Spray Liquid Length Research Articles

Diesel Spray Liquid Length Imaging at High Pressure

Engine efficiency and emissions depend on the fuel atomization and dispersion. The fuel atomization and dispersion depend heavily on the ambient pressure and temperature. In this work, to study Diesel sprays in engine conditions, an electrically heated, constant-volume, pressurized vessel was designed and manufactured. The controlling electronics and software were developed and tested to ensure safe and precise operation. A commercial Bosch six-hole automotive Diesel injector was used. The spray spatial and temporal development were studied. In the literature, spray liquid length and cone angle are extensively used to quantify fuel dispersion. In this work, these parameters were quantified using a high-speed shadowgraph technique. Models were derived to describe the temporal evolution of the liquid core. Such models can be used to predict the Diesel spray behaviour and the engine performance.

Evaporating spray characteristics of methanol-in-diesel emulsions

The main objective of this study is to investigate spray characteristics of methanol-in-diesel emulsions from a common rail diesel injection system under evaporating conditions using Mie-scattering and shadowgraphy techniques. The spray characteristics were measured in an optically-accessible constant volume chamber filled with nitrogen at a pressure of 50 bar and temperature of 900 K. Injection pressures of 500 bar, 1000 bar, and 1500 bar were investigated. Three surfactants (Span-80, Tween-80 and 1-dodecanol) were used to make stable emulsions containing up to 25 wt% of methanol in diesel. Interestingly, the liquid-length of the methanol-in-diesel emulsion spray with 10 wt% of methanol using a mixture of Span-80 and Tween-80 as a surfactant is higher by around 25% as compared to that of the diesel spray, even though methanol is far more volatile than diesel. This is attributed to the higher boiling point of the surfactant used, as confirmed by experiments with a low boiling point surfactant, i.e., 1-dodecanol. Further, microemulsions of methanol-in-diesel were produced by using 1-dodecanol as surfactant, which facilitated increasing the percentage of methanol in the microemulsion to up to 25 wt%. The evaporating spray liquid-length is observed to be insensitive to the methanol percentage in the emulsion when 1-dodecanol is used as the surfactant. Vapor penetration of the emulsions were similar to those of the diesel sprays at similar injection pressures. Overall, the current study provides measurements of detailed spray characteristics of methanol-in-diesel emulsions at engine-relevant conditions.

Spray combustion simulation study of waste cooking oil biodiesel and diesel under direct injection diesel engine conditions

Spray combustion characteristics of waste cooking oil biodiesel (WCO) and conventional diesel fuels were simulated using a RANS (Reynolds Averaged Navier Stokes) based model. Surrogates were used to represent WCO and diesel fuels in simulations. N-tetradecane (C14H30) and n-heptane (C7H16) were used as surrogates for diesel. Furthermore for WCO, surrogate mixtures of methyl decanoate, methyl-9-decenoate and n-heptane were used. Thermochemical and reaction kinetic data (115 species and 460 reactions) were implemented in the CFD code to simulate the spray and combustion processes of the two fuels. Validation of the spray liquid length, ignition delay, flame lift-off length and soot formation data were performed against previous published experimental results. The modeled data agreed with the trends obtained in the experimental data at all injection pressures. Further investigations, which were not achieved in previous experiments, showed that prior to main ignition, a first stage ignition (cool flame) characterized by the formation formaldehyde (CH2O) species at low temperature heat release occurred. The main ignition process occurred at high temperature with the formation of OH radicals. Furthermore, it was observed that the cool flame played a greater role in stabilizing the downstream lifted flame of both fuels. Increase in injection pressure led to the cool flame location to be pushed further downstream. This led to flame stabilization further away from the injector nozzle. WCO had shorter lift-off length compared to diesel as a result of its cool flame which being closer to the injector. Soot formation followed similar trends obtained in the experiments.

Experimental study on spray and combustion of gasoline/hydrogenated catalytic biodiesel blends in a constant volume combustion chamber aimed for GCI engines

GCI combustion mode has become an interesting topic for high thermal efficiency and low emissions, while ignition problem and knocking combustion limited its application. The blending fuel of gasoline/Hydrogenated Catalytic Biodiesel (HCB) can extend the working conditions for GCI engines because there is no mixed and ignited problem. In this paper, the spray liquid length, ignition delay and flame lift-off length of three gasoline/HCB blends with different blending ratio are measured simultaneously in a constant volume combustion chamber for providing enough data to guide the gasoline/HCB blends used in GCI combustion mode. The experimental results show that the ignition delay and lift-off length decrease with increasing the proportion of HCB in blends, while the spray liquid length shows an opposite trend. Moreover, for gasoline/HCB blends, chemical ignition delay plays a leading role in the total ignition delay and the cycle-to-cycle variation will be decreased with increasing the blending ratio of HCB. On the other hand, the spray and combustion characteristics of G70H30 and G50H50 are compared with those of diesel for further applying the blended fuel in compression ignition engines. The natural luminosity intensity of diesel is higher than that of G50H50 and G70H30 even the injection pressure of diesel is higher than that of blending fuel, which means the blending fuels have relatively lower soot emission. Meanwhile, the ignition delay and flame lift-off length of G50H50 are getting close to the diesel results. Moreover, there is a big difference in ignition delay for these three fuels under low oxygen concentration, while the difference decreases with increasing the oxygen concentration.

