Ariane 5 Kourou
|
Specific impulse is the parameter used to measure the efficiency of a rocket jet engine, and is basically the ratio of the useful jet impulse Ft (Ns) produced divided by the fuel flow-rate (mass per second in Kg/sec) required to produce that impulse . Specific impulse Isp is the index of performance for rocket engines and is defined by the following ratio :
|
|
Where the numerator is the total impulse obtained over the operating time of the rocket engine. Usually referred to as the ‘Burn time’. Defined by the time period from t0 to t1.seconds. Accompanied by a denominator which represents the total fuel mass flow necessary to produce the impulse during the same time period. ‘g’ is the acceleration due to gravity gearth at sea level m/s2The above expression can be simplified to the ratio given below if the flow rate and thrust are constant over the burn time. For liquid fueled rocket engines this is usually the case, so they can be represented by the ratio of the thrust force produced at the exit of the nozzle F divided by the product of gearth at sea level multiplied by the mass flow rate of fuel used to produce the thrust. Note: F is measured at tearth Specfic impulse
Isp
=
|
|
Where F is the Jet Thrust force at the outlet of the nozzle F = q * v2 N Newtons‘q’ is the volumetric flowrate * density r to give mass flow-rate of fluid leaving the nozzle Kgs/sec v2 is the exhaust jet velocity at the outlet of the nozzle m/sec M dt is the mass flowrate of fuel
|
|
Dimensional analysis of IspIsp =
|
|
Isp =
|
|
esa comparison of specific impulse for liquid propergols and electric propulsion Once you are out in space and have overcome aerodynamic drag of the atmosphere then the total impulse produced over a long period by a certain mass of fuel become significant.
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34201 Definition of Tsiolkovskis Formula Tsiolkovski modified end function http://en.wikipedia.org/wiki/Specific_impulse
© All rights reserved by John Gwynn Water Rocket Explorer 12/01/07
|
|
This site was created on the 15th April 2003 ©John Gwynn and sons2003 You're welcome to reproduce any material on this site for educational or other non commercial purposes as long as you give us proper credit (by referring to "The Water-Rocket Explorer" http://waterocket.explorer.free.fr).
|
|
|
|
Ariane 5 Envisat 2 |
|
" Great things are not done by impulse, but a
series of small things brought together". Ironic quotation which says that success is the result of assembling many simple existng systems or ideas in a new original way. |
sec
sec
Sec
Sec
