Laminar burning speeds and flame structures of spherically expanding flames of mixtures o f acetylene (C2H2) with air have been investigated over a wide range of equivalence ratios, temperatures, and pressures. Experiments have been conducted in a constant vol ume cylindrical vessel with two large end windows. The vessel was installed in a shadow graph system equipped with a high speed CMOS camera, capable of taking pictures up to 40,000 frames per second. Shadowgraphy was used to study flame structures and transi tion from smooth to cellular flames during flame propagation. Pressure measurements have been done using a pressure transducer during the combustion process. Laminar burning speeds were measured using a thermodynamic model employing the dynamic pressure rise during the flame propagation. Burning speeds were measured for tempera ture range o f300-590 K and pressure range of 0.5-3.3 atm, and the range of equivalence ratios covered from 0.6 to 2. The measured values of burning speeds compared well with existing data and extended for a wider range of temperatures. Burning speed measure ments have only been reported for smooth and laminar flames.
This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane in a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diameter of 135 mm and inside height of 135 mm. Two end of the vessel are equipped with optical windows. A high speed complementary metal oxide semiconductor (CMOS) camera capable of capturing pictures up to 40,000 frames per second is used to obsei-ve flow conditions inside the chamber. The injected fuel jet generates turbulence in the vessel and forms a turbulent heterogeneous fuel-air mixture in the vessel, similar to that in a compressed natural gas (CNG) directinjection (DI) engine. The fuel-air mixture is ignited by centrally located electrodes at a given spark delay timing of 1, 40, 75, and Hums. In addition to the four delay times, a 5 min waiting period was used in order to make sure of having laminar homogeneous combustion. Spray development and characterization including spray tip penetration (STP), spray cone angle (SCA), and overall equivalence ratio were investigated under 30-90 bar fuel pressures and 1-5 bar chamber pressure. Flame propagation images and combustion characteristics were determined via pressure-derived parameters and analyzed at a fuel pressure of 90 bar and a chamber pressure of 1 bar at different stratification ratios (S.R.) (from 0% to 100%) at overall equivalence ratios of Ó.6, 0.8, and 1.0. Shorter combustion duration and higher combustion pressure were observed in direct injection-type combustion at all fuel air equivalence ratios compared to those of homogeneous combustion. . Editor: Kevin M. Lyons. tants and it is very economical compared to conventional fuels [8]. Compressed natural gas has a high research octane number (RON= 110-130) and therefore can be easily employed in sparkignited (SI) intemal combustion engines. Due to the high RON of CNG, engines could be operated with a higher compression ratio for better thermal efficiency [9]. Furthermore, since CNG has a low carbon/hydrogen (C/H) ratio, it produces less CO2 per unit of energy released. Therefore, CNG appears to be an excellent fuel for SI engines [10].In recent years, a DI gasoline engine has been developed for automobile engines to improve fuel economy [2]. Direct-injection technology strongly increases the engine's volumetric efficiency, which permits the engine to run at higher speed and produce more overall power. Direct-injection technology also reduces the need for throttling for control purposes, thus reducing the cycle pumping loss. During low loads and low engine speeds, the DI engines operate with a stratified charge. The charge stratification in the combustion chamber permits extremely lean combustion without high cycle-to-cycle variations and with high combustion efficiency, although the problem of high nitrogen oxides (NOx) and particulate matter (PM) emissions remains [11][12][13][14].The spark-ignited direct-injection (SIDI) CNG engine adopts DI technology in an SI engine, and use...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.