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A figure incorporating a thrust curve for the Estes A10-PT rocket motor, as well as information about the impulse, fuel mass, and specific impulse.

Specific impulse (usually abbreviated I_sp) is a way to describe the efficiency of rocket and jet engines. It represents the impulse (change in momentum) per unit amount of propellant used.^[1] The unit amount may be given either per unit mass (such as kilograms), or per unit Earth-weight (such as kiloponds, since g is used for the latter definition).^[2] The higher the specific impulse, the less propellant is needed to gain a given amount of momentum.

The actual exhaust velocity is the average speed that the exhaust jet actually leaves the vehicle. The effective exhaust velocity is the speed that the propellant burned per second would have to leave the vehicle to give the same thrust. The two are about the same for a rocket working in a vacuum, but are radically different for an airbreathing jet engine that obtains extra thrust by accelerating air. Specific impulse and effective exhaust velocity are proportional.

Specific impulse is a useful value to compare engines, much like miles per gallon or litres per 100 kilometres is used for cars. A propulsion method with a higher specific impulse is more propellant-efficient.^[1] Another number that measures the same thing, usually used for air-breathing jet engines, is specific fuel consumption. Specific fuel consumption is inversely proportional to specific impulse and effective exhaust velocity.

General considerations

Propellant is normally measured either in units of mass, or in units of weight at sea level on Earth. If mass is used, specific impulse is an impulse per unit mass, which dimensional analysis shows to be a unit of speed, and so specific impulses are often measured in metres per second, and are often termed effective exhaust velocity. However, if propellant weight is used instead, an impulse divided by a force (weight) turns out to be a unit of time, and so specific impulses are measured in seconds. These two formulations are both widely used, and differ from each other by a factor of g, the dimensioned constant of gravitational acceleration at the surface of the Earth.

Essentially, the higher the specific impulse, the less propellant is needed to gain a given amount of momentum. In this regard a propulsion method is more propellant-efficient if the specific impulse is higher. This should not be confused with energy-efficiency, which can even decrease as specific impulse increases, since propulsion systems that give high specific impulse require high energy to do so.

In addition it is important that thrust and specific impulse not be confused with one another. The specific impulse is a measure of the impulse per unit of propellant that is expended, while thrust is a measure of the momentary or peak force supplied by a particular engine. In many cases, propulsion systems with very high specific impulses—some ion thrusters reach 10,000 seconds—produce low thrusts.^[3]

When calculating specific impulse, only propellant that is carried with the vehicle before use is counted. For a chemical rocket the propellant mass therefore would include both fuel and oxidizer; for air-breathing engines only the mass of the fuel is counted, not the mass of air passing through the engine.

Examples

Specific impulse of various propulsion technologies
Engine	Effective exhaust velocity (m/s)	Specific impulse (s)	Exhaust specific energy (MJ/kg)
Turbofan jet engine (actual V is ~300 m/s)	29,000	3,000	Approx. 0.05
Space Shuttle Solid Rocket Booster	2,500	250	3
Liquid oxygen–liquid hydrogen	4,400	450	9.7
NSTAR^[4] electrostatic xenon ion thruster	20,000–30,000	1,950–3,100
NEXT electrostatic xenon ion thruster	40,000	1,320–4,170
VASIMR predictions^[5]^[6]^[7]	30,000–120,000	3,000–12,000	1,400
DS4G electrostatic ion thruster^[8]	210,000	21,400	22,500
Ideal photonic rocket^[a]	299,792,458	30,570,000	89,875,517,874

For a more complete list see: Spacecraft propulsion#Table of methods

An example of a specific impulse measured in time is 453 seconds, or, equivalently, an effective exhaust velocity of 4,440 m/s, for the Space Shuttle Main Engines when operating in vacuum.

An air-breathing jet engine typically has a much larger specific impulse than a rocket: a turbofan jet engine may have a specific impulse of 6,000 seconds or more at sea level whereas a rocket would be around 200–400 seconds. An air-breathing engine is thus much more propellant efficient; this is because the actual exhaust speed is much lower, because air provides oxidizer, and because air is used as reaction mass. Since the actual, physical exhaust velocity is lower, for at least subsonic speeds the kinetic energy the exhaust carries away is lower and thus the jet engine uses far less energy to generate thrust. This is so even allowing for the fact that more air must be exhausted at lower speeds to get the same thrust as a smaller amount of air at higher speeds.

