Effects of Air Temperature and Oxygen Dilution on the Ignition Behavior of Liquid Fuels in an Optical Spray Chamber
Open Access
- Author:
- Mayo, Michael Peter
- Graduate Program:
- Chemical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 24, 2014
- Committee Members:
- Robert Martin Rioux Jr., Thesis Advisor/Co-Advisor
Andre Louis Boehman, Thesis Advisor/Co-Advisor - Keywords:
- constant volume combustion chamber
spray
ignition delay
CID
optical
PMT
oxygen dilution
diesel
biodiesel
heptane - Abstract:
- Spray ignition studies of liquid fuels provide important physical and chemical diagnostic information that support the advancement of combustion simulation models for rapid development of next-generation clean and efficient internal combustion (IC) engines. This work investigated the ignition behavior of n-heptane, ultra-low sulfur diesel (ULSD) and biodiesel blends in an optically-accessible constant volume combustion chamber (CVCC) under “low temperature combustion” conditions. Initial ambient air temperature was varied between 540 and 620°C. To simulate the gas mixture composition in a modern IC engine that utilizes exhaust gas recirculation (EGR), standard air was diluted with nitrogen and carbon dioxide which resulted in oxygen concentrations ranging from 21.8 to 9.6%. The optical CVCC was built by modifying a Cetane Ignition Delay (CID 510) instrument, manufactured by PAC, l.p. Two optical systems where integrated into the design of the apparatus. A spray visualization system utilized a high speed camera that captured images of the developing liquid fuel spray at 29,197 frames per second via direct optical access through a liquid-cooled borescope. These images were post-processed to calculate liquid penetration length and cone angle. In addition, natural light emissions from excited formaldehyde (CH2O*), OH*, CH*, and C2* were captured by a chemiluminescence detection system comprised of a UV/Vis optical probe, dichroic mirrors, band-pass filters, and photomultiplier tube modules. It was observed for each fuel sample that liquid penetration length and cone angle were insensitive to the changes in temperature and EGR dilution rates tested. A direct relationship between liquid length and cone angle was observed across transient and quasi-steady spray behavior; the ratio between these values developed a positive linear trend across the transient state followed by a constant value in the quasi-steady state. Increased ambient air temperature shortened ignition delay values for all fuel samples. ULSD and n-heptane displayed negative temperature dependence as temperature exceeded 580°C, consistent with well-understood hydrocarbon oxidation behavior. Higher rates of EGR dilution increased chemical ignition delay in an exponential manner. ULSD was the most sensitive to the decreasing ambient oxygen concentration, while B100 and n-heptane displayed stronger EGR tolerance. This trend was considered to be influenced most by fuel structure, as well as fuel-derived oxygen concentration to a lesser degree.