Droplet size and equivalence ratio effects on spark ignition of monodisperse n-heptane and methanol sprays
- Dept. of Mechanical Engineering and Mechanics, Drexel Univ., Philadelphia, PA (US)
The effects of the droplet size and the equivalence ratio on the ignition of monodisperse n-heptane and methanol sprays at atmospheric pressure were investigated using a capacitive discharge spark ignition system. The minimum ignition energy E/sub min/ of the sprays was measured over a range of droplet diameters, D = 30-57 m, and equivalence ratios, phi = 0.44-1.8. As expected, results showed that E/sub min/ decreased with decreasing droplet size, with increasing equivalence ratio, and with increasing fuel volatility. While the same trends have been observed previously for polydisperse sprays, this is the first study to quantify these effects for monodisperse sprays in this size range. The minimum ignition energy was also measured for fully prevaporized n-heptane and methanol. An optimum gas phase equivalence ratio for prevaporized n-heptane ignition was found between 1.5 < phi < 2.0. No corresponding optimum was obtained for prevaporized methanol due to difficulties in generating fuel-rich methanol mixtures. Comparison of the spray and prevaporized ignition results indicated the existence of an optimum droplet size, D < 30 m, for the ignition of fuel-lean sprays for both fuels. Extension of the lean prevaporized ignition limit phi = 0.55, was also observed for all sprays. Experimental ignition results were compared to the predictions of two existing ignition models for quiescent sprays: the characteristic time model for ignition, and the general ignition model. Both models, using a characteristic time approach, predicted the experimentally determined ignition energies accurately for most conditions. Model performance deteriorated, however, for leaner ratios, phi < 0.7, and for smaller droplet size, D < 35 m, with both models increasingly underpredicting E/sub min/.
- OSTI ID:
- 6629375
- Journal Information:
- Combust. Flame; (United States), Journal Name: Combust. Flame; (United States) Vol. 74:3; ISSN CBFMA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800 -- Combustion
Pyrolysis
& High-Temperature Chemistry
ALCOHOLS
ALKANES
COMBUSTION PROPERTIES
DROPLETS
ENGINES
EQUIVALENCE PRINCIPLE
HEAT ENGINES
HEPTANE
HYDROCARBONS
HYDROXY COMPOUNDS
IGNITION SYSTEMS
INTERNAL COMBUSTION ENGINES
METHANOL
ORGANIC COMPOUNDS
PARTICLES
SIZE
SPARK IGNITION ENGINES