While the actual exhaust velocity is lower for air-breathing engines, the effective exhaust velocity is very high for jet engines. This is because the effective exhaust velocity calculation essentially assumes that the propellant is providing all the thrust, and hence is not physically meaningful for air-breathing engines; nevertheless it is useful for comparison with other types of engines.

In some ways, comparing specific impulse seems unfair in the case of jet engines and rockets. However, in rocket- or jet-powered aircraft, specific impulse is approximately proportional to range, and suborbital rockets do indeed perform much worse than jets in that regard.

The highest specific impulse for a chemical propellant ever test-fired in a rocket engine was lithium, fluorine, and hydrogen (a tripropellant): 542 seconds (5,320 m/s). However, this combination is impractical; see rocket fuel.^[9]

Nuclear thermal rocket engines differ from conventional rocket engines in that thrust is created strictly through thermodynamic phenomena, with no chemical reaction. The nuclear rocket typically operates by passing hydrogen gas through a superheated nuclear core. Testing in the 1960s yielded specific impulses of about 850 seconds (8,340 m/s), about twice that of the Space Shuttle engines.

A variety of other non-rocket propulsion methods, such as ion thrusters, give much higher specific impulse but with much lower thrust; for example the Hall effect thruster on the SMART-1 satellite has a specific impulse of 1,640 s (16,100 m/s) but a maximum thrust of only 68 millinewtons. The hypothetical Variable specific impulse magnetoplasma rocket (VASIMR) propulsion would theoretically yield a minimum of 10,000−300,000 m/s but would probably require a great deal of heavy machinery to confine even relatively diffuse plasmas, and so would be unusable for high-thrust applications such as launch from planetary surfaces.

The proposed Project Orion nuclear propelled spaceship provided a specific impulse of 10,000—1,000,000 s.^[10]

Units

	Specific Impulse (by weight)	Specific Impulse (by mass)	Effective exhaust velocity	Specific fuel consumption
SI	=X seconds	=9.8066 X N·s/kg	=9.8066 X m/s	=(101,972/X) g/kN·s
English units	=X seconds	=X lbf·s/lb	=32.16 X ft/s	=(3,600/X) lb/lbf·h

By far the most common units used for specific impulse today is the second, and this is used both in the SI world as well as where English units are used. Its chief advantages are that its units and numerical value is identical everywhere, and essentially everyone understands it. Nearly all manufacturers quote their engine performance in these units and it is also useful for specifying aircraft engine performance.

The effective exhaust velocity of m/s is also in reasonably common usage; for rocket engines it is reasonably intuitive, although for many rocket engines the effective exhaust speed is not precisely the same as the actual exhaust speed due to, for example, fuel and oxidizer that is dumped overboard after powering turbopumps. For airbreathing engines it is not physically meaningful although can be used for comparison purposes nevertheless.

The N·s/kg is not uncommonly seen, and is numerically equal to the effective exhaust velocity in m/s (from Newton's second law and the definition of the newton.)

The units of ft/s were used by NASA during Apollo, but seems to have fallen into disuse, and NASA is moving towards using SI units wherever possible.^{[citation needed]}

The lbf·s/lb unit sees little use but is covered in some textbooks.^{[citation needed]}

Another equivalent unit is specific fuel consumption. This has units of g/kN.s or lbf/lb·h and is inversely proportional to specific impulse. This is used extensively for describing air-breathing jet engines.

Specific impulse in seconds

General definition

For all vehicles specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation^[11]:

\mathrm {F_{\rm {thrust}}} =I_{\rm {sp}}\cdot {\frac {\Delta m}{\Delta t}}\cdot g_{\rm {0}}\,

where:

\mathrm {F_{\rm {thrust}}}

is the thrust obtained from the engine, in newtons (or poundals).

I_{\rm {sp}}

is the specific impulse measured in seconds.

${\frac {\Delta m}{\Delta t}}$ is the mass flow rate in kg/s (lb/s), which is negative the time-rate of change of the vehicle's mass since propellant is being expelled.

g_{\rm {0}}

is the acceleration at the Earth's surface, in m/s² (or ft/s²).

(When working with English units, it is conventional to divide both sides of the equation by g₀ so that the left hand side of the equation has units of lbs rather than expressing it in poundals.)

