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Title:Spray visualization and characterization of a multi variable circular orifice (MVCO) injector coupled with a swirl adapter for diesel reformer applications
Author(s):Nithyanandan, Karthik
Advisor(s):Lee, Chia-Fon
Contributor(s):Lee, Chia-Fon; Ferreira, Placid M.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):multi variable circular orifice (MVCO)
Diesel reformer
Spray visualization
Abstract:The fuel spray generated by the injector is of primary importance to mixing and hence, combustion efficiency, due to the extremely short time scale of the combustion event inside an internal combustion engine. In this respect, the aim of the fuel injection system is to atomize the fuel droplets as fine as possible in order to provide a homogeneous mixture before combustion initiates. Spray visualization and characterization of a Micro-Variable Circular-Orifice (MVCO) fuel injector coupled with a swirl-producing adapter was studied. The spray characteristics such as spray penetration length, spray velocity etc. and the atomization performance were evaluated. The measurement was conducted on an engine facility where diesel fuel was delivered by a high pressure pump coupled with a common rail. Various injection pressures ranging from 300 bar to 700 bar were tested while the back pressure was kept at 1 bar. Compressed air at pressures of 30 psi and 60 psi were supplied to the swirl adapter. High speed Mie scattering images were recorded using a High speed camera to document the spray evolution. Images were acquired from both the front view and the bottom view. Phase Doppler Anemometry (PDA) measurement was conducted at different locations in the spray for the acquisition of droplets size and velocity distribution. Difficulties in measurements were encountered for high pressure injection, especially in the central part of the spray jet and near the nozzle exit region owing to the strong attenuation of the incident laser beams and the scattered light. Unlike traditional injectors which normally inject six fuel jets, the MVCO fuel injector presented a unique spray pattern by injecting more than twenty jets in an approximately axi-symmetric fashion. Due to the interaction between the spray jets, the breakup was much enhanced relative to conventional injectors, causing shorter spray tip penetration, finer droplet size and wider fuel droplets distribution. It is seen that distributions peaks lie at about 5-10 μm mainly due to the more violent breakup induced by the unique spray pattern of the MVCO. No apparent trend of the droplet size against injection pressure is observed which is desirable for engine optimization according to engine load. Note that the injection duration was kept constant, thus the injection pressure can be viewed as a reasonable representative of the engine load. At low load condition, the spray is characterized by a relatively narrow spray angle and shorter penetration so as to prevent wall wetting while at high load, the spray was widened to suit for higher power output. High speed images obtained for the MVCO injector coupled with the swirl adapter showed that the adapter caused the fuel spray to become wider. A higher degree of atomization was also achieved. PDA results displayed a clear rotational motion indicating a strong swirl being imparted to the fuel spray by the adapter. Such swirl flow can only further improve the mixing process for the MVCO as the turbulent kinetic energy delivered by the intake flow will induce the more violent breakup leading to finer droplets. Therefore a highly atomized spray with high level of mixing (swirl) was obtained which could potentially increase diesel reformer efficiency.
Issue Date:2012-09-18
Rights Information:Copyright 2012 Karthik Nithyanandan
Date Available in IDEALS:2012-09-18
Date Deposited:2012-08

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