Effect of Fuel Reactivity and End- Gas Temperature on Autoignition and Flame Propagation Rate in Primary Reference Fuel Mixtures at Elevated Temperature and Pressure
- Colorado State University
Knock in spark-ignited (SI) engines is initiated by autoignition in the unburned gases upstream of spark-ignited, propagating, turbulent premixed flames. In this study, knock propensity of SI fuels was quantified via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (n-heptane/isooctane) blends of varying reactivity were ignited using an Nd:YAG laser over a range of compressed temperatures and pressures, all in excess of 691 K and 18.8 bar. High-speed pressure measurements and schlieren images indicated the presence of EGAI in the unburned gases upstream of spherical, outwardly propagating flames. The fraction of the total heat release attributed to EGAI was found to vary with fuel reactivity and the time-integrated temperature of the end-gas prior to ignition. Flame propagation rates, measured using schlieren imaging, did not vary strongly with fuel reactivity but were affected by turbulence caused by variation in piston timing. Under conditions of low turbulence, measured flame propagation rates agreed with one-dimensional premixed laminar flame speed computations performed at the same conditions.
- Research Organization:
- Colorado State University
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
- DOE Contract Number:
- EE0008331
- OSTI ID:
- 1597501
- Country of Publication:
- United States
- Language:
- English
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End-Gas Autoignition Fraction and Flame Propagation Rate in Laser-Ignited Primary Reference Fuel Mixtures at Elevated Temperature and Pressure
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