This I_sp in seconds value is somewhat physically meaningful—if an engine's thrust could be adjusted to equal the initial weight of its propellant (measured at one standard gravity), then I_sp is the duration the propellant would last.

The advantage that this formulation has is that it may be used for rockets, where all the reaction mass is carried onboard, as well as aeroplanes, where most of the reaction mass is taken from the atmosphere. In addition, it gives a result that is independent of units used (provided the unit of time used is the second).

The specific impulse of various jet engines

Rocketry

In rocketry, where the only reaction mass is the propellant, an equivalent way of calculating the specific impulse in seconds is also frequently used. In this sense, specific impulse is defined as the change in momentum per unit weight-on-Earth of the propellant:

I_{\rm {sp}}={\frac {v_{\rm {e}}}{g_{\rm {0}}}}

where

I_sp is the specific impulse measured in seconds

$v_{\rm {e}}$ is the average exhaust speed along the axis of the engine in (ft/s or m/s)

g₀ is the acceleration at the Earth's surface (in ft/s² or m/s²)

In rockets, due to atmospheric effects, the specific impulse varies with altitude, reaching a maximum in a vacuum. It is therefore most common to see the specific impulse quoted for the vehicle in a vacuum; the lower sea level values are usually indicated in some way (e.g. 'sl').

Specific impulse as a speed (effective exhaust velocity)

Because of the geocentric factor of g₀ in the equation for specific impulse, many prefer to define the specific impulse of a rocket (in particular) in terms of thrust per unit mass flow of propellant (instead of per unit weight flow). This is an equally valid (and in some ways somewhat simpler) way of defining the effectiveness of a rocket propellant. For a rocket, the specific impulse defined in this way is simply the effective exhaust velocity relative to the rocket, v_e. The two definitions of specific impulse are proportional to one another, and related to each other by:

v_{\rm {e}}=g_{0}I_{\rm {sp}}\,

where

I_{\rm {sp}}\,

- is the specific impulse in seconds

v_{\rm {e}}\,

- is the specific impulse measured in m/s, which is the same as the effective exhaust velocity measured in m/s (or ft/s if g is in ft/s²)

g_{0}\,

- is the acceleration due to gravity at the Earth's surface, 9.81 m/s² (in English units units 32.2 ft/s²).

This equation is also valid for airbreathing jet engines, but is rarely used in practice.

(Note that different symbols are sometimes used; for example, c is also sometimes seen for exhaust velocity. While the symbol $I_{sp}$ might logically be used for specific impulse in units of N•s/kg, to avoid confusion it is desirable to reserve this for specific impulse measured in seconds.)

It is related to the thrust, or forward force on the rocket by the equation:

\mathrm {F_{\rm {thrust}}} =v_{\rm {e}}\cdot {\frac {\Delta m}{\Delta t}}\,

where

${\frac {\Delta m}{\Delta t}}$ is the propellant mass flow rate, which is the rate of decrease of the vehicle's mass

A rocket must carry all its fuel with it, so the mass of the unburned fuel must be accelerated along with the rocket itself. Minimizing the mass of fuel required to achieve a given push is crucial to building effective rockets. Using Newton's laws of motion it is not difficult to verify that for a fixed mass of fuel, the total change in velocity (in fact, momentum) it can accomplish can only be increased by increasing the effective exhaust velocity.

A spacecraft without propulsion follows an orbit determined by the gravitational field. Deviations from the corresponding velocity pattern (these are called Δv) are achieved by sending exhaust mass in the direction opposite to that of the desired velocity change.

Actual exhaust speed versus effective exhaust speed

Note that effective exhaust velocity and actual exhaust velocity can be significantly different, for example when a rocket is run within the atmosphere, atmospheric pressure on the outside of the engine causes a retarding force that reduces the specific impulse and the effective exhaust velocity goes down, whereas the actual exhaust velocity is largely unaffected. Also, sometimes rocket engines have a separate nozzle for the turbopump turbine gas, and then calculating the effective exhaust velocity requires averaging the two mass flows as well as accounting for any atmospheric pressure.

For airbreathing jet engines, particularly, turbofans, the actual exhaust velocity and the effective exhaust velocity are different by orders of magnitude. This is because a good deal of additional momentum is obtained by using air as reaction mass. This allows for a better match between the airspeed and the exhaust speed which saves energy/propellant and enormously increases the effective exhaust velocity while reducing the actual exhaust velocity.

