amount of oxygen.

Application of two-colour pyrometry for measuring the surface temperature of a body activated by laser pulses

The features of contactless measurements of the surface temperature of bodies by the method of two-colour pyrometry of samples activated by periodic laser pulses are considered. The requirements imposed on the parameters of laser radiation and a measuring circuit are formulated. It is shown experimentally that surface temperatures close to room temperature can be measured with an error not exceeding 3% after elimination of the superfluous static component of the excess temperature. The sensitivity of the method is estimated. Advantages of laser photothermal radiometry with repetitively pulsed excitation of surfaces over the case when samples are subjected to harmonic amplitude-modulated laser radiation are discussed.

The velocity and temperature of steel droplets during electric arc spraying

The average dynamic and thermal behaviour of electric arc sprayed Fe–0.8wt.%C droplets has been investigated using a laser based time of flight velocimeter system (Laser2Focus—L2F) and a two-colour pyrometry system (In-flight Particle Pyrometer—IPP) respectively. Radial and axial variations of the spray velocity and temperature have been investigated, together with their dependence on atomising gas type, arc voltage, atomising gas pressure, and wire feed rate. Under all conditions, the average spray temperature was significantly above the steel liquidus temperature indicating most droplets were fully molten. Once projected away from the region of atomisation, the droplet spray typically cooled at ∼1 °C mm −1 and ∼10 5 °C s −1 and typical axial velocities were 100 m s −1. Because of asymmetry in the arc itself and the resulting differences in the melting behaviour of the wires, the spray exhibited asymmetric radial variations of both velocity and temperature about the spray cone axis. The presence of oxygen in the atomising gas had a significant effect in increasing spray temperature via exothermic oxidation of the steel droplets. Processing maps have been constructed in which the variation of average spray velocity and temperature with arc voltage, gas pressure and wire feed rate have been fitted to a series of simple polynomial expressions. These maps have been explained in terms of the heat and momentum transfer processes occurring during atomisation and subsequent droplet flight.

An experimental investigation of factors affecting arc-cathode erosion

A specially designed thermal plasma reactor system for the investigation of arc-cathode erosion has been set up. By using an OMA-spectrometer system, emission spectroscopic measurements of electron temperature and electron number density in the cathode region have been performed, together with single-colour and two-colour pyrometry of cathode temperature distributions. Observation of cathode spot behaviour has been carried out simultaneously by employing a telemicroscope and a high-speed vision system. Cathodes have been examined by SEM and EDX after arcing. For pure tungsten cathodes, the initial cathode geometry has almost no effect on the cathode spot's behaviour due to the molten state of the cathode spot. The major erosion mechanism is the ejection of liquid droplets from the cathode spot. However, the initial cathode geometry has a certain influence on the cathode's erosion for 2% thoriated tungsten cathodes. A highly non-uniform erosion pattern will occur if the cathode is overcooled, probably due to ion bombardment in the low-temperature regions of the arc-attachment spot.

New Findings on Combustion Behavior of Oxygenated Synthetic Diesel Fuels

New results were obtained on pollutants evolution during the combustion of four oxygenated fuels, whichwere compared with n-tetradecane and n-octane combustion. Three different techniques were adopted on a single cylinder direct injection diesel engine, equipped with optical accesses: two-colour pyrometry for the measurement of in-cylinder soot loading, high speed cinematography for the visualization and analysis of spray and combustion, fast sampling valve for the measurements of in-cylinder combustion products. In particular, the sampling line downstream of the fast sampling valve was adapted for the in-cylinder aldheydes measurements. Heat release analysis and fast sampling valve have shown that CO2 formation rate and heat release rate during the diffusion phase of combustion increase with the fuel oxygen content. Acetylene concentrations are influenced by fuel cetane number and oxygen content but, at the same fuel cetane number, they decrease when oxygen content increases. In-cylinder aldheydes concentrations are connected with premixed phase fraction of combustion and then influenced by fuel cetane number. In comparison with n-tetradecane fuel combustion, high burning rate and low visible flame distribution were observed through high speed cinematography tests, when oxygenated fuels were burned. Investigation on in-cylinder soot loading showed a great difference between the combustion behavior of ethers and glycolethers. The glycolethers show lower soot loading at the same fuel oxygen content.

Heat Transfer Processes in Diesel Engines

The heat transfer processes taking place in the combustion chamber of direct-injection diesel engines are reviewed based on experiments performed in an atmospheric test rig, where a diesel engine spray was impinging vertically and at an angle onto a heated plate with and without a cross-stream of air simulating swirl, and in a single-cylinder engine incorporating a variable swirl mechanism. The convective heat transfer associated with the impinging spray on the wall of the piston-bowl and the radiative heat transfer associated with the high temperature soot particles formed during combustion were estimated for two swirl ratios, based on the measured temperature of the gas and the piston wall by means of two-colour pyrometry and fast-response thermocouples, respectively.

OH and soot concentration measurements in a high-temperature laminar diffusion flame

OH absorption and soot extinction coefficients have been determined in a sooting ethylene laminar diffusion flame produced above a Wolfhard-Parker burner. An oxidizer rich in oxygen provided a flame with a high-temperature combustion zone ( T ∼ 2500 K). Compared to an ethylene-air flame, the production of OH is more pronounced, and soot burns out; thus, it is easier to study the oxidation of soot. 2D fluorescence images were obtained with a laser sheet tuned on and off the OH resonance frequency. A strategy, based on the relative shape of the signal in the direction of the laser at a given height above the burner, was developed to derive the local OH absorption coefficient and, in the sooting zone, the extinction coefficient. On the flame's axis, the temperature was determined by two-colour pyrometry; the absolute concentration of OH was derived from the absorption coefficients. Along the flame's axis, profiles of OH and soot concentrations were obtained over the zone where soot oxidation takes place. The collision efficiency for OH was determined from these measurements. Just above the soot burn-out zone, [OH] was found to be lower than the value calculated assuming equilibrium.

A case study of an ausformed helical pinion gear: R.A.Queeney et al. (Pennsylvania State University, USA.)

Simultaneous measurement of the concentration of released atomic sodium, swelling, surface and internal temperature of a burning black liquor droplet under a fuel lean and rich condition has been demonstrated. Two-dimensional two-colour optical pyrometry was employed to determine the distribution of surface temperature and swelling of a burning black liquor droplet while planar laser-induced fluorescence (PLIF) was used to assess the temporal release of atomic sodium. The key findings of these studies are: (i) the concentration of atomic sodium released during the drying and devolatilisation stages was found to be correlated with the external surface area; and (ii) the insignificant presence of atomic sodium during the char consumption stage shows that sodium release is suppressed by the lower temperature and by the high CO2 content in and around the particle.