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Air–fuel ratio (AFR) is the mass ratio of air to a solid, liquid, or gaseous fuel present in a combustion process. The combustion may take place in a controlled manner such as in an internal combustion engine or industrial furnace, or may result in an explosion (e.g., a dust explosion). The air–fuel ratio determines whether a mixture is ...
In combustion physics, fuel mass fraction is the ratio of fuel mass flow to the total mass flow of a fuel mixture. If an air flow is fuel free, the fuel mass fraction is zero; in pure fuel without trapped gases, the ratio is unity. [1] As fuel is burned in a combustion process, the fuel mass fraction is reduced. The definition reads as = where ...
Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air–fuel ratio may be as lean as 65:1 (by mass). The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons.
Gasoline engines can run at stoichiometric air-to-fuel ratio, because gasoline is quite volatile and is mixed (sprayed or carburetted) with the air prior to ignition. Diesel engines, in contrast, run lean, with more air available than simple stoichiometry would require. Diesel fuel is less volatile and is effectively burned as it is injected. [16]
(The fuel-air ratio (FAR) is the reciprocal of the air-fuel ratio (AFR).) λ is the air-fuel equivalence ratio, and λ=1 means that it is assumed that the fuel and the oxidising agent (oxygen in air) are present in exactly the correct proportions so that they are both fully consumed in the reaction.
The mixture fraction definition is usually normalized such that it approaches unity in the fuel stream and zero in the oxidizer stream. [4] The mixture-fraction variable is commonly used as a replacement for the physical coordinate normal to the flame surface, in nonpremixed combustion.
The fuel-air ratio is decreased. This makes the flame to change its shape, then become unstable, and eventually blow-off. Static instability [ 2 ] or flame blow-off refer to phenomena involving the interaction between the chemical composition of the fuel-oxidizer mixture and the flow environment of the flame. [ 13 ]
These hydrogen engines burn fuel in the same manner that gasoline engines do. The theoretical maximum power output from a hydrogen engine depends on the air/fuel ratio and fuel injection method used. The stoichiometric air/fuel ratio for hydrogen is 34:1. At this air/fuel ratio, hydrogen will displace 29% of the combustion chamber leaving only ...