Energy efficiency

Rockets

For rockets and rocket-like engines such as ion-drives a higher $I_{sp}$ implies lower energy efficiency: the power needed to run the engine is simply:

{\frac {dm}{dt}}{\frac {V_{e}^{2}}{2}}

where V_e is the actual jet velocity.

whereas from momentum considerations the thrust generated is:

{\frac {dm}{dt}}V_{e}

Dividing the power by the thrust to obtain the specific power requirements we get:

{\frac {V_{e}}{2}}

Hence the power needed is proportional to the exhaust velocity, with higher velocities needing higher power for the same thrust, and thus are less energy efficient per unit thrust.

However, the total energy for a mission depends on total propellant use, as well as how much energy is needed per unit of propellant. For low exhaust velocity with respect to the mission delta-v, enormous amounts of reaction mass is needed. In fact a very low exhaust velocity is not energy efficient at all for this reason; but it turns out that neither are very high exhaust velocities.

Theoretically, for a given delta-v, in space, among all fixed values for the exhaust speed the value $v_{\text{e}}=0.6275\Delta v$ is the most energy efficient with respect to the final mass, see Tsiolkovsky rocket equation.

However, a variable exhaust speed can be more energy efficient still. For example, if a rocket is accelerated from some positive initial speed using an exhaust speed equal to the speed of the rocket no energy is lost as kinetic energy of reaction mass, since it becomes stationary.^[12] In this case the rocket keeps the same momentum, so its speed is inversely proportional to its remaining mass. During such a flight the kinetic energy of the rocket is proportional to its speed and, correspondingly, inversely proportional to its remaining mass. The power needed per unit acceleration is constant throughout the flight; the reaction mass to be expelled per unit time to produce a given acceleration is proportional to the square of the rocket's remaining mass.

Also it is advantageous to expel reaction mass at a location where the gravity potential is low, see Oberth effect.

Air breathing

Air-breathing engines such as turbojets increase the momentum generated from their propellant by using it to power the acceleration of inert air rearwards. It turns out that the amount of energy needed to generate a particular amount of thrust is inversely proportional to the amount of air propelled rearwards, thus increasing the mass of air (as with a turbofan) both improves energy efficiency as well as $I_{sp}$ .

Figures for real engines

Rocket engines in vacuum
Model	Type	First run	Application	TSFC		I_sp (by weight)	I_sp (by mass)
Model	Type	First run	Application	lb/lbf·h	g/kN·s	s	m/s
Avio P80	solid fuel	2006	Vega stage 1	13	360	280	2700
Avio Zefiro 23	solid fuel	2006	Vega stage 2	12.52	354.7	287.5	2819
Avio Zefiro 9A	solid fuel	2008	Vega stage 3	12.20	345.4	295.2	2895
Merlin 1D	liquid fuel	2013	Falcon 9	12	330	310	3000
RD-843	liquid fuel		Vega upper stage	11.41	323.2	315.5	3094
Kuznetsov NK-33	liquid fuel	1970s	N-1F, Soyuz-2-1v stage 1	10.9	308	331^[13]	3250
NPO Energomash RD-171M	liquid fuel		Zenit-2M, -3SL, -3SLB, -3F stage 1	10.7	303	337	3300
LE-7A	cryogenic		H-IIA, H-IIB stage 1	8.22	233	438	4300
Snecma HM-7B	cryogenic		Ariane 2, 3, 4, 5 ECA upper stage	8.097	229.4	444.6	4360
LE-5B-2	cryogenic		H-IIA, H-IIB upper stage	8.05	228	447	4380
Aerojet Rocketdyne RS-25	cryogenic	1981	Space Shuttle, SLS stage 1	7.95	225	453^[14]	4440
Aerojet Rocketdyne RL-10B-2	cryogenic		Delta III, Delta IV, SLS upper stage	7.734	219.1	465.5	4565
NERVA NRX A6	nuclear	1967				869