Simultaneous study on spray liquid length, ignition and combustion characteristics of diesel and hydrogenated catalytic biodiesel in a constant volume combustion chamber

Application of biodiesel is very important for reducing the consumption of fossil fuels and improving emissions performance of internal combustion engines in the transportation field. Hydrogenated catalytic biodiesel has attracted more attention due to the high quality and eco-friendly nature. Hence, in order to provide more fundamental data for applying this biodiesel in engines, the spray liquid length, ignition and combustion characteristics for both diesel and hydrogenated catalytic biodiesel has been researched in a constant volume combustion chamber to see their differences and similarities, which can be used for determination of the possible proportion of hydrogenated catalytic biodiesel in blends for further research in engines. The results show that the spray liquid length of hydrogenated catalytic biodiesel is shorter than that of diesel fuel, which indicates that hydrogenated catalytic biodiesel has better atomization and less chance for occurrence of wall-impingement. While a shorter ignition delay of hydrogenated catalytic biodiesel reveals that it cannot be applied in blends with a large proportion due to knocking combustion. However, a shorter ignition delay of hydrogenated catalytic biodiesel means that it is a highly active fuel which can be used to engines as a blend for new advanced combustion modes. The lift-off lengths were compared with different optical methodologies. Lift-off length is more sensitive to fuel properties rather than temperature under low ambient temperature conditions. The relationships between spray liquid length and lift-off length and between ignition delay and lift-off length were also compared.

Experimental and analytical study on capture spray liquid penetration and combustion characteristics simultaneously with Hydrogenated Catalytic Biodiesel/Diesel blended fuel

Hydrogenated Catalytic Biodiesel (HCB), with excellent volatility and cetane number while without contain oxygen and aromatic hydrocarbons, have great potential to improve engine performance and emission characteristics. In this study, the effect of HCB/Diesel blended fuels properties (by mass fraction of biodiesel in diesel) on spray combustion characteristics was investigated at inert and reacting conditions in a constant volume combustion chamber. Laser (532 nm) Mie-scattering, OH∗ chemiluminescence and high-temperature luminosity were used to capture the spray liquid length, flame lift-off length and ignition delay simultaneously with the help of two intensifier charge coupled device cameras and a high speed Complementary Metal Oxide Semiconductor camera. Encouraging results were obtained at different ambient conditions (temperatures, densities, oxygen concentration) and injection pressures. The results showed that fuels with high cetane number generate shorter ignition delay, and faster auto-ignition results in a shorter flame lift-off length. A new theory was used to interpret the effect of cetane number on lift-off length. Under reacting conditions, the combustion heat release shorten spray liquid length apparently as compared with the results under inert conditions. The liquid length was slightly affected by the injection pressure and oxygen concentrations under both reacting and inert conditions, while the flame lift-off length is significantly influenced by ambient parameters and injection pressure.

A study of soot quantification in diesel flame with hydrogenated catalytic biodiesel in a constant volume combustion chamber

In this work, diffused back-illumination extinction imaging and OH* chemiluminescence imaging were employed simultaneously to measure the soot production, spray liquid length and flame lift-off length. These experiments were conducted in a high-temperature, high-pressure constant-volume combustion chamber equipped with a common-rail fuel injector with a single 180-μm-diameter orifice. Soot formation characteristics of a blend fuel (B50) with 50% hydrogenated catalytic biodiesel (HCB) and 50% 0# fossil diesel in mass were studied. Besides, the pure 0# fossil diesel (B0) under the same operating conditions was also measured as a reference. Parametric variations of injection pressure (100 MPa, 150 MPa), ambient temperature (770 K, 820 K, 870 K) and oxygen concentration (15%, 18%, 21%) have been performed for each fuel. After analysis, it was found both liquid length and flame lift-off length of B50 are shorter than that of B0. Soot onset time of B50 appears earlier and soot initial location is closer to the nozzle than that of B0. Within the measured optical access, soot area of B50 is larger than that of B0 because of shorter lift-off length, while the difference on total soot production is less noticeable because fuel properties of B0 is more favorable for soot formation.

Simultaneous capture of liquid length of spray and flame lift-off length for second-generation biodiesel/diesel blended fuel in a constant volume combustion chamber

Simultaneous imaging of OH∗ chemiluminescence and Mie scattering of fuel spray have been performed under reacting conditions in a constant volume combustion chamber aimed for a second-generation biodiesel/diesel blended fuel. Mie scattering of 532nm laser light technique was used for the liquid fuel measurement. In order to remove the interference signal from soot radial, filtered Mie scattered light from the fuel droplet was recorded with a charge coupled device (CCD) camera. The spray liquid length and the flame lift-off length for this high cetane-number fuel were investigated under different ambient gas conditions (temperature, density, oxygen concentration) and injection pressure. Experiments showed that the spray liquid length under the reacting condition was shorter than that under non-reacting condition. The flame lift-off length was significantly influenced by the ambient gas temperature, density, oxygen concentration and injection pressure, while the spray liquid length was slightly affected by the injection pressure and oxygen concentration. The overlap between liquid fuel and combustion flame easily happened at high temperature, high oxygen concentration, and low injection pressure conditions.