james@castle.ed.ac.uk (J Gillespie) (11/20/90)
From: J Gillespie <james@castle.ed.ac.uk>
This may be a Frequently Asked Question, but what exactly is a
'scramjet'? I see occasional references to them, but have never seen an
explanation of how they work. Are they existing technology, or
just-around-the-corner, or what?
Thanks in advance,
--
__ /~~~~~~~~\
/ / @ @ \ "Happiness is being famous for your financial
/ / /\/\ / < \ ability to indulge in every form of excess"
\_/_/_/___/_/ \________/ \__________________________________________-- Calvinv064lnev@ubvmsd.cc.buffalo.edu (Zerxes Bhagalia) (11/22/90)
From: v064lnev@ubvmsd.cc.buffalo.edu (Zerxes Bhagalia) In article <1990Nov20.021943.27530@cbnews.att.com>, james@castle.ed.ac.uk (J Gillespie) writes... > >This may be a Frequently Asked Question, but what exactly is a >'scramjet'? I see occasional references to them, but have never seen an >explanation of how they work. Are they existing technology, or >just-around-the-corner, or what? This is a basic diagram of a Scramjet: air | | | | | | | v v v v v v v | | \ / \ / <- compressor | | | | <- heat | | / \ / \ | | | | | | | | | v v v v v v v thrust This is how it works: 1) great amounts of air enter the chamber 2) the air is compressed, increasing pressure 3) the air is heated, increasing pressur 4) the air is thrust out the rear There are many variations of this - some include replacing the air with either liquid hydrogen or liquid helium. As far as I know however, the scramjet engine is experimental, if not still theoretical. I only have a basic understanding of this system, and would explain how I might have a few small technical errors, so no flames please. I just thought I'd post what I know. Zerxes
eachus@linus.mitre.org (Robert I. Eachus) (11/22/90)
From: eachus@linus.mitre.org (Robert I. Eachus)
A SCRAMjet is a Supersonic Combustion RAMjet engine. In an
ordinary jet engine the incoming air is heated and compressed by
turbulence in the intake of a supersonic plane so that the combustion
(burning) of the fuel can take place under subsonic conditions. A
SCRAM uses Hydrogen fuel (with a much higher speed of sound at the
same temperature and pressure as air) and combustion takes place at
where the air hits a laminar flow of hydrogen. This reduction in
turbulence allows both higher speeds and higher efficiency.
Think of it this way, in a (very) high speed aircraft, most of the
heating of the incoming air occurs before combustion. There is a
limit reached where all of the thrust is being converted into heating
of incoming air (and leading edges). In a SCRAMjet the heating of the
airflow occurs in the combustion region, and much more of the thrust
can be devoted to moving the aircraft.
--
Robert I. Eachus
with STANDARD_DISCLAIMER;
use STANDARD_DISCLAIMER;
function MESSAGE (TEXT: in CLEVER_IDEAS) return BETTER_IDEAS is...deichman@cod.nosc.mil (Shane D. Deichman) (11/22/90)
From: deichman@cod.nosc.mil (Shane D. Deichman)
O.K., for all you wanna-be jet jockeys out there in NETland,
here's a short compilation of some of the different forms of
jet propulsion:
Ramjet -- A jet engine that propels aircraft by igniting fuel
with air taken and compressed by the engine in a fashion that
produces greater exhaust than intake velocity. You have to
be travelling supersonically for the ramjet to work since it
uses the airspeed and momentum of the plane to compress the
intake air.
Scramjet ("S"upersonic "C"ombustion Ramjet) -- A ramjet engine
that burns fuel in the supersonic airstream produced by the
plane after it reaches supersonic speeds by conventional means.
Pulse jet -- A jet engine in which air intake and combustion
occur intermittently, producing periodic rapid bursts of thrust.
Anybody else want to add to this partial list?