Jet engines with Reheat, static, sea level
Model	Type	First run	Application	TSFC		I_sp (by weight)	I_sp (by mass)
Model	Type	First run	Application	lb/lbf·h	g/kN·s	s	m/s
Turbo-Union RB.199	turbofan		Tornado	2.5^[15]	70.8	1440	14120
GE F101-GE-102	turbofan	1970s	B-1B	2.46	70	1460	14400
Tumansky R-25-300	turbojet		MIG-21bis	2.206^[15]	62.5	1632	16000
GE J85-GE-21	turbojet		F-5E/F	2.13^[15]	60.3	1690	16570
GE F110-GE-132	turbofan		F-16E/F	2.09^[15]	59.2	1722	16890
Honeywell/ITEC F125	turbofan		F-CK-1	2.06^[15]	58.4	1748	17140
Snecma M53-P2	turbofan		Mirage 2000C/D/N	2.05^[15]	58.1	1756	17220
Snecma Atar 09C	turbojet		Mirage III	2.03^[15]	57.5	1770	17400
Snecma Atar 09K-50	turbojet		Mirage IV, 50, F1	1.991^[15]	56.4	1808	17730
GE J79-GE-15	turbojet		F-4E/EJ/F/G, RF-4E	1.965	55.7	1832	17970
Saturn AL-31F	turbofan		Su-27/P/K	1.96^[16]	55.5	1837	18010
GE F110-GE-129	turbofan		F-16C/D, F-15EX	1.9^[15]	53.8	1895	18580
Soloviev D-30F6	turbofan		MiG-31, S-37/Su-47	1.863^[15]	52.8	1932	18950
Lyulka AL-21F-3	turbojet		Su-17, Su-22	1.86^[15]	52.7	1935	18980
Klimov RD-33	turbofan	1974	MiG-29	1.85	52.4	1946	19080
Saturn AL-41F-1S	turbofan		Su-35S/T-10BM	1.819	51.5	1979	19410
Volvo RM12	turbofan	1978	Gripen A/B/C/D	1.78^[15]	50.4	2022	19830
GE F404-GE-402	turbofan		F/A-18C/D	1.74^[15]	49	2070	20300
Kuznetsov NK-32	turbofan	1980	Tu-144LL, Tu-160	1.7	48	2100	21000
Snecma M88-2	turbofan	1989	Rafale	1.663	47.11	2165	21230
Eurojet EJ200	turbofan	1991	Eurofighter	1.66–1.73	47–49^[17]	2080–2170	20400–21300

