Turbulent flame propagation and combustion in spark ignition engines

Abstract

Pressure measurements synchronized with high-speed motion picture records of flame propagation have been made in a transparent piston engine. The data show that the initial expansion speed of the flame front is close to that of a laminar flame. As the flame expands, its speed rapidly accelerates to a quasi-steady value comparable with that of the turbulent velocity fluctuations in the unburned gas. During the quasi-steady propagation phase, a significant fraction of the gas behind the visible front is unburned. Final burnout of the charge may be approximated by an exponential decay in time.The data have been analyzed in a model independent way to obtain a set of empirical equations for calculating mass burning rates in spark ignition engines. The burning equations contain three parameters: the laminar burning speed st, a characteristic speed at, and a characteristic length IT. The laminar burning speed is known from laboratory measurements. Tentative correlations relating u T and IT to engine geometry and operating variables have been derived from the engine data.

Characterisation of flame development with ethanol, butanol, iso-octane, gasoline and methane in a direct-injection spark-ignition engine

“…It should be noted that this ratio remains nearly constant over most of the combustion event and this is a useful property because it simplifies the analysis [59].…”

Insights into Stoichiometric and Lean Combustion Phenomena of Gasoline–Butanol, Gasoline–Ethanol, Iso-Octane–Butanol, and Iso-Octane–Ethanol Blends in an Optical Spark-Ignition Engine

“…The ratio between unburned to burned gas density is approximately constant throughout the combustion and close to a value of 4 and the mass fraction burned x b can be calculated according to Beretta et al (1983). The gas densities were obtained by Morley (2005) for the in-cylinder conditions at stoichiometric spark timing (4.8 bar, 550 K) and a ratio of  u / b =4.7 was calculated.…”

Assessment of elliptic flame front propagation characteristics of iso-octane, gasoline, M85 and E85 in an optical engine

“…In previous engine research images of flames in cylinders showed a significant enflamed volume, but the pressure measurements were not accurate or sensitive enough to indicate the evolving flame kernels [21,15]. Therefore, optical investigation of combustion is preferred to pressure tracing at the early combustion stages.…”

“…The first two stages are of high importance in terms of in-cylinder pressure development [12][13][14][15][16]. These four stages are influenced by: spark energy and duration [17]; spark plug design and orientation [18]; in-cylinder flow field [19]; cyclic cylinder charging [20]; in-cylinder composition [21]; and other related factors. A detailed literature survey on the effects of these parameters on the four stages of combustion appeared in [12].…”

“…Generally, previous studies have assumed that the propagation of the spark-initiated oxidation is isotropic, i.e. spherical flame propagation [15,16,18,21,25,28,29,39,38,[30][31][32][33][34][35][36]. Only a few studies mentioned different flame-front geometries [14,15,30,39] and looked into implications arising from the assumption that the flame front surface had a spherical geometry.…”