-shane
"the Ayatollah of Rock-and-Rollah"
|\/\/\/\/|
| | "Cool your jets, dude!"
| |
| (o o) /
c _) /
| ,____/
| /
/______\megazone@wpi.WPI.EDU (MEGAZONE 23) (11/22/90)
From: megazone@wpi.WPI.EDU (MEGAZONE 23) In article <1990Nov20.021943.27530@cbnews.att.com> james@castle.ed.ac.uk (J Gillespie) writes: >This may be a Frequently Asked Question, but what exactly is a >'scramjet'? I see occasional references to them, but have never seen an A scramjet is a supersonic combustion ramjet. Usually burning liquid methane or liquid hydrogen. The combustion takes place in a supersonic airflow. >explanation of how they work. Are they existing technology, or >just-around-the-corner, or what? It is feasible to build one today, but there is no operational aircraft so equipped. (Well, there us there Aurora, but that may or may not exist.) Scramjets are undergoing extensive testing for use on the X-30, the National Aerospace Plane prototype. ############################################################################### # "Calling Garland operator 7G," EVE Email megazone@wpi.wpi.edu # # MEGAZONE, aka DAYTONA, aka BRIAN BIKOWICZ Bitnet Use a gateway. Sorry. # ###############################################################################
henry@zoo.toronto.edu (Henry Spencer) (11/22/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: J Gillespie <james@castle.ed.ac.uk> >This may be a Frequently Asked Question, but what exactly is a >'scramjet'? ... It's a semi-acronym, standing for "supersonic-combustion ramjet". Orthodox jet engines (including ramjets) decelerate incoming air to subsonic speed before mixing in fuel and burning it. At very high speeds this becomes problematic, because the compression involved generates heat, and when the incoming air temperature approaches the flame temperature, you don't get much thrust out of the engine. The only answer is to decelerate the air less, leaving it supersonic during combustion. This creates difficult design problems, not least being the very short time available to mix and burn the fuel, but it's the only way to build a highly-hypersonic air-breathing engine. >... Are they existing technology, or just-around-the-corner, or what? They're existing technology in a loose sense: a lot of testing and experimenting has been done, but nobody's ever flown an aircraft powered by a scramjet. One reason is that the aircraft and engine really have to be designed together, because airflow over the rest of the aircraft has a major influence on airflow in the scramjet intake. This drives up the price tag. The X-30 will use scramjets, if it ever gets built. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
beede@sctc.com (Mike Beede) (11/27/90)
From: beede@sctc.com (Mike Beede) deichman@cod.nosc.mil (Shane D. Deichman) writes: >Ramjet -- A jet engine that propels aircraft by igniting fuel >with air taken and compressed by the engine in a fashion that >produces greater exhaust than intake velocity. You have to >be travelling supersonically for the ramjet to work since it >uses the airspeed and momentum of the plane to compress the >intake air. No need for supersonic speed -- a ramjet can work fine at much lower speeds. There is certainly a minimum speed for any given application, though. -- Mike Beede Secure Computing Technology Corp beede@sctc.com 1210 W. County Rd E, Suite 100 Arden Hills, MN 55112 (612) 482-7420
ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) (11/27/90)
From: ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) *>It's a semi-acronym, standing for "supersonic-combustion ramjet". Orthodox *>jet engines (including ramjets) decelerate incoming air to subsonic speed *>before mixing in fuel and burning it. At very high speeds this becomes *>problematic, because the compression involved generates heat, and when the *>incoming air temperature approaches the flame temperature, you don't get *>much thrust out of the engine. The only answer is to decelerate the air *>less, leaving it supersonic during combustion. This creates difficult *>design problems, not least being the very short time available to mix *>and burn the fuel, but it's the only way to build a highly-hypersonic *>air-breathing engine. I recall seeing an illustration of an airplane equipped with scramjets. The artist's rendition showed the scramjets to be somewhat ope chambers mounted underneath the wing. Sort of like a series of small vertical strakes or fins projecting from under the wing. This suggests that the combustion takes place in the open. Is this true? ------------------------------------------------------------------------------- Iskandar Taib | The only thing worse than Peach ala Internet: NTAIB@AQUA.UCS.INDIANA.EDU | Frog is Frog ala Peach Bitnet: NTAIB@IUBACS !
terryh@ukcsd.uk (Terry Heatlie - Sun UK - Tech Support ) (11/29/90)
From: terryh@ukcsd.uk (Terry Heatlie - Sun UK - Tech Support ) In article <1990Nov27.045213.4141@cbnews.att.com>, ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) writes: |> |> *>It's a semi-acronym, standing for "supersonic-combustion ramjet". Orthodox As mentioned above, one of the problems with engines which work under hypersonic flow conditions is the heating which occurs decelerating the air prior to combustion. The concept in the illustration is an attempt to solve this problem by integrating the propulsion system and the aerodynamics of the craft. One can derive thrust from an external flow (ie the air flow over the vehicle) just like from an internal flow (eg that through a conventional jet engine). As I recall, the idea was to add energy to the flow under the body of the vehicle, which would be compressed by shock waves, this would seem to tie up with the channels under the wing. The external flow would not slow down very much, and so the heating effect would not be so great as in an internal flow. For what its worth, the people who were interested in hypersonic vehicles while I was at University (say 5 years ago) all thought external combustion was the way to go. REgards, Terry Heatlie.
