Soot characteristics of light naphtha in a constant volume combustion chamber using two-color pyrometry

Abstract

This study investigates the soot processes of light naphtha (LN) under diesel engine conditions with an outwardly opening piezo gasoline direct injection (GDI) fuel injector. Five ambient oxygen concentrations varying from 10% to 21% were selected to simulate both conventional diesel engine operation environment and low oxygen concentration combustion environment. A two-color pyrometry was applied to measure flame temperature and soot concentration (i.e., KL factor) distribution under different ambient conditions. KL factor is a measure of soot particulate concentration in which K is a measure of soot number density, and L is a measure of the path length along which the measurement is made. It is found that flame temperature ranges from 1500K to 2300K under selected conditions. A higher oxygen concentration could accelerate fuel combustion rate. High temperature areas are mainly located at the center or downstream of the flame. Flame upstream always has lower temperature than other regions. High KL factors are observed at flame periphery where flame temperature is lower than 1800K and has rapid temperature variation. Accumulated KL factor was calculated to evaluate overall soot amount. The lowest accumulated KL factors are observed at 1000 K ambient temperature condition when the ambient oxygen concentration is 21%.