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Title:Thermal properties of combustion chamber deposits and their effect on engine heat transfer and octane requirement increase
Author(s):Hayes, Timothy Keith
Doctoral Committee Chair(s):White, Robert A.
Department / Program:Mechanical Science and Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Automotive
Abstract:An investigation of the thermal properties of combustion chamber deposits and their effect on engine heat transfer and Octane Requirement Increase (ORI) has been completed. Deposits were grown in a Chrysler 4-cylinder 2.2 liter engine with total test times of 50- and 250-hours. Two fuels were used, both having the same unleaded premium fuel base, but one was doped with reformer bottoms which promoted deposit growth and octane requirement increase. Thicknesses were measured using a machinist's microscope and the thermal diffusivity and conductivity were measured with high speed thermocouples and steady and flash laser techniques.
The results indicate that the fuel with reformer bottoms produces deposits which are 15-25 percent thicker in the end gas region. The 250-hour test indicated that the deposits grow quickest in the end gas region, but stabilize there sooner, with the central region growing slower. The thermal diffusivity of the deposits grown with reformer bottoms was 1/2 to 1/3 that of the clean fuel. For the clean fuel, the thermal diffusivity ranged from 3.5 to 3.9 e-7 m$\sp2$/s, and for the fuel doped with reformer bottoms, the diffusivity ranged from 1 to 1.9 e-7 m$\sp2$/s. These deposit diffusivity values fall within the reported range in the literature of 0.39 to 27.2 e-7 m$\sp2$/s. For the doped fuel, the conductivity values ranged from 0.15 to 0.6 W/mK, while the clean fuel ranged from 0.3 to 1 W/mK. Reported values of thermal conductivity for unleaded fuel deposits in the literature ranged from 0.04 to 0.7 W/mK. Engine simulation calculations indicated that the clean fuel produces lower Octane Requirement Increase (ORI) and unburned temperatures. The simulation results also indicated that larger values of deposit conductivity and deposit diffusivity should be the aim of fuel additives in order to reduce ORI.
Issue Date:1991
Rights Information:Copyright 1991 Hayes, Timothy Keith
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210831
OCLC Identifier:(UMI)AAI9210831

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