VISUALIZATION STUDY ON THE IMPACTS OF DUCT LENGTH ON MACROSCOPIC SPRAY CHARACTERISTICS OF DUCTED FUEL INJECTION UNDER NONVAPORIZING CONDITIONS

Abstract Predicting details of aircraft engine combustion by means of numerical simulations requires reliable information about spray characteristics from liquid fuel injection. However, details of liquid fuel injection are not well documented. Indeed, standard droplet distributions are usually utilized in Euler-Lagrange simulations of combustion. Typically, airblast injectors are employed to atomize the liquid fuel by feeding a thin liquid film in the shear zone between two swirled air flows. Unfortunately, droplet data for the wide range of operating conditions during a flight is not available. Focusing on numerical simulations, Direct Numerical simulations (DNS) of full nozzle designs are nowadays out of scope. Reducing numerical costs, but still considering the full nozzle flow, the embedded DNS methodology (eDNS) has been introduced within a Volume of Fluid framework (Sauer et al., Atomization and Sprays, vol. 26, pp. 187–215, 2016). Thereby, DNS domain is kept as small as possible by reducing it to the primary breakup zone. It is then embedded in a Large Eddy Simulation (LES) of the turbulent nozzle flow. This way, realistic turbulent scales of the nozzle flow are included, when simulating primary breakup. Previous studies of a generic atomizer configuration proved that turbulence in the gaseous flow has significant impact on liquid disintegration and should be included in primary breakup simulations (Warncke et al., ILASS Europe, Paris, 2019). In this contribution, an industrial airblast atomizer is numerically investigated for the first time using the eDNS approach. The complete nozzle geometry is simulated, considering all relevant features of the flow. Three steps are necessary: 1. LES of the gaseous nozzle flow until a statistically stationary flow is reached. 2. Position and refinement of the DNS domain. Due to the annular nozzle design the DNS domain is chosen as a ring. It comprises the atomizing edge, where the liquid is brought between inner and outer air flow, and the downstream primary breakup zone. 3. Start of liquid fuel injection and primary breakup simulation. Since the simulation of the two-phase DNS and the LES of the surrounding nozzle flow are conducted at the same time, turbulent scales of the gas flow are directly transferred to the DNS domain. The applicability of eDNS to full nozzle designs is demonstrated and details of primary breakup at the nozzle outlet are presented. In particular a discussion of the phenomenological breakup process and spray characteristics is provided.

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Impacts of duct inner diameter and standoff distance on macroscopic spray characteristics of ducted fuel injection under non-vaporizing conditions

International Journal of Engine Research ◽

10.1177/1468087420914714 ◽

2020 ◽

pp. 146808742091471

Author(s):

Feng Li ◽

Chia-fon Lee ◽

Ziman Wang ◽

Yiqiang Pei ◽

Guoxiang Lu

Keyword(s):

Large Scale ◽

Fuel Injection ◽

Soot Formation ◽

Cone Angle ◽

Mie Scattering ◽

Standoff Distance ◽

Spray Characteristics ◽

Spray Cone Angle ◽

Spray Cone ◽

Inner Diameter

Ducted fuel injection spray is a new technology for reducing soot formation in heavy-duty diesel engines. In this work, the ducted fuel injection spray characteristics with different duct inner diameters and different standoff distances were investigated and compared with free spray. Duct inner diameter ranged from 1.5 to 4 mm, and standoff distance varied between 0.9 and 4.9 mm. Mie-scattering optical technique was used to characterize spray characteristics under various injection pressures in a constant-volume spray chamber. Ambient gas pressure of up to 6 MPa when spraying. The results showed that ducted fuel injection spray with smaller duct has better spray diffusion compared to those of ducted fuel injection sprays with larger ducts and free spray from the perspectives of spray tip penetration, spray cone angle and spray area. Increasing standoff distance could increase spray velocity. Ducted fuel injection spray with smaller duct formed a mushroom-shaped head and large-scale vortex flow close to the duct outlet. All the advantages of ducted fuel injection spray with smaller duct are interpreted as evidence of improving fuel–gas mixing quality significantly.