Dry jet engines, static, sea level
Model	Type	First run	Application	TSFC		I_sp (by weight)	I_sp (by mass)
Model	Type	First run	Application	lb/lbf·h	g/kN·s	s	m/s
GE J85-GE-21	turbojet		F-5E/F	1.24^[15]	35.1	2900	28500
Snecma Atar 09C	turbojet		Mirage III	1.01^[15]	28.6	3560	35000
Snecma Atar 09K-50	turbojet		Mirage IV, 50, F1	0.981^[15]	27.8	3670	36000
Snecma Atar 08K-50	turbojet		Super Étendard	0.971^[15]	27.5	3710	36400
Tumansky R-25-300	turbojet		MIG-21bis	0.961^[15]	27.2	3750	36700
Lyulka AL-21F-3	turbojet		Su-17, Su-22	0.86	24.4	4190	41100
GE J79-GE-15	turbojet		F-4E/EJ/F/G, RF-4E	0.85	24.1	4240	41500
Snecma M53-P2	turbofan		Mirage 2000C/D/N	0.85^[15]	24.1	4240	41500
Volvo RM12	turbofan	1978	Gripen A/B/C/D	0.824^[15]	23.3	4370	42800
RR Turbomeca Adour	turbofan	1999	Jaguar retrofit	0.81	23	4400	44000
Honeywell/ITEC F124	turbofan	1979	L-159, X-45	0.81^[15]	22.9	4440	43600
Honeywell/ITEC F125	turbofan		F-CK-1	0.8^[15]	22.7	4500	44100
PW J52-P-408	turbojet		A-4M/N, TA-4KU, EA-6B	0.79	22.4	4560	44700
Saturn AL-41F-1S	turbofan		Su-35S/T-10BM	0.79	22.4	4560	44700
Snecma M88-2	turbofan	1989	Rafale	0.782	22.14	4600	45100
Klimov RD-33	turbofan	1974	MiG-29	0.77	21.8	4680	45800
RR Pegasus 11-61	turbofan		AV-8B+	0.76	21.5	4740	46500
Eurojet EJ200	turbofan	1991	Eurofighter	0.74–0.81	21–23^[17]	4400–4900	44000–48000
GE F414-GE-400	turbofan	1993	F/A-18E/F	0.724^[18]	20.5	4970	48800
Kuznetsov NK-32	turbofan	1980	Tu-144LL, Tu-160	0.72-0.73	20–21	4900–5000	48000–49000
Soloviev D-30F6	turbofan		MiG-31, S-37/Su-47	0.716^[15]	20.3	5030	49300
Snecma Larzac	turbofan	1972	Alpha Jet	0.716	20.3	5030	49300
IHI F3	turbofan	1981	Kawasaki T-4	0.7	19.8	5140	50400
Saturn AL-31F	turbofan		Su-27 /P/K	0.666-0.78^[16]^[18]	18.9–22.1	4620–5410	45300–53000
RR Spey RB.168	turbofan		AMX	0.66^[15]	18.7	5450	53500
GE F110-GE-129	turbofan		F-16C/D, F-15	0.64^[18]	18	5600	55000
GE F110-GE-132	turbofan		F-16E/F	0.64^[18]	18	5600	55000
Turbo-Union RB.199	turbofan		Tornado ECR	0.637^[15]	18.0	5650	55400
PW F119-PW-100	turbofan	1992	F-22	0.61^[18]	17.3	5900	57900
Turbo-Union RB.199	turbofan		Tornado	0.598^[15]	16.9	6020	59000
GE F101-GE-102	turbofan	1970s	B-1B	0.562	15.9	6410	62800
PW TF33-P-3	turbofan		B-52H, NB-52H	0.52^[15]	14.7	6920	67900
RR AE 3007H	turbofan		RQ-4, MQ-4C	0.39^[15]	11.0	9200	91000
GE F118-GE-100	turbofan	1980s	B-2	0.375^[15]	10.6	9600	94000
GE F118-GE-101	turbofan	1980s	U-2S	0.375^[15]	10.6	9600	94000
General Electric CF6-50C2	turbofan		A300, DC-10-30	0.371^[15]	10.5	9700	95000
GE TF34-GE-100	turbofan		A-10	0.37^[15]	10.5	9700	95000
CFM CFM56-2B1	turbofan		C-135, RC-135	0.36^[19]	10	10000	98000
Progress D-18T	turbofan	1980	An-124, An-225	0.345	9.8	10400	102000
PW F117-PW-100	turbofan		C-17	0.34^[20]	9.6	10600	104000
PW PW2040	turbofan		Boeing 757	0.33^[20]	9.3	10900	107000
CFM CFM56-3C1	turbofan		737 Classic	0.33	9.3	11000	110000
GE CF6-80C2	turbofan		744, 767, MD-11, A300/310, C-5M	0.307-0.344	8.7–9.7	10500–11700	103000–115000
EA GP7270	turbofan		A380-861	0.299^[18]	8.5	12000	118000
GE GE90-85B	turbofan		777-200/200ER/300	0.298^[18]	8.44	12080	118500
GE GE90-94B	turbofan		777-200/200ER/300	0.2974^[18]	8.42	12100	118700
RR Trent 970-84	turbofan	2003	A380-841	0.295^[18]	8.36	12200	119700
GE GEnx-1B70	turbofan		787-8	0.2845^[18]	8.06	12650	124100
RR Trent 1000C	turbofan	2006	787-9	0.273^[18]	7.7	13200	129000

