Increased Efficiency in SI Engine with Air Replaced by Oxygen in Argon Mixture [electronic resource]

• Ngôn ngữ: eng
• Ký hiệu phân loại: 621.43 Internal-combustion engines
• Thông tin xuất bản: Livermore, Calif : Oak Ridge, Tenn. : Lawrence Livermore National Laboratory ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2010
• Mô tả vật lý: Size: PDF-file: 25 pages
• Bộ sưu tập: Metadata
• ID: 256015
• Chủ đề: 1. 30 direct energy conversion; 2. Air; 3. Argon; 4. Boundary layers; 5. Combustion; 6. Compression ratio; 7. Efficiency; 8. Engines; 9. Et al; 10. Heat transfer; 11. Mixtures

Tóm tắt

Basic engine thermodynamics predicts that spark ignited engine efficiency is a function of both the compression ratio of the engine and the specific heat ratio of the working fluid. In practice the compression ratio of the engine is often limited due to knock. Both higher specific heat ratio and higher compression ratio lead to higher end gas temperatures and increase the likelihood of knock. In actual engine cycles, heat transfer losses increase at higher compression ratios and limit efficiency even when the knock limit is not reached. In this paper we investigate the role of both the compression ratio and the specific heat ratio on engine efficiency by conducting experiments comparing operation of a single-cylinder variable-compression-ratio engine with both hydrogen-air and hydrogen-oxygen-argon mixtures. For low load operation it is found that the hydrogen-oxygen-argon mixtures result in higher indicated thermal efficiencies. Peak efficiency for the hydrogen-oxygen-argon mixtures is found at compression ratio 5.5 whereas for the hydrogen-air mixture with an equivalence ratio of 0.24 the peak efficiency is found at compression ratio 13. We apply a three-zone model to help explain the effects of specific heat ratio and compression ratio on efficiency. Operation with hydrogen-oxygen-argon mixtures at low loads is more efficient because the lower compression ratio results in a substantially larger portion of the gas to reside in the adiabatic core rather than in the boundary layer and in the crevices, leading to less heat transfer and more complete combustion.