Flame radiation characteristics in pulsed combustion of liquid motor fuels in a constant-volume combustion chamber

Abstract

Flame combustion of liquid hydrocarbon fuels occurs in augmented engines of transport vehicles and stationary power installations. Calculation of the radiative heat transfer from the flame to the combustion chamber walls represents a complicated problem whose solution requires reliable data on the in-chamber temperature distribution and flame radiation characteristics. Physically, the flame can be considered a complex disperse system consisting of gases and solid particles of soot carbon. The radiative properties of soot particles depend on a number of factors: their geometry, concentration, and optical properties. The burning in augmented small-size combustion chambers of diesel and gas turbine engines and other similar power units proceeds in either pulsed or strongly nonstationary regimes that differ considerably from stationary combustion. The difference consists in the short time of visible burning, the high rate of change in the main parameters of the combustion process, and the soot particle geometry, as well as the cyclicity of the working process. Radiation from the soot particles predominates over radiation of polyatomic gases in the process of heat transfer between the flame and the chamber walls. For this reason, the radiative properties of soot particles and the peculiarities of the heat transfer inside the chamber are given the most attention in the studying of pulsed combustion of liquid fuels. Experimental evidence and calculations are presented for the radiative characteristics of the flame in pulsed combustion of gasolines, kerosenes, and diesel fuels in a constant-volume chamber. The experimental results, along with literature data on the flame emission characteristics under stationary combustion of liquid fuels, are generalized in the form of empirical formulas that permit estimation of the flame radiation properties depending on combustion conditions (parameters). A comparison of the flame emission properties and radiative heat transfer rate calculated by the method developed by the authors shows satisfactory agreement with the results of measurements of these characteristics in diesel combustion chambers. Therefore the obtained formulas are recommended for an engineering analysis of radiative heat transfer in combustion chambers of internal combustion engines and other similar power installations.