Laser Absorption-scattering Technique Research Articles

Effects of split ratio of diesel spray injection on mixture formation and combustion process

The effects of the split ratio on the mixture formation and combustion process of a diesel spray in a constant-volume chamber were experimentally investigated. A commercial seven-hole injector was used in this experiment. The effects of the mass-dependent split ratio and dwell time were observed when the total fuel injection was 5.0 mg/hole. Three split ratios were considered: 3:7, 5:5 and 7:3, while the dwell time of 120 µs was fixed for every condition. A laser absorption-scattering technique was adopted to examine the formation of mixtures with regarding to the equivalence ratio. A high-speed video camera was used to observe natural flame luminosity, and a two-colour pyrometer system was employed to evaluate the temperature and soot concentrations in the flame. Among the distribution ratios tested in this study, the 7:3 split ratio exhibited the best performance for the lean mixture formation considering the overall equivalence ratio distribution. The air entrainment wave at the end of injection timing of the first injection caused the fuel near the nozzle to lean at a rapid rate. The soot formation process for the 3:7 and 5:5 split ratios was observed because the second injection fuel caught the flame of the previous injections; this deteriorated the combustion region and influenced soot formation. The result also revealed that for the 7:3 split ratio, accelerated the soot deduction rate to the cycle of soot oxidation during the combustion period.

Evaporation and mixture formation characteristics of diesel spray under various nozzle hole size and injection pressure condition employing similar injection rate profile

The current work demonstrates investigations of the effects of the nozzle hole size and injection pressure on the diesel spray under evaporating condition. Three single hole injectors with hole diameters of 0.101 mm, 0.122 mm and 0.133 mm were used and their injection rate profiles were shaped in a similar manner. Laser Absorption Scattering technique was implemented in the diesel spray experiments to visualize the vapor phase and measure the mixture concentration. Also, the experimental results were validated with the computational approach. The injection rate profile and initial spray trajectory angle are key inputs for the CFD simulation; thus, careful measurements were taken. The injection rate profiles were measured by Zeuch method and based on the start of injection with the High-speed Video camera frame, the 5 kHz Butterworth low pass filter was applied to the injection rate raw signal. Moreover, the near nozzle field microscopic spray imaging experiments were performed to measure the initial spray trajectory angle. The experimental results show that the 0.101 mm hole diameter injector promotes shorter liquid length, longer vapor length, higher evaporation ratio and higher entrained air mass. The computational results show a reasonable qualitative agreement with the experiments; however, a quantitative discrepancy can be noticed.

Quantitative measurement of binary-component fuel vapor distributions via laser absorption and scattering imaging

An ultraviolet-visible laser absorption-scattering technique (UV-LAS) was developed for obtaining the evaporation characteristics of binary-component fuel spray. P-xylene and fluorobenzene were selected as the substitutes for low and high boiling points components, respectively, in a binary fuel spray. The molar absorption coefficients (MAC) of p-xylene and fluorobenzene at 266 nm wavelength were measured with relative uncertainty of 2.8% in a calibration system, which was designed to facilitate control of the mixture temperature and vapor concentration. UV-LAS was applied to a quantitative detection of vapor concentration distributions of each component in a binary-component fuel spray injected into a high-temperature and high-pressure constant volume chamber. A difference in spatial stratification of each component fuel in the spray due to their volatility difference was observed. An uncertainty estimation of UV-LAS for binary-component fuel spray was performed, and the results show that the maximum uncertainty is less than 9.8% in measurement of vapor mass.