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Microscopic Spray Characteristics of Biodiesels Derived From Karanja, Jatropha, and Waste Cooking Oils

Journal of Energy Resources Technology ◽

10.1115/1.4047408 ◽

2020 ◽

Vol 142 (12) ◽

Author(s):

Chetankumar Patel ◽

Joonsik Hwang ◽

Choongsik Bae ◽

Rashmi A. Agarwal ◽

Avinash Kumar Agarwal

Keyword(s):

Fuel Injection ◽

Direct Injection ◽

Injection Pressure ◽

Axial Direction ◽

Waste Cooking Oil ◽

Injection System ◽

Ambient Atmosphere ◽

Ambient Conditions ◽

Spray Characteristics ◽

Spray Droplets

Abstract This study aims to assess the microscopic characteristics of Jatropha, Karanja, and Waste cooking oil-based biodiesels vis-a-vis conventional diesel under different ambient conditions in order to understand the in-cylinder processes, while using biodiesels produced from different feedstocks in the compression ignition engines. All test-fuels were injected in ambient atmosphere using a common-rail direct injection (CRDI) fuel injection system at a fuel injection pressure (FIP) of 40 MPa. Microscopic spray characteristics were measured using phase Doppler interferometer (PDI) in the axial direction of the spray at a distance of 60–90 mm downstream of the nozzle and at 0 to 3-mm distance from the central axis in the radial direction. All biodiesels exhibited relatively larger Sauter mean diameter (SMD) of the spray droplets and higher droplet velocities compared to baseline mineral diesel, possibly due to relatively higher fuel viscosity and surface tension of biodiesels. It was also observed that SMD of the spray droplets decreased with increasing distance in the radial and axial directions and the same trend was observed for all test-fuels.

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Scaling liquid penetration in evaporating sprays for different size diesel engines

International Journal of Engine Research ◽

10.1177/1468087419889835 ◽

2019 ◽

Vol 21 (9) ◽

pp. 1662-1677 ◽

Cited By ~ 3

Author(s):

Xinyi Zhou ◽

Tie Li ◽

Yijie Wei ◽

Ning Wang

Keyword(s):

Diesel Engine ◽

Diesel Engines ◽

High Speed ◽

Scaling Laws ◽

Fuel Injection ◽

Pollutant Emissions ◽

Liquid Penetration ◽

Spray Characteristics ◽

Penetration Length ◽

Air Mixing

Scaled model experiments can greatly reduce the cost, time and energy consumption in diesel engine development, and the similarity of spray characteristics has a primary effect on the overall scaling results of engine performance and pollutant emissions. However, although so far the similarity of spray characteristics under the non-evaporating condition has been studied to some extent, researches on scaling the evaporating sprays are still absent. The maximum liquid penetration length has a close relationship with the spray evaporation processes and is a key parameter in the design of diesel engine spray combustion system. In this article, the similarity of maximum liquid penetration length is theoretically derived based on the hypotheses that the spray evaporation processes in modern high-pressure common rail diesel engines are fuel–air mixing controlled and local interphase transport controlled, respectively. After verifying that the fuel injection rates are perfectly scaled, the similarity of maximum liquid penetration length in evaporating sprays is studied for three scaling laws using two nozzles with hole diameter of 0.11 and 0.14 mm through the high-speed diffused back-illumination method. Under the test conditions of different fuel injection pressures, ambient temperatures and densities, the lift-off law and speed law lead to a slightly increased maximum liquid penetration length, while the pressure law can well scale the maximum liquid penetration length. The experimental results are consistent with the theoretical analyses based on the hypothesis that the spray evaporation processes are fuel–air mixing controlled, indicating that the local interphase transports of energy, momentum and mass on droplet surface are not rate-controlled steps with respect to spray evaporation processes.

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