The flame speed is the measured rate of expansion of the flame front in a

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

reaction. Whereas ''flame velocity'' is generally used for a

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...

, a related term is explosive velocity, which is the same relationship measured for an

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

. Combustion

engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considerin ...

s differentiate between the

laminar flame speed Laminar flame speed is an intrinsic characteristic of premixed combustible mixtures.http://www.clarke-energy.com/2013/laminar-flame-speed/ Laminar Flame Speed It is the speed at which an un-stretched laminar flame will propagate through a quiescen ...

and

turbulent In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

flame speed. Flame speed is typically measured in m/s, cm/s, etc.

In engines

In an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

, the flame speed of a

is a property which determines its ability to undergo controlled combustion without

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with s ...

. Flame speed is used along with adiabatic flame temperature to help determine the engine's efficiency. According to one source,

"...high flame-speed combustion processes, which closely approximate constant-volume processes, should reflect in high efficiencies.''NASA Technical Note'', May 1977,
Emissions and Total Energy Consumption of a Multicylinder Piston Engine Running on Gasoline and a Hydrogen-Gasoline Mixture
"

The flame speeds are not the actual engine flame speeds, A 12:1 compression ratio gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry{{cite web , url=http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html , title=Gasoline FAQ - Part 3 of 4Section - 7. What parameters determine octane requirement?

References

Combustion

In engines

See also

References