Experimental study on spray characteristics under ultra-high injection pressure for DISI engines

In order to provide comprehensive information on gasoline spray characteristics under ultra-high fuel injection pressure for direct-injection spark-ignition engines, the macroscopic characteristics of gasoline sprays for both liquid and vapor phases, including overall spray structures, spray tip penetrations, and spray angles, were determined simultaneously via Laser Absorption-Scattering technique under non-vaporizing and vaporizing conditions. Empirical correlations of spray tip penetration for transient gasoline sprays were obtained and compared with those for diesel sprays. Experimental results showed that under non-vaporizing conditions, spray tip penetration was approximately proportional to time. Under vaporizing conditions, the spray plumes were compressed axially and expanded radially; fuel vapor was concentrated in the spray head, while fuel droplets in the tail. Vapor phase spray tip penetration shared similar values and temporal variations with liquid phase but with a subtle and regular difference. In contrast with diesel sprays, gasoline spray penetration of liquid phase showed larger dependence on ambient gas density and smaller dependence on fuel pressure drop through injector. Compared with liquid phase, vapor phase penetration showed a larger growth rate with time and presented a smaller falling slope against ambient gas temperature.

Laser absorption-scattering technique applied to asymmetric evaporating fuel sprays for simultaneous measurement of vapor/liquid mass distributions

This paper describes an Ultraviolet-Visible Laser Absorption-Scattering (UV-Vis LAS) imaging technique applied to asymmetric fuel sprays. Continuing from the previous studies, the detailed measurement principle was derived. It is demonstrated that, by means of this technique, cumulative masses and mass distributions of vapor/liquid phases can be quantitatively measured no matter what shape the spray is. A systematic uncertainty analysis was performed, and the measurement accuracy was also verified through a series of experiments on the completely vaporized fuel spray. The results show that the Molar Absorption Coefficient (MAC) of the test fuel, which is typically pressure and temperature dependent, is the major error source. The measurement error in the vapor determination has been shown to be approximately 18% under the assumption of constant MAC of the test fuel. Two application examples of the extended LAS technique were presented for exploring the dynamics and physical insight of the evaporating fuel sprays: diesel sprays injected by group-hole nozzles and gasoline sprays impinging on an inclined wall.

An experimental study on flat-wall-impinging spray of microhole nozzles under ultra-high injection pressures

The objective of the study is to provide information on the spray and mixture formation process of the microhole nozzle ( d=0.08mm) under an ultra-high injection pressure ( Pinj=300MPa). Flat-wall-impinging sprays were focused on and the laser absorption-scattering technique was adopted to obtain qualitative and quantitative information under various conditions. The spray and mixture characteristics of the conventional nozzle and microhole nozzles were compared; the advantages and disadvantages of microhole nozzles under different conditions were also discussed. Spray tip penetration length data were collected and compared with the predicted values using the gas jet theory. The results showed that the combination of the microhole nozzle and ultra-high injection pressure was very effective for obtaining the optimal penetration length, fast vaporization, and a high air entrainment rate.

Effect of Injection Temporal Splitting on the Characteristics of Fuel-air Mixture Formation in a Common Rail Diesel Spray

The mixture formation characteristics in a temporally split injection diesel spray were studied through a series of measurements based on the laser absorption-scattering technique (LAS), which was developed by the authors and adopted the second harmonic (532 nm) and the fourth harmonic (266 nm) of a pulsed Nd:YAG laser as the incident light, and dimethylnaphthalene (DMN) as the test fuel. By applying this technique, imaging was made of DMN sprays injected into a high- temperature (833 K) and high-pressure (4.0 MPa) constant-volume vessel by a single-hole nozzle and a common rail injection system for a direct injection (DI) diesel engine. Quantitative information of the vapour evaporation and fuel distribution was obtained, and furthermore the fuel-air mixture was characterized. The effect of injection temporal splitting on the mixture characteristics was analysed and correlated with the characteristics of NO x formation in a DI diesel engine.

Characterization of Droplets and Vapor Concentration Distributions in Split-Injection Diesel Sprays by Processing UV and Visible Images.

