Investigation of Combustion-Chamber Deposit Thermal Behavior Utilizing Optical RadiationMeasurements in a Fired Engine

Abstract

An infrared radiometer, which incorporated three optical paths and operated between 3.5-4.0 μm, was used to obtain transient surface temperatures in a fired engine. An integrated form of the equation of radiative transfer was applied to each optical path allowing gas emission, gas absorption and deposit surface radiation within the combustion-chamber to be characterized during a single cycle. Measurements of a simulated deposit were made at various temperatures and spark advance with the engine fired on methane and again on gasoline. Radiative characteristics of the combustion gases such as absorption and emission were investigated at several different operating conditions. A maximum error of 6% was found for temperature measurements between 660 and 900 Kelvins. Using a fast surface thermocouple with its junction located at the inner surface of the combustion-chamber wall, two combustion-chamber deposits were accumulated for different lengths of time. Deposit surface and interface temperatures were investigated at several different operating conditions for each deposit. Utilizing the experimentally obtained deposit surface and interface temperatures, deposit thermal conductivity (k) and heat capacity (Qc) were determined via a computational model which treated k as a function of temperature. Values obtained for k and Qc were well within the range of those reported for various forms of graphite.