Jet engines, cruise
Model	Type	First run	Application	TSFC		I_sp (by weight)	I_sp (by mass)
Model	Type	First run	Application	lb/lbf·h	g/kN·s	s	m/s
	Ramjet		Mach 1	4.5	130	800	7800
J-58	turbojet	1958	SR-71 at Mach 3.2 (Reheat)	1.9^[15]	53.8	1895	18580
RR/Snecma Olympus	turbojet	1966	Concorde at Mach 2	1.195^[21]	33.8	3010	29500
PW JT8D-9	turbofan		737 Original	0.8^[22]	22.7	4500	44100
Honeywell ALF502R-5	GTF		BAe 146	0.72^[20]	20.4	5000	49000
Soloviev D-30KP-2	turbofan		Il-76, Il-78	0.715	20.3	5030	49400
Soloviev D-30KU-154	turbofan		Tu-154M	0.705	20.0	5110	50100
RR Tay RB.183	turbofan	1984	Fokker 70, Fokker 100	0.69	19.5	5220	51200
GE CF34-3	turbofan	1982	Challenger, CRJ100/200	0.69	19.5	5220	51200
GE CF34-8E	turbofan		E170/175	0.68	19.3	5290	51900
Honeywell TFE731-60	GTF		Falcon 900	0.679^[23]	19.2	5300	52000
CFM CFM56-2C1	turbofan		DC-8 Super 70	0.671^[20]	19.0	5370	52600
GE CF34-8C	turbofan		CRJ700/900/1000	0.67-0.68	19–19	5300–5400	52000–53000
CFM CFM56-3C1	turbofan		737 Classic	0.667	18.9	5400	52900
CFM CFM56-2A2	turbofan	1974	E-3, E-6	0.66^[19]	18.7	5450	53500
RR BR725	turbofan	2008	G650/ER	0.657	18.6	5480	53700
CFM CFM56-2B1	turbofan		C-135, RC-135	0.65^[19]	18.4	5540	54300
GE CF34-10A	turbofan		ARJ21	0.65	18.4	5540	54300
CFE CFE738-1-1B	turbofan	1990	Falcon 2000	0.645^[20]	18.3	5580	54700
RR BR710	turbofan	1995	G. V/G550, Global Express	0.64	18	5600	55000
GE CF34-10E	turbofan		E190/195	0.64	18	5600	55000
General Electric CF6-50C2	turbofan		A300B2/B4/C4/F4, DC-10-30	0.63^[20]	17.8	5710	56000
PowerJet SaM146	turbofan		Superjet LR	0.629	17.8	5720	56100
CFM CFM56-7B24	turbofan		737 NG	0.627^[20]	17.8	5740	56300
RR BR715	turbofan	1997	717	0.62	17.6	5810	56900
GE CF6-80C2-B1F	turbofan		747-400	0.605^[21]	17.1	5950	58400
CFM CFM56-5A1	turbofan		A320	0.596	16.9	6040	59200
Aviadvigatel PS-90A1	turbofan		Il-96-400	0.595	16.9	6050	59300
PW PW2040	turbofan		757-200	0.582^[20]	16.5	6190	60700
PW PW4098	turbofan		777-300	0.581^[20]	16.5	6200	60800
GE CF6-80C2-B2	turbofan		767	0.576^[20]	16.3	6250	61300
IAE V2525-D5	turbofan		MD-90	0.574^[24]	16.3	6270	61500
IAE V2533-A5	turbofan		A321-231	0.574^[24]	16.3	6270	61500
RR Trent 700	turbofan	1992	A330	0.562^[25]	15.9	6410	62800
RR Trent 800	turbofan	1993	777-200/200ER/300	0.560^[25]	15.9	6430	63000
Progress D-18T	turbofan	1980	An-124, An-225	0.546	15.5	6590	64700
CFM CFM56-5B4	turbofan		A320-214	0.545	15.4	6610	64800
CFM CFM56-5C2	turbofan		A340-211	0.545	15.4	6610	64800
RR Trent 500	turbofan	1999	A340-500/600	0.542^[25]	15.4	6640	65100
CFM LEAP-1B	turbofan	2014	737 MAX	0.53-0.56	15–16	6400–6800	63000–67000
Aviadvigatel PD-14	turbofan	2014	MC-21-310	0.526	14.9	6840	67100
RR Trent 900	turbofan	2003	A380	0.522^[25]	14.8	6900	67600
GE GE90-85B	turbofan		777-200/200ER	0.52^[20]^[26]	14.7	6920	67900
GE GEnx-1B76	turbofan	2006	787-10	0.512^[22]	14.5	7030	69000
PW PW1400G	GTF		MC-21	0.51^[27]	14.4	7100	69000
CFM LEAP-1C	turbofan	2013	C919	0.51	14.4	7100	69000
CFM LEAP-1A	turbofan	2013	A320neo family	0.51^[27]	14.4	7100	69000
RR Trent 7000	turbofan	2015	A330neo	0.506^[b]	14.3	7110	69800
RR Trent 1000	turbofan	2006	787	0.506^[c]	14.3	7110	69800
RR Trent XWB-97	turbofan	2014	A350-1000	0.478^[d]	13.5	7530	73900
PW 1127G	GTF	2012	A320neo	0.463^[22]	13.1	7780	76300