henry@zoo.toronto.edu (Henry Spencer) (11/30/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) >... Sort of like a series >of small vertical strakes or fins projecting from >under the wing. This suggests that the combustion >takes place in the open. Is this true? It can be done that way; hypersonic shock waves close the open side, so to speak. Current designs seem to avoid open sides, perhaps because it's difficult to inject enough fuel quickly enough without a surrounding structure to mount injectors on. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
henry@zoo.toronto.edu (Henry Spencer) (12/03/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: beede@sctc.com (Mike Beede) >No need for supersonic speed -- a ramjet can work fine at much lower >speeds... Work, yes. Fine, no. :-) Subsonic ramjets can be built, but their performance is terrible. For practical purposes, ramjets are of little interest until speed is at least transonic, and preferably highly supersonic. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
elec140@csc.canterbury.ac.nz (12/04/90)
From: elec140@csc.canterbury.ac.nz In article <1990Dec3.050627.2654@cbnews.att.com>, henry@zoo.toronto.edu (Henry Spencer) writes: > From: henry@zoo.toronto.edu (Henry Spencer) >>From: beede@sctc.com (Mike Beede) >>No need for supersonic speed -- a ramjet can work fine at much lower >>speeds... > > Work, yes. Fine, no. :-) Subsonic ramjets can be built, but their > performance is terrible. For practical purposes, ramjets are of little > interest until speed is at least transonic, and preferably highly > supersonic. If this is true, then where is the distinction between a ramjet and a scramjet? Is it to do with an external combustion chamber, or is this only one implementation of a scramjet? ********************************************************* Chris Kaiser Postgrad - Elec Eng Dept Canterbury University Christchurch, NEW ZEALAND E.MAIL: c.kaiser@elec.canterbury.ac.nz *********************************************************
henry@zoo.toronto.edu (Henry Spencer) (12/05/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: elec140@csc.canterbury.ac.nz >> ...For practical purposes, ramjets are of little >> interest until speed is at least transonic, and preferably highly >> supersonic. > >If this is true, then where is the distinction between a ramjet and a scramjet? "Scramjet" stands for "supersonic *combustion* ramjet". The crucial distinction is not operating speed, but air velocity in the combustion region. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
megazone@wpi.WPI.EDU (MEGAZONE 23) (12/05/90)
From: megazone@wpi.WPI.EDU (MEGAZONE 23) In article <1990Dec4.003144.11017@cbnews.att.com> elec140@csc.canterbury.ac.nz writes: >If this is true, then where is the distinction between a ramjet and a scramjet? >Is it to do with an external combustion chamber, or is this only one >implementation of a scramjet? A ramjet, like a turbojet and all derivatives, slows the airflow to subsonic speeds prior to entering the combustion chamber(s). This allows the burning of less volitile fuels such as kerosene and also lowers temperature and pressure stresses on the engine. A scramjet is a Supersonic Combustion RAMJET. The combustion takes place in a supersonic airflow, requiring fuels like liquid hydrogen or liquid methane. However the scramjet allows for much higher aircraft speeds, there is a practical limit to how much you can slow the airflow for a ramjet. I believe it is in the Mach 6-7 range, any figures? Theoretically the scramjet should be able to push an aircraft up to Mach 25, but in practice this is a very difficult goal. A scramjet must also be designed as an integral part of the airframe, you can't just tack them on pylons or stick them on the fuselage like a turbojet or a ramjet. (There are some resrictions for ramjets too, but not nearly as strict.) The MAJOR difference between a scramjet and all other 'jet' engines is the supersonic combustion. Scramjets have yet to fly, officially, the first aircraft to be so equipped will be the X-30 National Aerospace Plane. Of course you may believe in the Aurora. :-) ############################################################################### # "Calling Garland operator 7G," EVE Email megazone@wpi.wpi.edu # # MEGAZONE, aka DAYTONA, aka BRIAN BIKOWICZ Bitnet Use a gateway. Sorry. # ###############################################################################