Recent experimental studies have shown that with split injection strategy, the soot and NOx emissions from a diesel engine can be reduced significantly in comparison with a conventional non-split injection. To understand the mechanism of emissions reduction, it is essential to clarify the process of mixture formation in the diesel spray. For characterizing the droplets and vapor concentration distributions inside a fuel spray, a dual-wavelength laser absorption-scattering technique (LAS) was developed by using the 2nd harmonic (532nm) and the 4th harmonic (266nm) of an Nd: YAG laser and using dimethylnaphthalene as a test fuel. By applying the ultraviolet-visible LAS imaging technique, the distributions of droplets and vapor concentrations in the spray, which was injected into a high-temperature and high-pressure nitrogen ambient in a constant volume vessel by a common-rail diesel injection system, were measured and quantitatively analyzed. The effect of injection mass ratio of double-pulse injections on distributions of equivalence ratios of vapor and droplets in the sprays was examined.

K-1920 レーザ吸収・散乱法による直噴ディーゼル噴霧内の蒸気相・液相濃度分布の同時計測(S24-3 燃料噴霧(2))(S24 燃料噴霧,ガス流動,混合気形成過程)

K-1920 レーザ吸収・散乱法による直噴ディーゼル噴霧内の蒸気相・液相濃度分布の同時計測(S24-3 燃料噴霧(2))(S24 燃料噴霧,ガス流動,混合気形成過程)

(1-22) Characterization of Droplets and Vapor Concentration Distributions in Split-Injection Diesel Sprays by Processing UV and Visible Images((FS-2)Fuel Sprays 2-Diesel sprays)

Some recent experimental studies have shown that with split injection strategy, the soot and NOx emissions from a diesel engine can be reduced significantly in comparison with the conventional non-split injection strategy. To understand the mechanism of emissions reduction, it is essential to clarify the process of the fuel mixture formation. In order to characterize the droplets and vapor concentration distribution inside the fuel sprays, a dual-wavelength laser absorption-scattering technique was developed by using the second harmonic (532nm) and the fourth harmonic (266nm) of a Nd : YAG laser and using dimethylnaphthalene as the test fuel. It was clarified that dimethylnaphthalene, which has physical properties similar to diesel fuel, is transparent in visible light near 532nm and is a strong absorber of ultraviolet light near 266nm. Based on this result, the vapor concentration in a fuel spray can be determined by the two separate measurements : a transmission measurement at a non-absorbing wavelength to detect the droplets optical thickness and a transmission measurement at an absorbing wavelength to detect the joint vapor and droplets optical thickness. The droplets density can be determined by extinction imaging through the transmission at the non-absorbing wavelength. By applying the ultraviolet-visible laser imaging technique, the distributions of droplets and vapor concentration in the spray, which was injected into a high-temperature and high-pressure nitrogen gas in a constant volume vessel, were measured and quantitatively analyzed. The effect of injection mass ratio of double-pulse injection on distributions of equivalence ratios of vapor and droplets was clarified. In the following figure, the contours of equivalence ratios of vapor and droplets in the diesel sprays with different injection ratios are shown. It has been found that the injection mass ratio has significant effect on the fuel distributions in the diesel spray ; the subsequent injection of a double-pulse injection scheme has a turbulent effect on the fuel-air mixing in the diesel spray injected in the preceding pulse.

Imaging of droplets and vapor distributions in a Diesel fuel spray by means of a laser absorption–scattering technique

The droplets and vapor distributions in a fuel spray were imaged by a dual-wavelength laser absorption-scattering technique. 1,3-dimethylnaphthalene, which has physical properties similar to those of Diesel fuel, strongly absorbs the ultraviolet light near the fourth harmonic (266 nm) of a Nd:YAG laser but is nearly transparent to the visible light near the second harmonic (532 nm) of a Nd:YAG laser. Therefore, droplets and vapor distributions in a Diesel spray can be visualized by an imaging system that uses a Nd:YAG laser as the incident light and 1,3-dimethylnaphthalene as the test fuel. For a quantitative application consideration, the absorption coefficients of dimethylnapthalene vapor at different temperatures and pressures were examined with an optical spectrometer. The findings of this study suggest that this imaging technique has great promise for simultaneously obtaining quantitative information of droplet density and vapor concentration in Diesel fuel spray.