References

^ ^a ^b "What is specific impulse?". Qualitative Reasoning Group. Retrieved 22 December 2009.
^ Benson, Tom (11 July 2008). "Specific impulse". NASA. Retrieved 22 December 2009.
^ "Mission Overview". exploreMarsnow. Retrieved 23 December 2009.
^ In-flight performance of the NSTAR ion propulsion system on the Deep Space One mission. Aerospace Conference Proceedings. IEEExplore. 2000. doi:10.1109/AERO.2000.878373.
^ Glover, Tim W.; Chang Diaz, Franklin R.; Squire, Jared P.; Jacobsen, Verlin; Chavers, D. Gregory; Carter, Mark D. "Principal VASIMR Results and Present Objectives" (PDF).
^ Cassady, Leonard D.; Longmier, Benjamin W.; Olsen, Chris S.; Ballenger, Maxwell G.; McCaskill, Greg E.; Ilin, Andrew V.; Carter, Mark D.; Gloverk, Tim W.; Squire, Jared P.; Chang, Franklin R.; Bering, III, Edgar A. (28 July 2010). "VASIMR R Performance Results" (PDF). www.adastra.com.
^ "Vasimr VX 200 meets full power efficiency milestone". spacefellowship.com. Retrieved 2021-05-13.
^ "ESA and Australian team develop breakthrough in space propulsion". cordis.europa.eu. 18 January 2006.
^ ARBIT, H. A., CLAPP, S. D., DICKERSON, R. A., NAGAI, C. K., Combustion characteristics of the fluorine-lithium/hydrogen tripropellant combination. AMERICAN INST OF AERONAUTICS AND ASTRONAUTICS, PROPULSION JOINT SPECIALIST CONFERENCE, 4TH, CLEVELAND, OHIO, Jun 10-14, 1968.
^ Project Orion entry in the Internet Encyclopedia of Science:
^ Rocket Propulsion Elements, 7th Edition by George P. Sutton, Oscar Biblarz
^ Note that this limits the speed of the rocket to the maximum exhaust speed.
^ "NK33". Encyclopedia Astronautica.
^ "SSME". Encyclopedia Astronautica.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag Nathan Meier (21 Mar 2005). "Military Turbojet/Turbofan Specifications". Archived from the original on 11 February 2021.
^ ^a ^b "Flanker". AIR International Magazine. 23 March 2017.
^ ^a ^b "EJ200 turbofan engine" (PDF). MTU Aero Engines. April 2016.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Kottas, Angelos T.; Bozoudis, Michail N.; Madas, Michael A. "Turbofan Aero-Engine Efficiency Evaluation: An Integrated Approach Using VSBM Two-Stage Network DEA" (PDF). doi:10.1016/j.omega.2019.102167.
^ ^a ^b ^c Élodie Roux (2007). "Turbofan and Turbojet Engines: Database Handbook" (PDF). p. 126. ISBN 9782952938013.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Nathan Meier (3 Apr 2005). "Civil Turbojet/Turbofan Specifications". Archived from the original on 17 August 2021.
^ ^a ^b Ilan Kroo. "Data on Large Turbofan Engines". Aircraft Design: Synthesis and Analysis. Stanford University. Archived from the original on 11 January 2017.
^ ^a ^b ^c David Kalwar (2015). "Integration of turbofan engines into the preliminary design of a high-capacity short-and medium-haul passenger aircraft and fuel efficiency analysis with a further developed parametric aircraft design software" (PDF).
^ "Purdue School of Aeronautics and Astronautics Propulsion Web Page - TFE731".
^ ^a ^b Lloyd R. Jenkinson & al. (30 Jul 1999). "Civil Jet Aircraft Design: Engine Data File". Elsevier/Butterworth-Heinemann.
^ ^a ^b ^c ^d "Gas Turbine Engines" (PDF). Aviation Week. 28 January 2008. pp. 137–138.
^ Élodie Roux (2007). "Turbofan and Turbojet Engines: Database Handbook". ISBN 9782952938013.
^ ^a ^b Vladimir Karnozov (August 19, 2019). "Aviadvigatel Mulls Higher-thrust PD-14s To Replace PS-90A". AIN Online.

User:Enginerd44: Difference between revisions

Revision as of 22:08, 3 July 2011

General considerations

Examples

Units

Specific impulse in seconds

General definition

Rocketry

Specific impulse as a speed (effective exhaust velocity)

Actual exhaust speed versus effective exhaust speed

Energy efficiency

Rockets

Air breathing

Figures for real engines

References

External links

See also